The patella is also known as the kneecap. It sits in front of the knee joint and protects the joint from damage. It is the largest sesamoid bone in the body, and lies within the quadriceps tendon. The kneecap is an example of a bone we are all familiar with, and which has a significant functional role. In this article we will discuss the anatomy and clinical relevance of the patella. We will also conclude with a summary and some review questions to test the reader’s understanding of the article content.
The patella is the largest sesamoid bone in the body and it lies within the quadriceps tendon in front of the knee joint. The bone originates from multiple ossification centres that develop from the ages of three to six, these ossification centres rapidly coalesce.
Patella is a thick flat triangular bone with its apex pointing downwards. The bone has a medial and lateral border, as well as its base which lies proximally. The patella is a dense trabecular bone and the apex of its triangular structure attaches the quadriceps muscles. The tendinous region of the quadriceps that attaches to the base of the patella is called the patellar tendon. The attachment of the quadriceps tendon is extended to the anterior surface of the patella. The vastus intermedius, medialis and lateralis all insert onto their respective sides on the posterior and anterior surface of the patella. The apex of the patella gives rise to the patellar ligament, which inserts onto the tibial tuberosity on the anterior surface of the tibia. The middle third of the patella has various vascular openings that allow for arteries to penetrate and supply the bone.
The patella is stabilized by the horizontal fibers of vastus medialis, as well as the anterior projection of the lateral femoral condyle. The tension in the medial patellar retinaculum also helps in its stability. The primary function of the patella is during knee extension. The fact that the patella sits atop the anterior surface of the femoral condyles, increases the angle at which the quadriceps tendon pulls on the shaft of the tibia. The patella also functions to allow for smooth movement of the knee in flexion and extension, and also protects the anterior surface of the knee joint.
The blood supply to the patella arises from the genicular arteries, branches of the popliteal artery. There is a superior lateral and medial, and inferior lateral and medial, a descending and anterior genicular. They form a peripatellar anastomosis and supply the patella and the knee joint.
The superior two thirds of the posterior articular surface of patella articulates with the anterior surface of the femoral condyles. The lateral articulating surface of the patella is usually larger than the medial articulating surface. However the medial femoral condyle is larger and projects further anteriorly than the lateral femoral condyle.