Patella Instability and Anterior Knee Pain

The patellofemoral joint is one of the three compartments in the knee. It consists of an articulation between the back of the kneecap (patella) and the front of the thigh bone (femur). The main role of the kneecap is to increase the lever arm of the thigh muscles (quadriceps), making it easier to extend (straighten) the knee. The longer the lever arm, the smaller the force that is needed to extend the knee.

The kneecap is normally held firmly in place owing to the action of muscles, ligaments and the overall shape of the joint, however as a result of the alignment of the shin bone (tibia) and the thigh bone there is a natural predisposition for the kneecap to move laterally (outwards). In some patients, the kneecap joint does not form normally and this makes them more likely to develop problems with kneecap instability.

When the knee dislocates it will become painful and often very swollen. There may be a feeling of instability in the knee and it may be difficult to walk. Those patients with traumatic dislocation can generally be expected to make a full recovery, although some may experience a lack of trust in the knee when they return to sports. In patients with atraumatic instability who have an underlying abnormality in their knee, further pain, swelling and instability is commonly experienced. More than half of this group of patients will experience another dislocation.

If it is the first time your knee has dislocated, it is accepted practice to treat this conservatively (without an operation). First-line treatment consists of RICE (Rest, Ice Compression and Elevation). In addition, painkillers and anti-inflammatory medication are advisable. You will be referred for physiotherapy to help strengthen the quadriceps muscles and regain full range of motion. In the past, patients were treated in plaster for 6 weeks with the knee held out straight, however we now know this is a bad idea because the knee becomes very stiff indeed and the thigh muscles waste away. If patellar dislocation becomes a recurrent problem and conservative treatment has failed, surgery will be offered