Patellar tendon rupture is a rupture of the tendon that connects the patella to the tibia. The patellar tendon is the terminal extension of the quadriceps muscle in the leg. The four muscles that make up the quadriceps each provide a tendon that is attached to the kneecap (patella).
The patella essentially lies within the quadriceps tendon and is therefore called a “sesamoid” bone. The quadriceps tendon becomes thicker and narrower as it travels from the kneecap to the shin bone (tibia).
This thicker and somewhat narrower tendon is called the patellar tendon because it starts at the patella and ends at the tibia.
The patellar tendon is instrumental in allowing a person to straighten his/her leg. When the quadriceps contract the force is transmitted through the quadriceps tendon and the patellar tendon, using the patella as a fulcrum and thus straightening the leg.
If any link in this chain is disrupted- whether through a quadriceps tendon rupture or the patellar tendon rupture, a patella fracture or inability to contract the quadriceps muscle- the leg cannot extend at the knee.
Are any athletes specifically at risk for a patellar tendon rupture?
A patellar tendon rupture tends to occur in people around the age of 40 and younger. After the approximate age of 40 years, the quadriceps tendon becomes the more common tear in the extensor mechanism.
Any condition that affects the quality of tendons or ligaments increases the risk of rupture for example, patients who take corticosteroids for an extended period of time for diseases like systemic lupus or rheumatoid arthritis.
A growing population at risk is athletes that take anabolic steroids to increase their performance. Steroids can weaken the tendon and increase the risk of their rupture.
How is it diagnosed?
An athlete that has a patellar tendon rupture has immediate pain and swelling in the knee area. He or she will often say they felt a “rip” or “tear” sensation and will be unable to ambulate because of weakness and pain.
On examination, there are several features in addition to pain and swelling in the knee. First, the athlete will be unable to actively straighten the leg. In addition, the examiner can usually palpate a defect in the tendon below the kneecap.
However, in some cases, the swelling in the knee joint (knee effusion) is severe enough. The knee effusion in combination with severe pain with motion often requires radiologic examination to assist in making the diagnosis.
Are any imaging studies utilized in diagnosing the patellar tendon rupture?
Knee X-rays are the first imaging studies that are obtained and can be very helpful. When the patellar tendon ruptures, the patella shifts superiorly because of muscle contraction of the quadriceps muscles.
This shift in the patella position is called “patella alta.” X-rays also evaluate the knee for any other injuries that can be present, similar to a patellar tendon rupture such as a fracture.
If any doubt remains after physical examination and X-rays, an ultrasound or magnetic resonance imaging (MRI) can be performed.
Ultrasonography is a safe, inexpensive and rapid test that can detect a tendon tear. However, the test is technician dependent and in some facilities is not a reliable diagnostic test. MRI is also a safe test but is more expensive and takes a longer time to perform.
However, an MRI can also evaluate any other potential problems in the knee such as ligament or cartilage injury.
In the vast majority of athletes who have suffered a patellar tendon rupture, an MRI is not suggested, as the diagnosis is made with X-rays and physical examination.
However, in the case of partial tears, chronic tears or an unusual presentation, an MRI can be a useful diagnostic tool.
Patellar tendon rupture treatment
For an athlete, surgical repair of the torn tendon is recommended. If the tear is treated non-operatively, athletes rarely have the ability to extend the leg and ambulate normally without assistance.
Surgical repair, while not an emergency, should be performed soon after the injury occurred. This facilitates an easier repair before a significant accumulation of scar tissue. Most surgeons perform a direct repair of the tendon if it is torn in the middle.
If the tendon is torn off of the bone, several different techniques can be utilized such as reattaching the tendon to the bone with a combination of sutures and bone tunnels.
Regardless of technique, the goal of surgical repair is to re-approximate the tendon ends in a secure fashion to allow it to heal.
If the patellar tendon is not repaired soon after the injury (within 5-6 weeks), surgical repair can become more difficult and can have suboptimal results. If the tendon cannot be repaired back to itself, a reconstruction can be performed with a graft from donor tissue (allograft) or tissue taken from another part of the patient’s body (autograft).