Treatment of Complex Patellofemoral Instability: Valgus and Torsional Deformities
摘要
Axial and coronal malalignments are less common and therefore less understood causes of patellofemoral instability. Increased tibial torsion and femoral torsion are both considered factors that promote patellar instability. Controversy remains regarding when to consider torsional malalignment, how to measure torsion on imaging, and when to consider surgery. There are several types of torsional malalignments because increased torsion within a segment is not always compensated for by that of the segment above or below. Some of these have been implicated in patellofemoral instability. On the femoral side, surgical correction by osteotomy is considered when internal torsion is greater than 40 degrees. For deformities between 25° and 40°, surgical correction is considered only in cases of concomitant valgus malalignment, lateral patellofemoral osteoarthritis, or revision. The procedure is not only effective in controlling patellar instability, but it is also safe; the most common adverse event appears to be nonunion. In contrast, proximal tibial derotation osteotomy has been reported only for anterior knee pain with or without patellofemoral instability. It carries a risk of peroneal nerve injury. Caution is recommended in determining indications and, in rare cases where intervention is warranted, gradual correction with an external fixator. Genu valgum may be associated with patellar malalignment and instability. Distal varus osteotomy should be considered for deformities ≥5°. This threshold may be lowered to ≥3° if lateral patellofemoral or tibiofemoral osteoarthritis is present. Closing-wedge or opening-wedge techniques can both be used and provide significant pain relief and improve patellofemoral stability.