Jordy van Sambeeck

General introduction 11 1 A B Adductor tubercle Patellofemoral ligament Anterior joint capsule Superficial medial collateral ligament Gracilis Semimembranosus Posterior oblique Semitendinosus Sartorius (cut) Figure 2. Medial aspect of the knee including the medial patellofemoral ligament. This figure was published in Insall & Scott Surgery of the Knee, Sixth Edition, 2018, Chapter 1 Anatomy, Figure 1.64, Page 32, Copyright Elsevier (2018). In a normal knee, the patella is stable during full range of motion of the knee, including flexion and full extension. This patellofemoral stability is maintained by static stabilization on one hand and by dynamic stabilization on the other hand. Static stability is provided by bony and soft tissue structures and includes indirect stabilization by alignment of the leg and direct stabilization by anatomy of the patella and the trochlear groove. Dynamic stability is provided by the action of muscles. Failure to stabilize the patella can lead to lateral patellar dislocation. In full extension of the knee, the normal position of the patella is lateral from the trochlear axis and the patella is disengaged from the trochlea. Then, in early knee flexion (6-20°), the patella translates medially, reflecting the initial contact against the proximal part of the lateral rim of the trochlea which is a bony restraint to lateralization 1 . TheMPFL is the primary static restraint to lateral patellar translation in early knee flexion up to 30°, contributing to 60% of the restraining force of the soft tissue structures 2 . The midpoint of the patellar median ridge crosses the proximal limit of the trochlear groove at around 22° of flexion 1 , indicating that more than half of the articular surface of the patella is in contact with the