High-grade trochlear dysplasia increases patellofemoral joint pressure and decreases the knee extension torque, and tibial tubercle anteriorisation does not correct these effects: Biomechanical study in vitro.

Purpose: High-grade femoral trochlear dysplasia is associated with anterior knee pain, patellar maltracking, instability and the development of osteoarthritis. Scientific studies have signified the importance of trochlear resection on the knee extensor mechanism, and dysplasia can be addressed by a groove-deepening trochleoplasty. Alternatively, tibial tubercle anteriorisation has been proposed to reduce patellofemoral joint (PFJ) pressure and alleviate pain from osteoarthritis. However, the relative contributions of articular changes in the sagittal and axial planes remain unknown. This study aimed to better understand the effect of these different osteotomies, that alter the sagittal plane geometry, on PFJ biomechanics.

Methods: Seven cadaveric knees were used to measure the following factors: (1) PFJ contact pressure; (2) Knee extension torque (KET); and (3) Patellar kinematics at 60°, 45°, 30°, 15° and 0° of knee flexion among four different osteotomy states: native, anteriorised trochlea, combined anteriorised trochlea and anteriorised tibial tubercle, and anteriorised tibial tubercle. Analysis was made using a two-way repeated-measures analysis of variance.

Results: Anteriorising the trochlea increased mean PFJ contact pressures ×2.9 at 0° (p = 0.024) and ×2.2 (p = 0.029) at 15° flexion compared to the native state. Peak pressures increased ×4.9 at 0° and ×3.3 at 15° (n.s.). Anteriorising the trochlea reduced KET 18% (p = 0.001) at 40° flexion and 19% (p = 0.009) at 50°. The patella was anteriorised 8 mm in the extended knee (p < 0.001) and flexed 8° at 45° knee flexion (p < 0.001) compared to the native state. Elevating the tibial tubercle, alone or combined with an anteriorised trochlea, did not have a significant effect on the respective outcome measurements.

Conclusion: An anteriorised trochlea elevated PFJ contact pressure, reduced KET and altered patellar position during knee flexion/extension movement, while a tibial tubercle anteriorisation had a negligible opposite effect. These findings indicate that symptoms associated with high grade trochlear dysplasia may be addressed better at the trochlea, rather than at the tibial tubercle.

Level of evidence: Basic science.