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Hip: J. G. Andrew, J. Palan, H. V. Kurup, P. Gibson, D. W. Murray, and D. J. Beard Obesity in total hip replacement J Bone Joint Surg Br 2008; 90-B: 424-429 [Abstract] [Full text] [PDF]

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Authors' reply:

David J Beard, David Murray, Glynne Andrew, HV Kurup and Peter Gibson.   (6 October 2008)

Obesity - a risk factor for joint replacement

Peter FM Choong, Michelle M Dowsey, Danny Liew   (10 June 2008)

Obesity in total hip replacement

Benedict A Rogers, Nick J Little, Joideep Phadnis   (8 May 2008)

Influence of obesity on total hip replacement

Manoj Todkar   (15 April 2008)

Authors' reply: 6 October 2008
David J Beard, University Research Lecturer University of Oxford, David Murray, Glynne Andrew, HV Kurup and Peter Gibson. Send letter to journal: Re: Authors' reply: david.beard{at}ndos.ox.ac.uk David J Beard, et al.	Sir, We thank Professor Choong et al for his letter and comments. With regard to the first point about conflicting evidence, we agree in part with their sensible comments regarding effect size. Indeed, many of the studies have small sample sizes, however, most are still large enough to be able to detect clinical effects of a certain magnitude. Together, they would identify any obvious or dangerous compromise requiring immediate attention. One could also argue that if the effect size is so small (requiring only large sample sizes of 1000+) then the clinical relevance of such findings is questionable. Hence, in our eyes at least, the evidence does remain conflicting. With regard to the second issue over infection, we have rechecked our data and analysis in great detail and have found that the data and analysis for the paper is correct. However, Professor Choong is quite right that a single printed p value for infection comparison (only) in the text is erroneous and should have read <0.05. Similarly to his own findings, the obese group has a significantly (statistically but not clinically) greater infection rate. Whilst this error should be documented for completeness we would suggest that it does little to change the message that obese patients are not compromised compared with non-obese patients. This is for the following reasons: 1. The incidence in all groups is very small (worst case is 1.4%). We agree with Professor Choong that whilst it can be expressed somewhat sensationally as a “sevenfold” difference, such comparisons need the appropriate context. A “sevenfold” increase in a very small value remains a small value. Again, we would suggest that the clinical relevence of a difference of about 1% is debatable. The 1.5% is still well within the published infection rates seen in many other papers (0.2% to 3.9%). 2. Interestingly, the morbidly obese group had no deep infection at all. Should obesity and infection be strongly linked then we would have expected some incidence of deep infection in the morbidly obese group. 3. In all other outcome measures there was no difference between the groups. This has two implications. Firstly, a small elevation in infection rate (in obese patients) appears not to affect outcome. Irrespective of their higher risk of infection, they still gain the same benefit of surgery as non-obese patients. Secondly, the evidence from arguably more meaningful outcome data (OHS, revision, dislocation, etc) shows that, in general, obese patients do equally well in terms of outcome as non-obese patients. In the paper, we are not condoning obesity, we are merely highlighting that in this current economic climate, such patients may not be offered surgery for fear of complications. It seems that this risk is very small to non-existent. We would like to express our thanks to our colleagues in Melbourne for their keen interest and highly appropriate observations relating to this work. D.J. BEARD, MSc, DPhil, University Research Lecturer, D. MURRAY, MD, FRCS, University of Oxford, Oxford, UK. G. ANDREW, MD, FRCS(Orth), H.V. KURUP, MS(Orth), MRCS P. GIBSON, FRCS(Orth)
Obesity - a risk factor for joint replacement 10 June 2008
Peter FM Choong, Professor & Director of Orthopaedics, St. Vincent's Hospital , Michelle M Dowsey, Danny Liew Send letter to journal: Re: Obesity - a risk factor for joint replacement sarcoma{at}bigpond.net.au Peter FM Choong, et al.	Sir, We read with interest the article by Andrew et al1 in the April 2008 issue entitled, "Obesity in total hip replacement", and wish to bring to attention two issues. Firstly, the authors mentioned in the Introduction that there was a conflicting background of evidence regarding the effect of obesity on clinical outcomes in total joint replacement. It is important to note that the studies which suggested that obese patients have no increased risk of complications following joint replacement were studies with small samples (130 to 341 subjects). In contrast, the studies that supported a positive correlation between obesity and surgical complications were significantly larger in size (1211 to 3309 subjects). Indeed, among studies throughout the literature that involve samples of 1000 or more, the consistent finding is that obesity confers a higher risk of complications after total joint replacement.2 As such, it is likely that the lack of difference arising in studies with small samples most likely reflects a lack of power. Secondly, Andrew et al appear to have made an error in the analyses of their data regarding the crucial outcome of deep infection after joint replacement. If, as indicated, two out of the 1071 (0.2%) non-obese subjects developed deep infection after joint replacement compared with five of the 332 obese subjects (1.5%), then application of a chi-square test to this difference yields a two-sided p value of 0.011, not 0.115 as reported. The interpretation should be that the incidence of deep infection in obese patients was 7.5 times higher than in non-obese patients, and statistically significantly so. This result concurs with the current literature, which includes a large study from our institution which found obesity to be an independent risk factor for prosthetic infection following primary total hip replacement.3 It is time to acknowledge that obesity is a risk factor for total joint replacement. The intent is not to deny patients surgery, but rather to identify high-risk patients so that their treatment can be tailored to ensure the best possible outcomes. P.F.M. CHOONG, MD, FRACS, FAOrthA, Professor and Director of Orthopaedics, St. Vincent's Hospital, M.M. DOWSEY, RN, BapplSci (Nursing) Departments of Orthopaedics and Surgery, D. LIEW, MBBS (Hon), FRACP, PhD, Associate Professor, Department of Medicine, University of Melbourne, Melbourne, Australia. 1. Andrew JG, Palan J, Kurup HV, et al. Obesity in total hip replacement. J Bone Joint Surg [Br] 2008; 90-B: 424-9. 2. Dowsey MM, Choong PF. Early outcomes and complications following joint arthroplasty in obese patients: a review of the published reports. ANZ J Surg 2008;78:439-44. 3. Dowsey MM, Choong PF. Obesity is a major risk factor for prosthetic infection after primary hip arthroplasty. Clin Orthop 2008;466:153-8.
Obesity in total hip replacement 8 May 2008
Benedict A Rogers, Specialist Registrar St Peter's Hospital, Chertsey, UK, Nick J Little, Joideep Phadnis Send letter to journal: Re: Obesity in total hip replacement benedictrogers{at}hotmail.com Benedict A Rogers, et al.	Sir, We read this paper with interest and would like to make the following points. 1. The methods highlight that this is a prospective non-randomised multi-centre study with the entire patient cohort subdivided based upon their body mass index (BMI). However, it is not clear when the BMI was actually recorded. If one assumes that the BMI was recorded solely prior to surgery, are the patient subgroups (non-obese, obese and morbidly obese) still valid at one year and five years post surgery? A record of the BMI at one year and five years would help to clarify this, since an increase in hip function following surgery may facilitate an increase in aerobic exercise. Indeed, did all patients in this study receive equal amounts of physiotherapy before and after surgery? Further, the study does not detail who recorded the BMI since a self-reported BMI has been shown to be significantly inaccurate.1 2. The Oxford Hip Score is a validated patient function questionnaire2 with no evaluation of range of hip movement. Considering the technical difficulties that may be encountered performing a total hip replacement (THR), a clinical score (such as the Harris hip score3) would provide a more objective measure of the effect of obesity on THR and its inherent wear. Further general health assessment tools, such as the SF-12, would be beneficial when evaluating obesity – a condition that has numerous medical and psychological effects. 3. This study assesses the varus/valgus alignment of positioning of the femoral component. How was valgus/varus malalignment defined, who measured it and using what imaging modality? If there were two or more measurers, what was the interobserver error? Were other factors relating to femoral component positioning, such as offset and leg length, assessed? 4. Obesity makes acetabular component positioning (version and abduction angle) more challenging to achieve. Was this assessed, and were similar acetabular components used in the different patient groups? Following surgery were any of the obese patients admitted to a higher level of care (HDU or ITU) with the associated cost implications? 5. Is a five-year follow-up long enough to validate the conclusions stated in this study? Whilst obesity is known as a risk factor for THR secondary to osteoarthritis,4,5 can the conclusions drawn from this study be extrapolated beyond the five-year follow-up stated ? In particular, we feel that the statement in the third paragraph of the discussion should read ‘this implies that the functional benefit of surgery is independent of BMI at five years’. 6. Several large multi-centre studies from different countries have drawn differing conclusions to this paper, with obesity being associated with a high infection risk,6,7 a high dislocation rate8 and thromboembolism.9,10 Do the authors feel that the differing conclusions of these studies are a result of small numbers and different definitions of obesity as stated in their discussion? B.A. Rogers, MA MSc MRCGP MRCS, Specialist Registrar Trauma & Orthopaedics N.J. Little, MSc MRCS, Specialist Registrar Trauma & Orthopaedics J. Phadnis, MRCS, ST2, St Peter's Hospital, Chertsey, UK. 1. Engstrom JL, Paterson SA, Doherty A, Trabulsi M, Speer KL. Accuracy of self-reported height and weight in women: an integrative review of the literature. J Midwifery Womens Health 2003;48:338-45. 2. Dawson J, Fitzpatrick R, Murray D, Carr A. Questionnaire on the perceptions of patients about total knee replacement. J Bone Joint Surg [Br] 1998;80-B:63-9. 3. Harris WH. Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty. An end-result study using a new method of result evaluation. J Bone Joint Surg [Am] 1969;51-A:737-55. 4. Karlson EW, Mandl LA, Aweh GN, et al. Total hip replacement due to osteoarthritis: the importance of age, obesity, and other modifiable risk factors. Am J Med 2003;114:93-8. 5. BourneR , Mukhi S, Zhu N, Keresteci M, Marin M. Role of obesity on the risk for total hip or knee arthroplasty. Clin Orthop 2007;465:185-8. 6. Dowsey MM, Choong PF. Obesity is a major risk factor for prosthetic infection after primary hip arthroplasty. Clin Orthop 2008;466:153-8. 7. Namba RS, Paxton L, Fithian DC, Stone ML. Obesity and perioperative morbidity in total hip and total knee arthroplasty patients. J Arthroplasty 2005;20(7 Suppl 3):46-50. 8. Azodi OS, Adami J, Lindstrom D, et al. High body mass index is associated with increased risk of implant dislocation following primary total hip replacement: 2,106 patients followed for up to 8 years. Acta Orthop 2008;79:141-7. 9. Mantilla CB, Horlocker TT, Schroeder DR, Berry DJ, Brown DL. Risk factors for clinically relevant pulmonary embolism and deep venous thrombosis in patients undergoing primary hip or knee arthroplasty. Anesthesiology 2003;99:552-60. 10. Beksac B, Gonzalez Della Valle A, Salvati EA. Thromboembolic disease after total hip arthroplasty: who is at risk? Clin Orthop 2006;453:211-24.
Influence of obesity on total hip replacement 15 April 2008
Manoj Todkar, Orthopaedic Surgeon Todkar Hospital, Pune, India Send letter to journal: Re: Influence of obesity on total hip replacement mtodkar{at}hotmail.com Manoj Todkar	Sir, I read this article with great interest. We carried out similar research at Dundee University to examine the influence of obesity on implantation of a cemented acetabular component in total hip replacement (THR). We included patients operated on by one surgeon where the same prosthesis was used in all the patients and all the operations were carried out with the same approach. We studied the anteversion and abduction angle in different classes of obesity and found that there is no statistically significant difference in orientation of acetebular component in obese and non-obese patients. M. Todkar, Orthopaedic Surgeon, Todkar Hospital, Pune, India.