The patellar tendon works with the muscles in the front of your thigh - the quadriceps - to straighten your leg. Although anyone can injure the patellar tendon, tears are more common among middle-aged people who play running or jumping sports. A complete tear of the patellar tendon is a disabling injury. It usually requires surgery to regain full knee function.
A very strong force is required to tear the patellar tendon.
Falls. Direct impact to the front of the knee from a fall or other blow is a common cause of tears. Cuts are often associated with this type of injury.
Jumping. The patellar tendon usually tears when the knee is bent and the foot planted, like when landing from a jump or jumping up.