A study on the diagnostic value of knee MRI parameters for lateral patellar compression syndrome: clinical application of P-PTA, LP and ISR

Introduction

Lateral patellar compression syndrome (LPCS) is characterized by increased lateral patellofemoral joint pressure caused by long-standing lateral patella tilt without dislocation, adaptive lateral retinaculum tightening, and an imbalance in stress between the lateral and medial femoral condyles (1,2). Further development of the disease causes articular cartilage damage, affects the normal activity of the knee joint, and causes great pain to the patient. Therefore, it is necessary to diagnose LPCS and take effective treatment measures as soon as possible (2,3). But, there is no established and widely accepted diagnostic reference standard. The diagnosis of LPCS relies mainly on clinicians’ subjective judgments and the results of various examinations, but lacks objective data support (4-7).

Both LPCS and knee osteoarthritis (KOA) patients may exhibit patellar chondromalacia. In LPCS, it is almost exclusively located in the lateral patellofemoral compartment, whereas in KOA the lesions are unpredictable and may occur medially, laterally, or both (1,2). Overlapping knee pain makes clinical distinction difficult (1,8,9). Yet treatment strategies diverge markedly: advanced KOA is typically managed with unicompartmental or total knee arthroplasty, while LPCS is addressed by isolated lateral retinacular release (8). Consequently, accurate differentiation is critical to avoid unnecessary arthroplasty and to tailor therapy appropriately.

To date, studies specifically focused on diagnosing LPCS with magnetic resonance (MR)-based quantitative parameters remain scarce. Most existing research has focused on patellofemoral and trochlear morphology, patellar position, and patellar chondromalacia—factors that are, however, closely linked to the etiology of LPCS (9-14). Magnetic resonance imaging (MRI), with its superior soft-tissue resolution and multiplanar capability, clearly delineates the margins of ligaments and other soft tissues while eliminating the magnification and distortion inherent to X-ray imaging caused by patient positioning or projection angle. Consequently, herein, we aimed to explore the feasibility of various structural measurement parameters of knee joint MRI to diagnose LPCS and to identify new MRI diagnostic indicators as references and guidance for LPCS clinical diagnosis. In addition, the differences of MR structural parameters between LPCS and KOA patients were discussed to provide reference imaging for clinical differentiation of the two diseases. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-858/rc).

Methods

Study participants

This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of Peking University Third Hospital of No. IRB00006761-M2024089. This study was a retrospective case-control study and all required variables were extracted from the picture archiving and communication system (PACS) and electronic medical record systems. According to the ethics committee, the study participants were exempted from providing informed consent. This study included 168 eligible patients from the Department of Sports Medicine, between March 2018 and February 2023. According to their diagnosis, all patients were divided into three groups: the LPCS group, the KOA group, and structurally normal group (n=56 per group). The patients with LPCS were diagnosed after treatment by doctors in the same department. The KOA group and the structurally normal group were defined according to the imaging classification of osteoarthritis (Kellgren-Lawrence grade). All patients included in the study had no history of patellar dislocation or femoral trochlear dysplasia.

LPCS diagnosis

A team of surgeons and radiologists diagnosed LPCS combining clinical symptoms, physical examination results, imaging feature analysis, and arthroscopic findings. The diagnostic criteria include the following aspects: (I) persistent pain in the anterior knee with patellofemoral joint compression-based aggravation; (II) there were tenderness points on the lateral edge or lateral fold of the patella during physical examination, accompanied by a positive patellar grinding test and a positive patellar slippage test; (III) upon imaging [MRI, computed tomography (CT) and X-ray], the patella showed a lateral tilt without dislocation, the patellofemoral joint space narrowed on contraction, the lateral patellar retinaculum fold showed thinning, and patellofemoral joint cartilage showed degeneration (Figure 1).

Figure 1 X-ray (A) and MR (B) images of a patient with LPCS. X-ray and MR images showed that the patella tilted laterally. MR images showed thickening and tightening of the lateral patellar retinaculum, and cartilage injury in the lateral space of the patellofemoral joint. LPCS, lateral patellar compression syndrome; MR, magnetic resonance.

Inclusion criteria and exclusion criteria for the LPCS group

Inclusion criteria: LPCS was confirmed based on lesions in unilateral knee joints, the imaging results, the arthroscopy findings, and knee joint pain symptoms. Exclusion criteria: patients with patellar dislocation, ligament injury, fractures, surgical contraindications, and incomplete clinical information.

Inclusion criteria and exclusion criteria for the KOA group

Inclusion criteria: patients who, on weight-bearing anteroposterior and lateral knee radiographs, were graded Kellgren-Lawrence II–IV, exhibiting definitive joint-space narrowing, osteophyte formation, and subchondral sclerosis or cystic changes characteristic of osteoarthritis. Exclusion criteria: patients with LPCS, patellar dislocation, ligament injury, fractures, surgical contraindications, and incomplete clinical information.

Inclusion criteria and exclusion criteria of the structurally normal group

The normal control group comprised participants who did not have LPCS or simple osteoarthritis. Patients attended the hospital because of knee discomfort. KOA grade I (Kellgren-Lawrence grade) could be included in this group. This group of patients was confirmed to have no significant structural abnormalities of the knee.

MR scanning protocol

GE, Siemens, or United Imaging MR scanners were used for standardized knee MR examination before the surgical treatment, including MR scanning position and scanning sequences. The scanning position was neutral: the patient lies supine on the examination table with the knee naturally extended and positioned within a dedicated knee coil, ensuring the midpoint of the knee aligns with the coil’s midpoint. The scanning sequences included sagittal and coronal fat-suppressed (FS) proton density-weighted imaging (PDWI) and sagittal T1-weighted imaging (T1WI). The parameters of PDWI included: echo time (TE) 30–40 ms; repetition time (TR) 2,000–3,000 ms; slice thickness 4 mm; spacing 0.5 mm; field of view (FOV) 160 mm × 160 mm; matrix 320×256; and number of excitations (NEX) 2–3. The parameters of T1WI included: TE 10–15 ms; TR 400–600 ms; slice thickness 4 mm; spacing 0.5 mm; FOV 160 mm × 160 mm; matrix 320×256; and NEX 2–3.

Image analyses

Image analysis was performed by two radiologists, with 10 years’ and 5 years’ experience, respectively, in imaging diagnosis of the musculoskeletal system. They used the picture PACS and a unified procedure to repeatedly determine the imaging indexes on the patients’ images. For each MRI parameter, two independent measurements were performed at an interval of ≥7 days, and the mean value was taken to minimize subjective measurement bias.

Imaging observation indicators

All MR observation indexes were performed in sagittal T1WI images. The measurement indexes included the patellar-patellar tibial angle (P-PTA), the quadriceps-patellar angle (Q-PA), the length of the patella (LP), the length of the patellar tendon (LT), the LP/LT ratio, the Insall-Salvati ratio (ISR). The P-PTA and Q-PA were employed to analyze the patella’s sagittal alignment on the patellofemoral joint. The P-PTA and Q-PA measurements were carried out on the midsagittal section where the upper and lower poles of the patella, the patellar tendon, and the quadriceps tendon could be observed. The P-PTA comprised the angle between the tuberosities tibia and the upper pole and lower pole (Figure 2). The Q-PA comprised the angle between the line passing behind the quadriceps tendon’s deepest fibers and a line drawn along the patella upper pole (Figure 3). The LP comprised the distance between the upper and lower poles of the patella. The LT comprised the distance between the tibial tubercle and the lowest point of the lower pole of the patella. The ISR is the ratio of LT to LP and is used to evaluate the patellar position (Figure 2) (15).

Figure 2 Measurement methods of LP, LT and P-PTA of knee joint. L1 is the LP, that is the distance between the upper pole and the lower pole of the patella. L2 is the LT, that is the connection through the lower pole of the patella and the tibial tubercle. The angle between L1 and L2 is P-PTA. LP, patellar length; LT, patellar tendon length; P-PTA, patellar-patellar tibial angle.

Figure 3 Q-PA measurement method of knee joint. L3 is a tangent along the inner edge of the quadriceps tendon, and L4 is a tangent along the upper edge of the patella. The angle between L3 and L4 is Q-PA. Q-PA, quadriceps-patellar angle.

Statistical considerations

The measured data are presented as the mean ± standard deviation. Normally distributed measurement data were compared using Univariate analysis of variance. Non-normally distributed measurement data were compared using the Kruskal-Wallis H test. In the different groups, the various indicators were analyzed using Bonferroni correction, and index comparisons within the same group were carried out using a T-test. A General Linear Model was employed to compare the differences in each MRI-derived parameter between genders. The intraclass-correlation coefficient (ICC) was used to assess the interobserver reliability of the measured values. The statistical data analysis and calculation of the area under curve (AUC) were carried out using SPSS 27.0 (IBM Corp., Armonk, NY, USA). A difference between values with a P value less than 0.05 was considered statistically significant.

The required sample size was determined using G power analysis. For a 0.5 effect size, we implemented a 0.05 alpha error rate and a 0.8 (1−beta) error rate. This indicated a required sample size of more than 144 participants (48 in the experimental group and 96 in the control group).

Results

This single-center retrospective case-control study extracted all data directly from the PACS system between March 2018 and February 2023, retaining only 168 patients whose images were complete and who met all inclusion and exclusion criteria. There was no active recruitment, screening, or follow-up process; therefore, the numbers of individuals at each stage and the reasons for exclusion were not reported.

Characteristics of the study participants

This study included 168 participants (59 males and 109 females; mean age: 47.9±14.5 years; range, 19–81 years), and the affected sides were no different among the three groups (P=0.359). The participants in the LPCS group were significantly older than those in the structurally normal group (P<0.001) (Table 1). There was a significant sex difference in the LPCS group (P=0.003) (Table 1). The sex matching of patients among the three groups was incomplete. There was no significant sex difference in each measurement index of each group (P=0.119, 0.286, 0.868, 0.866, 0.768 and 0.714, respectively).

Comparison of MR measurement parameters of knee joints between the three groups

Among the MR measurement parameters of the three groups, except for the Q-PA, the differences between the groups for the measurement parameters were statistically significant, including P-PTA, LP, LT and LP/LT (Table 2).

The LPCS group had a lower P-PTA than that in KOA and structurally normal groups (P=0.022 and P<0.001, respectively). The P-PTA was not significantly different between the KOA and structurally normal groups (P=0.090) (Table 2).

The LPCS group had a lower LP than that of the KOA and structurally normal groups (P=0.009 and P<0.001, respectively). The LT was not significantly different between the LPCS and KOA groups (P=0.492). However, the LPCS group had a higher LT than that in structurally normal group (P=0.015). The LP/LT ratio was not significantly different between the LPCS and KOA groups (P=0.073). However, the LPCS group had a smaller LP/LT ratio than that in the structurally normal group (P<0.001). For ISR, the differences between the three groups were all statistically significant (P<0.001). The LPCS group had a higher ISR than that of the KOA and structurally normal groups (P=0.030 and P<0.001). The KOA group had a higher ISR than that of structurally normal group (P=0.003) (Table 2).

The LPCS group had a larger Q-PA than that of the structurally normal group (P=0.034) (Table 2).

Analysis of the AUC of the MR measurement parameters

In the AUC analysis, the best cut-off value of the P-PTA was 146.45°, and values greater than this showed 67.86% sensitivity and 59.82% specificity for diagnosis. The best cut‑off value of the LP was 41.10 mm, and values greater than this showed 78.57% sensitivity and 55.36% specificity for diagnosis. The best cut-off value of the LP/LT was 0.85, and higher values showed 67.86% sensitivity and 58.93% specificity for diagnosis. The best cut-off value of the ISR was 1.19, and higher values showed 66.07% sensitivity and 60.71% specificity for diagnosis. The AUCs of the P-PTA, LP, LP/LT, and ISR were 0.673, 0.684, 0.665, and 0.668, respectively (Table 3 and Figure 4).

Figure 4 ROC curves of P-PTA, LP, LP/LT and ISR for differentiating LPCS from KOA and structurally normal groups. (A) ROC curves of P-PTA for differentiating LPCS from KOA and structurally normal groups. (B) ROC curves of LP for differentiating LPCS from KOA and structurally normal groups. (C) ROC curves of LP/LT for differentiating LPCS from KOA and structurally normal groups. (D) ROC curves of ISR for differentiating LPCS from KOA and structurally normal groups. ISR, Insall-Salvati ratio; KOA, knee osteoarthritis; LP, patellar length; LPCS, lateral patellar compression syndrome; LT, patellar tendon length; P-PTA, patellar-patellar tibial angle; ROC, receiver operating characteristic.

In the AUC analysis for differentiating LPCS from structurally normal group, the best cut-off value of the P-PTA was 146.45°, and values greater than this showed 67.86% sensitivity and 67.86% specificity for diagnosis. The best cut‑off value of the LP was 39.43 mm, and values greater than this showed 59.82% sensitivity and 81.25% specificity for diagnosis. The best cut-off value of the LP/LT was 0.85, and higher values showed 67.86% sensitivity and 71.43% specificity for diagnosis. The best cut-off value of the ISR was 1.19, and higher values showed 66.07% sensitivity and 73.21% specificity for diagnosis. The best cut-off value of the Q-PA was 46.45, and higher values showed 58.93% sensitivity and 71.43% specificity for diagnosis. The AUCs of the P-PTA, LP, LP/LT, ISR and Q-PA were 0.720, 0.740, 0.727, 0.731 and 0.641, respectively (Table 4 and Figure 5).

Figure 5 ROC curves of P-PTA, LP, LP/LT, ISR and Q-PA for differentiating LPCS from structurally normal group. (A) ROC curves of P-PTA for differentiating LPCS from structurally normal group. (B) ROC curves of LP for differentiating LPCS from structurally normal group. (C) ROC curves of LP/LT for differentiating LPCS from structurally normal group. (D) ROC curves of ISR for differentiating LPCS from structurally normal group. (E) ROC curves of Q-PA for differentiating LPCS from structurally normal group. ISR, Insall-Salvati ratio; LP, patellar length; LPCS, lateral patellar compression syndrome; LT, patellar tendon length; P-PTA, patellar-patellar tibial angle; Q-PA, quadriceps-patellar angle; ROC, receiver operating characteristic.

Discussion

The most important finding of our study is that knee MR measurements can be used for the identification and auxiliary diagnosis of LPCSs. The P-PTA and LP values in patients with LPCS were significantly lower than those in the KOA and normal control groups. The ISR of the patients with LPCS was larger than those of the KOA and the normal control groups. Our study also found that patients with LPCSs are generally older than patients with KOA (2), and women are more likely to suffer from LPCS than men.

At present, a number of studies have confirmed the correlation between the P-PTA and patellar softening, and this parameter is closely related to sagittal patellar tilt (9,10,16-22). Aksahin et al. (18) found that sagittal patellar tilt was associated with chondromalacia patellae, and thus might be one of the factors leading to chondromalacia patellae. That study identified a significant association between sagittal patellar tilt and the P-PTA, with the P-PTA in patients with chondromalacia patellae being significantly lower than that in the control group. The authors suggested the inclusion of sagittal patellar tilt in the routine index of patellofemoral joint evaluation. In our study, compared with that in the normal controls, the P-PTA in the LPCS group was significantly lower, which supported the results of Aksahin’s study (18). Our study observed a significantly reduced P-PTA in LPCS patients, indicating a “low-lying and tilted” patellar position in the sagittal plane. These findings align with the mechanism demonstrated by Banach et al. (19) via MRI, wherein the supratrochlear rim causes early high-stress contact between the patella and femur during knee flexion, and are consistent with the “medial femoral condylar ridge friction theory” proposed by Outerbridge (20-22). Our study attributes LPCS to “cartilage degeneration caused by long-term lateral high-pressure”, which is entirely consistent with the anatomic-mechanical model proposed by Piontek (23), who indicated that the “supratrochlear rim triggers early high-stress contact and causes isolated patellar chondromalacia”, suggesting that both share the same pathological basis. Therefore, P-PTA can serve as a radiographic parameter for quantifying this anatomic-mechanical conflict.

Damgacı et al. (9) studied the correlation between the alignment of the patella (both sagittal and lateral patellar tilt) and the occurrence and staging of chondromalacia patellae. The P-PTA of patients with severe chondromalacia patellae was observed to be significantly lower than that of the controls, indicating an association between chondromalacia patellae and sagittal patellar tilt. At the same time, the authors reported that lateral patellar tilt was closely related to chondromalacia patellae. The patients with severe chondromalacia patellae had a significantly lower lateral patellar tilt compared with that in the controls. That study showed that that the P-PTA value and the lateral patellar tilt angle were smaller in patients with chondromalacia patellae, and there was a positive correlation between the two parameters. This finding helps to explain our findings. Herein, we showed that the patients with LPCS had a significantly lower P‑PTA compared with that of the controls, while the lateral patellar tilt angle of the patients with LPCS was significantly smaller than that of normal controls. Therefore, we propose that the P-PTA can be used as a predictor of LPCS and for LPCS identification and auxiliary diagnosis.

Neyret et al. (24) found that the patellar ligament was longer in patients with patellar instability. They also reported that the cause of a high patella is a too long patellar ligament, rather than the low tibial insertion of the patellar ligament. In our study, the LT of the LPCS group was the longest compared with the LTs of the KOA and structurally normal groups. The patellar ligament of patients with LPCS is longer, the patellar position is higher, and the patellofemoral joint is not in good alignment, which are consistent with the pathological process of LPCS. Stefanik et al. (25) studied the relationship between a high patella and the occurrence and severity of patellofemoral osteoarthritis. The results showed that the larger the ISR (and the higher the patella position), the smaller the contact area of the patellofemoral articular cartilage, resulting in increased articular surface stress and more vulnerable articular cartilage. Stefanik further observed that as ISR rises, the lateral patellofemoral compartment bears higher contact stress than the medial side, predisposing its cartilage to earlier and more severe damage. Our study found that an ISR >1.19 indicates an increased risk of LPCS, consistent with the conclusion reported by Banach et al. (19) that “an Insall-Salvati ratio >1.2 is significantly correlated with isolated patellar chondral lesions”. These results further support the inclusion of ISR in the diagnostic criteria for LPCS to identify potential cases of patella alta. We observed that in patients with LPCS, the ISR was higher compared with that in both the KOA and structurally normal groups. Our findings suggest that, in patients with LPCS, a relatively high-riding patella and patellofemoral malalignment could concentrate forces on the lateral compartment, potentially predisposing it to cartilage injury.

In our study, patients with LPCS exhibited significantly shorter LP than the structurally normal group, suggesting secondary structural remodeling linked to chronic lateral high-pressure stress, distinct from medial hypoplasia in recurrent dislocation or patellar height anomalies in chondromalacia. Our study demonstrated shortened LP in LPCS patients, consistent with the “secondary patellar shortening due to chronic lateral hyper-pressure” observed intraoperatively by Crooks (26), indicating that LP may serve as an auxiliary marker reflecting long-term lateral stress remodeling (13,27). It is important to consider that the observed shortening of LP in the LPCS group may be influenced by the cohort’s older age, as previous studies have suggested that LP can decrease with age (28). However, even after considering this potential confounding effect, the significant difference in LP between the LPCS and the age-matched KOA group suggests that chronic lateral hyper-pressure in LPCS may contribute to additional, disease-specific morphological remodeling of the patella, as proposed by Crooks (26). Thus, LP shortening serves as an auxiliary imaging marker of LPCS, reflecting morphological remodeling due to chronic lateral stress (27,28).

Damgacı et al. (9) reported that the Q-PA was associated with chondromalacia patellae. The authors found that the Q-PA was significantly reduced in patients with severe disease compared with that in patients with mild disease. In addition, the Q-PA was lower in female patients than in male patients. By contrast, we found that in patients with LPCS, the Q-PA was higher compared with that in the normal controls. The clinical significance of this result is not clear; however, further analysis showed that as the Q-PA increased, the size of the patellofemoral joint space decreased, and there was an increase in the risk of cartilage injury. Further research is needed to verify the accuracy of this result and determine its clinical significance.

The parameters employed in this study demonstrated satisfactory sensitivity and specificity for distinguishing LPCS from normal controls; however, their ability to separate LPCS from both KOA and normal controls simultaneously was only modest. Our analysis may be related to the complexity of LPCS disease. The diagnosis of LPCS cannot be a single indicator, and multiple and different types of indicators may be required for diagnosis. Although the sensitivity and specificity are not high, the MR measurement indicators still have value as ancillary tools for LPCS diagnosis, providing new insights and ideas for clinical practice while also helping to distinguish LPCS from normal anatomical variants; they may thus contribute to further refinement of the diagnostic criteria for LPCS.

There are some limitations in this study. The age and sex of the patients did not match. It is likely that the KOA group included patients with concomitant patellofemoral chondromalacia, as patellofemoral compartment involvement is common in generalized osteoarthritis. The ’structurally normal’ control cohort consisted of patients who presented with knee discomfort but without definitive structural abnormalities on imaging. While this group serves as a practical clinical comparator, it does not represent a true asymptomatic healthy population. The study was limited by its single center and retrospective design. We did not include the patients’ body mass index and exercise status. Technical limitations may lead to errors in manual measurement data. Only MR images were evaluated, and the measurement results of other examination methods (CT, X-ray) were not included.

Conclusions

Based on a comparative MRI analysis, this study demonstrates that P-PTA and ISR serve as reliable ancillary diagnostic indices for LPCS. Patients with LPCS exhibited a significantly lower P-PTA (optimal cut-off 146.45°) and a higher ISR (optimal cut-off 1.19), indicating pronounced sagittal patellar tilt and patella alta. Meanwhile, a shortened LP can to some extent assist in diagnosing LPCS, as it reflects morphological remodeling caused by chronic lateral stress. Although individual parameters yield moderate sensitivity and specificity, their combined assessment effectively distinguishes LPCS from KOA, thereby providing objective imaging guidance for clinicians to select targeted treatments such as lateral retinacular release.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-858/rc

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-858/dss

Funding: This work was supported by the National Natural Science Foundation of China (Nos. 82371921 and 81971578), Proof of Concept Program of Zhongguancun Science City and Peking University Third Hospital (No. HDCXZHKC2022202), and Key Clinical and Cohort Construction Project of Peking University Third Hospital (No. BYSYDL2023013).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-858/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of Peking University Third Hospital of No. IRB00006761-M2024089. All required variables were extracted from the picture archiving and communication system and electronic medical record systems. According to the ethics committee, the study participants were exempted from providing informed consent.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Wu T, Tang S, Wang F. Treatment for lateral patellar impingement syndrome with arthroscopic lateral patelloplasty: a bidirectional cohort study. J Orthop Surg Res 2017;12:173. [Crossref] [PubMed]
2. Chen JB, Chen D, Xiao YP, Chang JZ, Li T. Efficacy and experience of arthroscopic lateral patella retinaculum releasing through/outside synovial membrane for the treatment of lateral patellar compression syndrome. BMC Musculoskelet Disord 2020;21:108. [Crossref] [PubMed]
3. Saper MG, Shneider DA. Diagnosis and treatment of lateral patellar compression syndrome. Arthrosc Tech 2014;3:e633-8. [Crossref] [PubMed]
4. Jeong JH, Chang MJ, Kang SB, Chang CB, Yoon C, Park J, Lee SA. Prevalence of excessive lateral pressure syndrome in varus osteoarthritic candidates for high tibial osteotomy. Knee 2018;25:1192-6. [Crossref] [PubMed]
5. Merchant AC, Fulkerson JP, Leadbetter W. The Diagnosis and Initial Treatment of Patellofemoral Disorders. Am J Orthop (Belle Mead NJ) 2017;46:68-75.
6. Rothermich MA, Glaviano NR, Li J, Hart JM. Patellofemoral pain: epidemiology, pathophysiology, and treatment options. Clin Sports Med 2015;34:313-27. [Crossref] [PubMed]
7. Fulkerson JP. Diagnosis and treatment of patients with patellofemoral pain. Am J Sports Med 2002;30:447-56. [Crossref] [PubMed]
8. Yang YP, Ling YD, Pang CN, Li N, Gong YN, Cui GQ, Gong X, Ao YF. Novel method for diagnosing lateral patellar compression syndrome using X-ray: a retrospective case-control study. Ann Transl Med 2021;9:445. [Crossref] [PubMed]
9. Damgacı L, Özer H, Duran S. Patella-patellar tendon angle and lateral patella-tilt angle decrease patients with chondromalacia patella. Knee Surg Sports Traumatol Arthrosc 2020;28:2715-21. [Crossref] [PubMed]
10. Chen Y, Li J, Yang H, Lv F, Sheng B, Lv F. Differences in Patellofemoral Alignment Between Static and Dynamic Extension Positions in Patients With Patellofemoral Pain. Orthop J Sports Med 2024;12:23259671231225177. [Crossref] [PubMed]
11. Ackermann J, Bergheim N, Hartmann M, Vlachopoulos L, Fucentese SF. Trochlear Dysplasia Is Associated With Increased Sagittal Tibial Tubercle Trochlear-Groove Distance in Patients With Patellar Instability. Arthroscopy 2025;41:1002-8. [Crossref] [PubMed]
12. Kong Y, Yu H. A study on the correlation between patellofemoral joint morphology and early patella malacia in young adults: quantitative analysis based on magnetic resonance. Ann Transl Med 2023;11:48. [Crossref] [PubMed]
13. Demir M, Şahan MH. Evaluation of the relationship between trochlear and patellar morphology and patellar chondromalacia with magnetic resonance imaging. Acta Orthop Belg 2023;89:409-16. [Crossref] [PubMed]
14. Drew BT, Redmond AC, Smith TO, Penny F, Conaghan PG. Which patellofemoral joint imaging features are associated with patellofemoral pain? Systematic review and meta-analysis. Osteoarthritis Cartilage 2016;24:224-36. [Crossref] [PubMed]
15. Verhulst FV, van Sambeeck JDP, Olthuis GS, van der Ree J, Koëter S. Patellar height measurements: Insall-Salvati ratio is most reliable method. Knee Surg Sports Traumatol Arthrosc 2020;28:869-75. [Crossref] [PubMed]
16. Arslan FZ, Yücel Oğuzdoğan G. Correlating quadriceps patellar tendon angle and lateral patellar tilt angle in patients with irregular alignment: a cross-sectional study with retrospective data. Quant Imaging Med Surg 2024;14:3695-706. [Crossref] [PubMed]
17. Kim YM, Joo YB, Lee WY, Park IY, Park YC. Patella-patellar tendon angle decreases in patients with infrapatellar fat pad syndrome and medial patellar plica syndrome. Knee Surg Sports Traumatol Arthrosc 2020;28:2609-18. [Crossref] [PubMed]
18. Aksahin E, Aktekin CN, Kocadal O, Duran S, Gunay C, Kaya D, Hapa O, Pepe M. Sagittal plane tilting deformity of the patellofemoral joint: a new concept in patients with chondromalacia patella. Knee Surg Sports Traumatol Arthrosc 2017;25:3038-45. [Crossref] [PubMed]
19. Banach A, Hata N, Crawford R, Piontek T. Supratrochlear Rim is Correlated with Isolated Patellar Chondromalacia on Magnetic Resonance Imaging of the Knee. Arthrosc Sports Med Rehabil 2024;6:100855. [Crossref] [PubMed]
20. Outerbridge RE, Dunlop JA. The problem of chondromalacia patellae. Clin Orthop Relat Res 1975;177-96. [Crossref] [PubMed]
21. Outerbridge RE. Further studies on the etiology of chondromalacia patellae. J Bone Joint Surg Br 1964;46:179-90.
22. Outerbridge RE. The etiology of chondromalacia patellae. J Bone Joint Surg Br 1961;43-B:752-7. [Crossref] [PubMed]
23. Piontek T, Bąbik B, Bąbik J, Banach A. Supratrochlear Rim Resection: Autologous Matrix-Induced Chondrogenesis-Based Arthroscopic Technique for Patients With Isolated Patellar Chondromalacia. Arthrosc Tech 2025;14:103571. [Crossref] [PubMed]
24. Neyret P, Robinson AH, Le Coultre B, Lapra C, Chambat P. Patellar tendon length--the factor in patellar instability? Knee 2002;9:3-6. [Crossref] [PubMed]
25. Stefanik JJ, Zhu Y, Zumwalt AC, Gross KD, Clancy M, Lynch JA, Frey Law LA, Lewis CE, Roemer FW, Powers CM, Guermazi A, Felson DT. Association between patella alta and the prevalence and worsening of structural features of patellofemoral joint osteoarthritis: the multicenter osteoarthritis study. Arthritis Care Res (Hoboken) 2010;62:1258-65. [Crossref] [PubMed]
26. Crooks LM. Chondromalacia patellae. Early results of a conservative operation. J Bone Joint Surg Br 1967;49:495-501.
27. Sheehan FT, Shah P, Boden BP. The Importance of Medial Patellar Shape as a Risk Factor for Recurrent Patellar Dislocation in Adults. Am J Sports Med 2024;52:1282-91. [Crossref] [PubMed]
28. Schneider MT, Rooks N, Besier T. Cartilage thickness and bone shape variations as a function of sex, height, body mass, and age in young adult knees. Sci Rep 2022;12:11707. [Crossref] [PubMed]