Risk factor analysis for early femoral failure in metal-on-metal hip resurfacing arthroplasty: the effect of bone density and body mass index

Thomas P Gross,Fei Liu

doi:10.1186/1749-799x-7-1

Abstract

BackgroundThe importance of appropriately selecting patients based on factors such as bone mineral density, body mass index, age, gender, and femoral component size has been demonstrated in many studies as an aid in decreasing the rate of revisions and improving the outcomes for patients after hip resurfacing arthroplasty (HRA); however, there are few published studies quantitatively specifying the potential risk factors that affect early femoral component failures. Therefore, the purpose of this study was to investigate the specific causes of early femoral component failures in hip resurfacing separately and more carefully in order to develop strategies to prevent these failures, rather than excluding groups of patients from this surgical procedure.MethodsThis retrospective study included 373 metal-on-metal HRAs performed by a single surgeon using the vascular sparing posterior minimally invasive surgical approach. The average length of follow-up was 30 ± 6 months. In order to understand the causes of early femoral failure rate, a multivariable logistic regression model was generated in order to analyze the effects of bone mineral density (T-score), gender, diagnosis, body mass index, femoral implant fixation type, age, and femoral component size.ResultsThe average post-operative Harris hip score was 92 ± 11 points and the average post-operative UCLA score was 7 ± 2 points. There were three revisions due to femoral neck fracture and two for femoral component loosening. These occurred in two female and three male patients. In the multi-variable regression model, only T-score and body mass index showed significant effects on the failure rate of femoral components. Patients with a lower T-score and a higher body mass index had a significantly increased risk of early femoral component failure.ConclusionWe recommend that dual energy x-ray absorptiometry scan T-score tests should be routinely performed on all hip resurfacing patients pre-operatively. If a patient has a low T-score (≤ -1.5), consideration should be given to additional precautions or treatments to alleviate his or her risk, especially when the patient has a higher body mass index (≥ 29 kg/m2).

Highlights

The importance of appropriately selecting patients based on factors such as bone mineral density, body mass index, age, gender, and femoral component size has been demonstrated in many studies as an aid in decreasing the rate of revisions and improving the outcomes for patients after hip resurfacing arthroplasty (HRA); there are few published studies quantitatively specifying the potential risk factors that affect early femoral component failures
It is most likely that the risk factors that apply to early femoral component failure are different than those that apply to other modes of failure, such as acetabular loosening and adverse wear
Based on a single surgeon’s experience with metal-onmetal HRA, the purpose of this study was: (1) to report our clinical results of a group of consecutive metal-onmetal HRA cases for which bone mineral density was recorded and alendronate was not administered; (2) to identify the underlying causes associated with an increased early femoral failure after hip resurfacing by using multivariable logistic regression models; and (3) to use univariate analysis to determine thresholds for each risk factor to make them clinically useful as well as analyze the combined effects of these factors in order to predict failure rates by using reduced model analysis based on the determined thresholds

Summary

Introduction

The importance of appropriately selecting patients based on factors such as bone mineral density, body mass index, age, gender, and femoral component size has been demonstrated in many studies as an aid in decreasing the rate of revisions and improving the outcomes for patients after hip resurfacing arthroplasty (HRA); there are few published studies quantitatively specifying the potential risk factors that affect early femoral component failures. This includes femoral neck fractures and femoral component loosening, which is suspected to take place as a result of the following thermal osteonecrosis of the underlying bone [2,10] Both of these complications are unique to hip resurfacing procedures and neither occurred in stemmed THAs. It is most likely that the risk factors that apply to early femoral component failure are different than those that apply to other modes of failure, such as acetabular loosening and adverse wear.

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