patella

The patella (= limpet) or kneecap is the best example of a sesamoid bone (a bone contained within a tendon which keeps the tendon clear of a joint).

The patella is contained within the tendon of the quadriceps muscle which continues on as the patellar ligament to be inserted on to the tibial tuberosity.

The patella is covered with hyaline cartilage on its posterior surface which articulates with the femur.

Although its position varies with knee movement, the patella is always above the knee joint proper.

The patella has potential stability problems since the line of pull of the quadriceps muscle will tend to displace it laterally - especially in women with a wider pelvic girdle.

This tendency is resisted by:

  1. the lateral condyle of the femur which acts as a bony barrier
  2. the fibres of the vastus medialis muscle which pass almost horizontally into the patella.