Short lateral posterior condyle is associated with trochlea dysplasia and patellar dislocation
Surgeons mainly consider the anterior anatomy of the distal femur in the treatment of patellar instability (PI) with trochlear dysplasia (TD). Through this research, the idea was to analyse the posterior femoral condyle length in TD. The research team posited the presence of morphological differences in the posterior part of the femoral epiphysis in TD compared to a control group. They also postulated that the posterior bicondylar angle (PCA), in the axial plane, was increased in TD.
This is a single-centre morphological study of 100 patients who had a computed tomography (CT) using the same protocol. 50 patients with PI (25 dysplasias A and 25 B-C-D according to the Dejour classification), and 50 controls were included. All patients presenting a clinical PI were considered for the study. None of these patients had undergone a surgical treatment prior to imaging. Demographic characteristics, BMI, and laterality were comparable in all patients. 20 pilot CT scans were used to establish the methodology. The following measurements were performed: anterior bicondylar angle, PCA, and condylar lengths with respect to the surgical transepicondylar axis. Ratios were calculated in relation to the femoral width. TD was classified according to the Dejour classification in grade A or grades B–C–D. An analysis of variance and a linear model were performed within some groups to investigate which parameters correlated with the classification’s grade.
This study showed a link between TD and the PCA: control group (1.4 ± 0.2°), type A group (1.6 ± 0.3°), and types B, C, D group (2.6 ± 0.3°) (p = 0.01). The difference between the control group and types B, C, D TD group was significant (p = 0.002). In groups B, C, D, the PCA was more important, which proves that in these groups the posterior part of the lateral condyle was relatively shorter compared to the medial condyle. The greater the dysplasia, the longer the medial condyle was in the anterior posterior (p = 0.02).
This study shows not only an anterior but also a posterior anomaly in PI with TD. There is a correlation between the severity of the anterior deformation and the PCA: in other words, the knee is placed in valgus in flexure which promotes the external dislocation of the patella. This anatomical study could open a field of research on the development of surgical treatments based on the correction of posterior condylar femoral anomalies in PI.
Level of evidence
KeywordsDistal femur morphology Condylar length Patellar instability Trochlear dysplasia Transepicondylar axis CT measurements
Group trochlear dysplastic group
Episodic patellar dislocation
Surgical transepicondylar axis
Anterior bicondylar line
Posterior condylar line
Posterior condylar angle
Femoral medial epicondyle
Femoral lateral epicondyle
Femoral medial condyle posterior (AP)
Femoral lateral condyle posterior (AP)
Femoral medial condyle anterior (AP)
Femoral lateral condyle anterior (AP)
Total medial condyle (AP)
Total lateral condyle (AP)
Mechanical lateral distal femoral angle
Standard error to the mean
We would like to thank the research team, and our administrative and secretarial support who actively contributed to data collection. We thank Fanny Blanchon (Associate Professor of English) and Oriane Di Marco who provided medical writing services. We thank Camille Chesnel and Philippe Wagner who provided statistical services.
JR performed the statistical analysis and drafted the manuscript. JR, SL, and CFB carried out the radiologic studies. JR, SC, SL, PHN, and ES carried out in the writing of the manuscript. SL, PHN and ES participated in the design of the study. ES, SL, and PHN conceived the study, coordinated and helped to draft the manuscript. All authors read and approved the final manuscript.
No funding source.
Compliance with ethical standards
Conflict of interest
JR: No conflict of interest. SL: consultant: Smith Nephew, Medacta; institutional support: Amplitude, Corin. SC: No conflict of interest. CFB: No conflict of interest. PHN: board membership: Effort Board; consultancy: Latilini; employment: Healthpoint; expert testimony: Healthpoint, Latilini; Royalties: Tornier; travel, accommodations: Latilini, Amplitude. ES: No conflict of interest.
The Ethics Committee of the Hospices Civils de Lyon approved the study (Groupement Hospitalier Est, Boulevard Pinel, 69,500 BRON). The ID number of the approval was 17-02.
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