Patient Education · Knee

Quadriceps & Patellar Tendon Repair

If the knee will not hold you up and you cannot lift your straight leg off the bed, this is usually why. It is also one of the few orthopedic problems where waiting genuinely costs you.

Dr. Darin W. Allred Darin W. Allred, MD Board-certified orthopedic surgery & sports medicine
UrgentBest repaired within the first week or two
~1 hrTypical time for the operation
6 weeksBrace locked straight for standing
4–6 moBack to full activity

The chain that straightens your knee

Straightening your knee depends on an unbroken chain: the quadriceps muscle, the quadriceps tendon, the kneecap, the patellar tendon, and the shin bone. Pull on the top and the bottom moves. Break the chain anywhere and the whole thing stops working.

Illustration of the normal quadriceps muscle, kneecap and patellar tendon
The normal arrangement: thigh muscle, quadriceps tendon, kneecap, patellar tendon, shin bone.

What tore, and how

The tendon gives way when the knee is forced to bend while the quadriceps is contracting hard to resist it — a stumble, a missed step, catching yourself as you fall.

Illustration of a ruptured quadriceps tendon above the kneecap
A quadriceps tendon rupture, above the kneecap. The chain that straightens your knee is broken.
  • A quadriceps tendon rupture (above the kneecap) is more common over about 40. Diabetes, kidney disease, gout, steroid use, and certain antibiotics all weaken the tendon and raise the risk.
  • A patellar tendon rupture (below the kneecap) tends to happen in younger, more athletic people, often in someone who had tendinitis there for a while first.

The story is nearly always the same: a pop, immediate collapse, and afterward the knee simply will not hold weight. There is usually a dent you can feel above or below the kneecap, and the kneecap itself sits too low or too high.

The test that settles it: lie flat and try to lift your straight leg off the bed. If you cannot — or can only lift it a little with the knee sagging — the chain is broken and you need to be seen promptly. Some people can still walk stiff-legged, which is exactly why this injury gets missed and called "a bad sprain."

Why the timing matters

Once the tendon is torn, the quadriceps muscle pulls the free end away and starts to shorten and scar. Repaired within the first week or two, the ends come back together easily and heal well. Left for weeks, the tendon must be stretched back down under tension, sometimes with a graft, and the results are not as good.

This is a repair I do not like to postpone.

How the operation goes

  1. Anesthesia. Spinal or general, with a block. Usually a same-day operation.
  2. An incision over the front of the knee at the site of the tear.
  3. Clear and prepare the torn ends and the patch of bone on the kneecap where the tendon belongs.
  4. Weave heavy sutures up into the tendon so the pull is spread through healthy tissue rather than concentrated on one stitch.
  5. Bring it back to bone — the sutures pass through small tunnels drilled in the kneecap, or through anchors set into it, and are tied down.
  6. Check the kneecap height against the other knee, and take the knee gently through its range to see how far it can safely bend.
  7. Close, and the leg goes into a brace locked straight.
Illustration of a torn patellar tendon below the kneecap
A patellar tendon tear, below the kneecap - the same injury at the other end of the chain.

Recovery: the two brace rules

The repair is strong in one direction and fragile in the other. Standing on a straight leg is safe. Bending against the pull of the quadriceps is what tears it apart. Two rules follow from that, and they matter more than anything else on this page.

  • Full weight is fine — but only with the brace locked straight. Every time you stand or walk, that brace is locked.
  • You may take the brace off lying in bed, but do not straighten the knee yourself. Letting the leg down actively uses exactly the muscle pulling on your repair. Your therapist will teach you a specific way to bend and straighten using gravity instead — wait until you have been shown before you try it.
  • First 2 weeksBrace locked straight for all standing and walking. Full weight allowed in it. Ankle pumps and thigh tightening. Keep the incision dry 48 hours. Therapy starts within a few days. Aspirin 81 mg twice daily for two weeks. Follow-up around two weeks.
  • 2–6 weeksThe brace opens on a schedule your therapist sets, a little more bend each week. Still locked straight for walking. Still no actively straightening the knee against gravity.
  • 6–12 weeksOut of the brace as quad control returns. Strengthening begins carefully. Bending continues to improve.
  • 3–6 monthsProgressive strengthening. Most people are back to ordinary life well before the end of this, with the last of the strength arriving toward six months.

The risks, honestly

  • The repair pulls apart The main risk, and nearly always from bending too far too soon or bearing weight with the brace unlocked. It usually means another operation.
  • Stiffness The commonest lasting problem. Protecting the repair and keeping the knee moving pull in opposite directions, and the balance between them is what your therapist is managing.
  • Lasting quadriceps weakness Some loss of strength is common, particularly after a quadriceps tendon repair in an older patient.
  • The kneecap sits too high or too low Affects how the knee tracks; checked carefully during surgery.
  • Infection or wound problems Uncommon, more likely in diabetes.
  • Blood clots A real consideration in a braced, less mobile leg — hence the aspirin and moving often.
This page is general education. It describes how I approach this and what most patients experience. If anything here does not match what you were told in clinic, ask — your own instructions always come first.