Patellar tendonitis is an overuse injury of the tendon connecting the patella (knee cap) to the tibia bone below. It is caused by repetitive jumping, kicking, running or plyometric movements that exert force on the knee. Symptoms include tenderness and pain below the knee before, during and after activity. Treatment involves rest, ice, anti-inflammatory medication, bracing and physical therapy exercises. Prevention through strength training of the quadriceps muscles and allowing for rest days can help avoid this overuse injury.