Behind the knee joint, a network of tendons plays a significant role in facilitating movement and supporting the leg. These strong, fibrous tissues connect muscles to bones, enabling the knee to bend, extend, and rotate while also providing shock absorption during daily activities.
Understanding the Tendons Behind Your Knee
The primary tendons located at the back of the knee originate from the hamstring muscles, along with contributions from the calf muscle and a smaller, deep muscle. The hamstring group includes three distinct muscles: the semitendinosus, semimembranosus, and biceps femoris. The tendons of the semitendinosus and semimembranosus muscles attach to the inner side of the upper shin bone (tibia), providing support to the medial aspect of the knee. The biceps femoris tendon, in contrast, connects the biceps femoris muscle to the outer side of the shin bone and the fibula, which is the smaller bone in the lower leg.
Further down, the gastrocnemius muscle, forming the bulk of the calf, also contributes tendons that cross behind the knee joint. These two heads of the gastrocnemius muscle originate from the lower part of the thigh bone (femur) above the knee. Deeper within the knee, a small triangular muscle called the popliteus plays a unique role, with its tendon originating from the outer side of the thigh bone and inserting onto the upper part of the shin bone.
How These Tendons Work
Tendons function as robust connectors, transmitting the force generated by muscle contractions to the bones, thereby enabling movement. The hamstring tendons are instrumental in knee flexion, which is the bending motion of the knee, and also contribute to hip extension, moving the leg backward. They also help to stabilize the knee joint, particularly during dynamic activities.
The gastrocnemius tendons, originating above the knee, assist in knee flexion, though their primary function is ankle plantarflexion, which involves pointing the foot downward. This dual action allows the gastrocnemius to influence both knee and ankle movements. The popliteus tendon and its associated muscle have a specialized function, primarily helping to “unlock” the knee from a fully straightened position by internally rotating the shin bone relative to the thigh bone. This unlocking mechanism is essential for initiating knee flexion and is crucial for activities like squatting and running.
Common Problems Affecting These Tendons
Several conditions can affect the tendons behind the knee, often leading to pain and limited mobility. Hamstring strains or tears are frequent injuries, especially in sports involving sprinting or sudden movements. These injuries occur when the hamstring muscles are overloaded, causing the muscle fibers or their connection to the tendon to tear. Symptoms typically include sudden, sharp pain in the back of the thigh, potentially accompanied by a popping sensation, swelling, tenderness, and sometimes bruising.
Another common issue is a Baker’s cyst, also known as a popliteal cyst, which presents as a fluid-filled lump behind the knee. These cysts usually form as a result of underlying knee problems, such as arthritis or cartilage tears, which cause the knee to produce excess fluid. While often painless, a Baker’s cyst can cause a feeling of tightness, knee pain, stiffness, or difficulty bending the knee, and symptoms may worsen with activity.
In some cases, a cyst can rupture, leading to sharp pain, swelling, and redness in the calf. Popliteal tendinopathy involves inflammation or degeneration of the popliteus tendon, often caused by overuse from repetitive knee movements, such as running downhill or on uneven surfaces. This condition typically results in pain on the outer side of the back of the knee, which may worsen with activities like walking downhill or using stairs. Weakness, stiffness, and balance problems can also occur with popliteal tendinopathy.
Keeping Your Knee Tendons Healthy
Maintaining the health of your knee tendons involves a combination of proper preparation, regular exercise, and attentive self-care. Warming up thoroughly before physical activity helps prepare muscles and tendons for exertion, while cooling down afterward promotes flexibility. Incorporating regular stretching, such as hamstring and calf stretches, can improve flexibility and range of motion in the knee and surrounding muscles. Examples include seated hamstring stretches, standing hamstring stretches, and wall calf stretches.
Strengthening exercises, particularly eccentric exercises where the muscle lengthens under tension, are beneficial for both preventing and rehabilitating hamstring injuries. Exercises like Nordic hamstring curls, Swiss ball hamstring curls, and single-leg deadlifts can target these muscles effectively. Gradually increasing the intensity and duration of physical activities allows tendons to adapt and reduces the risk of overuse injuries. Listening to your body and addressing pain promptly can prevent minor issues from becoming more significant problems.