Radiological analysis of component positioning in total hip arthroplasty using the anterior approach

Abstract

BACKGROUND: The direct anterior approach for total hip replacement is gaining popularity among surgeons and patients alike, as it is a minimally invasive technique, and a true muscle-sparing operation. Reported advantages of this approach include decreased post-operative pain, faster post-operative mobilisation and a low incidence of hip dislocation. Optimal component positioning is vital for the longevity of total hip replacements. Poor positioning leads to increased dislocation rates, accelerated bearing wear, limited range of motion and higher rates of revision surgery. Minimally invasive surgery strives for smaller incisions, and muscle-sparing dissection. This may result in poor acetabular exposure, and subsequent sub-optimal component positioning. The direct anterior approach is generally done supine on a traction table with/without the use of intra-operative fluoroscopy. This study describes the surgical technique performed with the patient in the lateral decubitus position, without the use of traction, and without intra-operative imaging. We then report on the radiographic outcomes and complications using this approach.  METHODS: We retrospectively reviewed 150 patients who had total hip replacements done via the direct anterior approach. Clinical notes were evaluated for patient demographics, body mass index, and post-operative complications. The post-operative radiographs were analysed for acetabular component position inclination and anteversion.  RESULTS: The radiographic analysis showed a mean cup inclination of 41.1° (range 27.9-61.1°) and anteversion of 18.33° (range 11.2-25.3°). A total of 95.97% (95% CI) of the components were within the safety zones, as described by Lewinnek, (inclination 40 ± 10°, anteversion 15 ± 10°).23 There were five outliers with regard to cup inclination. Three had excessively abducted cups, which were noted to be in patients with increased BMI >35 kg/ m2. The remaining two were excessively adducted. There were no outliers with regard to cup anteversion There were no dislocations, deep infections or femoral nerve palsies. Two patients required re-operation: one for a periprosthetic fracture and another for a greater trochanter fracture with late displacement. There were six cases of thigh swelling which resolved on discontinuation of oral anti-coagulation, four episodes of soft tissue inflammation responding to physiotherapy, four clinically observed leg length discrepancies, two minor stitch abscesses, and two transient lateral cutaneous nerve palsies.  CONCLUSION: The direct anterior approach, done in the familiar lateral decubitus position, as described in this study, is safe and reliable, with an acceptable complication rate. The radiographic results for acetabular component placement are comparable to other surgical approaches, as well as to the direct anterior approach using a fracture table and intraoperative imaging.