The Patellar Tendon:
The patellar tendon is an important part of the extensor mechanism of the lower extremity. The extensor mechanism includes the quadricps muscle, quadriceps tendon, patella (kneecap), and patellar tendon. These structures allow the knee to straighten, and can do so with significant strength.
Tearing the Tendon:
Typically the injury involves an awkward landing from a jumping position where the quadriceps muscle is contracting, but the knee is being forcefully straightened. This is a so-called eccentric contraction and places a tremendous stress on the tendon.
Cause of a Torn Patellar Tendon:
Tendon tears can also occur in non-athletic settings. Usually there is a reason for the patellar tendon to be weakened in these individuals, such as a systemic disease that weakens tendons or recent surgery on the knee the caused tendon weakening. Treatment is usually similar in athletes and non-athletes alike.
Making the Diagnosis:
An x-ray will be obtained, as a patellar fracture can cause similar symptoms, and should be excluded as a possible diagnosis. On the x-ray, the patella is usually up higher when compared to the opposite knee, as the quadriceps pulls up on the kneecap, and nothing is holding it down. While often not needed, an MRI may be used to confirm the diagnosis and inspect the knee for any other damage that may have occurred.
Treatment of a Patellar Tendon Tear:
The torn ends of the tendon need to be sewn together. The difficulty lies in the fact that it is important to restore proper tension to the tendon, not making it too tight or too loose. Also, it can be difficult to get a good repair, especially if the tendon has torn directly off the bone. In these situations, the sutures used to repair the tendon may have to be attached through the bone.
Recovery & Prognosis:
While most people heal completely from a patellar tendon surgery, there can be long-term weakness even with a successful repair.
Matava MJ. "Patellar Tendon Ruptures" J Am Acad Orthop Surg November 1996 vol. 4 no. 6 287-296