Patellar Tendon Rupture

The patellar tendon is the thick rope of tissue that runs from the bottom of your kneecap to the bump on the front of your shin — the bottom half of the chain that lets you straighten your leg. A rupture is when that tendon tears all the way through. It usually happens to people under 40 (older patients tend to tear the quadriceps tendon above the kneecap instead). The injury comes from a sudden, hard load on the tendon — a stumble in sport, a missed step, a hard landing — that overwhelms it. A tendon already worn down by chronic tendinopathy is much more likely to give way.

A sudden pop or tearing sensation just below the kneecap during a hard landing, sprint, or stumble. Immediate pain and swelling in the front of the knee, and you can't straighten your leg or lift it off the ground.

You may feel a gap or soft spot just below the kneecap where the tendon used to be taut. The kneecap may ride higher than normal because the tendon below it is no longer anchoring it down. Walking is difficult or impossible without the leg buckling.

Sudden pain below the kneecap, the inability to straighten your leg or lift it off the bed, and often a noticeable gap you can feel just below the kneecap. A side X-ray shows the kneecap riding higher than normal, because the tendon below it is no longer pulling it down. An MRI confirms the rupture and shows where in the tendon it tore.

A complete rupture needs surgery, and sooner is better. The longer you wait, the more the torn ends pull back into the leg and shorten — and the harder it becomes to stitch them back to where they belong.

External patient-education references and related OSI pages for additional background:

• Britannica — Tendon
• Britannica — Knee (anatomy)
• AAOS OrthoInfo — patient education library
• OSI glossary — orthopedic terminology in plain language