The tendons around the knee are of great importance for the stability of the joint. As muscle-tendon units, they function as primary movers of the knee joint. Knowledge of the anatomy is critical for the team physician. It helps the physician to understand the pathologic processes that he/she may encounter with different athletes suffering with tendon disorders.

The quadriceps group consists of four muscles that converge through a conjoined tendon to insert into the superior pole of the patella (1). Other than being a major part of the extensor mechanism and a stabilizer of the knee joint, the vastus medialis (with its oblique portion) and the vastus lateralis help maintain the patella centralized. The patella works to increase the effective lever arm of the quadriceps.

The hamstring group consists of the biceps femoris laterally and the semimembranosus and semitendinosus medially. Except for the short head of the biceps, they all span the hip and knee joints (1).

The pes anserinus is the tendinous insertion of the sartorius, gracilis, and semitendinosus muscles that insert into the anteromedial aspect of the proximal tibia. A bursa separates these structures from the medial collateral ligament.

The patellar tendon is closely related to the capsule, although its function is distinct from it. The tendon forms part of the extensor mechanism. The tendon extends in a slightly oblique fashion from the inferior pole of the patella to the tibial tuberosity. The infrapatellar bursa lies in close proximity to the patellar tendon (2,3,4).

The popliteus tendon lays posterolateral to the knee joint between the capsule and the synovial membrane. An area of bare tendon lies in contact with the lateral meniscus (2,5,6).

The iliotibial band is a thickened strip of the fascia lata that inserts into Gerdy’s tubercle. The band lies anterior to the lateral femoral epicondyle in full knee extension. At 30 degrees of flexion, the iliotibial band translocates posterior to the epicondyle.

There is a large gap between the stress that causes tendon failure and physiologic loads. The latter are reported to produce less than 4% strain (7). This is the “safe zone” of the stress-strain curve (Fig 42-1). The safe zone represents the straightening of the crimped collagen fibers when the tendon is perfectly elastic and recovers its original length after the load is removed. At 4% to 8% strain, the collagen fibrils slide past one another. At 8% to 10% strain, the tendon begins to fail and resist less force. Tendon healing will be discussed in the next section on biology; the healed tendon may be up to 30% weaker biomechanically than the normal healthy tendon (8).

The body’s response to any injury is an immediate inflammatory reaction. Tendinitis is the word used to describe inflammation of the tendon. A new concept has emerged for chronic tendon disorders. They are now widely called tendinosis. This refers to a degenerative condition of the tendon that seems to be related to both age and activity level. Histologically, surgical specimens show very few inflammatory cells and are more likely to show degeneration, with fatty mucoid and hyaline features. Inflammatory response to trauma seems most prevalent in tenosynovium and peritenon giving rise to the term “peritendinitis.” It is easier to understand these terms as points of a continuum rather than discrete clinical entities. In general, older patients with long standing symptoms and a history of repetitive activity will be more likely to have tendinosis. Young patients with acute onset of symptoms will be more likely to have peritendinitis. Tendonitis occurs when the tendon bears more load than it can withstand repeatedly. Damage and its sequelae inflammation and degeneration occurs. This can be due to excessive high loads across normal tendons or normal loads across degenerative tendons (8).

Tendons heal through three phases: inflammatory, reparative, and remodeling. The inflammatory response begins with the injury and may last from 2 to 7 days. Repair may start as early as 48 hours and last for 6 to 8 weeks. Remodeling starts from day 14 and may last up to one year (8).