What is a primary indication of patellar tendon tear?

A patellar tendon tear is primarily characterized by the inability to extend the knee. This is because the patellar tendon connects the kneecap (patella) to the shin bone (tibia) and plays a crucial role in the extension of the knee during movement. When this tendon is torn, the mechanism that allows for knee extension is compromised, leading to significant weakness or complete inability to straighten the leg.

In contrast, the ability to bend the knee remains relatively intact, especially if the injury is isolated to the patellar tendon rather than the knee joint itself. Swelling around the ankle and changes in skin color are not typical primary indications of a patellar tendon injury; they may be associated with other conditions but do not specifically indicate a tear in the patellar tendon.