Background
Trochlear dysplasia is frequently seen in patients with patellar instability and has shown to contribute to patellofemoral cartilage deterioration. Commonly, trochlear dysplasia is classified according to Dejour in four distinct types (A, B, C, and D), whereby type B and D seem to have a greater effect on patellofemoral kinematics compared to type A and C. Thus, surgical correction of trochlear dysplasia is currently recommended solely in patients with trochlear dysplasia type B and D. While previous studies reported that trochlear dysplasia is generally associated with other common patellofemoral anatomical risk factors, there is paucity in the literature regarding the differences seen when stratified by Dejour type.
Hypothesis/Purpose: The purpose of this study was therefore to investigate whether different types of trochlear dysplasia according to Dejour show distinct variations in other common patellofemoral anatomical variables in patients with patellar instability. It was hypothesized that severe trochlear dysplasia shows a stronger association with other patellofemoral anatomical parameters when compared to mild trochlear dysplasia.
Methods
This study evaluated 363 knees with trochlear dysplasia, who were scheduled to undergo surgery for the treatment of patellar instability at a single institution. All patients presented with a true lateral radiograph and preoperative MRI. Besides patient characteristics and trochlear dysplasia type according to Dejour, two independent reviewers assessed femorotibial (FT) rotation, tibial tuberosity trochlear groove (TTTG) distance, s(sagittal)TTTG, tibial tubercle-to-posterior cruciate ligament (TT-PCL) distance, supratrochlear spur height, sulcus depth, Merchants congruence angle, trochlea sulus angle, patellotrochlea index, patella tilt, patella angle, patella thickness, patella width and Caton-Deschamps index (CDI)
Results
The study cohort comprised 363 knees in 330 patients (66.7% female) with an average age of 22.5 ± 7.9 years and a mean BMI of 24.9 ± 5.4 kg/m2. Of the included knees, 62 (17.1%) presented with trochlea dysplasia type A, 122 (33.6%) with type B, 94 (25.9%) with type C and 85 (23.4%) with type D. When stratified by Dejour type, no statistically significant difference was found regarding age, sex, BMI, patellar width, patellar angle, patellar thickness, CDI, and TTPCL (n.s.). Yet, patients with Dejour types B and D had consistently greater values in the Merchants congruence angle (p=0.019), patellar tilt (p <0.001), patellotrochlar index (p=0.035), trochlea sulcus angle (p <0.001), supratrochlear spur height (p<0.001), TTTG (p<0.001), sTTTG (p<0.001) femoral-tibial rotation (p<0.001), and a smaller sulcus depth (p<0.001) compared to patients with Dejour types A and C, but accentuated in patients with Dejour type D.
Conclusion
Patients with trochlear dysplasia show distinct bony patellofemoral pathology. Particularly trochlear dysplasia type B and D shows increased values in other patellofemoral instability risk factors, when compared to type A and C. Thus, specifically patients with trochlear dysplasia type B and D should undergo thorough diagnostic assessment evaluating for further pathology to appraise and treat the entire patellofemoral dysplasia.