ABSTRACT
Locking is different from stiffness. The knee, quite suddenly, cannot be straightened fully, although flexion is still possible. This happens when a torn meniscus or loose body is caught between the articular surfaces. By wiggling the knee around, the patient may be able to ‘unlock’ it; sudden unlocking is the most reliable evidence that something mobile had previously obstructed full extension. Do not be misled by ‘pseudo-locking’, when movement is suddenly stopped by pain or the fear of impending pain.
