Which condition is characterized by knee pain and weakness during prolonged sitting and while climbing stairs?

Patellofemoral syndrome is characterized by knee pain that occurs particularly during activities that put stress on the joint, such as prolonged sitting (often referred to as "theater sign") and climbing stairs. This condition commonly affects individuals who are involved in activities that require repetitive knee use, especially those who engage in activities that involve squatting, jumping, or running.

The pain arises from issues with the patella (kneecap) tracking properly within the femoral groove, which can be a result of muscle imbalances, overuse, or anatomical factors that affect knee mechanics. As a result, individuals with patellofemoral syndrome often report discomfort and weakness in the knee during prolonged periods of flexion (such as sitting for extended times) and during activities that involve knee bending (like ascending stairs), which can create a specific pattern of pain.

This sets patellofemoral syndrome apart from other conditions. For example, runner's knee generally refers to inflammation of the knee due to repetitive motion, but the symptoms more often relate to activity-based pain rather than prolonged sitting specifically. Anterior cruciate ligament injury typically presents with sudden onset of pain and instability following a specific injury mechanism, rather than gradual onset during sitting or stair climbing.