Patellar Tendon Tear
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.
The knee and tendons
Tendons attach muscles to bones. The patellar tendon attaches the bottom of the kneecap (patella) to the top of the shinbone (tibia). It is actually a ligament that connects to two different bones, the patella and the tibia.
The patella is attached to the quadriceps muscles by the quadriceps tendon. Working together, the quadriceps muscles, quadriceps tendon and patellar tendon straighten the knee.
Patellar tendon tears can be either partial or complete.
Many tears do not completely disrupt the soft tissue. This is similar to a rope stretched so far that some of the fibers are torn, but the rope is still in one piece.
A complete tear will disrupt the soft tissue into two pieces.
The patellar tendon often tears where it attaches to the kneecap, and can break a piece of the bone as it tears. When the patellar tendon is completely torn, the tendon is separated from the kneecap. Without this attachment, you cannot straighten your knee.
When a tear is caused by a medical condition — like tendonitis — the tendon usually tears in the middle.
A very strong force is required to tear the patellar tendon.
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.
The patellar tendon usually tears when the knee is bent and the foot planted, like when landing from a jump or jumping up.
A weakened patellar tendon is more likely to tear. Several things can lead to tendon weakness.
Inflammation of the patellar tendon, called patellar tendonitis, weakens the tendon. It may also cause small tears.
Patellar tendonitis is most common in people who participate in activities that require running or jumping. While it is more common in runners, it is sometimes referred to as "jumper's knee."
Corticosteroid injections to treat patellar tendonitis are typically avoided in or around the infrapatellar tendon. Injections around this articular tendon have been linked to increased tendon weakness and increased likelihood of tendon rupture.
Weakened tendons can also be caused by diseases that disrupt blood supply. Chronic diseases which may weaken the tendon include:
- Chronic renal failure
- Hyper betalipoproteinemia
- Rheumatoid arthritis
- Systemic lupus erythmatosus (SLE)
- Diabetes mellitus
- Metabolic disease
Using medications like corticosteroids and anabolic steroids has been linked to increased muscle and tendon weakness.
Previous surgery around the tendon, such as a total knee replacement or anterior cruciate ligament reconstruction, might put you at greater risk for a tear.
When a patellar tendon tears there is often a tearing or popping sensation. Pain and swelling typically follow. Additional symptoms include:
- An indentation at the bottom of your kneecap where the patellar tendon tore
- Your kneecap may move up into the thigh because it is no longer anchored to your shinbone
- You are unable to straighten your knee
- Difficulty walking due to the knee buckling or giving way
Your doctor will discuss your medical history. Questions you might be asked include:
- Have you had a previous injury to the front of your knee?
- Do you have patellar tendonitis?
- Do you have any medical conditions that might predispose you to a quadriceps injury?
- Have you had surgery to your knee, such as a total knee replacement or an anterior cruciate ligament reconstruction?
To determine the exact cause of your symptoms, your doctor will test how well you can extend, or straighten, your knee. While this part of the examination can be painful, it is important to identify a patellar tendon tear.
To confirm the diagnosis, your doctor may order some imaging tests, such as an X-ray or magnetic resonance imaging (MRI) scan.
The kneecap moves out of place when the patellar tendon tears. This is often very obvious on a "sideways" X-ray view of the knee. Complete tears can often be identified with these X-rays alone.
This scan creates better images of soft tissues like the patellar tendon. The MRI can show the amount of tendon torn and the location of the tear. Sometimes, an MRI is required to rule out a different injury that has similar symptoms.