Tendons are specialized bands of fibrous tissue that connect muscle to bone, which is fundamental for generating movement and stabilizing joints. The knee joint is the largest and one of the most mechanically stressed joints in the body. It depends on several major tendons to manage the immense loads encountered during walking, running, and jumping. Understanding the three primary tendons of the knee helps explain how the leg moves and why these structures are susceptible to injury.
The Quadriceps Tendon
The quadriceps tendon is a thick, powerful band located immediately above the kneecap (patella). It serves as the collective insertion point for the four muscles that make up the quadriceps group on the front of the thigh. This tendon anchors the quadriceps muscles to the superior pole of the patella.
The primary function of this tendon is to transmit the massive force generated by the quadriceps muscle group. This force is necessary for the extension of the knee, which is the action of straightening the leg. The tendon’s integrity is directly related to a person’s ability to kick, climb stairs, or rise from a seated position. It is a mechanically robust structure that plays a central role in the knee’s extensor mechanism.
The Patellar Tendon
Directly below the kneecap lies the patellar tendon, which continues the line of the quadriceps tendon. It runs from the inferior pole of the patella down to the tibial tuberosity, a bony prominence on the shinbone. This structure is sometimes referred to as the patellar ligament because it connects two bones: the patella and the tibia.
Despite this bone-to-bone connection, it is functionally considered a tendon because it is the final link in the mechanism that transmits the quadriceps muscle’s force to the lower leg. The patellar tendon essentially completes the pulley system initiated by the quadriceps tendon, allowing the lower leg to be pulled forward and extended.
The Biceps Femoris Tendon
The biceps femoris tendon is located on the posterolateral (outer and rear) side of the knee, contrasting with the two anterior tendons. This tendon is a component of the hamstring muscle group, which is situated on the back of the thigh. It is formed by the convergence of the long and short heads of the biceps femoris muscle.
The tendon inserts on the head of the fibula, the smaller of the two bones in the lower leg. Its main actions are to facilitate the flexion of the knee (bending the leg) and to assist in the external rotation of the lower leg. This tendon contributes significantly to the stability of the knee’s outer aspect and is engaged in activities like sprinting.
Common Injuries of Knee Tendons
These three major knee tendons are susceptible to both chronic overuse injuries and acute traumatic tears. Overuse, especially from repetitive strain in sports like jumping or running, can lead to tendinopathy. This condition involves a breakdown and degenerative change within the tendon structure. Patellar tendinopathy, often called “jumper’s knee,” and quadriceps tendinopathy are frequent examples of this chronic issue.
Acute injuries involve a partial or complete tear (rupture) of the tendon fibers. A quadriceps or patellar tendon rupture often results from a sudden, forceful contraction of the quadriceps muscle against a heavy load, such as an awkward landing. A complete tear of these anterior tendons is a disabling injury that prevents the person from straightening the knee. The biceps femoris tendon is most frequently injured at the myotendinous junction, the area where the muscle meets the tendon, often during rapid acceleration in sprinting.