A patellar tendon tear is a serious injury that significantly impacts the ability to use the knee. This strong band of fibrous tissue is located at the front of the knee, connecting the kneecap (patella) to the shinbone (tibia). A tear, also known as a rupture, disrupts the primary mechanism that allows the leg to straighten. The severity ranges from a partial injury to a complete separation, often requiring immediate medical attention.
Structure and Function of the Patellar Tendon
The patellar tendon is a crucial component of the knee’s extensor mechanism, the system that allows a person to straighten their leg. It works with the large quadriceps muscles in the thigh and the kneecap (patella). The tendon originates at the bottom tip of the patella and inserts onto the tibial tuberosity, a bony prominence on the shinbone (tibia).
The tendon’s function is to transmit the force generated by the quadriceps muscles to the shinbone. The patella acts like a pulley, increasing the leverage of the quadriceps to efficiently extend the knee. Because the tendon handles high tensile forces involved in walking, running, and jumping, its integrity is fundamental to lower limb mobility. A tear immediately compromises the ability to perform a straight leg raise, a basic movement required for standing and walking.
Common Causes and Types of Tears
A patellar tendon tear typically results from a sudden, forceful event that places overwhelming stress on the tendon. The most common mechanism involves an eccentric contraction of the quadriceps muscle, meaning the muscle tries to contract forcefully while the knee is simultaneously bending. This often occurs during activities like landing awkwardly from a jump, missing a step on stairs, or experiencing a direct fall onto a bent knee.
The force required to cause a tear is substantial, but certain pre-existing factors can significantly weaken the tendon, making it more susceptible to rupture. Chronic conditions that impair blood supply and overall tissue health increase the risk, such as diabetes mellitus, chronic kidney failure, and systemic inflammatory diseases like rheumatoid arthritis or lupus. Furthermore, local steroid injections administered near the tendon have been linked to increased tissue weakness and a higher likelihood of tearing.
Patellar tendon injuries are classified into two categories based on the extent of the damage. A partial tear involves damage to only some of the tendon fibers, causing pain and difficulty with movement but does not completely sever the connection. A complete tear means the tendon is separated into two distinct pieces, entirely severing the connection between the kneecap and the shinbone. Complete tears most commonly occur where the tendon attaches to the lower part of the patella.
Recognizing the Signs of a Patellar Tendon Tear
The moment a patellar tendon tears is marked by acute symptoms at the front of the knee. Many individuals report hearing or feeling a distinct “pop” or tearing sensation at the time of the injury, followed immediately by sharp pain. Severe swelling and bruising around the knee joint develop quickly due to internal bleeding.
The most telling sign of a complete tear is the inability to actively extend or straighten the knee. This functional loss, sometimes called extensor lag, means the person cannot lift the lower leg when sitting or standing. This occurs because the force from the quadriceps muscle can no longer be transmitted through the severed tendon. A visual assessment may reveal a noticeable gap or indentation just below the kneecap where the tendon has separated. Additionally, the patella may appear to ride higher up the thigh than the uninjured knee due to the unopposed pulling force of the quadriceps muscle above it.
Medical Treatment and Rehabilitation
Treatment for a patellar tendon tear depends on the extent of the damage. Partial tears that do not significantly impair the ability to straighten the knee can sometimes be managed non-surgically. This typically involves immobilizing the knee in a brace or cast for several weeks to protect the healing fibers, followed by a structured physical therapy program.
Complete tears almost always require surgical repair to restore the knee’s function. The primary goal of surgery is to physically reattach the torn end of the tendon, usually to the bone of the patella, using strong sutures. Performing the repair soon after the injury is recommended to prevent the tendon from scarring and contracting into a shortened position, which can complicate the procedure and recovery.
The rehabilitation process following surgery is extensive and structured into distinct phases, often lasting six months or more for a full return to activity.
Initial Immobilization
Initially, the knee is kept immobilized in a brace, locked in a straight position for about six weeks to protect the repair. Weight-bearing is gradually introduced using crutches.
Regaining Range of Motion
The next phase focuses on carefully and progressively regaining the knee’s range of motion. Limits are placed on bending to prevent stress on the healing tendon.
Strengthening and Return to Activity
Physical therapy then transitions to strengthening the quadriceps and surrounding muscles. Exercises like mini-squats and leg presses are introduced after the initial healing period. High-impact activities, such as running and jumping, are typically not introduced until four to six months after the surgery. Full recovery of strength and endurance can take up to a year, emphasizing the need for consistent participation in the rehabilitation program.