chapter 2: Biomechanics of the Patellofemoral Joint

Abnormal Biomechanics

Even minor alterations in the knee joint can profoundly affect patellofemoral contact loading and retinacular stresses. Structural tilt of the patella will eventually result in adaptively shortened lateral retinaculum, which can abnormally increase loading of the lateral facet while reducing and distorting load on the distal medial facet of the patella. There is normally a broad distribution of contact along the distal patella at 30° of knee flexion. Flatow et al (49) showed a dramatic reduction of contact area with simulated lateral tilt (5°) and lateral translation (5 mm) of the patella. It is evident that even minor alterations of patellofemoral alignment can create peak loads on articular cartilage, which will eventually lead to pathological changes in the joint. Distal tethering of the patella (Fig. 2.12), as well as mediolateral imbalance, will cause abnormal peak stresses on articular cartilage. Subsequent chapters in this book will explore the clinical ramifications of these mechanical changes in detail.

Hagena et al (50) studied retropatellar forces after posterior cruciate ligament (PCL) rupture. Presumably related to the resulting posterior tibial translation following PCL rupture, these researchers noted elevated retropatellar contact pressures in PCL‑deficient knees, which may have long‑term implications for patellofemoral degeneration after PCL rupture.


Inside Chapter 2: