Does oversizing an uncemented cup increase post-operative pain in primary total hip arthroplasty?
It has been suggested that one of the factors related to persistent post-operative pain following total hip arthroplasty (THA) is to over sizing of the acetabular component. In order to investigate this potential issue, we retrospectively analysed a series of consecutive uncemented THA. We assessed the incidence of persistent post-operative pain and the size difference between the implanted acetabular component and the native femoral head.
A total of 265 consecutive THAs were retrospectively identified. Standardised pre-operative radiographs were analysed using validated techniques to determine the native femoral head diameter. Post-operative standardised radiographs were reviewed and the acetabular orientation determined. Patients were sent postal questionnaires regarding their outcome and level of pain.
Questionnaires were returned by 169 patients (189 hips, 71% response rate). A total of 17 were excluded due to inadequate radiographs., leaving 172 THA in the study group. The mean native femoral head (NFH) size was 47 mm. The most common implanted acetabular component size was 52 mm. The mean difference in cup to NFH diameter (delta) was 5.7 mm (range − 6.1 to 15.4 mm; 95% CI 5.3–6.2 mm). A delta of > 6 mm was found to be significant for predicting persistent post-operative pain (RR = 1.81; 95% CI 1.1–3.1; P = 0.027).
Our study confirms that a delta of > 6 mm is associated with an increased risk of persistent post-operative pain following THA. We recommend pre-operative templating in all uncemented THA to ensure the planned acetabular component is no more than 6 mm larger than the NFH diameter.
KeywordsHip Pain Oversize Arthroplasty Uncemented Ceramic
Thanks to the John Charnley Trust for their continued support and to the Lower Limb Research Unit at Wrightington Hospital for their ongoing support and help.
Compliance with ethical standards
Conflict of interest
One author reports he is Medical Director of the National Joint Registry of England and Wales (NJR), Chairman of the NJR Editorial Board and Past President of the International Society of Arthroplasty Registers (ISAR). The senior author reports grants and personal fees from DePuy Synthes, personal fees from Springer, outside the submitted work; he is Associate Editor of Hip International and a Research Committee Member for British Orthopaedic Association.
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