Patellar Tendon Rupture
A tear of the tendon connecting the kneecap to the shinbone
Quick Facts
- Type: Knee tendon injury
- Key sign: Cannot straighten the knee; kneecap rides high
- Common cause: Jumping or landing on a bent knee
- Treatment: Usually surgical repair, then rehab
Overview
The patellar tendon connects the bottom of the kneecap (patella) to the top of the shinbone (tibia). Together with the quadriceps muscle and tendon, it forms the mechanism that straightens the knee. A patellar tendon rupture is a tear of this tendon, which may be partial or complete.
A complete rupture breaks the chain that extends the knee, so the leg cannot be straightened or hold weight. It is a disabling injury that usually requires surgery to reconnect the tendon and is most common in active adults under about 40.
Symptoms
Symptoms usually start suddenly when the injury occurs:
- A pop or tearing feeling at the front of the knee, just below the kneecap
- Immediate pain and rapid swelling
- Inability to straighten the knee or to keep it straight
- The knee buckling or giving way when trying to stand
- The kneecap appearing to sit higher than normal
- A gap that can sometimes be felt below the kneecap
Walking becomes very difficult, and climbing stairs or rising from a chair may be impossible with a complete tear.
Causes
A patellar tendon rupture typically occurs when a powerful force is placed on the tendon while the knee is bent, such as:
- Landing from a jump in sports like basketball or volleyball
- A direct blow to the front of the knee
- Stumbling or falling onto a flexed knee
The tendon is more vulnerable if it has been weakened. Repeated stress (patellar tendinitis or "jumper's knee"), prior steroid injections near the tendon, certain medications, and chronic illnesses can all weaken the tendon and make a tear more likely.
Risk Factors
- Jumping sports and high-impact activity
- Pre-existing patellar tendinitis or chronic tendon strain
- Prior steroid injections around the knee
- Long-term corticosteroid use
- Chronic conditions such as kidney disease, diabetes, or lupus
- Previous knee surgery involving the tendon
Diagnosis
The diagnosis is suggested by the injury history and a physical exam showing an inability to straighten the knee and a high-riding kneecap. Tests include:
- X-rays: Show whether the kneecap sits abnormally high and help rule out a fracture.
- Ultrasound: Quickly confirms a tendon tear and its extent.
- MRI: Provides detailed views to distinguish partial from complete tears and plan repair.
Treatment
Treatment depends on the size of the tear and your activity level.
- Non-surgical care: Partial tears in which the knee can still be straightened may be treated with immobilization, rest, and progressive physical therapy.
- Surgical repair: Complete tears are repaired surgically, usually as soon as feasible, by reattaching the tendon to the kneecap. Early repair generally produces the best results.
After surgery, the knee is protected in a brace and rehabilitation rebuilds motion and strength over several months. Most people recover good knee function, though regaining full strength takes time and dedicated therapy.
Prevention
- Strengthen and stretch the thigh and leg muscles regularly
- Warm up before jumping or high-impact sport
- Treat patellar tendinitis (jumper's knee) early rather than playing through it
- Be cautious with repeated steroid injections near the knee
- Manage chronic conditions that weaken tendons
When to See a Doctor
Seek prompt care if, after a jump, fall, or blow to the knee, you cannot straighten the knee, cannot bear weight, notice your kneecap sitting high, or feel a gap below it. Early evaluation and repair improve the outcome.
Go to urgent or emergency care for severe pain, large swelling, or obvious deformity, since a kneecap fracture may also be present.
Frequently Asked Questions
What is the difference between a patellar and quadriceps tendon rupture?
Both disrupt the knee's straightening mechanism, but the patellar tendon is below the kneecap and the quadriceps tendon is above it. Patellar tendon ruptures more often affect younger, active adults, while quadriceps ruptures are more common in older people.
Does a patellar tendon rupture need surgery?
Complete tears almost always require surgical repair to restore the ability to straighten the leg and walk. Partial tears where the knee can still be straightened may be treated with bracing and physical therapy.
How long is recovery after surgery?
The knee is protected in a brace for several weeks, with physical therapy continuing over several months. Many people return to daily activities within a few months, though regaining full strength can take longer.
Can I prevent a patellar tendon rupture?
You cannot eliminate the risk, but keeping the leg muscles strong, warming up before sport, and treating jumper's knee early all help. Caution with steroid injections near the knee also reduces risk.
Is this injury an emergency?
It is an urgent injury that should be assessed quickly because early repair gives the best results. Seek emergency care if there is severe deformity, you cannot move the leg, or a fracture is suspected.
References
- American Academy of Orthopaedic Surgeons (OrthoInfo). Patellar Tendon Tear.
- Mayo Clinic. Knee tendon injuries.
- MedlinePlus, U.S. National Library of Medicine. Tendon injuries.
- National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS).