Variation in tibial tubercle-trochlear groove measurement as a function of age, sex, size, and patellar instability

Impact of sex and age on the lateralisation of the tibial tubercle in normal paediatric and adolescent populations

PURPOSE

Numerous methods have been proposed to characterise tubercle lateralisation. However, their normal values and related changes remain unclear. Accordingly, it was aimed to determine the potential sex and age effects and determined the optimal individualised method of diagnosing lateralisation of the tibial tubercle in patients with recurrent patellar dislocation (RPD).

METHODS

Measurements included the tibial tubercle-trochlear groove (TT-TG) distance, tibial tubercle-posterior cruciate ligament (TT-PCL) distance and tibial tubercle lateralisation (TTL); and the proximal tibial width (PTW), trochlear width (TW) and trochlear dysplasia index (TDI), for adjustment. A two-way analysis of variance was used to determine the effect of age, sex and their interaction within the normal group. When the age effect was statistically significant, a nonlinear regression was created. Areas under the receiver-operating characteristic curve (AUCs) were calculated to assess diagnostic accuracy.

RESULTS

A total of 277 normal participants (mean [SD] age, 13.5 [2.6] years; 125 [45.1%] female) and 227 patients with RPD (mean [SD] age, 13.5 [2.6] years; 161 [58.1%] female) were analysed. It was found that in the normal group, in patients aged 7-10, TT-PCL distance (p = 0.006), TTL (p = 0.007) and TT-PCL/PTW (p < 0.001) were significantly larger in females than in males. A significant sex effect was also detected on TT-TG/TW (p = 0.014). TT-TG distance, TT-PCL distance, TTL and TT-PCL/PTW (in male patients) approached an established normal adult value of 12.3 mm, 20.9 mm, 0.64 and 0.28, respectively, with increasing age (p < 0.001). The AUC was greater for TT-TG/TDI and TT-TG/TW (p ≤ 0.01) and TT-TG/TDI outperformed TT-TG/TW in patients aged 15-18 (p = 0.004).

CONCLUSIONS

Tubercle lateralisation increased with age and was affected by sex, with the exception of TT-TG distance and TT-TG/TDI. TT-TG/TDI is the optimal method of diagnosing a lateralized tibial tubercle in patients with RPD. These findings assist with the evaluation of tubercle lateralisation in that they provide a proper protocol for paediatric and adolescent populations with RPD; and thus, will help determine whether medial tubercle transfer should be included among the tailored surgical procedures considered for the treatment of patients with RPD.

LEVEL OF EVIDENCE

Level III.

The Tibial Tuberosity-Trochlear Groove Distance Can either Increase or Decrease during Adolescent Growth

Increased Tibial Tuberosity-Trochlear Groove (TT-TG) distance is a risk factor for recurrent lateral patella dislocations (RLPD). Population-based cross-sectional studies on healthy subjects demonstrate that the TT-TG increases gradually during growth until skeletal maturity, but changes in the TT-TG distance during adolescence in patients with RLPD on an individual basis have not been previously investigated. This study aimed to measure changes in TT-TG distance during skeletal maturity. The TT-TG of 13 consecutive patients with open physes (mean age 13 years) with RLPD was measured on MRI at baseline and three years later. The change in TT-TG distance over the three-year period was measured. The mean change in TT-TG distance from the baseline to the three-year follow-up increased overall (2.9 mm, 95% Confidence Interval (CI) 2.1-3.7). However, the TT-TG distance could either increase or decrease during final growth. Our results suggest that the TT-TG distance in patients suffering from RLPD may either decrease or increase individually during the growth spurt. This contradicts the current concept that the TT-TG distance increases gradually during growth.

Patho-morphology of patellar instability in children and adolescents: A systematic review and meta-analysis

BACKGROUND

Children and adolescents have the highest incidence of patellar instability among the population. We aimed to identify patho-morphological and epidemiological factors associated with patellar instability, and to identify factors predisposing to recurrence in children and adolescents.

METHODS

Published and unpublished literature databases, conference proceedings and the reference lists of included studies were searched to the 14th of March 2024. Studies were eligible if they compared history characteristics, examination features and radiological parameters between patients with and without instability, or evaluated risk factors for instability recurrence. A random-effects meta-analysis was performed. Included studies were appraised using tools respective of study design.

RESULTS

The evidence was moderate to low in quality. Forty-five studies (including 9000 patients) were eligible. Tibial tubercle - tibial groove (TT-TG) distance (weighted mean difference [WMD] 5.96 mm, 95% Confidence Interval [CI]: 4.94 to 6.99 mm), sulcus angle (WMD: 13.93˚, 95% CI: 9.1˚ to 18.8˚), and Insall-Salvati index (WMD: 0.2, 95% CI: 0.16 to 0.23) were greater in patients with patellar instability. Risk factors for recurrent dislocation included age less than 18 years (Odds ratio [OR]: 2.56, 95% CI: 1.63 to 4.0), skeletal immaturity (OR: 1.79, 95% CI: 1.21 to 2.64) and presence of trochlear dysplasia (OR: 3.37, 95% CI: 1.85 to 6.15).

CONCLUSION

Knowledge of patho-morphological factors associated with patellar instability could help explain its pathophysiological processes, allowing for the design of treatment approaches and the identification of patients at risk.

Tibial tubercle to trochlear groove and the roman arch method for tibial tubercle lateralisation are reliable and distinguish between subjects with and without major patellar instability

PURPOSE

Patellofemoral (PF) instability recurrence depends on several factors including the relative lateralisation of tibial tubercle (TT) regarding the trochlear groove (TG). TT relative lateralisation quantification has long been a topic of debate. Multiple measuring techniques have been described including TT-trochlear groove (TT-TG), TT-posterior cruciate ligament (TT-PCL) and TT-roman arch (TT-RA), with no clear consensus regarding the most reliable index or pathologic threshold. We set out to determine the normal value range of each index and their association with age, sex and PF instability status. Also, this study aims to determine a reliable pathologic distance threshold to effectively predict patellar dislocation.

METHODS

Skeletally mature patients up to 45 years of age who presented a CT Scan and an MRI of the same knee between 2014 and 2018 were included and divided into subgroups based on history of PF instability. Three indexes (TT-TG, TT-PCL and TT-RA) were assessed by two independent observers blinded to instability history. ROC curves were performed for each index to obtain the cut point that better predicts instability. Univariate and multivariate models adjusted by age, sex, instability history and type of imaging technique were performed to test the influence of these variables.

RESULTS

208 patients were included. Mean age was 27.93 ​± ​8.48 years, 67.3% were female and 71 patients (34.1%) presented major instability history. Good or excellent inter and intraobserver reliability was found for all three indexes. All indexes presented significantly different distributions between subjects with and without major instability (p ​< ​0.001), except for TT-PCL. Different cut point values differing between imaging modalities were found: 11.4 ​mm for MRI TT-TG, 17 ​mm for CT TT-TG, 15.6 ​mm for MRI TT-RA and 18.2 ​mm for CT TT-RA.

CONCLUSIONS

All indexes studied had good or excellent inter and intraobserver reliability. Measurements between imaging techniques (CT and MR) are not interchangeable. Both TT-TG and TT-RA correctly distinguish between subjects with and without major instability, while TT-PCL does not, recommending caution when evaluated on its own. Specific threshold values depending on imaging technique should be considered for surgical decision-making.

LEVEL OF EVIDENCE

Level IV, Diagnostic Test.

The Difference in Tibial Tuberosity to Trochlear Groove Distance Between CT and MRI Arises From the Degree of Knee Flexion During Imaging

BACKGROUND

Tibial tuberosity to trochlear groove distance (TT-TG) has been reported to have different values according to imaging modalities, usually higher in computed tomography (CT) than in magnetic resonance imaging (MRI). This difference is thought to be caused by the degree of knee flexion during imaging, but few studies have aimed to elucidate the cause.

METHODS

Five hundred eight patients with knee CT or MRI performed between ages of 6 to 16 years without underlying diseases affecting the musculoskeletal system were included. This study was conducted in 2 statistical ways. (1) Propensity score matching was performed for the imaging modality, and the bony TT-TG was compared between the 2 matched groups. (2) A regression model was fitted with 484 patients with either CT or MRI (a training set), and validation of the fitted model was performed with 24 patients with both CT and MRI simultaneously taken within a week (a test set). The predicted TT-TG values were compared with the measured values.

RESULTS

(1) Eighty-one patients were successfully matched by propensity score (all the standardized mean differences < 0.1) for each modality. In the matched patients, there was no significant difference in TT-TG according to the imaging modality (11.3 ± 3.7 mm for CT, 10.4 ± 3.8 mm for MRI, P = 0.126). (2) For the model fitting, different linear models were fitted before and after 10 degrees of knee flexion angle because there was a sharp change in TT-TG when the knee flexion angle was <10 degrees. The predicted TT-TG values did not significantly differ from the measured values (10.2 ± 4.3 mm vs. 9.0 ± 5.1 mm, P = 0.124).

CONCLUSIONS

This study is the first to statistically prove that the difference between TT-TG in MRI and CT originates from the different degrees of knee flexion. In addition, although more studies are needed, authors recommend imaging to be performed with the knee flexed at least 10 degrees for more reliable measurements because TT-TG changes sharply if the knee flexion angle is <10 degrees.

LEVEL OF EVIDENCE

III.

Trochlea dysplasia, increased TT-TG distance and patella alta are risk factors for developing first-time and recurrent patella dislocation: a systematic review

PURPOSE

The aim of the study was to perform a systematic review and best knowledge synthesis of the present literature concerning biomechanical risk factors for developing first-time and recurrent patella dislocation.

METHODS

The study was performed as a systematic review following PRISMA guidelines. PubMed and EMBASE were systematically searched. Studies investigating participants with risk factors for first-time as well as recurrent patella dislocation were included. The records were screened, and data extracted independently by two researchers supervised by a third independent assessor. The study was registered in PROSPERO.

RESULTS

A total of 6233 records were screened, and 50 studies met the inclusion criteria. The biomechanical risk factors: trochlear dysplasia, increased tibial tuberosity-trochlear groove distance (TT-TG), and patella alta were found to be statistically significantly associated with patella dislocation in several publications and were thus recognized as risk factors for patella dislocation. The soft-tissue stabilizers: longer and thinner MPFL ligament, increased number of type 2C and decreased number of type 1 muscle fibers, and joint laxity were found to be statistically significantly associated with patella dislocation in a few publications, but due to limited evidence, no conclusion was made on this matter.

CONCLUSION

There is strong evidence in the literature that abnormalities of bony stabilizers, trochlear dysplasia, increased TT-TG distance, and patella alta are risk factors for patella dislocation. There is less evidence that soft-tissue stabilizers are risk factors. The study emphasizes the importance of a thorough investigation of bony stabilizers in clinical decision-making.

LEVEL OF EVIDENCE

Level IV.

Comparison of Habitual Versus Recurrent Patellar Dislocation in Children and Adolescents: Differences in Radiological Features

Background

Recurrent patellar dislocation (RPD) and habitual patellar dislocation (HPD) in flexion are frequently encountered in children and adolescents.

Purpose

To compare the radiological features of RPD and HPD in children and adolescents.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

Imaging data were collected from patients aged 9 to 15 years who received surgical treatment for HPD or RPD at a single institution between June 2015 and September 2020. The prevalence of trochlear dysplasia, tibial tubercle lateralization, and lower limb rotational deformity was assessed through hip/knee/ankle computed tomography (CT) using the following quantitative indicators: trochlear depth index, lateral trochlear inclination, sulcus angle, tibial tubercle-trochlear groove (TT-TG) distance, ratio of TT-TG distance to femoral width, TT-TG angle, femoral anteversion angle, and tibial external rotation angle. The morphology of trochlea and patella were graded on knee CT using the Dejour and Wiberg classification. The Insall-Salvati index and Caton-Deschamps index were used to evaluate the height of the patella on lateral view radiographs. To evaluate lower limbs malalignment, the mechanical lateral distal femoral angle and medial proximal tibial angle were measured on weightbearing full-length radiographs. The collected data were analyzed and compared between the HPD and RPD groups.

Results

Enrolled were 15 patients (21 knees) diagnosed with HPD and 18 patients (22 knees) diagnosed with RPD. The age of first dislocation was significantly younger in the HPD group (7.6 ± 3.4 vs 11.2 ± 1.4 years; P = 0.003). Knees in the HPD group had a significantly higher proportion of Dejour type C dysplasia (57.1% vs 4.5%; P < .005) and Wiberg type 3 patella (66.7% vs 9.1%; P < .001). There were statistically significant differences between the groups in the trochlear depth index (HPD vs RPD: 1.1 ± 1.7 vs 2.2 ± 1.5 mm; P = .039), sulcus angle (170.3° ± 13.7° vs 157.3° ± 16.0°; P = .007), Insall-Salvati index (1.1 ± 0.2 vs 1.3 ± 0.2; P = .034), and tibial external rotation angle (31.3° ± 7.8° vs 38.4° ± 8.5°; P = .009).

Conclusion

Patients in the HPD group presented with poorer trochlear and patellar development, lower patellar height, and less tibial external rotation compared with patients in the RPG group.

Reliability of the TT-TG Index Versus TT-TG Distance on MRI: Morphometric Analyses in Asian Children and Adolescents

Background

The tibial tuberosity-trochlear groove (TT-TG) distance measured on magnetic resonance imaging (MRI) is commonly used to decide the treatment for patellar instability; however, the patient's joint size is not considered in this measurement. The TT-TG index has been proposed as a knee size-adjusted measurement for tibial tuberosity location.

Purpose

To evaluate the reliability of the TT-TG index compared with the TT-TG distance by analyzing variations in measurement according to age and sex in a pediatric Asian population.

Study Design

Cohort study (diagnosis); Level of evidence, 3.

Methods

A total of 698 knee MRI scans were collected in patients between 4 and 18 years of age who did not have any patellofemoral problems. Patient age, sex, height, and weight were recorded. The scans were divided into 5 groups according to patient age (4-6 years, 46 scans; 7-9 years, 56 scans; 10-12 years, 122 scans; 13-15 years, 185 scans; and 16-18 years, 289 scans); MRI scans were also divided by sex (497 male, 201 female). Three independent observers measured the TT-TG distance and TT-TG index on each scan, and age- and sex-based differences in the measurements were evaluated after adjusting for body mass index (BMI). The reliability of the measurements was calculated with the intraclass correlation coefficient (ICC).

Results

Good to excellent inter- and intraobserver agreement was found for TT-TG distance (ICC, 0.74) and TT-TG index (ICC, 0.88). The TT-TG distance was significantly different among the groups and increased with age, while variations in the TT-TG index were minimal between age groups and sexes. This finding was also consistent after compensating for the effect of BMI.

Conclusion

The TT-TG distance changed with age, while the TT-TG index was relatively constant. Therefore, the TT-TG index may be more reliable and effective for diagnosing and planning treatment, especially in children and adolescents.

Normative Values of Tibial Tubercle-Trochlear Groove Distance and Tibial Tubercle-Posterior Cruciate Ligament Distance in Children

BACKGROUND

Patellar instability is a common knee pathology in skeletally immature patients. In skeletally mature populations, a tibial tubercle-trochlear groove (TT-TG) distance of ≥20 mm is generally considered a pathological value. However, as pediatric patients grow and as the TT-TG distance varies with age, applying the same cutoff value as adult patients to them is unreasonable.

PURPOSE/HYPOTHESIS

This study aimed to analyze the normative values of the TT-TG and tibial tubercle-posterior cruciate ligament (TT-PCL) distances in children with no patellofemoral instability and to propose the cutoff value of the TT-TG and TT-PCL distances predictive of increased risk of patellofemoral instability in pediatric patients. We hypothesized that the TT-TG and TT-PCL distances increase with age in children and adolescents.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Magnetic resonance imaging scans of the knee were collected from the patellar instability group and the control group. The TT-TG and TT-PCL distances were measured. The normalized values of the TT-TG and TT-PCL distances were calculated by dividing them by the femoral width. Segmented analysis with 1 breakpoint was performed for both the TT-TG and the TT-PCL distances. The optimal cutoff values of the TT-TG and TT-PCL distances were calculated by maximizing the sum of the sensitivity and specificity.

RESULTS

A total of 87 patients had patellar instability, and 509 patients did not. The median values of TT-TG and TT-PCL distances in the control group (8.18 mm and 19.48 mm, respectively) were significantly smaller than those in the instability group (16.10 mm and 24.41 mm, respectively). For those aged <15 years, the TT-TG distance significantly increased by 0.39 mm as the age increased by 1 year. The TT-PCL distance increased by 1.14 mm/year until the age of 11 years. In our cohort, the cutoff value of the TT-TG distance of 14.90 mm yielded 66% sensitivity and 81.9% specificity for predicting an increased risk of patellar instability. The cutoff value of the TT-PCL distance of 23.68 mm yielded 63.9% sensitivity and 65.3% specificity for predicting an increased risk of patellar instability.

CONCLUSION

In our cohort of 596 participants, we have documented the normative values of the TT-TG and TT-PCL distances in children aged <20 years. During the surgery for patellar instability in pediatric patients, orthopaedic surgeons should consider the normative values of the TT-TG and TT-PCL distances according to age to determine which patients need distal realignment surgery.

Imaging evaluation of patellofemoral joint instability: a review

The multifactorial origin of anterior knee pain in patellofemoral joint disorders leads to a demanding diagnostic process. Patellofemoral misalignment is pointed out as one of the main causes of anterior knee pain. The main anatomical risk factors of patellofemoral instability addressed in the literature are trochlear dysplasia, abnormal patellar height, and excessive tibial tubercle-trochlear groove distance. Diagnostic imaging of the patellofemoral joint has a fundamental role in assessing these predisposing factors of instability. Extensive work is found in the literature regarding the assessment of patellofemoral instability, encompassing several metrics to quantify its severity. Nevertheless, this process is not well established and standardized, resulting in some variability and inconsistencies. The significant amount of scattered information regarding the patellofemoral indices to assess the instability has led to this issue. This review was conducted to collect all this information and describe the main insights of each patellofemoral index presented in the literature. Five distinct categories were created to organize the patellofemoral instability indices: trochlear dysplasia, patellar height, patellar lateralization, patellar tilt, and tibial tubercle lateralization.

Decrease of tibial tuberosity trochlear groove distance following mechanically aligned total knee arthroplasty

PURPOSE

Anterior knee pain (AKP) is common following total knee arthroplasty. The tibial tuberosity trochlear groove distance (TTTG) influences patellofemoral joint loading in the native knee. Increased TTTG may lead to maltracking of the patella and anterior knee pain. The purpose of this study was to investigate potential changes in TTTG following total knee arthroplasty (TKA).

METHODS

TTTG was measured on preoperative CT data on a consecutive series of patients scheduled to receive TKA with patient-specific instrumentation, and compared to a computer simulation of the postoperative TTTG. Preoperative TTTG was measured with a 3D planning software in 250 knees. The postoperative result was simulated and TTTG measured within the software. Three different groups were analysed: neutral (180° ± 3) (n = 50), valgus (> 190°) (n = 100), and varus (< 170°) (n = 100).

RESULTS

Median preoperative to simulated postoperative TTTG decreased from 15.0 [interquartile range (IQR) 6.0] mm to 6.5 (IQR 5.0) mm for all axes combined. A significant postoperative reduction of TTTG was found in each group (p < 0.001). The mean change in TTTG did not differ significantly between the groups [- 8.8 (IQR 5.5) mm neutral, - 8.3 (IQR 7.0) mm valgus, - 7.5 (IQR 5.8) mm varus, p = 0.223].

CONCLUSION

This computer-based study suggests that mechanically aligned TKA significantly decreases TTTG distance in neutral, valgus and varus knees, assuming that the postoperative result coincides with the preoperative planning. Further study is warranted to evaluate the clinical relevance of this finding.

The Tibial Tuberosity-Rotational Angle as a Novel Predisposing Parameter for Patellar Dislocation

Background

The tibial tuberosity (TT) in the axial plane is located on a curved line along the anterior cortex of the proximal tibia. Therefore, the linear measurement of TT position may not fully reflect TT malposition.

Purpose

To introduce TT-rotational angle (TT-RA) as a new anatomical parameter, which means the rotation of the TT relative to the dorsal condylar line of the tibia, and to validate its predictive value for patellar dislocation.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

Included were 46 patients with a history of patellar dislocation and 46 age- and sex-matched controls who underwent axial magnetic resonance imaging. Seven radiological parameters were measured and compared between the 2 groups, including TT-trochlear groove (TT-TG) distance, tibial tubercle-posterior cruciate ligament (TT-PCL) distance, TT-PCL ratio, TT lateralization (TTL), trochlear groove medialization (TGM), TT-RA, trochlear groove-posterior condylar axis angle (TG-PCA), and knee rotation. The predictive values of parameters for patellar dislocation were assessed using multiple logistic regression analysis.

Results

The intra- and interobserver correlation coefficients for measuring the radiographic parameters showed good to excellent values., respectively. There were significant differences in the TT-TG distance (13.9 vs 6.8 mm; P < .001), TT-RA (16.0° vs 9.1°; P < .001), TG-PCA (93.7° vs 95.4°; P = .017), and knee rotation (0.9° vs 5.3°; P < .001) between the 2 groups. However, there was no significant difference in TT-PCL distance (20.7 vs 19.4 mm; P = .075), TT-PCL ratio (28.0% vs 26.6%; P = .136), TTL (65.7% vs 64.9%; P = .270), or TGM (54.9% vs 55.0%; P = .923). Multivariable analysis showed that 3 parameters were significantly associated with patellar dislocation: TT-RA (OR, 1.57; P < .001), TT-TG distance (OR, 1.52; P = .002), and knee rotation (OR, 0.75; P = .022).

Conclusion

The TT-RA was a reliable predisposing parameter of patellar instability. It can be an alternative method of measurement when the TT-TG distance is not clearly defined.

Higher pathologic threshold of increased tibial tuberosity-trochlear groove distance should be considered for taller patients

PURPOSE

The aim of this study was to evaluate the correlation between tibial tuberosity-trochlear groove distance (TT-TG) and body height or knee size, and to find height-related pathologic thresholds of increased TT-TG.

METHODS

One-hundred and fifty-three patients with recurrent patellar instability and 151 controls were included. The TT-TG was measured on axial computed tomography (CT) images. Femora width and tibial width were selected to represent knee size. The correlation of TT-TG and gender, body height, femora width, and tibial width was evaluated. The height-related pathologic threshold of increased TT-TG was produced according to Dejour's method. To combine TT-TG with body height and knee size, three new indexes were introduced, ratio of TT-TG to body height (RTH), ratio of TT-TG to femoral width (RTF), and ratio of TT-TG to tibial width (RTT). The ability to predict patellar instability was assessed by the receiver-operating characteristic (ROC) curve, odds ratios (ORs), sensitivity, and specificity.

RESULTS

In patients with patellar instability, TT-TG showed significantly correlation with patient height, femoral width, and tibial width respectively (range r = 0.266-0.283). This correlation was not found in the control group. The pathologic threshold of TT-TG was 18 mm in patients < 169 cm (53%), and the mean TT-TG was 21 mm in patients ≥ 169 cm (54%). There was significant difference in RTH, RTF, and RTT between the two groups. RTH, RTF and RTT have similar large area under the curve (AUC) with TT-TG.

CONCLUSIONS

TT-TG showed significant correlation with body height and knee size, respectively. The pathologic threshold of increased TT-TG was suggested to be 21 mm for patients [Formula: see text] 169 cm and 18 mm for patients [Formula: see text] 169 cm. Body height-related pathologic threshold provided a supplement for indications of tibial tuberosity medialization.

LEVEL OF EVIDENCE

IV.

Individualized tibial tubercle-trochlear groove distance-to-patellar length ratio (TT-TG/PL) is a more reliable measurement than TT-TG alone for evaluating patellar instability

PURPOSE

To evaluate the intra/inter-rater and diagnostic reliability of the sagittal plane adjusted patellar instability ratios (PIRs) compared to tibial tubercle-trochlear groove (TT-TG) distance alone while employing a matched case-control analysis for age and sex to minimize a potential confounding effect.

METHODS

A retrospective case-control study was performed of all knee MRI studies of patients diagnosed with patellar instability, between 2005 and 2020 at a regional tertiary medical centre. Using a 1:1 case-control matching of sex and age at the time of the diagnosis, one control subject was assigned to each case of patellar instability. Measurements of TT-TG distance, sagittal patellar length (PL), sagittal patellar tendon length (PTL), TT-TG/PL ratio, and TT-TG/PTL ratio were conducted. Two orthopaedic surgery residents and a senior musculoskeletal radiologist were assigned to assess the intra- and inter-rater reliability. Inter-class coefficients were calculated (ICC). The receiver operating characteristic (ROC) curve and area under curve (AUC) for each parameter were compared to evaluate for diagnostic reliability. Odds ratios (OR) and their 95% confidence intervals (CI) were calculated and a multivariable logistic regression model was performed to control for possible confounders.

RESULTS

The study included 324 individuals (162 case-control matched pairs). In terms of intra- and inter-rater reliability, TT-TG/PL and TT-TG/PTL ratios showed an excellent correlation within and between readers (TT-TG/PL; intra-rater ICC 0.94 and inter-rater ICC 0.92, TT-TG/PTL; intra-rater ICC 0.91 and inter-rater ICC 0.88). The ROC curve showed a slightly greater AUC of the TT-TG/PL ratio compared to TT-TG distance alone (0.75 vs 0.73, p < 0.001). When applying the pathologic cutoff of TT-TG ≥ 20 mm and TT-TG/PL ≥ 0.5; the calculated odds ratios for the above cutoff were as follows; TT-TG distance alone had an OR of 14 (95% CI 1.8-106.5, p = 0.011) and OR for TT-TG/PL ratio was 23 (95% CI 3.1-170.3, p = 0.002). In the multivariable analysis, while controlling for height and weight, only the association between TT-TG/PL ratio and patellar dislocation remained statistically significant with an adjusted OR of 2.7 (CI 1.3-5.4, p = 0.006), compared to TTTG distance alone (OR = 1.9, n.s.).

CONCLUSIONS

Patellar instability ratios are significantly more reliable compared to TT-TG distance alone for the evaluation of patellar instability. Patellar instability ratios present superior diagnostic reliability, sensitivity and specificity, and intra\inter rater reliability. Thus, patellar instability ratios could function as a valuable diagnostic tool for the evaluation of patellar instability.

LEVEL OF EVIDENCE

III.

Different rotational alignment of tibial component should be selected for varied tibial tubercle locations in total knee arthroplasty

PURPOSE

The main purpose of this study was to identify how the accuracy of the tibial rotation reference axes varied in populations with different tibial tubercle locations. We hypothesized that the accuracy of the axes of tibial rotation would be affected by the changes of tibial tubercle locations.

METHODS

Surgical epicondylar axis (SEA), medial third of the patellar tendon (1/3MPT), medial third of the tibial tuberosity (1/3MTT), medial border of the tibial tuberosity (MTT) and Akagi line were drawn. The angle between SEA and horizontal line with the angle between the four tibial rotation axes and the horizontal line was compared by T test. Then, the correlation between TTTG with the angles between the four axes and SEA vertical lines was analyzed. The TTTG was divided into three subgroups (TTTG < 10 mm, 10 mm ≤ TTTG < 15 mm, TTTG ≥ 15 mm), then t test was performed for the angles between the vertical lines of the SEA and the four rotation axes of the tibia in each group.

RESULTS

Among the four tibial rotation axes, only the difference between MTT and the line perpendicular to SEA had no statistical significance (NS.). The four tibial rotational axes were all positively correlated with TTTG (p < 0.001). When TTTG ≥ 15 mm, Akagi line was 2.5° ± 6.9°internally rotated to the line perpendicular to SEA, while the 1/3MPT and MTT was 0.9° ± 5.3°and 1.3° ± 5.9°externally rotated to the line perpendicular to the SEA when TTTG < 10 mm and 10 mm ≤ TTTG < 15 mm, respectively.

CONCLUSIONS

MTT showed the best consistency with SEA. TT-TG had a significant positive correlation with all four tibial rotational axes. In patients with TTTG < 10 mm, 10 mm ≤ TTTG < 15 mm and TTTG ≥ 15 mm, the 1/3MPT, MTT and Akagi line demonstrated good alignment consistency with SEA, respectively.

Research Hotspots and Trends Analysis of Patellar Instability: A Bibliometric Analysis from 2001 to 2021

Background

Patellar instability is a common multifactorial disease in orthopedics, which seriously affects the quality of life. Because of the unified pathogeny, diagnosis and treatment, patellar instability has gradually attracted the interest of more scholars these years, resulting in an explosive growth in the research output. This study aims to summarize the knowledge structure and development trend in the field from the perspective of bibliometrics.

Methods

The data of articles and reviews on patellar instability was extracted from the Web of Science database. The Microsoft Excel, R-bibliometrix, CiteSpace, VOSviewer, Pajek software are comprehensively used to scientifically analyze the data quantitatively and qualitatively.

Results

Totally, 2,155 papers were identified, mainly from North America, Western Europe and East Asia. Until December 31, 2021, the United States has contributed the most articles (1,828) and the highest total citations (17,931). Hospital for Special Surgery and professor Andrew A Amis are the most prolific institutions and the most influential authors respectively. Through the analysis of citations and keywords based on a large number of literatures, “medial patellofemoral ligament construction”, “tibial tubercle-trochlear groove (TT-TG) distance”, “epidemiological prevalence”, “multifactor analysis of etiology, clinical outcome and radiographic landmarks “ were identified to be the most promising research directions.

Conclusions

This is the first bibliometric study to comprehensively summarize the research trend and development of patellar instability. The result of our research provides the updated perspective for scholars to understand the key information in this field, and promote future research to a great extent.

The Tibial Tubercle-Trochlear Groove Distance/Trochlear Dysplasia Index Quotient Is the Most Accurate Indicator for Determining Patellofemoral Instability Risk

PURPOSE

The primary aim of our study was to evaluate diagnostic accuracy of the tibial tubercle-trochlear groove (TT-TG) distance relative to associated quotients produced from trochlear width (TT-TG distance/TW) and trochlear dysplasia index (TT-TG distance/TDI) for detecting patellofemoral instability. Secondary aims included identifying thresholds for risk and comparing differences between cases and controls.

METHODS

Consecutive sampling of electronic medical records produced 48 (21 males, 27 females) patellofemoral instability cases (19 ± 7 years old) and 79 (61 males, 18 females) controls (23 ± 4 years old) who had a history of isolated meniscal lesion, as evaluated by magnetic resonance imaging. Standardized methods were employed with measurements executed in a blinded and randomized manner. A receiver operating characteristic curve assessed accuracy by area under the curve (AUC). The index of union (IU) was employed to identify a threshold for risk. Two-sample t-tests examined group differences. P < .05 denoted statistical significance.

RESULTS

The AUC values were .69 (.60, .79) for TT-TG distance, .81 (.73, .88) for TT-TG distance/TW, and .85 (.78, .91) for TT-TG distance/TDI. Thresholds were 14.7 mm for TT-TG distance, .36 for TT-TG distance/TW, and 1.88 for TT-TG distance/TDI. Cases demonstrated statistically significant (P < .001) greater values for each measure compared with controls: TT-TG distance (15.8 ± 4.2 mm vs 12.9 ± 3.6 mm, [1.4, 4.3]); TT-TG distance/TW (.51 ± .24 vs .31 ± .09, [.13, .27]); TT-TG distance/TDI (3.07 ± 1.55 vs 1.7 ± .7, [.9, 1.84]).

CONCLUSION

The TT-TG distance, TT-TG distance/TW, and TT-TG distance/TDI measures were 69%, 81%, and 85%, respectively, accurate for determining patellofemoral instability risk. Thresholds for risk were 14.7 mm for TT-TG distance, .36 for TT-TG distance/TW, and 1.88 for TT-TG distance/TDI. The thresholds reported in this study may help in advancing clinical decision-making.

LEVEL OF EVIDENCE

Level III, diagnostic retrospective comparative observatory trial.

Radiological evaluation of patellofemoral instability and possible causes of assessment errors

Patellofemoral instability (PI) is the disruption of the patella’s relationship with the trochlear groove as a result of abnormal movement of the patella. To identify the presence of PI, conventional radiographs (anteroposterior, lateral, and axial or skyline views), magnetic resonance imaging, and computed tomography are used. In this study, we examined four main instability factors: Trochlear dysplasia, patella alta, tibial tuberosity–trochlear groove distance, and patellar tilt. We also briefly review some of the other assessment methods used in the quantitative and qualitative assessment of the patellofemoral joint, such as patellar size and shape, lateral trochlear inclination, trochlear depth, trochlear angle, and sulcus angle, in cases of PI. In addition, we reviewed the evaluation of coronal alignment, femoral anteversion, and tibial torsion. Possible causes of error that can be made when evaluating these factors are examined. PI is a multi-factorial problem. Many problems affecting bone structure and muscles morphologically and functionally can cause this condition. It is necessary to understand normal anatomy and biomechanics to make more accurate radiological measurements and to identify causes. Knowing the possible causes of measurement errors that may occur during radiological measurements and avoiding these pitfalls can provide a more reliable road map for treatment. This determines whether the disease will be treated medically and with rehabilitation or surgery without causing further complications.

Inconsistencies in Reporting Risk Factors for Medial Patellofemoral Ligament Reconstruction Failure: A Systematic Review

BACKGROUND

Medial patellofemoral ligament (MPFL) reconstruction is a common surgical treatment for patients with recurrent patellar instability. A variety of risk factors, such as age, trochlear dysplasia, patella alta, and increased tibial tubercle-trochlear groove (TT-TG) distance, have been identified and may lead to postoperative failure or poor outcomes.

PURPOSE

While a large number of risk factors have been identified, significant heterogeneity exists in evaluating and reporting these risk factors in the literature. The goal of this study was to perform a systematic review to determine risk factors associated with worse outcomes after MPFL reconstruction and their consistency of being controlled for or analyzed among studies.

STUDY DESIGN

Systematic review; Level of evidence, 4.

METHODS

A systematic review of the literature was performed using the MEDLINE database to identify relevant clinical outcome studies after MPFL reconstruction for recurrent patellar instability. Eligible studies were evaluated for risk factors that were associated with MPFL failure, defined as recurrent instability or lack of improvement on patient-reported outcome (PRO) scores. Each study was then evaluated for inclusion of these risk factors.

RESULTS

Ten studies were included in the final analysis, comprising 1287 knees from 1275 patients who underwent isolated MPFL reconstruction. Of these 10 studies, 8 defined outcomes based on PROs and 3 defined outcomes based on postoperative recurrent instability (1 study included both outcomes). In the PRO failure group, 12 risk factors were found across all studies: trochlear dysplasia, trochlear bump height, elevated TT-TG, patellar tilt, hyperlaxity, age at first dislocation, age at surgery, body mass index, bilateral symptoms, WARPS/STAID score (weak atraumatic, risky anatomy, pain, and subluxation/strong, traumatic, anatomy normal, instability, and dislocation), femoral tunnel malposition, and femoral tunnel widening. In the recurrent instability failure group, 7 risk factors were found across all studies: trochlear dysplasia, bump height, patella alta, higher sulcus angle, higher congruence angle, preoperative J sign, and femoral tunnel malposition. Trochlear dysplasia and femoral tunnel malposition were consistently cited in several studies as risk factors for worse PROs and higher rates of recurrent instability. Patella alta was indicated as a significant risk factor for recurrent instability in 1 of 2 studies analyzing postoperative instability failures and was not associated with worse PROs in any of the studies analyzed. Similarly, elevated TT-TG distance was not a significant risk factor in any of the studies that analyzed recurrent instability as the failure endpoint.

CONCLUSION

While various risk factors are postulated to affect outcomes after MPFL reconstruction, there remains inconsistency within the literature regarding the inclusion of all risk factors in a given analysis. Furthermore, the significance of these risk factors varies among studies in terms of whether they affect postoperative outcomes. We found that more severe trochlear dysplasia (types C and D) and femoral tunnel malposition (>10 mm from Schöttle's point) appear to have the most consistent effect on producing higher rates of recurrent dislocation as well as worse PROs. Despite this, the role of concomitant bony procedures to adjust certain pathoanatomic risk factors in addition to MPFL reconstruction remains unknown. Future high-level studies must be conducted that respect the multifactorial nature of patellar instability and should analyze all risk factors (demographic, anatomic, and radiographic) reported to affect outcomes.

Influence of Articular Geometry and Tibial Tubercle Location on Patellofemoral Kinematics and Contact Mechanics

Trochlear groove geometry and the location of the tibial tubercle, where the patellar tendon inserts, have both been associated with patellofemoral instability and can be modified surgically. Although their effects on patellofemoral biomechanics have been investigated individually, the interaction between the two is unclear. The authors' aim was to use statistical shape modeling and musculoskeletal simulation to examine the effect of patellofemoral geometry on the relationship between tibial tubercle location and patellofemoral function. A statistical shape model was used to generate new knee geometries with trochlear grooves ranging from shallow to deep. A Monte Carlo approach was used to create 750 knee models by randomly selecting a geometry and randomly translating the tibial tubercle medially/laterally and anteriorly. Each knee model was incorporated into a musculoskeletal model, and an overground walking trial was simulated. Knees with shallow trochlear geometry were more sensitive to tubercle medialization with greater changes in lateral patella position (-3.0 mm/cm medialization shallow vs -0.6 mm/cm deep) and cartilage contact pressure (-0.51 MPa/cm medialization shallow vs 0.04 MPa/cm deep). However, knees with deep trochlear geometry experienced greater increases in medial cartilage contact pressure with medialization. This modeling framework has the potential to aid in surgical decision making.

[Tibial tubercle osteotomy in children and adolescents]

Patellofemoral instability (PFI) is one of the most common knee pathologies in children and adolescents. The high risk of re-dislocation necessitates a targeted risk analysis. A high-riding patella and a changed pulling direction of the extensor apparatus, which can be determined from the TTTG distance, are the main risk factors of PFI, also in a young population. The indication for surgical treatment, which is increasingly based on evidence, does not differ significantly from that of adults. However, due to the risk of disturbance of the growth plates, tibial tubercle osteotomy cannot be performed with open physis, which means that the surgical techniques must be adapted to the circumstances. A correction of a high-riding patella and an increased TTTG distance is possible with distal soft tissue procedures without impairing the growth plates, even in children and adolescents, and leads to better results compared with isolated MPFL reconstructions if the cut-off values of risk factors are exceeded and the indication is correct.

The Sagittal Tibial Tubercle-Trochlear Groove Distance as a Measurement of Sagittal Imbalance in Patients with Symptomatic Patellofemoral Chondral Lesions

Objective. To measure the sagittal alignment of the tibial tubercle through the sagittal tibial tubercle-trochlear groove (sTTTG) distance in patients with and without patellar chondral lesions. Design. Patients treated with patellofemoral cartilage restoration or repair procedures were retrospectively reviewed (group 1; N = 17). A control group of patients (group 2; N = 20) undergoing partial meniscectomy with normal patellar cartilage was included. An asymptomatic patellar chondrosis group (group 3; N = 15) was identified as patients undergoing partial meniscectomy with patellar cartilage wear. The sTTTG was measured on the preoperative axial T₂ magnetic resonance imaging (MRI) sequence. The first point was the nadir of the anterior trochlear cartilage, and the second point was the anterior tibial tubercle. A line was drawn between these points, perpendicular to the posterior condylar axis. Comparisons were made between the 3 groups using analysis of variance testing with Bonferroni corrections. Significance was defined as P < 0.05. Results. The mean sTTTG was significantly more posterior in group 1 (5.9 ± 5.5 mm posterior to the trochlear groove) relative to group 2 (0.8 ± 5.3 mm posterior; P = 0.018). The mean value for group 3 (2.7 ± 5.3 mm posterior) fell between group 1 and 3 but was not significantly different from group 1 (P = 0.31) or group 2 (P = 0.89). There were no significant differences with regards to sulcus angle, Caton-Deschamps Index, TTTG, or knee flexion angle on the MRI scan. Conclusions. A more posteriorly positioned tibial tubercle was observed in patients with patellar cartilage lesions relative to those with intact patellar cartilage. Intermediate positioning was observed in patients with asymptomatic patellar chondral wear. Level of Evidence. Level 3 diagnostic study.

Abnormal femur rotation in patients with recurrent patellar dislocation: A study on upright standing three-dimensionally reconstructed EOS images

BACKGROUND

The measurements of lower extremity rotational deformities in patients with recurrent patellar dislocation (RPD) in the standing position are available with the application of the EOS imaging system. The aim of our case-control study was to identify the differences on the femur rotation between the supine and standing positions, and to investigate the differences of anatomical and functional femur rotation between RPD patients and controls.

METHODS

Thirty-five lower extremities affected by RPD from 30 patients and 27 intact lower extremities from 27 controls with acute meniscus tear or anterior cruciate ligament injury were recruited. Anatomical femoral anteversion (AFA), functional femoral anteversion (FFA), femorotibial rotation (FTR) and distal femoral torsion (DFT) of all subjects were measured with the EOS imaging system. Computed tomography scans were carried out to analyze the AFA and FFA in the supine position in PRD patients. The differences in FFA between supine and standing position and in AFA, FTR and DFT between RPD and controls were analyzed. The predictor importance of each variable on RPD was observed after cluster analysis.

RESULTS

The EOS images were available in all subjects. The FFA was significantly smaller in the standing position than in the supine position (P < 0.05) in RPD patients. When comparing with the controls, RPD patients showed higher AFA, FTR and DFT (P < 0.05) but comparable FFA (P < 0.05). The cluster model prompted that FTR and DFT had higher predictor importance than AFA.

CONCLUSION

Larger AFA but comparable FFA in patients with RPD than the controls in an upright standing position suggested more internally rotated distal femur in the RPD patients. AFA may be inadequate and FFA should also be considered while planning the treatment for RPD. DFT and FTR should be taken into consideration when evaluating the abnormalities in femur rotation in RPD patients.

The patellofemoral morphology and the normal predicted value of tibial tuberosity-trochlear groove distance in the Chinese population

Background

Our objective was to obtain normal patellofemoral measurements to analyse sex and individual differences. In addition, the absolute values and indices of tibial tuberosity-trochlear groove (TT-TG) distances are still controversial in clinical application. A better method to enable precise prediction is still needed.

Methods

Seventy-eight knees of 78 participants without knee pathologies were included in this cross-sectional study. A CT scan was conducted for all participants and three-dimensional knee models were constructed using Mimics and SolidWorks software. We measured and analysed 19 parameters including the TT-TG distance and dimensions and shapes of the patella, femur, tibia, and trochlea. LASSO regression was used to predict the normal TT-TG distances.

Results

The dimensional parameters, TT-TG distance, and femoral aspect ratio of the men were significantly larger than those of women (all p values < 0.05). However, after controlling for the bias from age, height, and weight, there were no significant differences in TT-TG distances and anterior-posterior dimensions between the sexes (all p values > 0.05). The Pearson correlation coefficients between the anterior femoral offset and other indexes were consistently below 0.3, indicating no relationship or a weak relationship. Similar results were observed for the sulcus angle and the Wiberg index. Using LASSO regression, we obtained four parameters to predict the TT-TG distance (R² = 0.5612, p < 0.01) to achieve the optimal accuracy and convenience.

Conclusions

Normative data of patellofemoral morphology were provided for the Chinese population. The anterior-posterior dimensions of the women were thicker than those of men for the same medial-lateral dimensions. More attention should be paid to not only sex differences but also individual differences, especially the anterior condyle and trochlea. In addition, this study provided a new method to predict TT-TG distances accurately.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04454-8.

Varus inclination of the tibia is related to patellofemoral osteoarthritis in Japanese female patients with moderate knee osteoarthritis

PURPOSE

The aim of this study was to investigate whether the tibial tuberosity-trochlear groove (TT-TG) distance and lateral patellar tilt, which induce patellofemoral osteoarthritis (OA), are related to the coronal deformity of the lower limb in varus knee OA. It was hypothesized that varus inclination of the tibia was negatively correlated with the TT-TG distance and lateral patellar tilt in Japanese female patients with moderate knee OA.

METHODS

A total of 104 female patients (139 knees) scheduled to undergo knee osteotomy for varus knee OA were enrolled. The coronal lower limb alignment was measured on anteroposterior whole-leg radiographs. The TT-TG distance, patellar tilt angle, and the patellofemoral joint space were measured both medially and laterally on computed tomography images. The correlations between coronal lower limb alignment and the TT-TG distance or patellar tilt angle, and the correlations between the TT-TG distance or patellar tilt angle and patellofemoral joint space were evaluated.

RESULTS

The medial proximal tibial angle was negatively correlated with the TT-TG distance (r =  - 0.383, P < 0.01) and patellar tilt angle (r =  - 0.34, P < 0.01). Lateral patellofemoral joint space was negatively correlated with the TT-TG distance (r =  - 0.256, P = 0.002) and patellar tilt angle (r =  - 0.205, P = 0.016).

CONCLUSIONS

Varus inclination of the proximal tibia may induce lateralization of the tibial tuberosity and lateral patellar tilt. The tibial tuberosity lateralization and lateral patellar tilt may induce lateral patellofemoral OA in patients with varus knee OA.

LEVEL OF EVIDENCE

III.

Comparing the Tibial Tuberosity-Trochlear Groove Distance Between CT and MRI in Skeletally Immature Patients With and Without Patellar Instability

Background:

The tibial tubercle–trochlear groove (TT-TG) distance was originally described for computed tomography (CT), but it has been measured on magnetic resonance imaging (MRI) in patients with patellar instability (PI). Whether the TT-TG measured on CT versus MRI can be considered equivalent in skeletally immature children remains unclear.

Purpose:

To investigate in skeletally immature patients (1) the effects of CT versus MRI imaging modality and cartilage versus bony landmarks on consistency of TT-TG measurement, (2) the difference between CT and MRI measurements of the TT-TG, and (3) the difference in TT-TG between patients with and without PI.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

We retrospectively identified 24 skeletally immature patients with PI and 24 patients with other knee disorders or injury but without PI. The bony and cartilaginous TT-TG distances on CT and MRI were measured by 2 researchers, and related clinical data were collected. The interrater, interperiod (bony vs cartilaginous), and intermethod (CT vs MRI) reliabilities of TT-TG measurement were assessed with intraclass correlation coefficients.

Results:

The 48 study patients (19 boys, 29 girls) had a mean age of 11.3 years (range, 7-14 years). TT-TG measurements had excellent interrater reliability and good or excellent interperiod reliability but fair or poor intermethod reliability. TT-TG distance was greater on CT versus MRI (mean difference, 4.07 mm; 95% CI, 2.6-5.5 mm), and cartilaginous distance was greater than bony distance (mean difference, 2.3 mm; 95% CI, 0.79-3.8 mm). The TT-TG measured on CT was found to increase with the femoral width. Patients in the PI group had increased TT-TG distance compared with those in the control group, regardless of landmarks or modality used (P > .05 for all).

Conclusion:

For skeletally immature patients, the TT-TG distance could be evaluated on MRI, regardless of whether cartilage or bony landmarks were used. Its value could not be interchanged with CT according to our results; however, further research on this topic is needed.

Medial Patellofemoral Ligament Isometry in the Setting of Patella Alta

PURPOSE

To investigate alterations in technique for medial patellofemoral ligament (MPFL) reconstruction in the setting of patella alta and describe the effect of these alterations on MPFL anatomometry.

METHODS

Ten cadaveric knees were used. Four candidate femoral attachment sites of MPFL were tested. The attachment sites were Schottle's point (SP), 5 mm distal to SP, 5 mm proximal to SP, and 10 mm proximal to SP. A suture anchor was placed at the upper 40% of the medial border of the patella with the emanating suture used to simulate the reconstructed ligament. MPFL maximum length change was calculated through a range of motion between 0° and 110°. Recordings at all 4 candidate femoral attachments sites were repeated after a flat tibial tubercle osteotomy and transfer to achieve alta as measured by the Caton-Deschamps Index (CDI) of 1.3, 1.4, and 1.5.

RESULTS

The 10 specimens had an average CDI of 0.99, range 0.87 to 1.16. In the native tibial tubercle condition, SP was more isometric through 20° to 70° range of motion, or anatomometric, than any other candidate femoral attachment location. With patella alta with a CDI of 1.3 and 1.4, attachment site 5 mm proximal to SP exhibited more anatomometry than SP. With patella alta with a CDI of 1.5, attachment site 10 mm proximal to SP exhibited more anatomometry than SP.

CONCLUSIONS

Increased patella alta significantly alters MPFL anatomometry. With increasing degrees of patella alta, more proximal candidate femoral attachment sites demonstrate decreased change in length compared with SP. None of the varied femoral attachments produced anatomometry over the entirety of the flexion range from 20° to 70°, suggesting that in cases of significant patella alta, proximalization the femoral attachment site of MPFL reconstruction may be necessary to achieve an anatomometric MPFL reconstruction.

CLINICAL RELEVANCE

A standardized, isolated MPFL reconstruction may be prone to failure in the setting of patella alta, given the anisometry demonstrated. Alternative femoral attachment sites for MPFL reconstruction should be considered in these patients.

Establishing the reference value for tibial tubercle-trochlear groove distance on MRI in Southern Chinese population and its correlation with age, sex, height, weight and size: A multi-centre study

Objective:

The first objective of this study is to determine the reference Tibial Tubercle-Trochlear Groove (TT-TG) distance on MRI in Southern Chinese population. The second objective is to investigate the correlation between TT-TG distance and (i) age, (ii) sex, (iii) height, (iv) weight and (v) Body Mass Index (BMI) respectively.

Method:

Three hundred MRI knees performed in two different centres between August 2017 and October 2018 were included. All patients were prospectively recruited after MRI referral from Orthopaedics department. The TT-TG distances were measured by two radiologists independently. Measurement reliability was assessed using intraclass correlation coefficient (ICC). One sample t-test was used to compare the results between this study and other published studies. Spearman’s rank correlation coefficient was used to determine correlations between the TT-TG distance and age, sex, height, weight and BMI respectively.

Result:

There was no statistical significance between the mean of TT-TG distances from the two radiologists ( P-value = 0.32). The measurement reliability was excellent (ICC = 0.922 ± 0.02). The mean of averaged TT-TG distance was 8.32 ± 0.33 mm (range 2.01 to 17.48 mm). There were no statistical significant differences in means of TT-TG distance between laterality and gender. There were statistically significant correlations between (i) TT-TG distance and age ( p-value = 0.009), and (ii) TT-TG distance and height ( p-value = 0.014).

Conclusion:

The reference TT-TG distance on MRI in Southern Chinese population was 8.32 ± 0.33 mm. Statistically significant correlations were established between (i) TT-TG distance and age; and (ii) TT-TG distance and height.

Tibial Tubercle-Midepicondyle Distance Can Be a Better Index to Predict the Outcome of Medial Patellofemoral Ligament Reconstruction Than Tibial Tubercle-Trochlear Groove Distance

Purpose

To compare the clinical utility of tibial tubercle-midepicondyle (TT-ME) and tibial tubercle-trochlear groove (TT-TG) distances in predicting the risk for recurrent instability after isolated MPFL reconstruction.

Methods

A consecutive series of patients with recurrent patellar dislocation who underwent isolated MPFL reconstruction made up the study population. The patients were followed for a minimum of 2 years. In assessment of surgical outcome, the patient was deemed to exhibit “postoperative recurrent patellar instability” when ≥1 of the following 3 conditions was identified: redislocation, positive apprehension sign, and positive J-sign (manifestation of abnormal patellar tracking). As for radiological parameters for position of the tibial tubercle, TT-ME distance (transverse distance between the tibial tubercle and midpoint of the transepicondylar line) and TT-TG distance were measured on axial computed tomography images. The clinical utility as a factor to predict the outcome of MPFL reconstruction was compared between the 2 distances using receiver operating characteristic (ROC) analysis. In addition, various radiological indices potentially influencing the surgical outcome were subjected to multivariable logistic regression analysis.

Results

We examined 38 knees in 38 patients with a mean age at surgery of 17.6 years. Postoperative recurrent patellar instability was encountered in 8 of the 38 knees. The ROC curve analysis showed the TT-ME distance to be a significantly better indicator in predicting surgical outcome than the TT-TG distance (P = .001). The univariate analysis for radiological factors demonstrated that the TT-ME distance was significantly associated with postoperative recurrent patellar instability (odds ratio 1.42, P = .012) whereas all other factors including the TT-TG distance did not correlate with recurrent instability. The multivariable logistic regression analysis revealed that only the TT-ME distance was significantly associated with recurrent instability (P = .035).

Conclusions

Analysis of our patient population undergoing isolated MPFL reconstruction showed that the TT-ME distance was a significantly better indicator than the TT-TG distance to predict the risk for recurrent instability after isolated MPFL reconstruction performed for patellar instability.

Level of Evidence

Level IV, therapeutic case series.

Tibial tuberosity-tibial intercondylar midpoint distance measured on computed tomography scanner is not biased during knee rotation and could be clinically more relevant than current measurement systems

PURPOSE

The purpose of this retrospective cross-sectional case-control study was to evaluate an alternative imaging test for lateralization of the tibial tuberosity, unbiased towards knee rotation.

METHODS

On axial CT images of 129 knees, classified as cases (two or more patellar luxations) and controls (no patellar luxations), two raters gauged the standard tibial tuberosity-trochlear groove (TT-TG) distance, tibial tuberosity-femoral intercondylar midpoint (TT-FIM) distance, and new tibial tuberosity-tibial intercondylar midpoint (TT-TIM) distance singly, and knee longitudinal rotation angles (LRAs), and the presence of femoral trochlear dysplasia (FTD) jointly.

RESULTS

All imaging tests intercorrelated and discriminated between stability groups. TT-TIM had the lowest values with the highest precision. Though poorly, TT-TG and TT-FIM negatively correlated with age and LRAs regarding femur, but positively with presence of FTD, whereas TT-TIM was unbiased. The accuracy of TT-TG (> 20 mm), TT-FIM (> 20 mm), and TT-TIM (> 13 mm) was good with almost perfect reproducibility. Only TT-TIM was sex-biased (p = 0.009), with > 12 mm cut-off in females and (presumably) > 14 mm in males.

CONCLUSION

TT-TIM is an alternative imaging test for lateralization of the tibial tuberosity, unbiased towards knee rotation.

New standardization method of tibial tubercle-posterior cruciate ligament distance according to patient size in patients with patellofemoral instability

BACKGROUND

Large differences in tibial tubercle-posterior cruciate ligament (TT-PCL) distance were described in several reports between countries, suggesting that abnormal TT-PCL distance is variable due to individual patient size. This study aimed to clarify the relationship between TT-PCL distance and patient size, and to determine a method for describing individualized TT lateralization.

METHODS

We analyzed 41 patients with recurrent patellar dislocation (RPD) and 41 age-matched patients without patellar instability who underwent primary anterior cruciate ligament reconstruction (control). TT-PCL distance and tibia width (TW) were measured based on preoperative T2-weighted magnetic resonance imaging. Then, TT-PCL distance was standardized based on TW (TT-PCL ratio), and TT-PCL distance and ratio were compared between groups. Correlations were investigated among TT-PCL distance, TT-PCL ratio and each measurement (patient height, weight, TW).

RESULTS

Strong positive correlations were observed between TW and patient height, and weak or moderate positive correlations were found between TT-PCL distance and each parameter. The mean TT-PCL distance was 21.2 and 20.6 mm (P = .39), while the mean TT-PCL ratio was 31.6% and 29.0% (P = .0093) in the RPD and control groups, respectively. The TT-PCL ratio was <34% in 39 of 41 knees (95.1%) in the control group. No correlation was indicated between the TT-PCL ratio and patient size.

CONCLUSIONS

Our findings demonstrate that the TT-PCL ratio is not affected by patient size, although the TT-PCL distance is associated with knee size and patient height. The TT-PCL ratio could be an important index for identifying patients for whom distal realignment surgery should be considered.

Isolated versus combined medial patellofemoral ligament reconstruction for lateral instability of the patella

INTRODUCTION

Medial patellofemoral ligament reconstruction (MPFLR) is regularly combined with a tibial tuberosity transfer (TTT) in cases of recurrent patellar instability with underlying structural deformity. However, these indications for a TTT have recently come into question. This study aimed to assess the traditional indications by comparing the outcomes of isolated and combined MPFLR for the treatment of recurrent lateral patellar dislocation.

METHODS

A systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Included studies were those which reported the outcomes of either isolated or combined or both MPFLR. Studies were required to report at least one of the following: redislocation rate, revision due to instability, or the Kujala score.

RESULTS

We found no difference between isolated and combined MPFLR in terms of redislocation ( p = 0.48), revisions due to instability ( p = 0.36), positive apprehension tests ( p = 0.25), or the Kujala score ( p = 0.58). Combined reconstruction presented more complications compared to isolated procedures ( p = 0.05). Subgroup analysis revealed no significant difference between studies investigating isolated medial patellofemoral ligament reconstruction MPFLR performed in patients with normal tibial tuberosity-trochlear groove (TT-TG) distances only or in patients with both normal and elevated TT-TG distances.

CONCLUSIONS

According to the published data, there is no difference in outcomes between isolated and combined MPFLR. Underlying structural deformity did not demonstrate any significant effect on the success of the isolated MPFLR. Although there are definite indications for combined reconstruction, the current evidence suggests that our inclusion criteria may not be entirely correct. Further study is required to clarify and refine the true indications for combined MPFLR.

LEVEL OF EVIDENCE

III, meta-analysis of nonrandomized studies.

A robust and semi-automatic quantitative measurement of patellofemoral instability based on four dimensional computed tomography

Patellofemoral instability is a motion related disease, featured as the patella dislocating from the trochlear groove. Four dimensional computed tomography (4DCT) enables full assessment of the patellofemoral movement. Nevertheless, the quantitative measurements of patellofemoral instability are still under research and currently of limited practical use. The aim of this study is to develop a robust and semi-automatic workflow to quantitatively describe the patellofemoral movement in a patient group of eight suffering from patellofemoral instability. The initial results show agreement with manual observations of the tibial tubercle - trochlear groove (TT-TG) distance in routine practice, and the possibility to evaluate both TT-TG distance and patellar centre - trochlear groove (PC-TG) distance dynamically during active flexion-extension-flexion movement of the knee.

Does Preoperative tibial tuberosity: Trochlear groove distance effect on postoperative patellar instability in the patients with knee arthroplasty due to medium-advanced knee osteoarthritis?

Objectives: Determining tibial tubercle-trochlear groove distance range as measured before the operation in the patients to whom total knee prosthesis will be applied due to mid to advanced level of osteoarthritic and seeing the post-operative variations in tibial tubercle-trochlear groove distance and evaluating whether it has any impact on the patellofemoral instability that might develop after the operation. 46 knees planned to be applied total knee prosthesis due to mid-advanced level of osteoarthritic were examined. Methods: In the preoperative and postoperative magnetic resonance images MRI routinely taken, tibial tubercle-trochlear groove distance was measured. Later it was examined whether there was correlation between these preoperative and postoperative tibial tubercle-trochlear groove measurements and the data recorded before operation. Results: Preoperative tibial tubercle-trochlear groove distance was found to be 8.83 ± 3.54, postoperative tibial tubercle-trochlear groovedistance was found to be 8.30 ± 3.89 and preoperative-postoperative tibial tubercle-trochlear groove variation was found to be 0,52 ± 3,64 (p = 0,337). In the patients whose alignment was 10 degrees or less, Pre-Op tibial tubercle-trochlear groove distance was measured as 8.74 ± 3.18 and in the patients whose alignment was more than 10 degrees, it was measured as 8.89 ± 3,83 (p = 0.888). In the patients whose alignment was 10 degrees or less, Post-Op tibial tubercle-trochlear groove distance was measured as 8.00 ± 2.85 and in the patients whose alignment was more than 10 degrees, it was measured as 8.52 ± 4.52 (p = 0.661). In the patients whose alignment was 10 degrees or less, tibial tubercle-trochlear groove distance variation was measured as 0.74 ± 3.25 and in the patients whose alignment was more than 10 degrees, it was measured as 0.37 ± 3.95 (p = 0.741). Coclusion: As a result, although tibial tubercle-trochlear groove distance was observed with a great variation in the osteoarthritic knees at stage 3-4, it was nonetheless measured within normal limits and Post-Op variation was not meaningful. Since this is the first study in the literature on the measurement of tibial tubercle-trochlear groove distance in the total knee prosthesis applications, we hope that it would shed some light on similar studies to be conducted in the future.

Computed Tomography-based Analysis of Tibial Tuberosity-Trochlear Groove Distance in Indian Population

Aim To study the tibial tuberosity-trochlear groove distance (TT-TG) in normal Indian population and the variation of the same in relation to tibial size using computed tomography (CT) of knee. Methods CT of 100 knees (62 males and 38 females) were assessed. TT-TG distance and maximal medio-lateral (MML) distance of tibia was measured on axial CT scans. The modified TT-TG (mTT-TG) was calculated as the ratio of TT-TG and MML. Results The average TT-TG distance was 13.01 (±2.84) mm for the entire group with males and females having 12.82 (±2.95) and 13.32 (±2.66) mm, respectively (p > 0.05). The MML distance was 75.99 (±3.78) and 66.77 (±4.33) mm for males and females, respectively (p < 0.05). The average modified TT-TG was 0.18 ± 0.04. The TT-TG distance of Indian knees was similar to values obtained in Caucasian knees and higher than other Asian knees (p < 0.05). Conclusion The average TT-TG distance in Indian population is 13.01 mm, with no difference between males and females. The ML/TT-TG ratio was 0.18. The TT-TG distance in Indian population is found to be similar to the Western population and significantly higher than other Asian population.

VCAN Canonical Splice Site Mutation is Associated With Vitreoretinal Degeneration and Disrupts an MMP Proteolytic Site

Purpose

To gain insight into the pathophysiology of vitreoretinal degeneration, the clinical course of three family members with Versican Vitreoretinopathy (VVR) is described, and a canonical splice site mutation in the gene encoding for versican (VCAN) protein was biochemically analyzed.

Methods

A retrospective chart review, human eye histopathology, Sanger DNA sequencing, protein structural modeling, and in vitro proteolysis assays were performed.

Results

The proband (II:1), mother (I:2), and younger sibling (II:2) suffered retinal degeneration with foveal sparing and retinal detachments with proliferative vitreoretinopathy, features that were confirmed on histopathologic analysis. All affected members carried a heterozygous adenine to guanine variant (c.4004-2A>G) predicted to result in exon 8 skipping or the deletion of 13 amino acids at the beginning of the GAGβ chain (VCAN p.1335-1347). This deleted region corresponded to a putative MMP cleavage site, validated using fluorescence resonance energy transfer (FRET)-based proteolysis assays. Proteomic network analysis identified 10 interacting partners in the human vitreous and retina linked to retinal detachment and degeneration.

Conclusions

VVR causes significant ocular disease, including retinal detachment and retinal dystrophy. The intronic VCAN mutation removes an MMP cleavage site, which alters versican structure and results in abnormal vitreous modeling. Disruption of a versican protein network may underlie clinicopathologic disease features and point to targeted therapies.

Tibial Tubercle-Trochlear Groove Distance Is a Reliable and Accurate Indicator of Patellofemoral Instability

BACKGROUND

Tibial tubercle-trochlear groove (TT-TG) distance is a measurement generally made on CT scans that is commonly used to quantify the risk of patellofemoral instability (PFI); however, its interrater reliability and accuracy as an indicator of PFI in patients is poorly characterized.

QUESTIONS/PURPOSES

The purposes of our study were (1) to primarily analyze interrater reliability of the TT-TG distance among orthopaedists with varied experience as measured by MRI, (2) to secondarily compare TT-TG distances between PFI and control groups, and (3) to determine an accurate TT-TG distance threshold indicative of PFI.

METHODS

The electronic medical records of a senior fellowship-trained orthopaedic sports medicine surgeon were surveyed between 2012 and 2016 for patients who had experienced at least one episode of patellar subluxation or dislocation, who reported no other knee-related history, and who underwent MRI due to persistent PFI signs and symptoms. The records of 48 PFI patients (23 males, 25 females; 19 ± 4 years of age) were compared with 83 controls (60 males, 23 females; 31 ± 8 years of age) having no history of PFI, presenting with an isolated meniscal lesion as determined from MRI and treated by the same orthopaedist during this time. All records meeting study criteria were consecutively included to offset selection bias of the retrospective analysis. Two sports medicine fellows, one who had just completed orthopaedic residency training, and another with a year of experience after residency, and a sports medicine subspecialist with more than 15 years of experience in practice independently recorded TT-TG distance, indicative of tibial tubercle lateralization relative to the femoral trochlea, to the nearest millimeter (mm) in a blinded and randomized fashion. Intraclass correlation coefficient computed interrater reliability accompanied by standard error of measurement (SEM); a one-tailed, two-sample t-test analyzed group differences with accompanying effect size per Cohen's d; receiver operating characteristic (ROC) curve determined accuracy and threshold for PFI risk. A p value < 0.05 denoted statistical significance.

RESULTS

Interrater reliability was excellent, at 0.93 (95% confidence interval [CI], 0.84-0.97; SEM = 0.6 mm) for PFI patients and 0.95 (95% CI, 0.91-0.97; SEM = 0.4 mm) for controls. Distance was greater (95% CI, 2-5; p < 0.001) in PFI patients (14 ± 4 mm; range = 7-24 mm) than controls (10 ± 3 mm; range = 3-19 mm) with an effect size of 1 (95% CI, 0.3-2). Area under the ROC curve was 0.75 (95% CI, 0.66-0.83) and threshold was 13 mm (sensitivity = 0.52, 1-specificity = 0.25), suggesting the measure is a fairly accurate indicator of risk and values of 13 mm or greater are better suited to rule in PFI. Respective positive and negative likelihood ratios of 2 and 0.6 at this threshold confirm that this distance yields a small increase in probability for PFI and a minimal decrease in probability for risk; specifically, a 13-mm TT-TG distance is two times more likely to be found in patients with PFI. Furthermore, this threshold is estimated to increase a correct PFI diagnosis by approximately 15%.

CONCLUSIONS

The MRI-specific TT-TG distance, based on a single measurement using cartilaginous-tendon landmarks within a standardized trochlear range, is reliable as performed by orthopaedists of varied experience. Patients with PFI display a 4-mm greater distance than controls, which may represent a difference large enough for clinicians to discern in practice using MRI. A 13-mm TT-TG distance is two times more likely seen in patients with PFI. However, this threshold increases a correct PFI diagnosis by only about 15%; therefore, clinical decision-making should not be influenced by this criterion alone and instead used in conjunction with other relevant variables.

LEVEL OF EVIDENCE

Level IV, diagnostic study.

Distal alignment procedures for patellofemoral instability: comprehensive review of the literature

Patellofemoral disorders are a common cause of complaint in adolescent patients. Several distal realignment procedures performed in isolation or combination with proximal alignment have been described. To clarify the role of distal alignment for patellofemoral instability, a systematic review of the literature was conducted. Two independent reviewers accessed the following databases: PubMed, Medline, CINAHL, Cochrane, EMBASE and Google Scholar. A total of 1478 patients with a mean age of 22.78 years were included. The mean follow-up was 86.53 months. The average Kujala score improved from 57.66 to 82.73. The average Lysholm score improved from 63.25 to 87.87, and the average Tegner score from 3 to 4.16. VAS score improved from an average 8 to 2.56. We account a total of 46 major complications, 45 minor complications and 95 recurrences. The risk of a recurrence is 6.42%. A total of 122 additional surgeries were performed during the follow-up. This systematic review of literature suggests the importance to identify the pathological background that predisposes patients for developing patellofemoral instability and its implications for the decision-making process. The optimal treatment for patellofemoral instability should be individualized to address the specific anatomical abnormalities that contribute to patellofemoral dislocations. Distal alignments are a feasible solution to restore correct patellar biomechanics and tracking, leading to an improvement of patients' quality of life.

Patterns in Outcomes Reporting of Operatively Managed Pediatric Patellofemoral Instability: A Systematic Review and Meta-analysis

BACKGROUND

Traumatic patellofemoral dislocation is a common injury in pediatric patients, and surgical treatment is often recommended. Increasingly, it has been recognized that clinical studies need to report age-appropriate treatment outcomes. However, the variability and appropriateness of outcomes reporting in the youth patellar instability literature are unknown.

PURPOSE

To analyze the patterns of outcomes reporting in studies published in high-impact orthopaedic journals after operative management of pediatric patellar instability.

STUDY DESIGN

Systematic review; Level of evidence, 4.

METHODS

Six high-impact orthopaedic journals were searched using PubMed and EMBASE to identify studies reporting outcomes of operative management of pediatric patellar instability. Studies containing adults were excluded. Clinical and radiographic outcomes were recorded from included articles. Descriptive statistics were calculated for overall instability recurrence rates, return-to-activity rates, and changes in Kujala and Tegner scores.

RESULTS

Of 545 identified articles, 8 studies met the inclusion criteria. These studies encompassed 213 patients and 230 knees (mean age, 13.2 years; range, 4.5-18.3 years). Seven of 8 studies reported patients' physeal status, but only 4 studies limited their outcomes reporting to patients with open physes. Two studies reported postoperative radiographic measures, and 5 studies reported preoperative radiographic findings. Six studies reported patient-reported outcome measures (PROMs). Seven unique PROMs were reported. All but one study reported complication rates and types of complications. The mean postoperative change in Tegner scores was -0.07 (range, -0.6 to 1.0). Among studies examining medial patellofemoral ligament reconstruction with adequate data, the mean return-to-activity rate was 86% (range, 81%-92%), the instability recurrence rate was 3% ± 20%, and the mean improvement in Kujala scores postoperatively was 22.1 (range, 19.9-26).

CONCLUSION

There is a need for more pediatric-specific outcomes studies regarding operatively managed traumatic patellofemoral instability. Of the outcomes reported, both radiographic outcomes and PROMs should be standardized. Among radiographic outcomes, there is a need for more studies that report tibial tubercle-trochlear groove distances and use Caton-Deschamps and/or Blackburne-Peel indices to assess patellar height. Among PROMs, there is a need for studies that use PROMs validated in pediatric populations, such as the International Knee Documentation Committee Pediatric Form or the Hospital for Special Surgery Pediatric Functional Activity Brief Scale.

Tibial tubercle-trochlear groove distance and angle are higher in children with patellar instability

PURPOSE

The purpose of this study was to assess the variations in tibial tubercle-trochlear groove distance and angle as a function of age and gender in a population of children without patellar instability (PI) compared with those with PI.

METHODS

A retrospective review of 869 children's knee MRIs, ages 5 to 15 years, were evaluated using a control group (792 children) without evidence of PI and a group with PI (77 children). Tibial tubercle-trochlear groove distance (TT-TGd) and angle (TT-TGa) were measured twice by two readers to assess intra- and inter-observer reliability and compared between PI and control groups. In both groups, functions of age and gender on TT-TGd and TT-TGa values were evaluated.

RESULTS

Both TT-TGd and TT-TGa measurements showed excellent intra- and inter-observer reliability. The mean TT-TGd for the PI group was 17.2 mm (SD 6.6) and significantly higher than the mean TT-TGd for the control group (10.4 SD 3.8 mm, P = 0.001). The mean TT-TGa for the PI was 20.8° (SD 8.3°), which was also significantly higher than the mean TT-TGa for the control group (12.5° SD 4.6°, P < 0.001). Control group revealed a positive correlation between age and TT-TGd measurements (r = 0.243, P < 0.001). The mean TT-TGa for girls (13.3° SD 4.7°) was higher than the mean TT-TGa for boys (11.9° SD 4.4°) in the control group (P < 0.001).

CONCLUSION

TT-TGa and TT-TGd are reliable and can be used for the evaluation of the extansor mechanism alignment in children with and without PI. However, it must be considered that TT-TGd is increasing in growing patients. Soft-tissue procedures may be prone to failure, since bony procedures for patellar alignment cannot be done until skeletal maturity.

LEVEL OF EVIDENCE

III.

Individualizing the tibial tubercle to trochlear groove distance to patient specific anatomy improves sensitivity for recurrent instability

PURPOSE

An initial episode of patellar instability poses a treatment challenge given the absence of a valid, reproducible, and universally applicable predictor of recurrence. Recently, a series of patellar instability ratios (PIRs) were described. Each ratio consisted of the traditional tibial tubercle to trochlear groove (TT-TG) distance normalized to patient-specific measures. The purpose of this study was to investigate the reliability and validity of these novel measures.

METHODS

Eighty-seven patients experiencing a first-time lateral patellar dislocation were identified in a retrospective manner. Magnetic resonance imaging (MRI) studies obtained at the time of injury were reviewed. The TT-TG distance, patellar width (PW), trochlear width (TW), patellar length (PL), and trochlear length (TL) were obtained by two observers in a blinded, randomized fashion. Measurement reliability was assessed using intra-class correlation coefficients (ICCs). Patients were divided into those having a single dislocation (Group 1) and those experiencing recurrent instability (Group 2). The ability of the TT-TG distance and each PIR to predict recurrent instability was assessed by calculating odds ratios (ORs) with 95% confidence intervals (CIs). Sensitivity and specificity were also calculated for each measure.

RESULTS

Excellent inter-rater agreement was observed with ICCs > 0.75 for all patellofemoral joint measurements obtained on MRI. The TT-TG distance alone was predictive of recurrent patellar instability with an OR of 8.9 (p < 0.001). However, the isolated TT-TG distance had the lowest sensitivity at 25.6%. Among ratios, a TT-TG/PL ≥ 0.5 was the most predictive of recurrent instability with an ORs of 6.1 (p = < 0.001). A TT-TG/TL ≥ 0.8 was also predictive of recurrence (OR 4.9, p = 0.027) and had the highest sensitivity of any measure at 94.9%.

CONCLUSION

The results of the current study support the reproducibility and predictive ability of PIRs. While a TT-TG ≥ 20 mm was the strongest predictor of recurrent patellar instability, it was a relatively insensitive measure. Sensitivity may be improved by normalizing the TT-TG distance to patient-specific axial and sagittal plane patellofemoral measurements on MRI. Ultimately, PIRs are reproducible measures that may serve as an additional tool when clinically assessing the unstable patellofemoral joint.

LEVEL OF EVIDENCE

III.

Patellofemoral joint alignment is a major risk factor for recurrent patellar dislocation in children and adolescents: a systematic review

Importance

The complex interplay of risk factors that predispose individuals to recurrent patellar dislocation is poorly understood, especially in paediatric patients who exhibit the most severe forms.

Objective

The primary aim of this study was to systematically review the current literature to characterise the lower limb alignment, patellofemoral morphology and soft tissue restraints of the patellofemoral joint (PFJ) through medical imaging measurements in paediatric recurrent patellar dislocators and age-matched control participants. The secondary aims were to synthesise the data to stratify the factors that influence PFJ stability and provide recommendations on the assessment and reporting of PFJ parameters in this patient population.

Evidence review

A systematic search was performed using CINAHL, the Cochrane Library, EMBASE, PubMed and Web of Science databases until June 2017. Two authors independently searched for studies that included typical children and adolescents who experienced patellar dislocation and also had direct measures of structural and dynamic risk factors. The methodological quality of the included studies was assessed through a customised version of the Downs and Black checklist. Weighted averages and SDs of measures that have been reported in more than one study were computed. A fixed-effects model was used to estimate the mean differences with 95% CIs regarding the association of recurrent patellar dislocation with patella alta, tibial tuberosity to trochlear groove (TT-TG) distance and bony sulcus angle.

Findings

20 of 718 articles met the inclusion criteria. Thirty-one risk factors were found; however, only 10 of these measurements had been assessed in multiple articles and only four had both dislocator and control population results. With respect to controls, patients with recurrent patellar dislocations had higher TT-TG distance (p<0.01) and higher bony sulcus angle (p<0.01).

Conclusions and relevance

Based on the current scientific literature, increased TT-TG distances and bony sulcus angles predispose children and adolescents to recurrent patellar dislocation. Besides these measurements, studies reporting on recurrent patellar dislocation in children and adolescents should also include characterisation of lower limb alignment in coronal and axial planes and assessment of generalised ligamentous laxity.

Level of evidence

Systematic review of prognostic studies, Levels II–IV.

Variation in tibial tuberosity lateralization and distance from the tibiofemoral joint line: An anatomic study

BACKGROUND

To describe variation in tibial tuberosity position in a normal adult population and inter-rater reliability of measurements of tibial tuberosity position.

METHODS

Surface models of 161 proximal tibia specimens (83 female, 78 male; 80 black, 81 white; age 28.7years, SD 7.5) were created with a three-dimensional laser scanner. Percent lateralization, tuberosity-eminence angle, and distance from joint surface were measured for each specimen. Variation in tuberosity position by sex, race, age, height, and BMI was calculated. Multivariate regression was used to assess for demographic factors independently associated with tuberosity positioning.

RESULTS

Mean percent lateralization was 57.9% (SD 2.4, range 52.4-64.9%). Tuberosity-eminence angle mean was 11.03° (SD 2.8, range 0-18.7°). Percent lateralization and tuberosity-eminence angle were not influenced by sex, race, age, height or, BMI (p>0.05). Mean tuberosity distance from joint surface was 29.2mm (SD 3.5, range 16.6-38.6mm) and larger in males than females (30.7mm (SD 2.9), 27.6mm (SD 3.3); p<0.001). Tuberosity distance from joint surface increased 0.18mm on average per 1.0cm increase in height (p<0.001). Inter-rater reliability was high for distance from joint surface (Cronbach alpha=0.99) and percent lateralization.

CONCLUSIONS

Tibial tuberosity percent lateralization falls in a narrow range for individuals, whereas tuberosity-eminence angle and distance from joint line are more variable. Inter-rater reliability is high for percent lateralization and distance for the joint surface. Distance of tibial tuberosity from joint surface is associated with sex and height.

When and How Far to Move the Tibial Tuberosity in Patients With Patellar Instability

The many factors contributing to patellar instability have led to various surgical techniques that are used commonly today. When surgery is deemed necessary, the operation should be tailored to the patient's specific pathoanatomy. Patients with malalignment can often be stabilized by moving the tibial tuberosity to a more medial, anteromedial, or distal position. Subsequent changes in the forces acting on the patellofemoral joint will depend on the direction and distance of the tuberosity repositioning. When planning tuberosity osteotomies, it is crucial to understand how to use clinical and imaging modalities to measure and quantify tuberosity position accurately to achieve the desired degree of realignment.

Evaluation of the Effect of the Sulcus Angle and Lateral to Medial Facet Ratio of the Patellar Groove on Patella Tracking in Aging Subjects with Stable Knee Joint

Purpose

To determine whether the sulcus angle and the lateral to medial facet ratio correlate with patella lateral displacement and tilt in patients without patella instability.

Methods

Computed tomography images of the lower limb of 64 patients without known arthropathy were collected. Three-dimensional models of the lower limb with a unified coordinate system were rebuilt by using Mimics software. The sulcus angle, lateral to medial facet ratio, lateral trochlear inclination of the patellar groove, tibial tuberosity-trochlear groove (TT-TG) distance, bisect offset index, and lateral tilt of the patella were measured. Pearson's correlation test was used to determine the relationship between the aforementioned parameters.

Results

Data from 51 patients were analyzed. The sulcus angle was negatively correlated with lateral tilt inclination (p < 0.001, r = 0.8406) and positively correlated with the bisect offset index (p = 0.003, r = 0.634) and patellar tilt (p = 0.03, r = 0.551); the lateral to medial facet ratio was positively correlated with TT-TG distance (p = 0.003, r = 0.643) and bisect offset index (p = 0.026, r = 0.559).

Conclusion

The sulcus angle and lateral to medial facet ratio of the patellar groove can influence patella tracking in patients with stable knee joints.

Articular Cartilage Repair of the Knee in Children and Adolescents

Articular cartilage predominantly serves a biomechanical function, which begins in utero and further develops during growth and locomotion. With regard to its 2-tissue structure (chondrocytes and matrix), the regenerative potential of hyaline cartilage defects is limited. Children and adolescents are increasingly suffering from articular cartilage and osteochondral deficiencies. Traumatic incidents often result in damage to the joint surfaces, while repetitive microtrauma may cause osteochondritis dissecans. When compared with their adult counterparts, children and adolescents have a greater capacity to regenerate articular cartilage defects. Even so, articular cartilage injuries in this age group may predispose them to premature osteoarthritis. Consequently, surgery is indicated in young patients when conservative measures fail. The operative techniques for articular cartilage injuries traditionally performed in adults may be performed in children, although an individualized approach must be tailored according to patient and defect characteristics. Clear guidelines for defect dimension–associated techniques have not been reported. Knee joint dimensions must be considered and correlated with respect to the cartilage defect size. Particular attention must be given to the subchondral bone, which is frequently affected in children and adolescents. Articular cartilage repair techniques appear to be safe in this cohort of patients, and no differences in complication rates have been reported when compared with adult patients. Particularly, autologous chondrocyte implantation has good biological potential, especially for large-diameter joint surface defects.

What's New in Pediatric Sports Conditions of the Knee?

BACKGROUND

Sports injuries are common in pediatric and adolescent patients and the evaluation and treatment of these injuries continues to evolve. The purpose of this review is to provide a comprehensive appraisal of the literature, highlighting recent updates on sports-related knee injuries in the pediatric athlete. We specifically examined literature on tibial spine fractures, osteochondritis dissecans (OCD) of the knee, and patellar instability. Because of the volume of literature on the subject, pediatric, and adolescent anterior cruciate ligament injuries were not included in this review.

METHODS

An electronic search of the PubMed, EMBASE, and Google Scholar databases was performed for keywords related to pediatric: tibial spine fractures, patellar instability, and osteochondritis dissecans (OCD). Search results were filtered by publication date to yield articles published electronically or in print on or after January 1, 2013. Papers were selected based on expert opinion and consensus by the authors and included if deemed to have contributed important findings to the above topics.

RESULTS

A total of 31 articles were deemed to have contributed significant findings to the literature: 5 tibial spine, 17 patellar instability, and 9 OCD. The level of evidence for most studies was either level III or IV.

CONCLUSIONS

The optimal treatment for tibial spine fractures remains controversial. The evaluation of risk factors for recurrent patellar instability is important in determining the optimal treatment strategy following first-time patellar dislocation. Future multicenter studies on pediatric OCD have the potential to further understanding of this difficult problem. High-level, comparative outcomes research on a variety of pediatric sports related injuries is lacking and this review may help inform topics for future study.

LEVEL OF EVIDENCE

Level IV-literature review.

Anisometry of Medial Patellofemoral Ligament Reconstruction in the Setting of Increased Tibial Tubercle-Trochlear Groove Distance and Patella Alta

PURPOSE

To assess the impact elevated tibial tubercle-trochlear groove (TT-TG) distance and patella height, as measured by the Caton-Deschamps Index (CDI), have on the isometry of a reconstructed medial patellofemoral ligament (MPFL).

METHODS

Nine fresh-frozen cadaveric knees were placed on a custom testing fixture, with a fixed femur and a mobile tibia. A suture fixed to the MPFL origin on the patella and free to move at the Schöttle point on the femur represented a reconstructed MPFL. A local coordinate system was established, and retroreflective markers attached to the suture quantified MPFL length changes by use of a 3-dimensional motion capture system. The tubercle was transferred to create TT-TG distances of 20 mm and 25 mm and CDIs of 1.2 and 1.4 (patella alta). Recordings of the MPFL suture length change as the knee was brought through a range of motion were made using all combinations of tubercle anatomy in a randomized order for each specimen. A generalized estimating equation modeling technique was used to analyze and control for the clustered nature of the data.

RESULTS

Knees with native tibial tubercle anatomy showed MPFL isometry through 20° to 70° range of motion. Tibial tubercle lateralization (increased TT-TG distance) significantly altered MPFL isometry with a TT-TG distance of 20 mm (P < .0001). Patella alta significantly altered MPFL isometry with a CDI of 1.2 (P = .0182). The interaction of tibial tubercle lateralization combined with patella alta significantly increased the amount of anisometry seen in the reconstructed MPFL (P < .001).

CONCLUSIONS

Increased tibial tubercle lateralization and patella alta produce anisometry in an MPFL reconstruction using currently recommended landmarks, leading to potentially increased graft tension and potential failure.

CLINICAL RELEVANCE

Tibial tubercle transfer should be considered when performing an MPFL reconstruction for recurrent patellofemoral instability in the setting of significant patella alta and an elevated TT-TG distance-especially when both are present-because an isolated MPFL reconstruction will be prone to failure given the anisometry shown in this study.