Patellar dislocation

This paper looks at patellar dislocation only in the sports injury context. It does not refer to congenital and habitual dislocation.

Dislocation is simply divided into two groups, acute and recurrent (fig 1). Recurrent dislocation is a consequence of abnormal anatomy, either secondary to previous trauma or from the basic structure of the knee.

PRIMARY ACUTE DISLOCATION

This type of dislocation is caused by a high energy transfer. This implies that a lot of force was needed to displace the patella. This may take the form of a tangential blow across the front of the knee or may be a very violent twisting flexing movement.

The diagnosis is usually clear from the history. Examination may disclose the patella still lying lateral to the joint, but more usually the dislocation has been reduced and there is a swollen knee with a tender line parallel to the medial border of the patella reflecting the retinacular tear.

It is important to realise that the anatomy was normal before injury and therefore treatment should be directed at restoring this normality. If the patella lies normally centred in the femoral groove and there is no separated fragment of bone from the patella (medial edge or apex of the ridge) or the lateral femoral condyle, conservative treatment is appropriate. This should take the form of initial aspiration to relieve the pressure within the joint, followed by some form of immobilisation. My preferred treatment is to apply a brace to restrict flexion to a few degrees at first and then, after two to three weeks, to gradually increase the amount of bending. Healing tissue must be subjected to some strain so that it heals with collagen that does not subsequently stretch.¹

On computed tomography (CT) scan, the …