Abstract
Introduction Correct component positioning is critical for the stability of the prosthesis in total hip arthroplasty (THA). Malpositioning of either the femoral or acetabular component may lead to impingement or dislocation. This study aims to assess the accuracy of placement of the acetabular component in THA.
Methods Forty-six total hip arthroplasties were studied. The surgeon’s estimates of intra-operative inclination and anteversion of the acetabular component were recorded. Post-operative inclination of the acetabular component was measured from routine plain antero-posterior (AP) radiographs of the pelvis. Planar anteversion of the acetabular component was determined from AP radiographs with the beam centred over the hip using the method described by Pradhan. Planar anteversion was then corrected to ‘true’ anteversion correcting for inclination. The surgeons estimate of intra-operative cup inclination and anteversion and the radiographic position were compared.
Results The mean difference between the estimated and true cup inclination was 1.5° more than planned (range of −13° to 16°, SD 6.75). The mean difference between estimated and true values of anteversion was 1.8° less than planned (range of −32° to 25°, SD 11.07). Allowing plus or minus five degrees of error, 37% of the cups were outside the estimated inclination and 35% outside the estimated anteversion. There was a poor correlation for both inclination (Spearman’s correlation coefficient equals 0.20) and anteversion (Spearman’s correlation coefficient equals 0.25) between perceived and true cup positioning. Using the ‘safe zones’ for inclination and anteversion described by Lewinnek et al for minimising dislocation, 48% of the cups were unsafely positioned in either inclination, anteversion or both.
Conclusions Our study showed that positioning of the ace-tabular component cannot be reliably performed even by experienced surgeons. Acetabular component placement is of high importance for preventing dislocation or impingement. A tool, such as a navigation device, may be beneficial in improving acetabular component placement.
In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source.
The abstracts were prepared by Mr Jerzy Sikorski. Correspondence should be addressed to him at the Australian Orthopaedic Association, Ground Floor, William Bland Centre, 229 Macquarie Street, Sydney NSW 2000, Australia.
