If a person overuses a tendon during activities such as dancing, cycling, or running, it may elongate or undergo microscopic tears and become inflamed. Trying to break a fall may also cause the quadriceps muscles to contract and tear the quadriceps tendon above the knee cap (patella) or the patellar tendon below it. This type of injury is most likely to happen in older people whose tendons tend to be weaker and less flexible. Tendonitis of the patellar tendon is sometimes called jumper’s knee because in sports that require jumping, such as basketball, the muscle contraction and force of hitting the ground after a jump strain the tendon. After repeated stress, the tendon may become inflamed or tear.
People with tendonitis of the knee may feel pain during running, hurried walking, or jumping. Knee tendonitis can increase risk for ruptures or large tears to the tendon. A complete rupture of the quadriceps or patellar tendon is not only painful, but also makes it difficult for a person to bend, extend, or lift the leg, or to bear weight on the involved leg.