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

Simultaneous MPFL reconstruction and guided growth result in low rates of recurrent patellofemoral instability

PURPOSE

Implant-mediated guided growth (IMGG) is used to address coronal plane deformity in skeletally immature patients. Few studies have reported on IMGG and simultaneous medial patellofemoral ligament (MPFL) reconstruction for paediatric patients with concurrent genu valgum and patellofemoral instability (PFI). This study aimed to report on the outcomes of these simultaneous procedures.

MATERIALS AND METHODS

This was a retrospective review of paediatric patients undergoing simultaneous MPFL reconstruction and IMGG between 2016 and 2023. Mechanical lateral distal femoral angle (mLDFA), hip-knee-ankle angle (HKA) and mechanical axis deviation (MAD) were measured on full-length hip-to-ankle plain radiographs. Measurements were taken preoperatively, prior to implant removal and/or at final follow-up with minimum 1-year clinical follow-up.

RESULTS

A total of 25 extremities in 22 patients (10 female) underwent simultaneous IMGG and MPFL reconstruction. The mean age at surgery was 12.6 ± 1.7 years. The mean duration of implant retention was 18.6 ± 11.3 months. Nineteen extremities (76%) underwent implant removal by final follow-up. Preoperative HKA corrected from a mean of 5.8 ± 2.3° to -0.8 ± 4.5° at implant removal or final follow-up (p < 0.001), with mLDFA and MAD similarly improving (both p < 0.001). HKA corrected a mean of 0.7 ± 0.9° per month, while mLDFA and MAD corrected a mean of 0.5 ± 0.6°/month and 2 ± 3 mm/month, respectively. At the time of implant removal or final follow-up, 88% of patients demonstrated alignment within 5° of neutral. Only one extremity experienced subsequent PFI (4%). For 14 patients who underwent implant removal with further imaging at a mean of 7.8 ± 4.9 months, only one patient (7%) had a valgus rebound to an HKA > 5°.

CONCLUSION

Simultaneous MPFL reconstruction and IMGG provided successful correction of lower extremity malalignment with only one recurrence of PFI. This approach is a reliable surgical option for skeletally immature patients with genu valgum and PFI.

LEVEL OF EVIDENCE

Level 4 case series.

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.

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.

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.

CT and MRI measurements of tibial tubercle lateralization in patients with patellar dislocation were not equivalent but could be interchangeable

PURPOSE

To compare the values and the relationship of tibial tubercle lateralization measurements between computerized tomography (CT) and magnetic resonance imaging (MRI).

METHODS

Sixty patients with patellar dislocation who underwent both CT and MRI of the same knee joint from November 2021 to February 2022 were included in our study. The intraclass correlation coefficient (ICC) and Bland-Altman analysis were performed to evaluate the reliability of tibial tubercle-trochlear groove (TT-TG), tibial tubercle-Roman arch (TT-RA), and tibial tubercle-posterior cruciate ligament (TT-PCL) distance measurements. The values of CT and MRI measurements using the same bony landmarks were compared for the difference. Pearson correlation analysis and linear regression analysis were performed to assess the correlation between CT and MRI measurements. Finally, the estimated values obtained from the regression equation were compared with the actual values obtained from the radiological measurement to evaluate the accuracy of the equations.

RESULTS

A total of 60 patients with patellar dislocation who underwent both CT and MRI of the same knee joint were included in this study. The included measurements showed excellent agreement with ICCs > 0.9. TT-TG distance measured on CT (19.5 ± 5.1 mm) had a mean of 7.1 mm higher than that on MRI (12.4 ± 4.7 mm) (P < 0.001). The mean value of TT-RA distance was 22.5 ± 3.7 mm on CT and 16.7 ± 4.9 mm on MRI (P < 0.001), showing a mean difference of 5.8 mm. The values of TT-TG distance measured by CT and MRI were significantly correlated (R = 0.5, P < 0.001). The values of TT-RA distance between these two modalities showed a better correlation than that of TT-TG distance (R = 0.6, P < 0.001). The interchange values of TT-TG distance and TT-RA distance between CT and MRI can be obtained using regression equations (TT-TG distance: y = 0.6x + 12.3; TT-RA distance: y = 0.5x + 14.4).

CONCLUSION

The values of tibial tubercle lateralization measured by MRI may be underestimated compared with those measured by CT. Although the values measured on CT and MRI are not equivalent, the value in the other modality can be estimated. Therefore, an additional CT scan for tibial tubercle lateralization evaluation may not be necessary.

LEVEL OF EVIDENCE

Level II.

Patellar Tendon-Trochlear Groove Angle Measured on a Single Computed Tomography Slice of the Distal Femoral Trochlear Groove Is a Reliable Measurement for the Evaluation of Patellar Instability

PURPOSE

To verify the reliability of patellar tendon-trochlear groove angle (PTTG-A) measured by computed tomography (CT) and the clinical significance in evaluation of patellar instability.

METHODS

A retrospective study of hospitalized patients with knee pain or injury and had knee CT from January 2017 to June 2021 was performed. PTTG-A and tibial tuberosity-trochlear groove (TT-TG) distance were measured on CT. Spearman correlation analysis was analyzed between the 2 measurements. The intraclass correlation coefficient was determined for inter- and intraobserver reproducibility. The capacity of PTTG-A and TT-TG to predict patellar instability was evaluated by the receiver operating characteristic curve. Data from the control group were used to determine the pathologic thresholds and logistic regression analysis.

RESULTS

Included were 113 patients. There were 60 patients with the history of at least 2 episodes of patellar dislocation (study group) and 53 patients without a history of patellar dislocation (control group). The respective PTTG-A and TT-TG distances in the study group (35.2 ± 8.4° and 19.6 ± 4.6 mm) were significantly greater than those of the controls (20.8 ± 5.8° and 13.3 ± 4.5 mm) (P < .001). The correlation between the 2 measurements was strong (r = 0.730, P < .001). The inter- and intraobserver reliability of the PTTG-A were better than TT-TG distance in both groups. The AUC of PTTG-A was greater than that of the TT-TG distance (0.895 vs 0.769, respectively). With the cutoff value of PTTG-A and TT-TG being 26.3° and 16.3 mm, the value of the pathologic threshold of PTTG-A was 30.0°, with a dominance ratio of 16.88 (95% confidence interval 2.88-98.89, P = .002).

CONCLUSIONS

The PTTG-A measured on a single CT slice of the distal femoral trochlear groove is a more reliable measurement than TT-TG distance for the prediction of patellar instability.

LEVEL OF EVIDENCE

III; A retrospective cohort study.

Assessment of the reliability and validity of imaging measurements for patellofemoral instability: an updated systematic review

OBJECTIVE

To provide an update on the reliability and validity of all radiological measures used to assess patients presenting with patellofemoral instability.

METHODS

A search of the CINHAL, EMBASE, MEDLINE, and SCOPUS databases and the Cochrane library was conducted. All studies assessing the validity, reliability, sensitivity, and specificity of radiological measures of the patellofemoral joints of patients with patellofemoral instability from 2010 onwards were considered for inclusion. Discrimination validity, inter- and intra-observer reliability, and the sensitivity and specificity of specific imaging measures were evaluated.

RESULTS

Seventy-three studies met the selection criteria and were included for analysis. We identified eight radiological measures in four categories with good reliability and validity: the tibial tubercle to trochlear groove distance, specific measures of patellar height (Blackburne-Peel index, Caton-Deschamps index and Insall-Salvati ratios), three measures of trochlear dysplasia (sulcus angle, trochlear depth, and lateral trochlear inclination), and the tibial tubercle to posterior cruciate ligament distance. No included studies examined the reliability and validity of patellofemoral instability ultrasound measures.

CONCLUSION

Our updated review demonstrated good inter- and intra-observer reliability and discrimination validity for the tibial tubercle-trochlear groove distance, specific patellar height, and trochlear dysplasia measures on MRI. The tibial tubercle to posterior cruciate ligament distance, an indirect measure of rotational asymmetry, was a valid and reliable measure on MRI. Due to a lack of assessments across more than one study, there are a variety of proposed measures with insufficient evidence to determine their validity, reliability, sensitivity, and specificity.

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.

Comparison of post-operative outcomes following anterior cruciate ligament reconstruction between patients with vs. without elevated tibial tubercle-trochlear groove (TT-TG) distance

PURPOSE

It is unclear if an elevated tibial tubercle-trochlear groove (TT-TG) distance is a risk factor for poor outcomes following ACLR. Therefore, the purpose of this study was to determine whether patients with an elevated TT-TG have an increased risk of retear following primary ACLR compared to controls with a normal TT-TG.

METHODS

All patients who underwent primary ACLR between July 2018 and June 2019 with an available preoperative magnetic resonance imaging (MRI) were eligible for inclusion. TT-TG distance was measured on preoperative MRI scans by two independent investigators. Clinical outcomes, return-to-sport rates, and Lysholm scores were compared between patients with a TT-TG < 12.5 mm (normal) and those with a TT-TG ≥ 12.5 mm (elevated).

RESULTS

Overall, 159 patients were included, 98 with normal TT-TG distance and 61 with elevated TT-TG distance. Patients with an elevated TT-TG distance had worse post-operative Lysholm scores than patients with a normal TT-TG distance (83.0 vs. 95.0, p = 0.010). In patients who received a bone-patellar tendon-bone (BTB) graft, an elevated TT-TG distance was associated with higher rates of subjective instability (13.0% vs. 3.0%, p = 0.041), reoperation (13.0% vs. 1.5%, p = 0.012), and post-operative complications (25.0% vs. 8.2%, p = 0.026), as well as lower ACL psychological readiness scores (324.1 vs. 446.7, p = 0.015).

CONCLUSION

Patients with an elevated pre-operative TT-TG distance have worse Lysholm scores than patients with normal TT-TG distance. Patients with an elevated pre-operative TT-TG distance who underwent ACLR with BTB grafts had significantly higher rates of subjective instability, reoperation, and post-operative complications.

LEVEL OF EVIDENCE

III.

Radiographic Evaluation of Pediatric Patients with Patellofemoral Instability

PURPOSE OF REVIEW

The purpose of this review is to highlight the radiographic assessments of utility in the evaluation of a pediatric patient with patellofemoral instability to facilitate a thorough work-up. Understanding of these measures is useful in understanding evolving research in this field, providing accurate patient risk assessment, and appropriately directing surgical decision-making.

RECENT FINDINGS

Recent literature has broadened the radiographic characterization of the pediatric patellar instability and its anatomic risk factors. Knee MRI can inform the assessment of skeletal maturity and novel axial alignment measurements may enhance our identification of patients at increased risk of recurrent instability. Additional improvements have been made in the objective measurement and classification of trochlear dysplasia. Knee MRI-based skeletal age assessments may obviate the need for hand bone age assessments in growing children with patellofemoral instability. Novel objective measures exist in the evaluation of pediatric patellar instability both in the assessment of axial alignment and trochlear dysplasia. Future work should focus on how these measures can aid in guiding surgical decision-making.

Reliability of the Tibial Tubercle-Roman Arch Distance for Evaluating Tibial Tubercle Malposition and Predicting Patellar Dislocation via Magnetic Resonance Imaging

Background:

The tibial tubercle (TT)–trochlear groove (TT-TG) distance has low reproducibility in patients with a dysplastic trochlea, whereas the clinical value of the TT–posterior cruciate ligament (TT-PCL) distance remains controversial.

Purposes:

To establish a method to assess the position of the TT on magnetic resonance imaging (MRI) scans using the TT–Roman arch (TT-RA) distance, compare this method with the TT-TG and TT-PCL distance, and provide the pathological threshold value of the TT-RA distance in patients with patellar dislocation.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

The TT-RA distance, TT-TG distance, and TT-PCL distance were measured on MRI scans in 70 patients with a history of patellar dislocation and 70 healthy individuals. Inter- and intraobserver reliability of each measurement parameter were evaluated. The discriminatory capacity and the interrelationship of the 3 measurement parameters were investigated using Pearson correlation and the receiver operating characteristic curve. The pathological threshold values of these measurements were calculated according to the data of healthy individuals. Finally, logistic regression analysis was performed using these values.

Results:

Patients with patellar dislocation had a greater TT-RA distance compared with healthy individuals (18.05 ± 4.16 vs 13.86 ± 2.90 mm; P < .001). The TT-RA distance had a stronger diagnostic capacity, with an area under the curve of 0.802 compared with 0.625 for TT-PCL distance. Excellent reproducibility was seen for TT-RA distance measurement at any degree of trochlear dysplasia (all intraclass correlation coefficients [ICCs] >0.90). The inter- and intraobserver ICCs of the TT-TG distance measurements were extremely low for Dejour type D dysplasia (ICC, 0.509 and 0.616, respectively). The pathological TT-RA distance threshold was calculated as 19.5 mm. Logistic regression showed that patients with a TT-RA distance >19.5 mm were 11.7 times more likely to sustain patellar dislocation than were those with TT-RA distance less than this value.

Conclusion:

The TT-RA distance was a more reliable parameter with which to evaluate TT position than was TT-TG distance in patients with trochlear dysplasia. The TT-PCL distance was the least reliable among the 3 parameters studied.

Future Directions in Patellofemoral Imaging and 3D Modeling

PURPOSE OF REVIEW

Patellofemoral instability involves complex, three-dimensional pathological anatomy. However, current clinical evaluation and diagnosis relies on attempting to capture the pathology through numerous two-dimensional measurements. This current review focuses on recent advancements in patellofemoral imaging and three-dimensional modeling.

RECENT FINDINGS

Several studies have demonstrated the utility of dynamic imaging modalities. Specifically, radiographic patellar tracking correlates with symptomatic instability, and quadriceps activation and weightbearing alter patellar kinematics. Further advancements include the study of three-dimensional models. Automation of commonly utilized measurements such as tibial tubercle-trochlear groove (TT-TG) distance has the potential to resolve issues with inter-rater reliability and fluctuation with knee flexion or tibial rotation. Future directions include development of robust computational models (e.g., finite element analysis) capable of incorporating patient-specific data for surgical planning purposes. While several studies have utilized novel dynamic imaging and modeling techniques to enhance our understanding of patellofemoral joint mechanics, these methods have yet to find a definitive clinical utility. Further investigation is required to develop practical implementation into clinical workflow.

Diagnostic Performance of MRI Versus CT in the Evaluation of Intra-articular Osteochondral Fracture in Pediatric Patients With Acute Traumatic Lateral Patellar Dislocation

Background:

Evaluation of intra-articular osteochondral fractures in children with acute traumatic lateral patellar dislocation (LPD) is important for determining treatment options.

Purpose:

To (1) compare the diagnostic accuracy of computed tomography (CT) and magnetic resonance imaging (MRI) for evaluating intra-articular osteochondral fractures; (2) compare the interpretation of CT and MRI images between radiologists and pediatric orthopaedic surgeons (POS); and (3) investigate any clinical factors influencing the accuracy of CT and MRI evaluations.

Study Design:

Cohort study (diagnosis); Level of evidence, 2.

Methods:

We reviewed 35 knees in 35 patients (mean age, 12.2 ± 1.2 years; 12 boys and 23 girls) who were treated arthroscopically for acute traumatic LPD; 71% of the patients had patellar fractures, 54% had femoral fractures, and 60% had free osteochondral fracture fragments. All presurgical MRI and CT images were reviewed by POS who were blinded to both the reports of the radiologists and surgical records. We compared the accuracy of CT and MRI in diagnosing intra-articular osteochondral fractures against the arthroscopic findings and compared the interpretation of the images by the POS (MRI-O, CT-O) with those of the radiologists (MRI-R, CT-R).

Results:

There was no significant difference in diagnostic accuracy between CT and MRI for overall intra-articular osteochondral fractures by the POS or the radiologists; however, the CT-O images had a higher diagnostic specificity (84.2% vs 69.6%; P < .001) and sensitivity (88.1% vs 70.1%; P < .001) versus the MRI-R images. Regarding free fracture fragments, the CT-R images had a higher diagnostic accuracy than the MRI-R images (73.5% vs 47.1%; P = .026). When backed by clinical data, the MRI-O images had greater diagnostic accuracy (78.7% vs 60.3%; P = .001) and sensitivity (88.1% vs 30.7%; P = .021) but lower specificity compared with the MRI-R images, and the CT-O images had similar diagnostic accuracy but greater sensitivity than the CT-R images (70.1% vs 52.2%; P < .001). The diagnostic accuracy of MRI-O images was lower for children under 12 years versus children 12 years and over (67.5% vs 83.3%; P = .040).

Conclusion:

Compared with MRI, CT scans had better diagnostic performance in the evaluation of intra-articular osteochondral fractures in pediatric patients with acute traumatic LPD. Clinical data enhanced the diagnostic sensitivity of MRI and CT but decreased the specificity of MRI. MRI evaluations remain challenging for both POS and radiologists.