The patella

04 May 2024
The patella

The patella is the technical name for the kneecap, the triangular-shaped bone at the front of the knee joint. The patella is held in place by muscles, the lower end of which surrounds the patella and is then attached to the upper part of the tibia (shin) by patellar tendons. The patella protects the knee joint.

The patellar ligament

The patellar ligament is a band of connective tissue that connects the patella, or kneecap, to the tibia. It forms a vital link in the musculoskeletal system of the lower limb and occasionally is the site of joint injury.

Anatomy of the patellar ligament

The patellar ligament is a thin, flat band of fibrous connective tissue about 2 to 3 inches (5 to 8 cm) long. It is located in the anterior region of the knee distal to the patella and anterior to the tibia. Like all other ligaments, the patellar ligament is made of dense regular connective tissue with its many collagen fibers running vertically. On its proximal end, the patellar ligament arises from a wide region of the patella along its anterior and distal surfaces. It crosses the knee anterior to the joint capsule to insert to the tibial tuberosity of the tibia. The tendons of the vastus lateralis and vastus medialis muscles run parallel to the patellar ligament to connect these muscles to the tibia.

The patellar ligament is structurally continuous with the common tendon of the quadriceps femoris muscle, which connects the quadriceps to the patella. At birth, the patella is a small mass of cartilage found within the quadriceps tendon. Throughout early childhood this cartilage mass grows and ossifies, forming the patella and dividing the quadriceps tendon into two distinct structures. The distal structure becomes the patellar ligament as it now connects two bones together.

Physiology of the patellar ligament

The patellar ligament plays an important role in the function of the knee joint and the lower limb as a whole. Contraction of the quadriceps femoris muscle group pulls the patella proximally toward the thigh through the quadriceps tendon. The patella, in turn, pulls on the tibia through the patellar ligament to extend the leg at the knee. This action is important for walking and running, but is especially strong during jumping and kicking.

A tear or rupture of the patellar ligament may result from stress to the ligament from jumping or from the impact during a fall. A partial tear will result in pain and irritation in the joint, and should be treated with rest or physical therapy. Complete tears result in the patella dislocating proximally toward the thigh and disabling the function of the knee. The only treatment for a complete tear is surgical reattachment of the ligament followed by rest and physical therapy.

The lateral patellar

The lateral patellar retinaculum, or canal, in the patella, allows muscle and tissue to pass through from the femur (thigh bone). The patellar ligament is the center of the common tendon, which continues from the patella (knee cap) to the tibia. It is a very strong, flat band, the fibers of which are continuous over the front of the patella with tendons that extend and pass down the sides of the patella into the extremity of the tibia along the sides of its rounded prominence. It is separated from the joint by a large padding of fat.

The medial patellar retinaculum

The medial patellar retinaculum is a tendon of the knee that crosses the knee joint on the medial side of the patella. It plays important roles in the formation of the fibrous capsule of the knee and in the extension of the knee joint. Extension of the knee joint through the medial patellar retinaculum is vital to such movements as walking, running and kicking a ball.

The medial patellar retinaculum is the branch of the tendon of insertion of the quadriceps femoris that crosses the knee on the medial side of the patella. Most of the fibers of the medial patellar retinaculum originate in the medial femoral region from the vastus medialis muscle, just superior to the patella. From the femoral region, they extend obliquely across the medial side of the knee’s anterior, between the medial edge of the patella and the medial (tibial) collateral ligament (MCL). At its inferior end, the medial patellar retinaculum inserts into the medial epicondyle of the tibia.

Several other important connections are formed between the medial patellar retinaculum and its surrounding structures. On its anterior edge, some collagen fibers extend to form connections to the patella and merge with the fibers of the patellar ligament. Posteriorly the fibers weave together with the fibers of the medial collateral ligament.

Like all other tendons, the medial patellar retinaculum is made of dense regular connective tissue. Many strong collagen fibers in this tissue are arranged in a regular pattern with their long axis running vertically. The result is an incredibly strong tissue in the vertical axis, although strength is sacrificed in other directions. Between the collagen fibers are some elastin fibers to provide elasticity to the tissue, as well as fibroblast cells that produce new collagen fibers to replace broken and worn out fibers.

The medial patellar retinaculum plays two important roles in the knee:

1. It forms part of the fibrous capsule of the knee.
2. It serves as the insertion of the vastus medialis on the tibia.

The fibrous capsule of the knee protects the delicate synovial membrane inside and seals the lubricating synovial fluid within the joint capsule. It also helps to maintain the proper position of the bones within the knee to prevent injury and premature wear. The medial patellar retinaculum fills in the gap between the patella, patellar ligament, and medial collateral ligament to seal the fibrous capsule.

Acting as a tendon of insertion, the medial patellar retinaculum forms the connection of the vastus medialis to the medial condyle of the tibia. Contraction of the vastus medialis extends the leg at the knee by pulling on the medial patellar retinaculum, which in turn pulls the tibia anteriorly and straightens the knee. This motion is assisted by the contraction of the other muscles of the quadriceps femoris group, which simultaneously pull on the tibia to extend the knee.