Quantifying the effects of extensor mechanism medializatlon procedures using MRI: a cadaver-based study.

Background: Patellofemoral joint kinematics are dependent on a variety of anatomical features. One of the most common causes of patellar instability is malalignment of the quadriceps extensor mechanism. The Southwick-Fulkerson osteotomy focuses on correcting malalignment of the quadriceps extensor mechanism through medialization of the tibial tubercle. MRI, in conjunction with established patellofemoral indices, allows quantitative evaluation of the patellofemoral joint during active quadriceps extension both pre- and postoperatively.
Purpose: This study aims to quantitatively evaluate the effects of extensor mechanism medialization procedures using established patellofemoral indices in order to establish a relationship between tubercle transfer distance and patellar tracking. It is believed that a 15mm medial transfer of the tibial tubercle will produce statistically significant changes in patellar tracking when evaluated during active quadriceps contraction.
Methods: Four fresh-frozen cadavers underwent a modified Fulkerson osteotomy. The central quadriceps tendon was identified and traction was applied with a vector parallel to the femoral diaphysis using sutures, to simulate active quadriceps contraction. MRI images were obtained following Omm (control) and 15mm tibial tubercle medialization. Each knee was evaluated at 30, 20, 10, and 0 degrees of flexion.
Results: Quantitative evaluation of patellar tracking during active quadriceps contraction detected significant changes in patellar translation following 15mm medial transfer of the tibial tubercle as compared to the control. The significantly reduced indices suggest reduced patellar lateralization and improved patellar tracking during the critical range of motion from 30 to 0 degrees of flexion.
Conclusions: The results of this study indicate that significant quantitative changes in patellar tracking occur following 15mm tibial tubercle medialization when evaluated during active quadriceps contraction using MRI in conjunction with established patellofemoral indices. These findings suggest that quantitative evaluation of patellar tracking may be a valuable pre- and postoperative tool when coupled with qualitative clinical findings.