Instability After Total Hip Replacement: Aetiology, Prevention and Management

Abstract

Instability after total hip arthroplasty and consequent dislocation has, since long, been a cause of grave concern for the patient and surgeon, particularly when it is recurrent. Incidence rates have been reported at about 2% in primary and 10% in revision THR surgery and about 40% of these are recurrent.

Predisposing causes for recurrent dislocation include patient factors like obesity, alcoholism, dementia and other neurological diseases and disease pathologies such as fracture of the neck of femur, DDH and avascular necrosis. Implant characteristics such as femoral head size, acetabular liner design and dual mobility cups influence hip stability, as do meticulous surgical technique to avoid injury to the abductor mechanism, secure capsular repair and accurate component alignment. Important steps to prevent post-operative recurrent instability are careful pre-operative planning and intra-operative confirmation of hip stability through appropriate tests before closure. Special precautions applicable in high-risk patients are outlined.

Early dislocations give over 60% success with non-operative methods whereas late dislocations usually require partial or complete revision. The causes of recurrent dislocation, as classified by Wera et al., are acetabular component malposition, femoral component malposition, abductor insufficiency, implant/bony impingement, polyethylene wear and unknown causes. The treatment algorithm involves specific diagnosis and correction of the underlying cause of the condition. Revision surgery should not be undertaken without establishing a definite diagnosis of the reason for instability.