Patellar Tendon Rupture

What the patellar tendon does

The large quadriceps muscle on the front of the thigh joins the top of the kneecap through the quadriceps tendon. The patellar tendon continues from the bottom of the kneecap to a bump on the front of the shinbone (the tibial tubercle). Together they form the extensor mechanism, which straightens the knee. It lets you stand from a chair, climb stairs, jump and walk without the knee buckling.

When the patellar tendon ruptures, the quadriceps can no longer pull on the shinbone, so the knee cannot be actively straightened.

How it happens

Most tears occur when the quadriceps contracts forcefully while the knee is bent and the foot is planted, such as:

• landing from a jump in basketball or volleyball
• stumbling and trying to avoid a fall
• a fall onto a bent knee

Less often a direct blow or a cut causes it.

Risk factors

A healthy tendon is very strong, so most ruptures happen through a tendon already weakened by:

• patellar tendinopathy (jumper's knee), long-standing tendon degeneration from repetitive jumping
• corticosteroid injections into or near the tendon
• fluoroquinolone antibiotics such as ciprofloxacin or levofloxacin
• long-term steroid tablets
• chronic kidney disease, diabetes, rheumatoid arthritis and lupus
• previous knee surgery, including ACL reconstruction using part of the patellar tendon, or knee replacement

Symptoms

• a tearing or popping sensation at the time of injury
• pain and swelling just below the kneecap
• bruising
• a dent or soft gap where the tendon should be
• the kneecap sitting higher up the thigh than on the other side (patella alta)
• inability to straighten the knee fully, or to lift the leg straight off the bed
• the knee giving way when you try to stand or walk

A partial tear may allow some straightening, but with pain and weakness.

Patellar vs quadriceps tendon rupture

Both injuries cause the same loss of knee straightening and are managed similarly.

Diagnosis

A doctor will ask how the injury happened and examine the knee. The key test is the straight leg raise: lying on your back, you try to lift the leg with the knee straight. Being unable to do so, or the knee bending as you lift, suggests the extensor mechanism is broken. The doctor also feels for a gap and compares kneecap height with the other side.

Imaging includes:

• X-ray: a side view shows the kneecap sitting abnormally high and rules out a kneecap fracture or a chip of bone pulled off with the tendon.
• Ultrasound: quick and useful for confirming the tear.
• MRI: shows whether the tear is partial or complete, its exact location, and other injuries such as ligament or meniscus damage.

These injuries are sometimes missed at first, because swelling makes the knee hard to examine, so mention any pop and inability to straighten the leg.

Treatment

Partial tears

Small partial tears with intact straightening can be treated without surgery: a knee brace or immobilizer keeping the knee straight for about 3 to 6 weeks, crutches, then a gradual increase in bending and strengthening with physical therapy.

Complete tears

Complete tears need surgical repair. Results are best when surgery is done early, ideally within 2 to 3 weeks. After that, the tendon and quadriceps scar and shorten, making repair harder and sometimes requiring a tendon graft.

During surgery, the torn tendon ends are stitched together and, when the tear is at the kneecap, the stitches are passed through small tunnels drilled in the kneecap or fixed with suture anchors. Surgeons may add a reinforcing wire, cable or strong suture to protect the repair.

Recovery timeline

• First weeks: a brace locked straight. You can usually put weight on the leg with crutches.
• About 2 to 6 weeks: the brace hinge is gradually adjusted to allow controlled bending, guided by your surgeon.
• About 6 to 12 weeks: walking without a brace and progressive strengthening.
• 3 to 4 months: most daily activities, including stairs and light exercise.
• 6 to 12 months: return to running, jumping and sport, once strength and control are close to the other leg.

Physical therapy is essential. Restoring full bending and quadriceps strength takes months.

Complications

• stiffness and loss of full knee bending
• persistent quadriceps weakness
• re-rupture, especially with early overloading
• infection or wound problems
• kneecap sitting too low after repair (patella baja)
• pain at the front of the knee
• blood clots after surgery

Delayed diagnosis and repair lead to poorer results.

Outlook

Most people who have early repair regain near-normal strength and range of motion and return to daily activities. Many return to recreational sport. Some athletes do not reach their previous level, and mild weakness or loss of a few degrees of bending is common.

Frequently asked questions

Can you walk with a torn patellar tendon?

Walking is very difficult with a complete tear, because the knee buckles without the ability to straighten it. Some people can shuffle with the leg kept stiff. With a partial tear, walking may be possible but painful and weak. Either way, the knee needs urgent assessment.

How long does it take to recover from a patellar tendon rupture?

After surgical repair, most people walk without a brace by about 6 to 12 weeks and return to most daily activities by 3 to 4 months. Full strength and a return to jumping or running sports usually take 6 to 12 months, depending on the injury and rehabilitation.

Does a torn patellar tendon need surgery?

A complete tear almost always needs surgery to restore the ability to straighten the knee. Small partial tears with intact straightening can often heal in a straight-leg brace followed by physical therapy. Surgery works best within 2 to 3 weeks of injury.

What does a ruptured patellar tendon feel like?

People usually describe a sudden pop or tearing feeling below the kneecap, followed by pain, swelling and the knee giving way. You may notice a soft dent below the kneecap and the kneecap sitting higher than on the other side, and you cannot lift your leg straight while lying down.

What is the difference between patellar tendinitis and a patellar tendon rupture?

Patellar tendinitis, or tendinopathy, is gradual pain and degeneration in the tendon from overuse, often in jumping athletes. A rupture is a sudden tear that stops the knee from straightening. Long-standing tendinopathy and steroid injections into the tendon can weaken it and make a rupture more likely.