Patellar Tilt and Patellar Tendon-Trochlear Groove Angle Present the Optimum Magnetic Resonance Imaging Diagnostic Reliability for Patients With Patellar Instability

Patellar tilt calculation utilizing artificial intelligence on CT knee imaging

BACKGROUND

In the diagnosis of patellar instability, three-dimensional (3D) imaging enables measurement of a wide range of metrics. However, measuring these metrics can be time-consuming and prone to error due to conducting 2D measurements on 3D objects. This study aims to measure patellar tilt in 3D and automate it by utilizing a commercial AI algorithm for landmark placement.

METHODS

CT-scans of 30 patients with at least two dislocation events and 30 controls without patellofemoral disease were acquired. Patellar tilt was measured using three different methods: the established method, and by calculating the angle between 3D-landmarks placed by either a human rater or an AI algorithm. Correlations between the three measurements were calculated using interclass correlation coefficients, and differences with a Kruskal-Wallis test. Significant differences of means between patients and controls were calculated using Mann-Whitney U tests. Significance was assumed at 0.05 adjusted with the Bonferroni method.

RESULTS

No significant differences (overall: p = 0.10, patients: 0.51, controls: 0.79) between methods were found. Predicted ICC between the methods ranged from 0.86 to 0.90 with a 95% confidence interval of 0.77-0.94. Differences between patients and controls were significant (p < 0.001) for all three methods.

CONCLUSION

The study offers an alternative 3D approach for calculating patellar tilt comparable to traditional, manual measurements. Furthermore, this analysis offers evidence that a commercially available software can identify the necessary anatomical landmarks for patellar tilt calculation, offering a potential pathway to increased automation of surgical decision-making metrics.

Radiological Risk Factors for Osteochondral Fractures in Patients With First-Time and Recurrent Patellar Instability: Data From the JUPITER Cohort

BACKGROUND

Radiological risk factors for an osteochondral fracture (OCF) associated with patellar instability are rarely studied, particularly in patients with recurrent instability.

PURPOSE

To identify specific radiological characteristics that relate to the increased prevalence of OCFs associated with patellar instability.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

Patient data (n = 730) from the Justifying Patellar Instability Treatment by Early Results (JUPITER) multicenter study were reviewed for radiological findings. Trochlear crossing sign, Caton-Deschamps index (CDI), tibial tubercle-trochlear groove (TT-TG) distance, patellar tilt, trochlear depth, trochlear bump, sulcus angle, and patellar subluxation were measured on radiography or magnetic resonance imaging and classified into 2 categories based on pathological thresholds for general patellar instability. Patients were grouped according to the presence or absence of an OCF and analyzed with the Mann-Whitney test, chi-square test, and multivariate regression.

RESULTS

A high CDI was associated with a 0.43 decreased odds of an OCF, while a high TT-TG distance was a risk factor for an OCF, with a 2.17 times increased odds. Although a first-time dislocation increased the odds of an OCF by 4.72 times, recurrent instability was found to have the same predictive relationship of CDI and TT-TG distance with fracture incidence. A lower CDI, a shallower trochlear depth, a smaller trochlear bump, and the presence of a patellar subluxation were more common in patients with OCFs. A lower CDI, positive trochlear crossing sign, and shallower trochlear depth were more common in the subset of patients with recurrent instability and associated OCFs.

CONCLUSION

Patella alta was protective of OCFs in patients with first-time and recurrent instability, while a lateralized tibial tubercle was a risk factor. These radiological characteristics should guide health care professionals on the risk of future OCFs during treatment planning after a patellar instability event.

Low lateral inclination angle, high sulcus angle, high trochlear height and patella alta are risk factors for first lateral patellar dislocation and complete MPFL rupture, comparative study

Purpose

To identify risk factors for complete medial patello-femoral ligament (MPFL) rupture after first lateral patellar dislocation (LPD) and to develop a model to predict the risk of rupture.

Methods

Patients who presented with first LPD between February 2019 and June 2024 and were diagnosed with complete MPFL rupture on magnetic resonance imaging (MRI) were retrospectively reviewed. Patients with normal MRI findings in a 1:1 ratio were selected as the control group by computer-assisted randomisation.All patients in both groups were asked to perform MRI on, tibial tuberosity-trochlear groove (TT-TG) distance, lateral trochlear inclination (LTI) angle, sulcus angle (SA), medial femoral condyle height (MFCH), lateral femoral condyle height (LFCH), trochlear height (TH), patellotrochlear index (PTI), Koshino-Sugimoto Index (KSI), Caton-Deschamps Index (CDI) and Insall-Salvati Index (ISI) were measured and recorded. All measurements were made by two different orthopaedists and intra-observer reliability was evaluated. The measurements between the groups were compared statistically.

Result

A total of 98 patients, including 49 patients with complete MPFL rupture (study group) and 49 patients in the control group, were included in the study. Thirty of the patients in both groups were males and 19 were females. Mean age was 23.55 years in the study group and 24.29 years in the control group (p = 0.447). Satisfactory ICC scores were obtained in all measurements. LTI was lower in the study group than in the control group (p = 0.002), while SA was higher in the study group than in the control group. Both CDI and ISI were statistically significantly higher in the study group compared to the control group (p = 0.002, p = 0.003). The probability of predicting the risk of complete MPFL rupture of the risk analysis model created with radiological risk factors for complete MPFL rupture was 70.4%.

Conclusion

LTI, SA, TH and patella alta are risk factors for complete MPFL rupture after first LPD. Risk analysis of complete MPFL rupture after first dislocation can be successfully performed with MRI findings. This risk analysis can be used to predict the risk of developing complete MPFL after primary LPD, especially in risky patient groups, and can be used in a simple way to decide which patients will receive a preventive programme without the need for additional examination.

Level of Evidence

Level III, case-control study.

Extension patellar engagement index: a new measurement of patellar height

INTRODUCTION

Patellar instability is a multifactorial pathology requiring precise evaluation of its contributing factors, particularly patella alta. Patellotibial height measurement indexes, such as the Caton-Deschamps index, have the disadvantage of being referenced to the tibia. Patellotrochlear indexes are more appropriate but fail to account for variable knee flexion during magnetic resonance imaging (MRI).

OBJECTIVE

This study aims to validate a new MRI-based patellotrochlear measurement, the extension patellar engagement (EPE) index, which is reproducible and measures patellar height relative to the trochlea independently of knee flexion during MRI.

MATERIALS AND METHODS

A retrospective study was conducted on 77 MRIs (37 unstable patients with a history of patellar dislocation, 40 controls with meniscal injury). The EPE index is the ratio between the patellar engagement length on the cartilaginous trochlea and the patellar cartilage length, measured on a knee virtually extended. Four measurements on multiple sagittal slices were used to calculate the EPE index.

RESULTS

The inteobserver intraclass correlation coefficient (ICC) was excellent (0.79). The mean EPE index's value for all knees was 0.22. It was significantly higher (p = 0.034) in the instability group (0.26) compared to the control group (0.19). The average knee flexion during MRI was 11 ° (range: -8 ° to 25 °).

DISCUSSION

The EPE index is reproducible. It is an anatomical index to classify patella alta when the patella does not reach the trochlea in knee extension (EPE index ≤0). It is also a functional index, with a mean value of 0.19 in the control group.

CONCLUSION

The EPE index measures the patellar engagement on the trochlea taking into account the knee flexion during MRI. It may guide surgical decision-making for patellar distalization and quantify the required correction.

LEVEL OF EVIDENCE

III; retrospective comparative study.

Adapting the Dejour classification of trochlear dysplasia from qualitative radiograph- and CT-based assessments to quantitative MRI-based measurements

PURPOSE

To adapt the current D. Dejour trochlear dysplasia classification (v2.0) to only rely on quantitative magnetic resonance imaging (MRI) measurements (v3.0) to maximize objectivity and repeatability.

METHODS

A consecutive series of adult knee MRIs were divided into objective patellar instability (OPI, n = 127) or controls (n = 103; isolated meniscal tears) and postprocessed with multiplanar reconstruction (MPR) to standardize the sagittal plane and ensure true lateral views. Thresholds for sulcus angle, lateral trochlear inclination (LTI) and central bump were established using regression tree models to distinguish OPI from controls. The sensitivity and specificity of sulcus angle and LTI combinations to diagnose OPI were then evaluated, and the combination yielding the highest sensitivity was selected as basis for trochlear dysplasia classification. Finally, sulcus angle and LTI measurability and presence of a central bump >5 mm were used to grade dysplasia as low, moderate or high.

RESULTS

The regression tree models produced thresholds of ≥157° for sulcus angle and <14° for LTI to distinguish OPI from controls. 'Sulcus angle ≥157° OR LTI < 14°' yielded the highest sensitivity (87%) to diagnose OPI. The quantitative MRI classification was sulcus angle <157° AND LTI ≥ 14° for Type 0 (No dysplasia); (sulcus angle ≥ 157° OR LTI < 14°) AND central bump <5 mm for Type 1 (Low-grade dysplasia); (sulcus angle OR LTI are 'unmeasurable') AND central bump <5 mm for Type 2 (Moderate-grade dysplasia); (sulcus angle ≥ 157° OR 'unmeasurable' OR LTI < 14° OR 'unmeasurable') AND central bump ≥5 mm for Type 3 (High-grade dysplasia).

CONCLUSION

This MRI classification depends exclusively on quantitative measurements, has excellent interobserver agreement, and yields high sensitivity to diagnose OPI. The MRI imaging protocol with MPR mode and standardized measurements could be quickly adopted and correctly applied by clinicians worldwide in any type of institution to determine the ideal treatment plan.

LEVEL OF EVIDENCE

Level III.

Anatomic Risk Factors for Lateral Patellar Instability

With an incidence of approximately 42 per 100,000 persons annually, patellar instability is a debilitating condition that can result in dysfunction of the normal patellar tracking and potential cartilage damage. The stability of the patellofemoral (PF) joint involves an intricate relationship between muscular forces, soft tissues, trochlear and patellar geometry, and limb alignment. Several anatomic patellar risk factors (APRFs) have been identified including patella alta (Caton Deschamps >1.2; Insall-Salvati >1.2), rotational malalignment (femoral anteversion >30°, knee rotation >10°, and tibial rotation >35°), genu valgum (Valgus: zone 2 or greater), a lateralized tibial tubercle (tibial tubercle-trochlear grove distance >17 mm; tibial tubercle-posterior cruciate ligament distance >21 mm), and trochlear dysplasia. The importance of APRFs is highlighted by their overwhelming association with patellar instability; >80% of patients with patellar instability have at least 1 risk factor. Biomechanically, these risk factors increase lateralizing forces on the patella, increase maltracking (patellar tilt and subluxation), decrease contact area, and increase pressure in the PF joint. In addition, there is greater anisometry of the medial PF ligament reconstruction. Clinically, the presence of APRFs increases the chances of recurrence after a first episode as well as failure rates of medial PF ligament reconstruction. Initially described by Dejour on lateral radiographs, current APRF evaluation includes standard radiographs along with axial slice imaging, with magnetic resonance imaging being more commonly used currently. In some instances, mechanical axis radiographic views and axial computed tomography rotational alignment studies may be indicated. Each risk factor can be assessed independently, as there are good-quality studies defining abnormal thresholds for individual APRF. However, there is a lack of robust clinical data defining use of these thresholds for guiding decisions regarding nonsurgical/surgical treatment, specifically, which factors need to be surgically managed and at what threshold for optimal outcomes. It is important to understand that there is an intricate and complex interaction between risk factors that need to be considered during PF evaluation. Overall, evaluation of APRF is one of the core elements of PF instability management.

Morphological analysis of patellofemoral joint in haemophilic arthropathy: A case-control study

INTRODUCTION

Knees affected by haemophilic arthropathy exhibit distinct differences in both bone morphology and soft tissue behaviour. This study aims to analyse the morphological characteristics of the distal femur and patellofemoral joint in patients with haemophilia in comparison to normal healthy population.

MATERIAL AND METHODS

Study was conducted as pair-matched case-control study with 43 individuals in both the haemophilia group and the control group. Patellar luxation, patellar tilt (PT), length of the patella in both axis (pAP, pML), depth and angle of trochlear sulcus (SD, SA), lateral trochlear inclination (LTI), medial and lateral femoral facet length (mFL, LFL), intercondylar depth (ID), transepicondylar axis (TEA) and lateral condyle length (LCL) were assessed on knee MRI. Correlation between Pettersson score and measured variables were also analysed.

RESULTS

PT was medial sided in 10 (23.2%) cases in haemophilic group. Mean values of pAP, pML, PT were significantly lower in haemophilia group (p < .001, p: .007, p = .001 respectively). There were no significant changes in SA (p = .628), SD (p = .340), LTI (p = .685), LFL (p = .241) and MFC-LFC (p = .770) whilst mFL was significantly longer in haemophilia group (p = .009). ID (p < .001), TEA (p = .007) and LCL (p = .001) were all shorter in haemophilia group. Pettersson score was inversely correlated with pAP, pML, ID, TEA, LCL, pML/SA and ID/LCL.

CONCLUSION

Morphological changes in haemophilic arthropathy involve a smaller and medially-tilted patella, narrowed lateral condyle and transepicondylar axis, combined with reduced intercondylar depth. These alterations must keep in mind especially in pre- and intraoperative assessments for arthroplasty procedures.

The larger patellar tilt angle and lower intercondylar notch angle might increase posterior cruciate ligament injury risk: a retrospective comparative study

BACKGROUND

Posterior cruciate ligament (PCL) injuries are common ligament injuries of the knee, and previous studies often focused on the associations between the morphology of the knee and PCL injuries. Studies on the correlation between PCL injuries and patellofemoral alignment are limited.

METHODS

This retrospective study included 92 patients with PCL injured and 92 patients with PCL intact. Measurement parameters were compared between the two groups, including patellar tilt angle, congruence angle, patellar height, hip-knee-ankle angle, lateral trochlear inclination, femoral condyle ratio, bicondylar width, intercondylar notch width and index, notch angle, trochlear facet asymmetry, and trochlear sulcus depth and angle. Independent risk factors associated with PCL injuries were identified by logistic regression analyses.

RESULTS

In the PCL injured group, the patellar tilt angle was significantly larger (13.19 ± 5.90° vs. 10.02 ± 4.95°, P = 0.04); the intercondylar notch angle was significantly lower (60.97 ± 7.83° vs. 67.01 ± 6.00°, P = 0.004); the medial and lateral femoral condyle ratio were significantly larger (0.63 ± 0.64 vs. 0.60 ± 0.56, P = 0.031; 0.65 ± 0.60 vs. 0.58 ± 0.53, P = 0.005) than in the PCL intact group. There were 11 patients with patellar dislocation in the PCL injured group, accounting for 12%. In these patients, the patellar height was higher (1.39 ± 0.17 vs. 1.09 ± 0.25, P = 0.009); the trochlear sulcus angle was larger (157.70 ± 8.7° vs. 141.80 ± 8.78°, P < 0.001); and the trochlear sulcus depth was shallower (3.10 ± 1.20mm vs. 5.11 ± 1.48mm, P = 0.003) than those in the patients without patellar dislocation. Multivariate analyses showed that patellar tilt angle (each increase 1 degree, OR = 1.14) and intercondylar notch angle (each increase 1 degree, OR = 0.90) were independent risk factors for PCL injuries.

CONCLUSION

The patients with PCL injuries had larger patellar tilt angles, lower intercondylar notch angles, and longer posterior femoral condyles than patients with PCL intact. The larger patellar tilt angle and lower intercondylar notch angle might be risk factors for PCL injuries.

Editorial Commentary: Evaluation of Patellofemoral Instability Is Complex and Multifactorial

The work-up of patellofemoral instability is complex and multifactorial. Patient factors (i.e., age, activity demand, goals/expectations), clinical presentation (pain, instability, or both), and physical examination (i.e., J-sign, apprehension into flexion), must be correlated with imaging findings (radiographs, magnetic resonance imaging, computed tomography) and anatomic risk factors, including patella alta, trochlear dysplasia, patellar tilt, lateralized force vector, valgus, femoral anteversion, and tibial torsion. Thus, developing a standard battery of reliable and reproducible radiographic measures of patellofemoral instability is a challenge. Imaging cut-offs provide insight into relative risk of recurrent instability. We still fall short in using imaging parameters to predict when to operate, what procedure(s) to perform, and how the patient might do. Future directions include the use of artificial intelligence and 3-dimensional measurements to help simplify a complex problem.