The muscles that make up the posterior compartment of the leg include the biceps femoris, the semitendinosus, and the semimembranosus.[8] Two heads make up the biceps femoris, a short head, and a long head. The semitendinosus and biceps femoris long head muscles sit superficial to the semimembranosus and biceps femoris short head muscles. The perforating branches of the deep femoral artery provide blood supply to all four muscles. The biceps femoris short head originates from the linea aspera and lateral supracondylar line of femur.[9] The biceps femoris long head, semitendinosus, and semimembranosus muscles all originate from the ischial tuberosity. The biceps femoris muscles attach to the lateral side of the head of the fibula. The semitendinosus and semimembranosus attach to the medial surface of the tibia.  As a group, the hamstring muscles primarily work to extend the hip and flex the knee. The exception to this rule is the short head of the biceps femoris, which only acts to flex the knee. These movements are an integral part of normal gait and daily function. The hamstrings provide stability while standing by securing the hip joint so the body can remain upright. Additionally, the hamstrings provide slight external or internal rotation based on insertion points distally.[10] The innervation for these muscles is via the sciatic nerve. However, the short head of the biceps femoris receives specific innervation via the common peroneal division of the sciatic nerve. All other hamstrings receive innervation from the tibial division of the sciatic nerve.

One of the most common tendons used in orthopedic surgery is the semitendinous tendon. The use of this tendon can result in negative changes for the locomotor system, also as the knee biomechanics.

After the use of semitendinous tendon in orthopedic surgery, the knee can be more unstable during the rehabilitation phase, and as the semitendinous muscle is a medial rotator, the individual can develop a lateral rotation movement dominance that can lead to overuse of biceps femoris and dysfunctions of near joints, also by overuse.[11]

The popliteal fossa is of clinical importance when considering posterior knee dislocation or needing to harvest a vessel for graft. The diamond-shaped fossa is bound by the semimembranosus and semitendinosus superomedially, the lateral and medial heads of the gastrocnemius inferolaterally and inferomedially, the biceps femoris superolaterally, and the skin and popliteal fascia superficially. The most superficial structure in the popliteal fossa is the sciatic nerve, which splits at the apex of the fossa into the tibial and common peroneal nerves. The next deepest structure is the popliteal vein. Finally, the popliteal artery is the deepest neurovascular structure before reaching the knee joint. The popliteal artery gives off five genicular branches that supply the knee capsule and ligaments. If there were a mass or injury that caused occlusion to the popliteal artery, then the blood supply to the knee would be compromised.

Sciatica is a term commonly used to describe radiating leg pain. It refers to inflammation or compression of the sciatic nerve roots. There is no clear definition of sciatica, leading to variation in distinguishing it from other sources of low back pain. Some common signs and symptoms of sciatica are pain that radiates from the lower back down the posterior thigh, knee weakness, difficulty in rotating the ankle, and slow ankle reflexes. There are paresthesia, numbness, and weakness in areas innervated by the sciatic nerve. The etiology of sciatica is multifactorial and can stem from anything related to compression and inflammation of the nerve or its nerve roots. Some common examples are piriformis syndrome, pregnancy, herniated vertebral discs, or lumbar stenosis. An anomaly seen in roughly 10% of the population that is related to piriformis syndrome occurs when the sciatic nerve either penetrates the piriformis muscle or travels superior to the muscle before descending the posterior thigh. These variations lead to an easier mechanism of compression of the sciatic nerve with only slight hypertrophy in the piriformis muscle.[12][13][14]

A common injury among athletes of all levels is a hamstring strain. The injury typically occurs with sudden lengthening of the hamstrings or rapid changes in speed or direction. These actions are common for people involved in high-risk activities like football, track, and rugby. In addition to being highly prevalent, hamstring injuries tend to recur due to poor rehabilitation or premature return to activity. Because the biceps femoris has the greatest musculotendinous stretch, it is the most frequently injured muscle of the hamstrings from running. A typical hamstring strain is characterized by pain in the posterior thigh, which can be exacerbated by passive knee extension, resisted knee flexion, or hip extension. When evaluating anyone with a possible hamstring injury, clinicians must consider other diagnostic possibilities such as tight quadriceps tendon, lumbosacral radiculopathy, piriformis syndrome, strong lumbopelvic muscles, or adductor strain.[15]