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.
A patellar tendon tear can be partial or complete.
A partial patellar tendon tear means that the soft tissue will not be completely disrupted. Some fibers are torn.
A complete patellar tendon tear means a total separation between the patellar tendon and the kneecap. Without this attachment, the knee cannot be straightened.
The patellar tendon often tears at the place where it attaches to the kneecap, and a piece of bone can break off along with the tendon. When a tear is caused by a medical condition — like tendonitis — the tear usually occurs in the middle of the tendon.
A very strong force is required to tear the patellar tendon:
- Falls – 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.
- Jumping – 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 have been linked to increased tendon weakness and increased likelihood of tendon rupture. These injections are typically avoided in or around the patellar tendon.
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 the patient at greater risk for a tear.
Signs & Symptoms
The following symptoms can be present for someone with a patellar tendon tear:
- The patient is unable to continue activity
- The patient can’t resume weightbearing or does so only with assistance
- An indentation at the bottom of the kneecap where the tendon tore
- A proximally displaced patella (kneecap), because it’s no longer anchored to the shinbone
- Incomplete extensor function
- Walking is difficult due to the knee buckling or giving way
Sometimes patients can feel a tearing or popping sensation, followed by pain and swelling.
An athlete that has a patellar tendon tear has immediate pain and swelling in the knee. 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 tell-tale features in addition to pain and swelling in the knee.
First, the athlete will be unable to actively straighten the leg.
In addition, the surgeon 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 that this is difficult to appreciate. The knee effusion in combination with severe pain with motion often requires imaging tests to assist in making the diagnosis:
- X-rays – 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.
- MRI – 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.
Several factors are considered when planning treatment, including:
- The type and size of tear
- Patient’s activity level
- Patient’s age
Very small, partial tears respond well to non-surgical treatment.
Wearing a knee immobilizer or brace. This will keep the knee straight to help it heal. Most likely will need crutches to help avoid putting entire body weight on the leg. Can expect to be in a knee immobilizer or brace for 3 to 6 weeks.
Once the initial pain and swelling has settled down, physical therapy can begin. Specific exercises can restore strength and range of motion.
While wearing the brace, exercises to strengthen quadriceps muscles may be recommended. Straight-leg raises are often prescribed. As time goes on, the brace will be unlocked. This will allow patient to move more freely with a greater range of motion. More strengthening exercises will be prescribed as healing continues.
Most patients require surgery to regain knee function. Surgical repair reattaches the torn tendon to the kneecap.
Patients who require surgery do better if the repair is performed soon after the injury. Early repair may prevent the tendon from scarring and tightening into a shortened position.
Although tendon repairs are sometimes done on an outpatient basis, most patients do stay in the hospital at least one night after this operation. This depends on patient’s medical needs.
The surgery may be performed with regional (spinal) anesthetic which numbs the lower body, or with a general anesthetic.
To reattach the tendon, sutures are placed in the tendon and then threaded through drill holes in the kneecap. The sutures are tied at the top of the kneecap. The sutures are then carefully tied to get the correct tension in the tendon. This will also make sure the position of the kneecap closely matches that of the uninjured kneecap.
A recent development in patellar tendon repair is the use of suture anchors. Surgeons attach the tendon to the bone using small metal implants (called suture anchors). Using these anchors means that drill holes in the kneecap are not necessary. This is a new technique, so data is still being collected on its effectiveness. Most orthopaedic research on patellar tendon repair involves the direct suture repair with the drill holes in the kneecap.
If the tendon has shortened too much before surgery, it will be hard to re-attach it to the kneecap. The surgeon may need to add tissue graft to lengthen the tendon. This sometimes involves using donated tissue (allograft).
Tendons often shorten if more than a month has passed since the injury. Severe damage from the injury or underlying disease can also make the tendon too short.
The exact timeline for physical therapy (post-surgery) and the type of exercises prescribed will be individualized to the patient. The rehabilitation plan will be based on the type of tear, surgical repair, medical condition, and patient’s needs.
Complete recovery takes about 6 months. Many patients have reported that they required 12 months before they reached all their goals.