Letters to the Editor Risk factors for early dislocation after total hip arthroplasty: a matched case-control study

1. Dudda M, Gueleryuez A, Gautier E, Busato A, Roeder C. Risk factors for early dislocation after total hip arthroplasty: a matched case-control study. J Orthop Surg (Hong Kong) 2010;18:179–83. 2. Jolles BM, Bogoch ER. Posterior versus lateral surgical approach for total hip arthroplasty in adults with osteoarthritis. Cochrane Database Syst Rev 2006;3:CD003828. To the Editor: We read with interest the article by Dudda et al.1 The authors concluded that “surgical approach, combined cup and stem positioning, and femoral head size were significant risk factors for dislocation. We have concerns with the evidence used to draw these conclusions. The data were taken from 1978 to 2004 representing a large time frame that operative techniques, implant designs, and postoperative management is subject to considerable change. It would have been useful to know exactly when the majority of dislocations occurred. When the posterior approach was first used, it was not a routine to repair the posterior capsule and external rotators, and this may account for the higher dislocation rates. However, in current practice entailing better techniques for posterior repair and better access to the acetabulum and the preservation of the hip abductors, the posterior approach has become favourable. In fact, one review indicated no significant difference in the dislocation rate between posterior and lateral approaches.2 Therefore, with no mention of when the reported dislocations ensued and whether the external rotators were repaired, the conclusion that this surgical approach is a risk factor is outdated. Many confounding factors that could have contributed to the differences in dislocation rates were not considered. The data encompassed many different operative techniques and postoperative rehabilitation regimens. Yet whether cemented or uncemented implants were used was not mentioned, and many of the 26 different cup types and 59 different stems that were used may have been outdated. Although it is difficult to eliminate all confounding factors while trying to achieve a suitable sample size, these key variables should have been taken into account when interpreting the results.