Clin Orthop Relat Res (2015) 473:3981–3982 / DOI 10.1007/s11999-015-4561-x
Clinical Orthopaedics and Related Research® A Publication of The Association of Bone and Joint Surgeons®
Published online: 9 September 2015
Ó The Association of Bone and Joint Surgeons1 2015
Letter to the Editor Letter to the Editor: Do Complication Rates Differ by Gender After Metal-on-metal Hip Resurfacing Arthroplasty? A Systematic Review Harlan Amstutz MD, Michel Le Duff MA
To the editor, e read the study by Haughom and colleagues with great interest. We would like to acknowledge the efforts made by the authors to produce a thorough investigation and a highquality review on the topic. However, the authors conclude that ‘‘moving forward studies should report outcomes by gender (particularly
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(Haughom BD, Erickson BJ, Hellman MD, Jacobs JJ. Do Complication Rates Differ by Gender After Metal-on-metal Hip Resurfacing Arthroplasty? A Systematic Review. Clin Orthop Relat Res. 2015;473:2521–2529). The authors certify that they, or any members of their immediate families, have no commercial associations (eg, consultancies, stock ownership, equity interest, patent/ licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research1 editors and board members are on file with the publication and can be viewed on request. The opinions expressed are those of the writers, and do not reflect the opinion or policy of CORR1 or The Association of Bone and Joint Surgeons1.
complications).’’ This statement suggests that gender itself is responsible for differences in the outcome of hip resurfacing arthroplasty. Although an association between female gender and higher failure rates or complications is undeniable as shown in the review by Haughom and colleagues, causation, on the other hand, is certainly not demonstrated. When it comes to determination of risk factors for a procedure, a multivariate model is impractical if the wrong variables are being studied. For hip resurfacing, using gender as one of the variables creates collinearity, and usually precludes the study of variables that are correlated with gender but have a much stronger rationale for affecting the outcome, such as component size [1, 5] or an etiology of developmental dysplasia [1, 3] (which increases the H. Amstutz MD (&) Joint Replacement Institute, 2400 South Flower Street, Los Angeles, CA 90007, USA e-mail: [email protected] M. Le Duff MA Joint Replacement Institute, Los Angeles, CA, USA
chances of cup malposition, a variable that can only be studied using a threedimensional (3-D) analysis and calculating the contact patch to rim distance, which has the strongest correlation with elevated wear [4, 6]). Recent publications [4, 6] have highlighted the importance of proper acetabular component positioning, both in the frontal and sagittal planes for hip resurfacing arthroplasty to be successful, and to avoid edge-loading of the components, leading to abnormal wear patterns of the device [4, 6]. Large databases such as registries certainly present the advantage of high statistical power but completely lack the ability to record the variables that truly affect the outcome of hip resurfacing, such as a 3-D assessment of acetabular component positioning. For patients with small components, the safe zone of implantation is reduced. This certainly applies to many women, but not all of them. Additionally, not all hip resurfacing devices have the same coverage of the head by the socket [2] and such differences in the small sizes can greatly affect the outcome of hip resurfacing arthroplasty.
123
Clinical Orthopaedics and Related Research1
3982 Amstutz and Le Duff
Letter to the Editor
This is particularly important in our overly litigated society because every time a publication is made that suggests female gender is a risk factor, it reinforces the use of simplistic treatment algorithms and perfectly suitable female patients get denied the opportunity to be treated with hip resurfacing arthroplasty. Gender is a variable that usually gets included in studies more by tradition and availability for every patient, in every database, than because of its actual value to answer the research question. Women with hip resurfacing arthroplasty do not fail more often than men because they are women, but because
123
of confounding variables that should be the object of study to refine inclusion criteria for the procedure.
References 1. Australian Orthopaedic Association. National joint replacement registry. 2014 annual report. Available at: https://aoanjrr.dmac.adelaide.edu.au/ en. Accessed September 2, 2015. 2. Griffin W, Nanson C, Springer B, Davies M, Fehring T. Reduced articular surface of one-piece cups: a cause of runaway wear and early failure. Clin Orthop Relat Res. 2010;468:2328–2332. 3. Gross T, Liu F. Prevalence of dysplasia as the source of worse outcome in young female patients after hip
resurfacing arthroplasty. Int Orthop. 2012;36:27–34. 4. Matthies A, Henckel J, Cro S, Suarez A, Noble P, Skinner J, Hart A, Predicting wear and blood metal ion levels in metal-on-metal hip resurfacing. J Orthop Res. 2014;32:167– 174. 5. McBryde C, Theivendran K, Thomas A, Treacy R, Pynsent P, The influence of head size and sex on the outcome of birmingham hip resurfacing. J Bone Joint Surg Am. 2010;92:107–112. 6. Yoon J, Le Duff M, Johnson A, Takamura K, Ebramzadeh E, Amstutz HC, Contact patch to rim distance predicts metal ion levels in hip resurfacing. Clin Orthop Relat Res. 2013.471:1615–1621.
Clinical Orthopaedics and Related Research® A Publication of The Association of Bone and Joint Surgeons®
Published online: 9 September 2015
Ó The Association of Bone and Joint Surgeons1 2015
Letter to the Editor Letter to the Editor: Do Complication Rates Differ by Gender After Metal-on-metal Hip Resurfacing Arthroplasty? A Systematic Review Harlan Amstutz MD, Michel Le Duff MA
To the editor, e read the study by Haughom and colleagues with great interest. We would like to acknowledge the efforts made by the authors to produce a thorough investigation and a highquality review on the topic. However, the authors conclude that ‘‘moving forward studies should report outcomes by gender (particularly
W
(Haughom BD, Erickson BJ, Hellman MD, Jacobs JJ. Do Complication Rates Differ by Gender After Metal-on-metal Hip Resurfacing Arthroplasty? A Systematic Review. Clin Orthop Relat Res. 2015;473:2521–2529). The authors certify that they, or any members of their immediate families, have no commercial associations (eg, consultancies, stock ownership, equity interest, patent/ licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research1 editors and board members are on file with the publication and can be viewed on request. The opinions expressed are those of the writers, and do not reflect the opinion or policy of CORR1 or The Association of Bone and Joint Surgeons1.
complications).’’ This statement suggests that gender itself is responsible for differences in the outcome of hip resurfacing arthroplasty. Although an association between female gender and higher failure rates or complications is undeniable as shown in the review by Haughom and colleagues, causation, on the other hand, is certainly not demonstrated. When it comes to determination of risk factors for a procedure, a multivariate model is impractical if the wrong variables are being studied. For hip resurfacing, using gender as one of the variables creates collinearity, and usually precludes the study of variables that are correlated with gender but have a much stronger rationale for affecting the outcome, such as component size [1, 5] or an etiology of developmental dysplasia [1, 3] (which increases the H. Amstutz MD (&) Joint Replacement Institute, 2400 South Flower Street, Los Angeles, CA 90007, USA e-mail: [email protected] M. Le Duff MA Joint Replacement Institute, Los Angeles, CA, USA
chances of cup malposition, a variable that can only be studied using a threedimensional (3-D) analysis and calculating the contact patch to rim distance, which has the strongest correlation with elevated wear [4, 6]). Recent publications [4, 6] have highlighted the importance of proper acetabular component positioning, both in the frontal and sagittal planes for hip resurfacing arthroplasty to be successful, and to avoid edge-loading of the components, leading to abnormal wear patterns of the device [4, 6]. Large databases such as registries certainly present the advantage of high statistical power but completely lack the ability to record the variables that truly affect the outcome of hip resurfacing, such as a 3-D assessment of acetabular component positioning. For patients with small components, the safe zone of implantation is reduced. This certainly applies to many women, but not all of them. Additionally, not all hip resurfacing devices have the same coverage of the head by the socket [2] and such differences in the small sizes can greatly affect the outcome of hip resurfacing arthroplasty.
123
Clinical Orthopaedics and Related Research1
3982 Amstutz and Le Duff
Letter to the Editor
This is particularly important in our overly litigated society because every time a publication is made that suggests female gender is a risk factor, it reinforces the use of simplistic treatment algorithms and perfectly suitable female patients get denied the opportunity to be treated with hip resurfacing arthroplasty. Gender is a variable that usually gets included in studies more by tradition and availability for every patient, in every database, than because of its actual value to answer the research question. Women with hip resurfacing arthroplasty do not fail more often than men because they are women, but because
123
of confounding variables that should be the object of study to refine inclusion criteria for the procedure.
References 1. Australian Orthopaedic Association. National joint replacement registry. 2014 annual report. Available at: https://aoanjrr.dmac.adelaide.edu.au/ en. Accessed September 2, 2015. 2. Griffin W, Nanson C, Springer B, Davies M, Fehring T. Reduced articular surface of one-piece cups: a cause of runaway wear and early failure. Clin Orthop Relat Res. 2010;468:2328–2332. 3. Gross T, Liu F. Prevalence of dysplasia as the source of worse outcome in young female patients after hip
resurfacing arthroplasty. Int Orthop. 2012;36:27–34. 4. Matthies A, Henckel J, Cro S, Suarez A, Noble P, Skinner J, Hart A, Predicting wear and blood metal ion levels in metal-on-metal hip resurfacing. J Orthop Res. 2014;32:167– 174. 5. McBryde C, Theivendran K, Thomas A, Treacy R, Pynsent P, The influence of head size and sex on the outcome of birmingham hip resurfacing. J Bone Joint Surg Am. 2010;92:107–112. 6. Yoon J, Le Duff M, Johnson A, Takamura K, Ebramzadeh E, Amstutz HC, Contact patch to rim distance predicts metal ion levels in hip resurfacing. Clin Orthop Relat Res. 2013.471:1615–1621.
