The Medial Patellar Retinaculum

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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.