Dynamic three-dimensional in vivo tracking of the abnormal extensor mechanism

This study addresses the effects of extensor mechanism realignment (EMR) on patellar tracking patterns in pathologic knees. Ten patients diagnosed with patellar maltracking, subluxation, or patellofemoral malalignment and requiring an EMR participated in the study. Lateral release and vastus medialis obliquus (VMO) advancement were performed unilaterally in all ten patients. Tibial tubercle transfer was conducted in five of these patients. Electromagnetic sensors were used to dynamically measure patellar and tibial motion relative to the femur in three dimensions. Patella flexion, rotation, tilt, and shift were measured as the knee was passively flexed from full extension to 90° knee flexion. Lateral release had little effect on patellar spin and flexion patterns, although it did increase net medial shift in seven of ten cases. Following VMO advancement the rate of patellar flexion and net medial patellar spin increased in seven cases. Net lateral patellar tilt increased in seven cases and medial shift increased in five cases. Due to a limited amount of data, conclusive observations could not be made regarding tibial tubercle transfer