Patella dislocations are relatively unusual and usually occur in adolescents or young adults. The patella or kneecap usually jumps or runs out of its retaining groove, sometime becoming visible in an abnormal location on the outside of the knee. The injury is associated with significant pain and associated muscle spasm but the dislocation normally reduces when the knee is gently straightened with assistance.
Medical imaging is usually required to exclude the presence of associated fracture or injury to chondral cartilage, and very occasionally the dislocation can be associated with the separation of a fragment of cartilage or bone which falls into the knee joint itself. These injuries are normally treated with a period of splintage followed by rehabilitation supervised by a physiotherapist. Occasionally a kneecap will dislocate on more than one or even several occasions and in these patients patella stabilisation operations are sometimes required.