169 C OPYRIGHT Ó 2016
BY
T HE J OURNAL
OF
B ONE
AND J OINT
S URGERY, I NCORPORATED
A commentary by Nader Toossi, MD, and Norman A. Johanson, MD, is linked to the online version of this article at jbjs.org.
Effect of Body Mass Index on Complications and Reoperations After Total Hip Arthroplasty Eric R. Wagner, MD, Atul F. Kamath, MD, Kristin M. Fruth, BS, William S. Harmsen, MS, and Daniel J. Berry, MD Investigation performed at the Mayo Clinic, Rochester, Minnesota
Background: High body mass index (BMI) is associated with increased rates of complications after total hip arthroplasty. Studies to date have evaluated risk mainly as a dichotomous variable according to BMI thresholds. The purpose of this paper was to characterize the risk of complications and implant survival according to BMI as a continuous variable. Methods: Using prospectively collected data from our institutional total joint registry, we analyzed 21,361 consecutive hips (17,774 patients) treated with primary total hip arthroplasty between 1985 and 2012 at a single institution. The average BMI at the time of surgery was 28.7 kg/m2 (range, 15 to 69 kg/m2). Estimates of revision surgery and common complications associated with BMI were analyzed using the Kaplan-Meier method of assessing survivorship, with associations of outcomes assessed using a Cox model. Results: Utilizing smoothing spline parameterization, we found that reoperation (p < 0.001) and implant revision or removal rates (p = 0.002) increased with increasing BMI. Increasing BMI was associated with increased rates of early hip dislocation (p = 0.02), wound infection, and, most strikingly, deep periprosthetic infection (a hazard ratio of 1.09 per unit of BMI >25 kg/m2; p < 0.001). However, we found no association between increasing BMI and any revision for mechanical failure of the implant or between increasing BMI and revision for aseptic implant loosening. There was an inverse correlation between increasing BMI and risk of revision for bearing wear. Conclusions: The rates of reoperation, implant revision or removal, and common complications after total hip arthroplasty were strongly associated with BMI. Level of Evidence: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.
Peer Review: This article was reviewed by the Editor-in-Chief and one Deputy Editor, and it underwent blinded review by two or more outside experts. It was also reviewed by an expert in methodology and statistics. The Deputy Editor reviewed each revision of the article, and it underwent a final review by the Editor-in-Chief prior to publication. Final corrections and clarifications occurred during one or more exchanges between the author(s) and copyeditors.
T
he prevalence of obesity continues to rise, and it is estimated1,2 that approximately 35% of adults in the United States have a body mass index (BMI) of ‡30 kg/m 2 . Obesity also has become a worldwide epidemic, with 30% of adults worldwide classified as obese3. As the average BMI has increased, the health-care burden associated with obesity has become an important consideration in elective procedures 4,5.
A high BMI is an independent risk factor for the development of osteoarthritis of the hip6. It is estimated that onethird of patients undergoing total hip arthroplasty have a BMI of ‡30 kg/m2, with many being younger individuals6-8. Understanding the influence of BMI on the risk of complications and on implant survivorship is important when making decisions concerning the risks and benefits of such elective procedures.
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. In addition, one or more of the authors has a patent or patents, planned, pending, or issued, that is broadly relevant to the work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
J Bone Joint Surg Am. 2016;98:169-79
d
http://dx.doi.org/10.2106/JBJS.O.00430
170 TH E JO U R NA L O F B O N E & JO I N T SU RG E RY J B J S . O RG V O LU M E 98-A N U M B E R 3 F E B R UA RY 3, 2 016 d
d
d
Recent studies have demonstrated an increase in some early complications among obese patients undergoing total joint arthroplasty 9-13. Morbidly obese patients (those with a BMI of ‡40 kg/m2) have increased risks such as superficial wound infection, hip dislocation, and venous thromboembolism13-15. Although studies have begun to correlate early outcomes among patients according to BMI categories, no previous study, to our knowledge, has comprehensively examined the effects of obesity as a continuous variable across all BMIs, and it has not been established whether there are BMI thresholds that separate those at increased risk for complications. The effect of BMI on longer-term implant survivorship and mechanical failure of implants has been controversial, as studies have failed to find an association16,17. However, the results of a recent meta-analysis suggested increased rates of aseptic loosening requiring revision surgery in obese patients after total hip arthroplasty11. The purpose of this study was to examine the effect of patient BMI on the risk of complications, reoperations, and implant revision or removal after total hip arthroplasty. Materials and Methods
A
fter institutional review board approval, this investigation was carried out 18 utilizing a large, single-institution total joint registry . This registry prospectively captures patient demographics; operative details; information regarding complications, reoperations, and implant revisions; and clinical outcome scores for patients treated with total joint arthroplasty. Patients routinely are asked to follow up with the surgeon twice during the year after the arthroplasty procedure, at postoperative years two and five, and subsequently at five-year intervals. Patients who are unable to attend follow-up appointments 19 in person are contacted to complete a standardized questionnaire .
Study Population All patients who underwent a primary total hip arthroplasty between January 1, 1985, and December 31, 2012, at our institution were included in this study, with the exception of those who declined to provide research authorization or who underwent total hip arthroplasty for tumor or acute hip fracture. Using our total joint registry, we identified patient BMI, demographics, primary diagnoses, and surgical indications. The study cohort consisted of 21,361 primary total hip arthroplasties (17,774 consecutive total hip arthroplasty patients).
E F F E C T O F B O D Y M A S S I N D E X O N C O M P L I C AT I O N S R E O P E R AT I O N S A F T E R T O TA L H I P A R T H R O P L A S T Y
AND
Outcome Measures The primary outcome measures were reoperation, implant revision or removal for any reason, dislocation within six months postoperatively, and superficial or deep infection. Implant survival and the risks of revision, reoperation, dislocation, and infection were calculated according to BMI. The effects of other variables (e.g., age, sex, primary diagnosis, and surgical indication) as a function of BMI were examined.
Statistical Analysis Descriptive statistics are reported as the mean (and standard deviation) or the number (and percentage). The Kaplan-Meier method was used for survival estimates. The association of joint arthroplasty outcomes with patient variables was assessed using Cox proportional hazards regression. Results are reported as hazard ratios (HRs) with 95% confidence intervals (CIs). Models adjusted for correlations between the two hips in patients who had bilateral primary total hip arthroplasty. The main variable was BMI. The association of BMI with each outcome was evaluated using a smoothing spline and plotted to demonstrate the HR as a function of BMI. Then, the observed pattern (e.g., does risk increase at a specific threshold?) was used to guide the inclusion of BMI thresholds into the models. We examined BMI between 20 and 50 kg/m2, setting BMI values of 50 kg/m2 as being equal to 50 kg/m2, because few patients were beyond these extremes. A second analysis was conducted using commonly used ranges of BMI (
BY
T HE J OURNAL
OF
B ONE
AND J OINT
S URGERY, I NCORPORATED
A commentary by Nader Toossi, MD, and Norman A. Johanson, MD, is linked to the online version of this article at jbjs.org.
Effect of Body Mass Index on Complications and Reoperations After Total Hip Arthroplasty Eric R. Wagner, MD, Atul F. Kamath, MD, Kristin M. Fruth, BS, William S. Harmsen, MS, and Daniel J. Berry, MD Investigation performed at the Mayo Clinic, Rochester, Minnesota
Background: High body mass index (BMI) is associated with increased rates of complications after total hip arthroplasty. Studies to date have evaluated risk mainly as a dichotomous variable according to BMI thresholds. The purpose of this paper was to characterize the risk of complications and implant survival according to BMI as a continuous variable. Methods: Using prospectively collected data from our institutional total joint registry, we analyzed 21,361 consecutive hips (17,774 patients) treated with primary total hip arthroplasty between 1985 and 2012 at a single institution. The average BMI at the time of surgery was 28.7 kg/m2 (range, 15 to 69 kg/m2). Estimates of revision surgery and common complications associated with BMI were analyzed using the Kaplan-Meier method of assessing survivorship, with associations of outcomes assessed using a Cox model. Results: Utilizing smoothing spline parameterization, we found that reoperation (p < 0.001) and implant revision or removal rates (p = 0.002) increased with increasing BMI. Increasing BMI was associated with increased rates of early hip dislocation (p = 0.02), wound infection, and, most strikingly, deep periprosthetic infection (a hazard ratio of 1.09 per unit of BMI >25 kg/m2; p < 0.001). However, we found no association between increasing BMI and any revision for mechanical failure of the implant or between increasing BMI and revision for aseptic implant loosening. There was an inverse correlation between increasing BMI and risk of revision for bearing wear. Conclusions: The rates of reoperation, implant revision or removal, and common complications after total hip arthroplasty were strongly associated with BMI. Level of Evidence: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.
Peer Review: This article was reviewed by the Editor-in-Chief and one Deputy Editor, and it underwent blinded review by two or more outside experts. It was also reviewed by an expert in methodology and statistics. The Deputy Editor reviewed each revision of the article, and it underwent a final review by the Editor-in-Chief prior to publication. Final corrections and clarifications occurred during one or more exchanges between the author(s) and copyeditors.
T
he prevalence of obesity continues to rise, and it is estimated1,2 that approximately 35% of adults in the United States have a body mass index (BMI) of ‡30 kg/m 2 . Obesity also has become a worldwide epidemic, with 30% of adults worldwide classified as obese3. As the average BMI has increased, the health-care burden associated with obesity has become an important consideration in elective procedures 4,5.
A high BMI is an independent risk factor for the development of osteoarthritis of the hip6. It is estimated that onethird of patients undergoing total hip arthroplasty have a BMI of ‡30 kg/m2, with many being younger individuals6-8. Understanding the influence of BMI on the risk of complications and on implant survivorship is important when making decisions concerning the risks and benefits of such elective procedures.
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. In addition, one or more of the authors has a patent or patents, planned, pending, or issued, that is broadly relevant to the work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
J Bone Joint Surg Am. 2016;98:169-79
d
http://dx.doi.org/10.2106/JBJS.O.00430
170 TH E JO U R NA L O F B O N E & JO I N T SU RG E RY J B J S . O RG V O LU M E 98-A N U M B E R 3 F E B R UA RY 3, 2 016 d
d
d
Recent studies have demonstrated an increase in some early complications among obese patients undergoing total joint arthroplasty 9-13. Morbidly obese patients (those with a BMI of ‡40 kg/m2) have increased risks such as superficial wound infection, hip dislocation, and venous thromboembolism13-15. Although studies have begun to correlate early outcomes among patients according to BMI categories, no previous study, to our knowledge, has comprehensively examined the effects of obesity as a continuous variable across all BMIs, and it has not been established whether there are BMI thresholds that separate those at increased risk for complications. The effect of BMI on longer-term implant survivorship and mechanical failure of implants has been controversial, as studies have failed to find an association16,17. However, the results of a recent meta-analysis suggested increased rates of aseptic loosening requiring revision surgery in obese patients after total hip arthroplasty11. The purpose of this study was to examine the effect of patient BMI on the risk of complications, reoperations, and implant revision or removal after total hip arthroplasty. Materials and Methods
A
fter institutional review board approval, this investigation was carried out 18 utilizing a large, single-institution total joint registry . This registry prospectively captures patient demographics; operative details; information regarding complications, reoperations, and implant revisions; and clinical outcome scores for patients treated with total joint arthroplasty. Patients routinely are asked to follow up with the surgeon twice during the year after the arthroplasty procedure, at postoperative years two and five, and subsequently at five-year intervals. Patients who are unable to attend follow-up appointments 19 in person are contacted to complete a standardized questionnaire .
Study Population All patients who underwent a primary total hip arthroplasty between January 1, 1985, and December 31, 2012, at our institution were included in this study, with the exception of those who declined to provide research authorization or who underwent total hip arthroplasty for tumor or acute hip fracture. Using our total joint registry, we identified patient BMI, demographics, primary diagnoses, and surgical indications. The study cohort consisted of 21,361 primary total hip arthroplasties (17,774 consecutive total hip arthroplasty patients).
E F F E C T O F B O D Y M A S S I N D E X O N C O M P L I C AT I O N S R E O P E R AT I O N S A F T E R T O TA L H I P A R T H R O P L A S T Y
AND
Outcome Measures The primary outcome measures were reoperation, implant revision or removal for any reason, dislocation within six months postoperatively, and superficial or deep infection. Implant survival and the risks of revision, reoperation, dislocation, and infection were calculated according to BMI. The effects of other variables (e.g., age, sex, primary diagnosis, and surgical indication) as a function of BMI were examined.
Statistical Analysis Descriptive statistics are reported as the mean (and standard deviation) or the number (and percentage). The Kaplan-Meier method was used for survival estimates. The association of joint arthroplasty outcomes with patient variables was assessed using Cox proportional hazards regression. Results are reported as hazard ratios (HRs) with 95% confidence intervals (CIs). Models adjusted for correlations between the two hips in patients who had bilateral primary total hip arthroplasty. The main variable was BMI. The association of BMI with each outcome was evaluated using a smoothing spline and plotted to demonstrate the HR as a function of BMI. Then, the observed pattern (e.g., does risk increase at a specific threshold?) was used to guide the inclusion of BMI thresholds into the models. We examined BMI between 20 and 50 kg/m2, setting BMI values of 50 kg/m2 as being equal to 50 kg/m2, because few patients were beyond these extremes. A second analysis was conducted using commonly used ranges of BMI (
