The knee joint is a complex structure central to human movement, bearing significant weight and facilitating actions like walking, running, jumping, and squatting. It connects the thigh bone (femur) to the shin bone (tibia). An intricate network of bones, ligaments, muscles, and tendons provides stability and a wide range of motion.
Key Tendons at the Back of the Knee
The back of the knee, known as the popliteal region, houses several important tendons. The most prominent are the hamstring tendons. Located at the back of the thigh, the hamstring muscles consist of three distinct muscles: the semitendinosus, semimembranosus, and biceps femoris. Their tendons attach around the knee joint.
The semitendinosus and semimembranosus tendons are on the inner (medial) side of the back of the knee. The semitendinosus attaches to the medial surface of the tibia, while the semimembranosus attaches to the medial tibial condyle. On the outer (lateral) side, the biceps femoris tendon inserts into the head of the fibula. These hamstring tendons converge as they approach the knee, forming distinct cords in the popliteal fossa, the hollow area behind the knee.
Another significant tendon is from the gastrocnemius, a major calf muscle. It has two heads originating from the lower femur just above the knee. These heads descend to form part of the Achilles tendon, connecting to the heel bone. Though primarily a calf muscle, its origin above the knee means its tendons influence posterior knee mechanics.
The popliteus tendon, though smaller, is also deep within the posterior knee. It originates from the lateral condyle of the femur and inserts onto the proximal tibia, playing a role in knee rotational movements.
How These Tendons Function
The tendons at the back of the knee perform actions fundamental to leg movement and knee stability. Hamstring tendons are primarily responsible for flexing, or bending, the knee joint. They also contribute to extending the hip, which involves moving the thigh backward. These dual actions are important for activities like walking, running, jumping, and climbing stairs.
The gastrocnemius tendons contribute to both knee flexion and plantarflexion (pointing the toes downward). The gastrocnemius is most effective as a knee flexor when the knee is extended. This muscle aids in propelling the body forward during walking and running, and helps maintain balance and posture.
The popliteus tendon, often called the “key to unlock the knee,” initiates knee flexion from a fully extended or “locked” position. It achieves this by rotating the femur on the tibia or vice versa, contributing to knee stability, especially during twisting movements.
Common Issues Affecting These Tendons
The tendons at the back of the knee are susceptible to various issues, particularly due to high demands during physical activity. Hamstring strains, commonly known as “pulled hamstrings,” are frequent injuries, especially in sports involving sprinting, sudden acceleration, or rapid changes in direction. These injuries can range from mild overstretching (Grade 1) to partial or complete tears (Grade 2 or 3). Symptoms typically include sharp pain in the back of the thigh, tenderness, swelling, and sometimes bruising or a popping sensation.
Tendinitis, or tendinopathy, can also affect these tendons, often from overuse or repetitive stress. This condition involves irritation and inflammation, leading to localized pain and stiffness, particularly after activity. Chronic tendinopathy may involve degeneration of the tendon tissue. In severe cases, a tendon can completely tear away from the bone, known as an avulsion injury. This type of injury can sometimes pull a piece of bone with it and may require surgical intervention.
Keeping Your Knee Tendons Healthy
Maintaining knee tendon health involves preventive measures and self-care. Regular exercise strengthening knee-supporting muscles enhances tendon resilience. Strengthening exercises (e.g., hamstring curls) and flexibility routines (e.g., hamstring and calf stretches) improve range of motion and reduce muscle imbalances. Dynamic stretches before activity and static stretches afterward prepare muscles and tendons for exertion and aid recovery.
Gradually increasing physical activity intensity and duration prevents overuse injuries. Avoiding sudden increases in training load allows tendons to adapt and strengthen. Listening to your body and taking adequate rest days prevent fatigue and allow muscles and tendons to repair. Proper warm-up and cool-down routines minimize the risk of strains and tears.