A patellar tendon rupture is a serious injury affecting the knee’s function. The patellar tendon is a strong, fibrous cord running from the bottom of the kneecap (patella) down to the top of the shinbone (tibia). A rupture occurs when this tendon partially tears or completely separates, typically near the kneecap or where it connects to the shinbone. A complete tear breaks the connection needed to straighten the leg.
Understanding the Patellar Tendon and Injury Mechanisms
The patellar tendon is a component of the knee’s extensor mechanism, working with the quadriceps muscle to enable leg straightening. It transmits the force generated by the quadriceps muscles, located on the front of the thigh, through the kneecap and down to the shinbone. This extension is necessary for actions like walking, running, and climbing stairs.
A rupture typically requires a substantial, sudden force, often occurring when the leg is partially bent and the quadriceps muscle forcefully contracts. This mechanism is common during activities such as landing from a jump, abruptly changing direction, or attempting to stop a fall. The tensile load placed on the tendon during these movements exceeds its structural capacity, causing it to tear.
While an acute, traumatic event is the direct cause, pre-existing conditions can weaken the tendon, making it more susceptible to rupture. Chronic degeneration (tendinopathy or tendinitis) reduces its strength and elasticity. Systemic diseases like diabetes or chronic kidney failure, or past corticosteroid injections, can also compromise the tendon’s integrity.
Key Indicators of a Ruptured Tendon
A patellar tendon rupture begins with sharp, acute pain felt just below the kneecap. Many individuals report hearing or feeling a distinct tearing or popping sensation at the moment of injury. Following the rupture, the knee usually swells rapidly, becomes tender to the touch, and is often accompanied by visible bruising.
The inability to actively straighten the knee is a key indicator of a complete tear. Since the connection between the kneecap and the shinbone is severed, the patient cannot perform a straight leg raise or maintain a passively extended knee. This loss of the extensor mechanism often causes the leg to buckle when attempting to bear weight.
Upon physical examination, a characteristic sign is a palpable gap or indentation in the soft tissue directly below the kneecap where the tendon has separated. This separation allows the kneecap to ride higher than its normal position (patella alta), as the unopposed pull of the quadriceps muscle draws the patella upward.
Treatment and Rehabilitation for Full Tears
A complete rupture of the patellar tendon almost always necessitates surgical intervention to restore the extensor mechanism. Surgeons re-establish the connection by securely reattaching the torn tendon end to the bone, typically the inferior pole of the patella. They often use strong, non-absorbable sutures passed through tunnels drilled into the kneecap (transosseous repair) to hold the tendon in place while it heals.
Following surgical repair, the knee is immobilized in a brace or cast, usually in a fully extended position, to protect the repair site. This initial post-operative phase focuses on wound healing and controlling pain and swelling. Weight-bearing activities are restricted, often starting with only “toe-touch” weight bearing with crutches, to prevent excessive strain on the healing tendon.
Physical therapy is then systematically introduced to restore both range of motion and muscle strength, which is essential for a successful outcome. Initial exercises focus on regaining passive knee extension and controlled, limited flexion, typically avoiding active extension against resistance for the first six weeks. Rehabilitation progresses gradually to include strengthening the quadriceps and hamstrings, with a return to full activity often taking between six to twelve months, depending on the severity of the tear.