Dislocation of the kneecap (patellofemoral joint) is a relatively common injury that may be either due to an acute traumatic event (most commonly a sporting injury), due to a long-standing abnormality of the kneecap joint (trochlear dysplasia) or possibly due to hyperlaxicity of soft tissues. The treatment of patella dislocations varies based upon the underlying cause.
Acute traumatic patella dislocation usually occurs as either the result of a sudden twisting injury of the knee or a direct blow to the kneecap itself. Traumatic dislocations are nearly always lateral (the kneecap flips around to the outside of the knee) and are sometimes associated with injuries to the cartilage and underlying bone (chondral or osteochondral defects). The diagnosis is usually made by clinical examination with the assistance of x-rays. Immediate management involves reducing the patella back in place and simple first aid measures. Subsequent investigation may involve an MRI scan to rule out a loose fragment of bone or cartilage that may need a surgical repair. Rehabilitation is then usually supervised by the physiotherapists. Patella dislocations may occur just once or become recurrent. Further surgery may become necessary with recurrent dislocations in the form of medial patellofemoral ligament reconstruction.
Trochlear Dysplasia describes a condition where the kneecap joint is too shallow and did not develop properly during childhood. In mild forms this may go unnoticed for a number of years and only become apparent when the patella dislocates. With more severe forms of dysplasia, patients commonly present with permanently subluxed or dislocated patellae. Diagnosis is usually based upon a clinical evaluation with a knee specialist with the assistance of an MRI scan. Surgery for dislocated patellae is complicated and may involve a number of different procedures that include reconstructing the medial patellofemoral ligament and deepening the groove for the kneecap (Trochleoplasty).
Hyperlaxicity of soft tissues can predispose patients with normal kneecap joints to dislocate, often with relatively little trauma. Physiotherapy is often the mainstay of treatment for these patients although in some isolated patients with intractable symptoms surgery may become necessary.