Patellar Tendon Injuries

The patellar tendon is a strong, thick band of tissue located just below the kneecap. It connects the bottom of the kneecap (patella) to the top of the shinbone (tibia). Together with the quadriceps muscles in the front of the thigh and the quadriceps tendon above the kneecap, it forms the “extensor mechanism” of the knee. This system allows you to straighten your leg, rise from a chair, climb stairs, run, and jump. When the patellar tendon becomes irritated, inflamed, weakened, or torn, knee function can be significantly affected.

Patellar tendon injuries are either caused by overuse or trauma. The most common overuse condition is patellar tendonitis, often referred to as “jumper’s knee.” Despite the name, this condition is not always caused by jumping. It develops when repeated stress on the tendon leads to small areas of damage. Over time, the tendon fibers begin to break down faster than the body can repair them. This process is more accurately described as tendinopathy, meaning degeneration of the tendon tissue rather than simple inflammation.

More severe injuries include partial tears and complete ruptures. A partial tear means some of the tendon fibers have been disrupted but the tendon is still intact. A complete rupture means the tendon has torn entirely, separating the kneecap from the shinbone. This is a serious injury that usually requires prompt surgical treatment.

Patellar tendon injuries most often develop from excessive repetitive strain on the knee or a sudden forceful trauma to the knee. Activities that involve frequent jumping, sprinting, or abrupt stopping place high forces across the tendon. Basketball, volleyball, soccer, and track athletes are particularly at risk. However, recreational runners and active adults can also develop tendon problems over time.

Several factors increase the likelihood of injury including tight quadriceps or hamstring muscles which can increase tension on the tendon. Weak hip or core muscles may alter movement patterns and overload the knee. Poor training techniques, sudden increases in activity intensity, and inadequate recovery between workouts can all contribute.

Age also plays a role. As tendons age, they become less flexible and less able to tolerate repetitive strain. Chronic medical conditions such as diabetes or inflammatory disorders can weaken tendon tissue. In rare cases, a direct blow to the knee or a sudden forceful contraction of the quadriceps muscle can cause a tendon rupture.

Complete ruptures are more likely to occur in individuals over 40 or in those with preexisting tendon degeneration. Certain medications, including corticosteroid injections into the tendon, may increase rupture risk if used improperly.

Symptoms vary depending on the severity of the injury. With early tendonitis or tendinopathy, pain is usually the first and most noticeable symptom. The discomfort is typically located just below the kneecap. It may begin as a mild ache after activity and gradually progress to pain during activity. In more advanced cases, pain can occur even at rest.

Other common symptoms include:

• Tenderness to touch below the kneecap
• Stiffness in the front of the knee
• Swelling in the tendon area
• Pain when squatting, kneeling, running, or climbing stairs
• Weakness when trying to straighten the leg

In the case of a partial tear, the pain is usually sharper and more sudden. Swelling may develop quickly. Patients may feel instability or weakness when attempting to bear weight.

With a complete rupture, symptoms are more dramatic. Many people describe a popping sensation at the time of injury. There is immediate pain and swelling. It becomes difficult or impossible to straighten the knee or lift the leg while lying flat. The kneecap may appear higher than normal because it is no longer anchored to the shinbone.

Accurate diagnosis begins with a thorough history and physical examination. At OrthoIllinois Knee Center, specialists carefully evaluate when symptoms started, what activities worsen the pain, and whether there was a specific injury event.

During the physical exam, the knee is inspected for swelling, tenderness, and alignment. The provider will gently press along the tendon to identify areas of pain. Range of motion and strength testing help determine whether the extensor mechanism is intact. The ability to straighten the knee against resistance is an important sign.

Imaging studies are often used to confirm the diagnosis and assess severity. X-rays may be ordered to evaluate bone alignment and rule out fractures. In cases of chronic tendinopathy, small calcium deposits may sometimes be visible.

Magnetic resonance imaging (MRI) is particularly useful when a tear is suspected. MRI provides detailed images of soft tissues, allowing specialists to see partial tears, complete ruptures, or degenerative changes within the tendon. Ultrasound may also be used to evaluate tendon structure in real time.