Relationship between the Patellar Ridge and the Femoral Trochlea in the Patellar Tracking.

OBJECTIVE: To investigate the anatomic morphology of the patellar ridge and how it matches the femoral trochlea in patellar tracking.

METHOD: We selected 40 volunteers, 20 males (age, 28 ± 5 years) and 20 female (age, 27 ± 6 years), who were completely asymptomatic with normal knee structures. We measured the right or left legs of volunteers, and the region from the distal femur to the tibial tuberosity was scanned by computed tomography (CT) with flexion at 0°, 30°, 60°, and 90°. CT data was reconstructed using image analysis software (Mimics). Variables such as the angle between the patellar ridge and patellar long axis, the tibial external rotation angle, as well as the best matching position between the patellar ridge and femoral trochlea at different knee flexion angles were measured. A single experienced orthopedic surgeon performed all the measurements, and the surgeon was blinded to the subject identifying information. We analyzed the differences between the various angles using a one-way analysis of variance. The differences between genders were analyzed using the t test.

RESULTS: The intraclass correlation coefficient (ICC) values were greater than 0.81 for all measurements, and the ICC value is almost in perfect agreement. The angle between the patellar ridge and the patellar long axis was 11.13° ± 4.1°. The angle in male participants was 10.87° ± 4.5° and it was 12.09° ± 3.7° in female participants. There were significant differences between each angle (0°, 30°, 60°, and 90°). The angles between the patellar ridge and femoral trochlear groove did not greatly increase with the knee flexion. The tibial internal rotation angle also showed a gradually increase at knee flexion of 0°-60°, and a gradually decrease at 60°-90°. The best-fit point between the patellar ridge and femoral trochlear groove gradually increased along with the knee flexion. There were no significant differences between male and female participants at all angles ( P < 0.05).

CONCLUSION: The anatomic morphology of the patellar ridge allows better matching between the patellar ridge and femoral trochlea during knee flexion, which is an important mechanism for the regulation of patellar tracking.