Kneecap dislocation occurs when the triangle-shaped bone covering the knee (patella) moves or slides out of place. The problem usually occurs toward the outside of the leg.
Dislocation - kneecap; Patellar dislocation or instability
Kneecap (patella) dislocation is often seen in women. It usually occurs after a sudden change in direction when your leg is planted. This puts your kneecap under stress.
Dislocation may also occur as a direct result of injury. When the kneecap is dislocated, it can slip sideways and around to the outside of the knee.