Introduction
Trochlear dysplasia is considered a major contributing factor for patellar instability. More recently, trochleoplasty procedures have become popularized to address this morphological abnormality. Both thick and thin flap trochleoplasty techniques exist, with the goal to deepen the trochlea while avoiding perforation of the trochlear cartilage during the procedure. However, the relative cartilage thickness in the dysplastic trochlea has not been well described. This study aimed to assess trochlear cartilage thickness and volume in knees with and without patellar instability and the relationship to measurements of trochlear dysplasia.
Methods
25 knees with symptomatic patellar instability were compared with 25 gender-matched knees. Retrospective chart review was performed to obtain demographic data. On sagittal images, trochlear cartilage thickness (TCT) and trochlear cartilage volume (TCV) were analyzed at the center, medial border, and lateral border of the trochlea. TCT was defined as the cartilage thickness halfway along the trochlear length at its maximum dimension. TCV was defined by total area of cartilage proximal to the plane of the intercondylar midpoint. Symptomatic and control values were compared using paired sample t-test. Stepwise multivariate linear regression was performed to assess for associations with standard radiographic parameters of trochlear dysplasia.
Results
TCT was significantly different between the medial, central and lateral trochlea in both the symptomatic and control groups (p<0.001). Only lateral TCT demonstrated a significant difference between groups, which was 20.3% (p=0.035) thicker in the symptomatic cohort compared to controls. No significant differences existed in TCV between symptomatic and control groups. In females, central TCT was 28.3% thicker in the symptomatic cohort (p=0.024), while medial TCV was 2.3x greater (p = 0.019). Males failed to demonstrate gender specific differences. Regression analysis demonstrated that patient height showed a significant relationship with all measurements except for medial TCV. Central TCT demonstrated a significant, independent relationship with trochlear depth (Coefficient 0.38, p = 0.011), while central TCV demonstrated a significant, independent relationship with trochlear depth (Coefficient 9.9, p <0.001), sulcus angle (Coefficient 1.1, p <0.001), and lateral trochlear inclination (Coefficient -1.1, p <0.001).
Conclusion
While trochlear dysplasia typically refers to abnormal bony morphology, this study demonstrates the role of differential contributions of chondral thickness and volume between knees with and without patellar instability, and that these measurements correlated with severity of dysplasia. Future studies should further investigate the relationship between TCT and TCV with other dysplasia parameters to better inform the surgical considerations of performing trochleoplasty in the treatment of patellar instability.