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The Influence of Head Size and Sex on the Outcome of Birmingham Hip Resurfacing
Callum W. McBryde, MD, FRCS(Tr&Orth)1; Kanthan Theivendran, MRCS1; Andrew M.C. Thomas, FRCS1; Ronan B.C. Treacy, FRCS(Tr&Orth)1; Paul B. Pynsent, PhD1
1 Research and Teaching Centre, Royal Orthopaedic Hospital, Bristol Road South, Northfield, Birmingham B31 2AP, United Kingdom. E-mail address for C.W. McBryde: cwmcbryde@hotmail.com
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Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from the British Hip Society (The McMinn Scholarship). In addition, one or more of the authors or a member of his or her immediate family received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (Smith and Nephew PLC).

Investigation performed at the Royal Orthopaedic Hospital, Birmingham, United Kingdom

Copyright ©2010 American Society for Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2010 Jan 01;92(1):105-112. doi: 10.2106/JBJS.I.00197
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Abstract

Background: 

Hip resurfacing has gained popularity for the treatment of young and active patients who have arthritis. Recent literature has demonstrated an increased rate of revision among female patients as compared with male patients who have undergone hip resurfacing. The aim of the present study was to identify any differences in survival or functional outcome between male and female patients with osteoarthritis who were managed with metal-on-metal hip resurfacing.

Methods: 

A prospective collection of data on all patients undergoing Birmingham Hip Resurfacing at a single institution was commenced in July 1997. On the basis of the inclusion and exclusion criteria, 1826 patients (2123 hips, including 799 hips in female patients and 1324 hips in male patients) with a diagnosis of osteoarthritis who had undergone the procedure between July 1997 and December 2008 were identified. The variables of age, sex, preoperative Oxford Hip Score, component size used, surgical approach, lead surgeon, and surgeon experience were analyzed. A multivariate Cox proportional hazard survival model was used to identify which variables were most influential for determining revision.

Results: 

The mean duration of follow-up was 3.46 years (range, 0.03 to 10.9 years). The five-year cumulative survival rate for the 655 hips that were followed for a minimum of five years was 97.5% (95% confidence interval, 96.3% to 98.3%). There were forty-eight revisions. Revision was significantly associated with female sex (hazard rate, 2.03 [95% confidence interval, 1.15 to 3.58]; p = 0.014) and decreasing femoral component size (hazard rate per 4-mm decrease in size, 4.68 [95% confidence interval, 4.36 to 5.05]; p < 0.001). Revision was not associated with age (p = 0.88), surgeon (p = 0.41), surgeon experience (p = 0.30), or surgical approach (p = 0.21). A multivariate analysis including the covariates of sex, age, surgeon, surgeon experience, surgical approach, and femoral component size demonstrated that sex was no longer significantly associated with revision when femoral component size was included in the model (p = 0.37). Femoral component size alone was the best predictor of revision when all covariates were analyzed (hazard rate per 4-mm decrease in size, 4.87 [95% confidence interval, 4.37 to 5.42]; p < 0.001).

Conclusions: 

The present study demonstrates that although female patients initially may appear to have a greater risk of revision, this increased risk is related to differences in the femoral component size and thus is only indirectly related to sex. Patient selection for hip resurfacing is best made on the basis of femoral head size rather than sex.

Level of Evidence: 

Prognostic Level II. See Instructions to Authors for a complete description of levels of evidence.

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    References

    Accreditation Statement
    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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    Callum W. McBryde, MD, FRCS(Tr&Orth)
    Posted on June 02, 2010
    Dr. McBryde and colleagues respond to Mr. Brogan and Mr. Rogers
    Royal Orthopaedic Hospital, Birmingham, United Kingdom

    We would like to thank Mr. Brogan and Mr. Rogers for their interest in our article.

    The decision on whether to offer a patient hip resurfacing procedure is based on many factors. These include factors such as bone quality, location and size of bone cysts, hip geometry as well as size. This study demonstrates that although females may initially appear to have a higher failure rate than their male counterparts this is not the case when corrections are made for size. Although it has been demonstrated that patients likely to require small components have a higher revision rate this is in itself not a contra-indication to the procedure. Many patients with small heads do well in the long term but patient selection and surgical technique are clearly important. Patients requiring smaller hip resurfacings should alert the surgeon that intra-operatively there is less room for error for implant orientation and should seek to ensure accurate placement to minimize any further risks.

    We agree that component orientation is an important factor when considering why resurfacings fail and a number of published studies have shown this. In this series, the most frequent mode of failure, although rare, was femoral neck fracture. We agree that varus/valgus positioning of the femoral component influences this mode of failure but correct alignment of anteversion and retroversion is also important. The position of the acetabular component is also likely to influence outcome. We did not measure component orientation of resurfacings in our study. However, radiological measurements of the cup inclination angles may be underestimated as an acetabular component with a radiological inclination of 45° will have an effective inclination angle of between 50° and 63° depending on the type and size of the component (1). The anteversion of the acetabular component also will have an effect on the longevity of the prosthesis.

    The choice of implant is also crucial. In this study, the implant used exclusively was the Birmingham Hip. Implant design and manufacture is clearly important as has been demonstrated by the withdrawal of other devices such as the ASR in some countries due to unacceptable revision rates.

    Although we agree that there are number of other factors influencing revision, such as component position, we believe that there is a clear relationship between size and failure. What is reassuring is that in the large sizes failures have been very rare and that in the smaller sizes the vast majority of patients do well. What is not clear is whether in the smaller sizes they would be any better served with a total hip replacement. We continue to offer hip resurfacing to smaller patients but our data allows for more informed counseling of the likely benefits.

    Reference

    1. Board TN, Walter WL. When is 45 degrees not 45 degrees? Analysis of the true inclination angle of resurfacing sockets. J Bone Joint Surg Br. 2010;92:397-c.

    Kit Brogan, MRCS(Ed)
    Posted on April 20, 2010
    Is There a Head Size Cut-Off Below Which a Resurfacing Procedure Should Not Be Done?
    Kent Surry & Sussex Deanery, United Kingdom

    To the Editor:

    We read with interest the January 2010 article by McBryde et al. (1) entitled, "The Influence of Head Size and Sex on the Outcome of Birmingham Hip resurfacing" and would like to make the following points.

    As mentioned in the Discussion, the findings of this study are similar to those of The Australian Orthopaedic Association National Joint Replacement Registry report (2), suggesting that head size is the significant factor associated with risk for revision rather than gender. Both studies demonstrate a head size of 50 mm or less is associated with a statistically significant increase in the failure rate of metal on metal resurfacing and this risk increases for every 2 mm reduction in head size. Do the authors view it inappropriate to perform metal on metal resurfacing in any patient, male or female, below a certain head size? We would be interested in the authors' opinion on this matter and in particular what head size should be the threshold.

    It is reported that 64% of hip resurfacing revisions of are performed for mal-position of the acetabular component (3), leading to a higher level of serum metal ions (4). Further, a small degree of varus malpositioning of the femoral component can lead to abnormal load distribution within the femoral neck inducing fracture (5,6). A recent review of this topic concluded that, although many of the factors that influence the outcome of hip resurfacing are inter-related, the component geometry and particularly the orientation of the acetabular component, are the most influential factors (7). In view of this, do the authors consider the factors assessed in their study more or less influential in determining the outcome of hip resurfacing arthroplasty that component geometry and alignment?

    The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.

    References

    1. McBryde CW, Theivendran K, Thomas AM, Treacy RB, Pynsent PB. The influence of head size and sex on the outcome of Birmingham hip resurfacing. J Bone Joint Surg Am. 2010;92:105-12.

    2. Australian Orthopaedic Association National Joint Replacement Registry. Annual report 2008. http://www.dmac.adelaide.edu.au/aoanjrr/documents/aoanjrrreport_2008.pdf.

    3. Siebel T, Maubach S, Morlock MM. Lessons learned from early clinical experience and results of 300 ASR hip resurfacing implantations. Proc Inst Mech Eng H. 2006;220:345-53.

    4. De Haan R, Pattyn C, Gill HS, Murray DW, Campbell PA, De Smet K. Correlation between inclination of the acetabular component and metal ion levels in metal-on-metal hip resurfacing replacement. J Bone Joint Surg Br. 2008;90:1291-7.

    5. Anglin C, Masri BA, Tonetti J, Hodgson AJ, Greidanus NV. Hip resurfacing femoral neck fracture influenced by valgus placement. Clin Orthop Relat Res. 2007;465:71-9.

    6. Davis ET, Olsen M, Zdero R, Waddell JP, Schemitsch EH. Femoral neck fracture following hip resurfacing: the effect of alignment of the femoral component. J Bone Joint Surg Br. 2008;90:1522-7.

    7. Shimmin AJ, Walter WL, Esposito C. The influence of the size of the component on the outcome of resurfacing arthroplasty of the hip: a review of the literature. J Bone Joint Surg Br. 2010;92:469-76.

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