An inability to extend the knee is typically indicative of which condition?

The inability to extend the knee is primarily associated with a patellar tendon tear. The patellar tendon plays a crucial role in the extension of the knee; it connects the patella (kneecap) to the tibia (shin bone) and is integral in the mechanism of straightening the leg. When this tendon is torn, it results in a significant loss of function, making it difficult or impossible to actively extend the knee.

In contrast, while a meniscus tear can affect knee function and may cause pain or locking, it does not directly prevent knee extension to the same degree. A quadriceps strain can lead to discomfort and weakness but typically does not result in the complete inability to extend the knee. Anterior cruciate ligament (ACL) injuries often result in instability and may impact knee movement but are characterized more by joint instability and pain rather than a definitive inability to extend the knee.

Thus, a patellar tendon tear is the condition that most directly correlates with an inability to extend the knee effectively.