Dislocations of the knee joint are rare injuries and occur in high velocity accidents. They are associated with injury to the blood vessels and the posterior cruciate ligament. They need admission to a hospital and careful evaluation for presence of pulses. Dislocations of the kneecap are more common. The kneecap slides in the trochlear groove of the femur. It is retained in place by the anatomical configuration and by the ligamentous restraints. These are similar to the reins controlling a horse. When the inner checkrein is weak then the patella will have a tendency to dislocate outwards. When the outward movement is only partial then it is called a subluxation and when it is complete, it is called a dislocation.

.The kneecap may dislocate and the person falls unexpectedly. .The knee may appear mangled and the kneecap is felt out of place. .Pain .Recurrent episodes of subtle subluxation are called instability and is characterised by swelling. Clinically the patella may be lax. .Long standing instability leads to wear of the kneecap and results in chondromalacia patella and swelling.

.Double joint ness refers to people with lax ligaments. Such people can bend their elbow backwards. .Injuries as a fall or an accident in a contact sport. .Abnormal tissue and ligamentous restraints. Once the kneecap dislocates then the tissues on the inner side are torn and do not heal. There is a tendency for repeated dislocation. .Repeated knee dislocation leads to arthritis.

.Physiotherapy to strengthen the quadriceps muscle. .Use of a knee brace to keep the kneecap in place. .If there is a tendency for repeated dislocation then an arthroscopy is done to confirm the abnormal mobility of the patella. Simultaneously, a release of the tight ligaments on the outside of the kneecap can be done. .If there is a recurrence then an open operation is necessary to realign the patella.