Patellar Tendon Rupture

What is a patellar tendon rupture?

Patellar tendon ruptures can be partial — the tendon is still in one piece — or complete, presenting as two separate parts. When the tendon is completely torn, extension is no longer possible at the knee joint. Most frequently, the patellar tendon tears at its attachment to the kneecap.

When a patellar tendon rupture is caused by a medical condition — such as tendinitis — the tendon usually tears in its central portion.

Although a patellar tendon rupture can happen to anyone, it is more common in middle-aged patients who play sports involving running and jumping.

What causes a patellar tendon rupture?

Trauma

A very large traumatic force is required for a patellar tendon rupture to occur.

• Direct trauma. A direct impact to the front of the knee is a frequent cause of patellar tendon rupture. Lacerations are also associated with this type of injury.
• Jumping. The patellar tendon usually tears following overload with the knee flexed, as in landing from a jump.

Weakening of the tendon

A weakened tendon ruptures more easily. There are several situations in which the tendon is weakened:

• Tendinitis. Inflammation of the patellar tendon, known as patellar tendinitis, weakens the tendon. It can also cause small structural injuries.
• Chronic diseases. Weakened tendons can also result from diseases that interrupt the blood supply. Such chronic conditions include chronic kidney failure, gout, leukaemia, rheumatoid arthritis, systemic lupus erythematosus and diabetes.
• Steroid use. This has been associated with weakening of the tendons.

Surgical causes

Previous surgery in the vicinity of the tendon, such as total knee replacement or cruciate ligament reconstruction, is a risk factor for patellar tendon rupture.

What are the symptoms?

When a patellar tendon ruptures, there is frequently a sound and a sensation of tearing. Pain and swelling then follow. Additional symptoms include:

• A gap at the lower pole of the kneecap, where the tendon tore away
• An uneven contour in the area
• Restricted movement
• The kneecap may change position
• Inability to straighten the lower leg
• Difficulty walking