The patella (kneecap) sits between the quadriceps tendon and patella tendon at the front on the knee. It normally rests in a groove on the femur (trochlea). Its function is to improve the efficiency of the quadriceps muscle and during activity it slides up and down the trochlear groove. In patella instability the patella can slip out of the groove either partially (subluxation) or completely (dislocation).
Patella dislocation usually occurs during twisting movements or change of direction. This can occur during a number of activities such as sports or dancing. There are a number of recognised predisposing causes of patella dislocation which places some people at increased risk.
Patella dislocation results in pain and giving way (buckling) of the knee folowed by swelling. It almost always results in a fall. The patella may relocate spontaneously but occasions it requires manual relocation either on the spot or if this is not possible then in hospital with pain killers and sedation. Partial dislocation (subluxation) can also occur. This can also result in giving way (buckling) of the knee but sometimes presents simply as intermittent pain at the front of the knee.
Initial management of patella dislocation is to manually relocate the patella. Investigations at this stage may include an xray as on occasions the dislocation can result in a fracture of the knee joint surface. The knee should then be splinted and painkillers given. The splint should subsequently be replaced with a suitable patella brace and physiotherapy arranged to aid rehabilitation and reduce the risk of recurrent instability. Subsequent investigation may include an MRI scan to assess for associated joint surface and ligament damage.
Recurrent instability and dislocation can occur despite appropriate initial management. Occasionally surgical stabilisation or patella realignment may be required. The need for this and the type of surgery required should be discussed with your orthopaedic knee surgeon.
Surgical procedures which may be indicated for recurrent patella instability include: