The patellar tendon is the structure that connects the kneecap (patella) to the shinbone (tibia). A ligament is a structure that connects one bone to another bone, and therefore some people refer to this as the patellar ligament.

However, this structure is really connecting the quadriceps muscle to the shin bone, and a tendon connects muscle to bone, and therefore patellar tendon is the more common description.

The patellar tendon is an important part of the extensor mechanism of the lower extremity. The extensor mechanism includes the quadriceps muscle, quadriceps tendon, patella (kneecap), and patellar tendon. These structures function together to allow the knee to straighten, and can do so with significant force.

The extensor mechanism is critical to normal functions ranging from walking and stair climbing to athletic activities including running and kicking. Without an intact extensor mechanism, all of these activities can become difficult to perform.

Illustration by JR Bee, Verywell

Patellar Tendon Tear Symptoms

The typical individual who sustains a torn patellar tendon is a young, male athlete. As more middle-aged people are remaining physically active, this injury is becoming more common in an older population.﻿﻿

The injury usually 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 tremendous stress on the tendon.

Athletes who sustain the injury may feel a snapping or popping sensation and will typically be unable to walk following the injury.

The typical signs of a torn patellar tendon include: Pain directly under the kneecap

Swelling and bruising in the front of the knee

A defect, or soft spot, where the tendon should be tight

Difficulty walking or doing sports activities

Causes

It has been found that in nearly all patients who sustain a patellar tendon rupture there is abnormal tendon tissue consistent with a chronic tendinosis.﻿﻿ The patellar tendon is usually injured in the watershed region of the tendon, where blood flow to the tissue is poor, and the tendon is weakest.

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.

Diagnosis

Making the diagnosis of a torn patellar tendon is usually obvious on clinical examination. People who tear the tendon will be unable to extend their knee against gravity, and unable to perform a straight leg raise test. The examiner can usually feel the gap in the tendon, just below the kneecap.

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 in its normal position.

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

A torn patellar tendon does not heal well on its own, and left untreated will lead to weakness of the quadriceps muscle and difficulty with routine activities, including walking. Surgery to repair the torn tendon is relatively straightforward in concept but can be difficult to perform.

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 directly through the bone.﻿﻿

Recovery and Prognosis

Recovering from a torn patellar tendon is difficult and takes time. One of the most important prognostic factors for recovery is the time to surgery, and surgery delayed beyond a few weeks can limit recovery ability.

It is known that early mobility after surgery, protected strengthening, and preventing excessive stress on the repair will speed overall recovery. Even with these steps, there is a minimum of three months until the return of normal daily activities, and four to six months until sports should be resumed.﻿﻿

While most people heal completely from a patellar tendon surgery, there can be long-term weakness even with a successful repair.

Athletes who are attempting to return to competitive sports may take a year or longer to return to their preinjury level of function. Performing guided physical therapy can be helpful to ensure athletes are able to resume their normal sports activities.