Quadriceps Tendon Rupture

The knee extensor mechanism

The quadriceps muscles at the front of the thigh join into the quadriceps tendon, which attaches to the top of the kneecap. The patellar tendon then runs from the bottom of the kneecap to the shin. Together, they straighten the knee. A tear anywhere in this chain prevents you from straightening the knee against gravity.

Causes

• eccentric loading: the quadriceps contracts strongly while the knee is bending, for example when landing from a jump, missing a step or trying to stop a fall
• direct blow or cut to the front of the thigh, less often
• weakened tendon from degeneration, tendinitis or medical conditions

Risk factors

• age over 40, and male sex
• chronic kidney disease and dialysis
• diabetes
• gout and rheumatoid arthritis
• obesity
• long-term corticosteroid use or steroid injections near the tendon
• fluoroquinolone antibiotics (such as ciprofloxacin), which are linked to tendon rupture
• anabolic steroid use
• previous knee surgery

Ruptures on both sides at once are rare and usually point to an underlying condition.

Symptoms

• a tearing or popping sensation
• immediate knee pain above the kneecap
• swelling and bruising
• an indentation or gap above the kneecap
• the kneecap may sit lower than normal
• inability to straighten the knee or perform a straight-leg raise (complete tears)
• knee buckling or giving way when walking

Partial tears cause pain and weakness, but you may still be able to straighten the leg.

Diagnosis

• examination: a gap above the kneecap and testing whether you can lift the straight leg
• X-rays: show a low-riding kneecap, small bone fragments, or a kneecap fracture that can cause similar symptoms
• ultrasound or MRI: confirm the tear, distinguish partial from complete tears and look for other injuries

Quadriceps tendon ruptures are missed in a significant number of cases at first because swelling can hide the gap and some people can still partly move the knee. Early diagnosis matters because delayed repair is harder.

Treatment

Partial tears

Small partial tears in which the knee can still be straightened may be treated with:

• a knee immobilizer or hinged brace locked straight for about 4 to 6 weeks
• crutches
• gradually increasing knee bending in a brace
• physical therapy to restore strength

Complete tears

Surgery is needed to restore the ability to straighten the knee. The surgeon reattaches the tendon to the kneecap, usually by passing strong sutures through tunnels drilled in the kneecap or using suture anchors. Repair within the first 2 to 3 weeks gives the best results. Delayed repairs may need tendon grafts or lengthening procedures.

Rehabilitation

• initial phase: brace locked in extension, weight bearing as instructed with crutches
• weeks 2 to 6: gradual, controlled bending in the brace
• weeks 6 to 12: walking without a brace, strengthening
• months 3 to 6: functional training, balance, return to most activities
• sport: often 6 months or longer

Complications

• weakness of the quadriceps
• loss of full knee bending
• re-rupture
• infection or wound problems
• blood clots after surgery

Outlook

Most people who have prompt surgical repair regain good knee function and return to normal activities. Some have mild lasting weakness or stiffness. Delayed diagnosis and repair lead to poorer outcomes.

Frequently asked questions

What does a quadriceps tendon rupture feel like?

People usually feel a sudden pop or tearing above the kneecap, followed by pain and swelling. With a complete tear, you cannot straighten your knee or lift your straight leg, and the knee may buckle when you try to walk. There may be a dent above the kneecap.

Can a quadriceps tendon tear heal without surgery?

Small partial tears can heal with a straight-leg brace and physical therapy. Complete tears do not heal properly on their own and need surgical repair to restore the ability to straighten the knee.

How long does it take to recover from quadriceps tendon repair?

Most people walk without a brace by about 6 to 12 weeks and return to most daily activities within 4 to 6 months. Full strength and return to sport can take 6 months to a year. Physical therapy is essential throughout.

Who is at risk of a quadriceps tendon rupture?

Men over 40 are most often affected. Risk is higher with chronic kidney disease, diabetes, gout, rheumatoid arthritis, obesity, long-term steroid use, fluoroquinolone antibiotics and previous knee surgery.

What is the difference between quadriceps and patellar tendon rupture?

The quadriceps tendon is above the kneecap and tears more often in people over 40. The patellar tendon is below the kneecap and tears more often in people under 40, frequently athletes. Both prevent straightening the knee and usually need surgery.