Patellar tendon

What it is

Because it connects two bones, the patellar tendon is sometimes called the patellar ligament, but it works as the final link of the extensor mechanism. It is about 5 centimetres long in most adults and is easy to feel just below the kneecap when the leg is straight. A pad of fat, Hoffa's fat pad, sits directly behind it.

Why it matters for patients

Repeated jumping and landing, as in basketball, volleyball, handball and some gym training, can overload the tendon and cause patellar tendinopathy, often called jumper's knee. It causes pain just below the kneecap that is worse with jumping, squatting and stairs. It usually improves with a gradual loading programme over several months rather than rest alone.

In growing children, the same pull can irritate the growth areas at either end, causing Osgood–Schlatter disease at the shin or Sinding-Larsen–Johansson at the kneecap. Complete rupture of the patellar tendon is less common, usually happens under 40 with a forceful landing, and needs early surgical repair. The central third of the tendon, with bone at each end, is also a well-established graft for ACL reconstruction.

How it is examined

A surgeon presses along the tendon, checks its tension and watches a single-leg squat. Ultrasound and MRI show thickening, tears or ruptures.