Abstract
Reports in the literature of the incidence of dislocation following primary total hip arthroplasty (THA) vary from 0.5% to 5%. Contributing factors include surgical approach, loss of the abductor mechanism, a decreased offset of the hip joint, malorientation of the components, specific design features of the components, soft tissue laxity and lack of patient compliance.
The increased rate of dislocation with a posterior approach has been dramatically reduced with an enhanced posterior soft tissue repair. Component features associated with an increased risk of dislocation include reduced head/neck offset, an asymmetrical cup and possibly the head size.
Component malorientation is probably the most important factor leading to recurrent dislocation. With the patient in a lateral position, there can be unpredictable variation in the position of the pelvis, and intraoperative movements aggravated this. Uncertainty about the position of the pelvis at the time of insertion of the acetabular component may lead to malpositioning.
The surgeon should attempt to ensure adequate repair of the posterior capsule and external rotators. It is important to reproduce the offset, insert the components with the correct orientation, avoid impingement, and ensure patient compliance in the early postoperative period.
Dislocations are considered early if they occur within three months of THA and late after three months, and management varies accordingly.
While every effort should be made to avoid dislocation following THA, there is no learning curve: reviewing a series of 10 400 THA procedures performed at the Mayo Clinic, Woo and Morrey (1982) reported that the dislocation rate remained between 2% and 3%.
The abstracts were prepared by Professor M. B. E. Sweet. Correspondence should be addressed to him at The Department of Orthopaedic Surgery, Medical School, University of Witwatersrand, 7 York Road, Parktown, Johannesburg, 2193 South Africa
