The patella is the largest sesamoid bone in the human body. It lies within the quadriceps tendon/patella ligament and forms part of the knee joint.
The patella is triangular in shape with an superior base and inferior apex. The posterior surface is smooth, composed of articular cartilage, and is divided into medial and lateral facets. The anterior surface is rough, for attachment of tendons and ligaments.
The ossification centers of the patella appear between 3 and 6 years. They fuse at puberty, with higher levels of activity.
The medial and lateral facets of the patella articulate with the medial and lateral condyles of the femur, respectively, to form the patellofemoral component of the knee joint.
The patella serves for attachment of the quadriceps tendon (superiorly) and the patella ligament or tendon (which attaches to the tibial tubercle, inferiorly), although few quadriceps tendon fibers are continuous of the anterior surface.
The medial and lateral patellar retinaculum, which are condensations of fascia rather than true ligaments, attach the patella margins to surrounding fascia. The medial patellar retinaculum attaches to the vastus medialis/sartorius fascia and is often disrupted in lateral patellar dislocation. The lateral patellar retinaculum attaches to the fascia of vastus lateralis and iliotibial band 3.
The quadriceps muscle pulls the patella obliquely and laterally in relation to the femur. There are factors that prevent such displacement: larger lateral condyle of femur, tension in the medial retinacular fibers and direction of insertion of fibers of the vastus medialis muscle.
Arterial blood enters via the anterior surface of the patella and an anastomotic patella ring is formed supplied by the paired superior and inferior geniculate arteries as well as the anterior tibial recurrent artery 2.
- bipartite patella
- multipartite patella
- absent patella
- variation in shape (see: Wiberg classification)
- dorsal defect of the patella (may occasionally be asymptomatic)