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Characteristics and Complications of Super-Obese Patients Who Underwent Total Knee Arthroplasty

Julio J. Jauregui, MD; Randa K. Elmallah, MD; Steven F. Harwin, MD; Todd P. Pierce, MD; Jeffrey J. Cherian, DO; Qais Naziri, MD; Michael A. Mont, MD

Abstract

Preoperative demographic characteristics, comorbidities, length of stay and surgery, and postoperative complications were compared between super-obese (n=1042) and nonobese (n=19,929) patients who underwent total knee arthroplasty. Super-obese patients were younger, were predominantly women, had an increased incidence of comorbid conditions such as diabetes and hypertension as well as a high rate of superficial and deep wound infections, and had a longer mean length of stay and operative time. Although super-obese patients have unique demographic characteristics and increased postoperative complications and length of stay, they may still benefit from total knee arthroplasty. Surgeons should note their high incidence of infections. [Orthopedics. 2016; 39(4):e800–e805.]

Abstract

Preoperative demographic characteristics, comorbidities, length of stay and surgery, and postoperative complications were compared between super-obese (n=1042) and nonobese (n=19,929) patients who underwent total knee arthroplasty. Super-obese patients were younger, were predominantly women, had an increased incidence of comorbid conditions such as diabetes and hypertension as well as a high rate of superficial and deep wound infections, and had a longer mean length of stay and operative time. Although super-obese patients have unique demographic characteristics and increased postoperative complications and length of stay, they may still benefit from total knee arthroplasty. Surgeons should note their high incidence of infections. [Orthopedics. 2016; 39(4):e800–e805.]

Currently, obesity is recognized by the World Health Organization as a pandemic affecting more than 500 million people, and its prevalence is postulated to be on the rise.1 It is a well-defined risk factor for knee osteoarthritis, and often leads to end-stage degenerative joint disease requiring total knee arthroplasties (TKAs) at younger ages.2 Consequently, the incidence of TKAs has paralleled the rising obesity rate, and currently more than 500,000 of these procedures are being performed in the United States annually.2–4 Furthermore, the proportion of “super-obese” individuals, or those who have a body mass index (BMI) of greater than 50 kg/m2, has also increased, posing new obstacles for orthopedists.5 To ensure the continued success of TKAs, it is important to determine the implications that obesity, and particularly super-obesity, has for this surgery.

There have been numerous reports of the characteristics, outcomes, and complications of TKAs in obese patients. Previous studies6 have shown that patients who have a BMI of greater than 40 kg/m2 are 32 times more likely to undergo a TKA than those who have a BMI of less than 25 kg/m2. In addition,7 these patients may have TKAs up to 13 years earlier than patients who have a BMI of less than 25 kg/m2. The current authors anticipate that these findings may be more evident in the super-obese population. Studies of obese patients have also found a higher incidence of comorbidities such as diabetes, hypertension, and chronic obstructive pulmonary disease (COPD) as well as an increase in postoperative complications including superficial and deep wound infections, deep venous thrombosis (DVT), and pulmonary emboli.8–10 However, only a few small cohort studies and a Medicare database study have evaluated the outcomes of these patients.7,8,10–12

Due to the lack of all-inclusive cohort studies evaluating TKA outcomes in super-obese patients, this study evaluated this population compared with a nonobese cohort using the National Surgical Quality Improvement Program (NSQIP), a database prospectively maintained by the American College of Surgeons. The authors assessed the database for (1) preoperative demographic characteristics, (2) comorbidities, (3) surgery time and length of stay, and (4) postoperative complications of obese and nonobese patients who underwent TKA.

Materials and Methods

Using the NSQIP database, the authors evaluated patients who underwent a TKA from 2006 to 2012. This database contained information regarding demographics, preoperative risk, laboratory data, operative data, and 30-day postoperative metrics. Using the Current Procedural Terminology code 27447 (total knee arthroplasty), the authors identified and selected 51,629 patients. They then substratified these patients into 3 categories according to BMI: (1) less than 30 kg/m2 (n=19,929); (2) 30 to 49.9 kg/m2 (n=30,658); and (3) 50 kg/m2 or greater (n=1042). The authors then specifically compared the super-obese cohort (BMI > 50 kg/m2) with the cohort of patients who were nonobese (BMI < 30 kg/m2). Patients who had a BMI between 30 and 49.9 kg/m2 were excluded. Because the evaluated data were Health Insurance Portability and Accountability Act compliant, institutional review board approval was not required prior to initiating this study.

The authors then substratified and analyzed the information according to demographic characteristics, preoperative comorbidities, hospitalization details, and 30-day postoperative complications. Demographic characteristics included age, gender, race, and primary diagnosis. Preoperative comorbidities included diabetes, hypertension, COPD, a history of previous cardiac disease, the American Society of Anesthesiology (ASA) risk classification, and the prevalence of social factors (current tobacco and alcohol consumption). The assessed hospitalization details included the length of operative time and the duration of hospitalization. The 30-day incidence of postoperative complications was assessed, including superficial and deep wound infections, DVT, pulmonary emboli, pneumonia, peripheral nerve injuries, and bleeding episodes requiring transfusion.

Statistical Analysis

Compiled data were exported into a Microsoft Excel Workbook (Microsoft Corporation, Redmond, Washington). Statistics were generated with the aid of GraphPad Prism version 5.01 statistical software (GraphPad Software Inc, La Jolla, California), with the authors comparing the prevalence of demographic characteristics, incidence of comorbidities, mean length of stay, mean operative time, and 30-day incidence of postoperative complications between the 2 cohorts. This was done using the unpaired 2-tailed t test. The Z-test was used for proportional data.

Results

The super-obese cohort underwent TKA at a significantly younger mean age than the nonobese cohort (60 vs 70 years; P=.0001), and there were significantly more women in the super-obese cohort (79% vs 60%; P=.0001). There were no significant differences between the groups regarding race (P>.05) or primary diagnosis (P>.05) (Table 1).


Demographic Characteristics of Super-Obese Patients Versus Nonobese Patients

Table 1:

Demographic Characteristics of Super-Obese Patients Versus Nonobese Patients

There was a higher incidence of multiple comorbidities, including diabetes, hypertension, and COPD, among the super-obese cohort. In the super-obese cohort, there was a significantly higher incidence of diabetes (33.9% vs 10.6%; P<.0001), hypertension (79.0% vs 59.5%; P<.0001), and COPD (5.1% vs 3.2%; P=.0006). Super-obese patients had a significantly lower frequency of previous cardiac disease (2.7% vs 5.7%; P=.001). A higher proportion of the super-obese patients had ASA risk classifications III (77.9% vs 35.8%; P<.0001) and IV (6.7% vs 1.3%; P<.0001). No significant differences were seen between the 2 cohorts in the prevalence of tobacco and alcohol consumption (P=.12 and P=.09, respectively; Table 2).


Preoperative Comorbidities and American Society of Anesthesiology Risk Classifications of Super-Obese Patients and Nonobese Patients

Table 2:

Preoperative Comorbidities and American Society of Anesthesiology Risk Classifications of Super-Obese Patients and Nonobese Patients

Operative time and hospital length of stay were significantly longer in the super-obese cohort. The mean operative time was 103 minutes (range, 37–331 minutes) for super-obese patients vs 94 minutes (range, 22–589 minutes) for nonobese patients (P=.0001). The hospital length of stay was 3.57 days (range, 1–22 days) for super-obese patients vs 3.37 days (range, 1–34 days) for nonobese patients (P=.0005) (Table 3).


Detailed Hospital Course of Super-Obese Patients and Nonobese Patients

Table 3:

Detailed Hospital Course of Super-Obese Patients and Nonobese Patients

On evaluation of 30-day postoperative complication rates, only infection rates were higher. The authors found that the super-obese cohort had a significantly higher incidence of superficial and deep wound infections (1.8% vs 0.5% and 0.4% vs 0.1%, respectively; P=.0001). No significant difference was found between the cohorts regarding the incidence of pneumonia (0.4% vs 0.4%; P=.99), pulmonary emboli (0.5% vs 0.6%; P=.67), DVT (0.9% vs 1.1%; P=.54), or peripheral nerve injuries (0.1% vs 0.04%; P=.33) (Table 3).

Discussion

The rising demand for TKAs has been partly attributed to the increasing prevalence of obesity.4,6 Subsequently, studies have been aimed at identifying the demographic characteristics, preoperative risks, comorbidities, and postoperative complications of obese patients that may influence outcomes. However, few analyses have focused on super-obese cohorts.13 In this study, the authors noted that super-obese patients underwent TKA at a younger mean age, had a higher incidence of comorbidities, and had longer operative times. These patients also had a significantly higher incidence of superficial and deep wound infections.

This study had several limitations. Because the NSQIP database reports data collected postoperatively for 30 days, it was beyond the scope of this study to assess long-term complications. Information for this study was restricted to the NSQIP database, which typically involves larger, teaching-oriented hospitals that have both the finances and the interest to invest in improving quality of care. Therefore, the database may not be representative of smaller, community institutions. Moreover, the database contained information from more than 280 institutions with differing standards regarding surgical approaches, intraoperative antibiotic prophylaxis protocols, postoperative DVT prophylaxis protocols, implant preferences, infection rates, and discharge criteria. Despite these limitations, the NSQIP has proven to be an effective tool in assessing the quality of patient care.14 Thus, the authors believe that it was appropriate for use in this study and that their conclusions have minimal bias.

When examining demographic characteristics, the mean age of patients undergoing TKA was significantly younger in the super-obese cohort, which is supported by several studies. Changulani et al7 found that severely obese (BMI > 35 kg/m2) and morbidly obese (BMI > 40 kg/m2) patients underwent TKAs at significantly younger ages (65 and 61 years, respectively) than patients with a BMI of less than 25 kg/m2 (74 years; P<.0001). Similarly, Gandhi et al,15 in a study of 804 TKAs, found that patients undergoing TKA who had a BMI of greater than 35 kg/m2 had a mean age of 61 years, which was significantly younger than patients who had a BMI of less than 25 kg/m2 (68 years; P<.05). Stickles et al11 found that patients who had a BMI of greater than 40 kg/m2 underwent TKA at a mean age of 64 years, which was significantly younger than those who had a BMI of less than 25 kg/m2 (74 years; P<.0001). However, in contrast to the current authors' findings, Werner et al10 evaluated a Medicare database of 7666 super-obese patients and found that the incidence of tobacco use was twice as much as that in the current study (18.8% vs 9.7%). Similar findings have been reported by other studies (Table 4).12,16,17


Studies of the Effect of Body Mass Index on Age at Total Knee Arthroplasty

Table 4:

Studies of the Effect of Body Mass Index on Age at Total Knee Arthroplasty

Various studies have reported greater preoperative comorbidities and higher ASA risk classifications in obese patients. Vulcano et al8 reported that patients who had a BMI exceeding 40 kg/m2 had a significantly increased proportion of hypertension, diabetes, and chronic pulmonary disease compared with patients who had a BMI of less than 25 kg/m2 (34%, 22%, and 5% increase, respectively; P<.05). Additionally, Davenport et al18 found that patients who had a BMI of greater than 35 kg/m2 had a 4.22 odds ratio of having a higher ASA classification. Other studies investigating BMI and perioperative complications also found obese patients to have a significantly higher ASA classification(P=.0001).19 All of these studies suggested that patients with a BMI of greater than 35 kg/m2 had more preoperative comorbidities and operative risks, reflected by the ASA classification, which was consistent with the current findings in super-obese patients. Therefore, these results should be considered during the preoperative evaluation of super-obese patients.

There have also been reports of increased operative times and lengths of stay in super-obese patients. Naziri et al20 assessed the survivorship and complications of 101 knees, reporting that the mean surgical time of super-obese patients was 98 minutes (range, 72–120 minutes), significantly longer than that of a matched group of patients with a BMI of less than 30 kg/m2 (90 minutes; range, 62–134 minutes; P<.05). Similarly, Gadinsky et al,21 in a study of 454 TKAs, found that patients with a BMI of greater than 40 kg/m2 had a mean operative time that was 23 minutes longer (P<.001) than that of patients with a BMI of less than 25 kg/m2. Batsis et al22 evaluated the length of stay of more than 5500 primary TKA patients, determining that there was no statistical difference in length of stay between those who had a BMI of greater than 35 kg/m2 and those with a BMI of less than 25 kg/m2 (P=.30).

Morbidly obese patients may also have higher rates of postoperative infections. D'Apuzzo et al23 found that morbidly obese TKA patients had an increased risk of postoperative infections with no increased risk of thrombo-embolic-related complications. Also, a meta-analysis of more than 15,000 patients revealed that those with a BMI of greater than 30 kg/m2 had a significantly increased incidence of superficial and deep wound infection (odds ratios, 2.1 and 2.3, respectively) but not DVT and pulmonary emboli (odds ratio, 1.19; 95% confidence interval, 0.78–1.82).24 Similar studies have also suggested that those who had a BMI of greater than 40 kg/m2 had a significantly increased rate of wound infections but not thromboses or emboli.25

In response to the growing obesity epidemic, some have advocated limiting care for these patients. In the United Kingdom, many institutions in the National Health Service have refused to perform arthroplasties for super-obese patients.26 Specifically, one hospital trust had controversially denied hip or knee surgeries for anyone who had a BMI of greater than 30 kg/m2. However, despite potentially worse outcomes, the current authors believe that this super-obese cohort derived an overall improvement in quality of life from undergoing surgery.

Conclusion

Super-obese patients may often have a higher incidence of preoperative comorbidities and may have an increased rate of superficial and deep wound infections. Yet, despite increased risks, these patients may still benefit from undergoing TKA. However, all attempts should be made to reduce these complications with the use of preoperative health optimization, adequate postoperative care, and thorough discussions between surgeon and patient. In addition, longer-term studies and cost-comparison analyses are needed to further evaluate the effectiveness of TKAs in super-obese patients.

References

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  24. Kerkhoffs GM, Servien E, Dunn W, Dahm D, Bramer JA, Haverkamp D. The influence of obesity on the complication rate and outcome of total knee arthroplasty: a meta-analysis and systematic literature review. J Bone Joint Surg Am. 2012; 94(20):1839–1844. doi:10.2106/JBJS.K.00820 [CrossRef]
  25. Friedman RJ, Hess S, Berkowitz SD, Homering M. Complication rates after hip or knee arthroplasty in morbidly obese patients. Clin Orthop Relat Res. 2013; 471(10):3358–3366. doi:10.1007/s11999-013-3049-9 [CrossRef]
  26. Rojas J-PF. Obese and smokers denied treatment ‘to save money’. http://www.telegraph.co.uk/news/health/news/9127486/Obese-and-smokers-denied-treatment-to-save-money.html. Accessed August 1, 2014.

Demographic Characteristics of Super-Obese Patients Versus Nonobese Patients

CharacteristicSuper-Obese PatientsNonobese PatientsP
Body mass index, mean (range), kg/m255 (50–85)26 (14–20).0001
Age, mean (range), y60 (28–87)70 (19–89).0001
Gender
  Men20.9%39.9%.0001
Race.36
  White75.2%76.5%
  Hispanic3.5%5.5%
  Black12.5%4.4%
  Asian0.38%3.2%
  Unknown/other8.4%10.9%
Primary diagnosis
  Osteoarthritis97%95%.06
  Rheumatoid arthritis0.19%0.39%.32
  Avascular necrosis0.1%0.26%.3
  Other2.7%4.4%.05

Preoperative Comorbidities and American Society of Anesthesiology Risk Classifications of Super-Obese Patients and Nonobese Patients

ParameterSuper-Obese PatientsNonobese PatientsP
Comorbidity
  Diabetes33.9%10.6%<.0001
  Hypertension79.0%59.5%<.0001
Chronic obstructive pulmonary disease5.1%3.2%.0006
Previous cardiac disease2.7%5.7%.001
American Society of Anesthesiology risk classification
  I0.9%3.7%<.0001
  II14.5%59.2%<.0001
  III77.9%35.8%<.0001
  IV6.7%1.3%<.0001
Social factor
  Current tobacco use9.7%8.3%.012
  Current alcohol use0.3%1.4%.09

Detailed Hospital Course of Super-Obese Patients and Nonobese Patients

ParameterSuper-Obese PatientsNonobese PatientsP
Complication
  Superficial wound infection1.82%0.53%.0001
  Deep wound infection0.38%0.14%.0001
  Pulmonary embolism0.48%0.58%.67
  Deep venous thrombosis0.86%1.06%.54
  Pneumonia0.38%0.38%.99
  Peripheral nerve injury0.10%0.04%.33
  Bleeding requiring transfusions9.69%16.18%.0001
Hospital course
  Operative time, mean (range), min103 (37–331)94 (22–589).0001
  Length of stay, mean (range), d3.57 (1–22)3.37 (1–34).0005

Studies of the Effect of Body Mass Index on Age at Total Knee Arthroplasty

Body Mass Index, kg/m2Category Within StudyNaziri et al,20 2013Changulani et al,7 2008Gandhi et al,15 2010Stickles et al,11 2001Current Study
<25No.-59197146-
Mean age at surgery, y-7469.174.2-
25 to 29.9No.10113429030419,929
Mean age at surgery, y597366.870.970
P (age at TKA)-.5.34--
Survivorship97%----
30 to 34.9No.-104201271-
Mean age at surgery, y-7264.969.3-
P (age at TKA)-.15.17--
35 to 39.9No.-36116149-
Mean age at surgery, y-6561.268.3-
P (age at TKA)-.001.02--
≥40No.-11-92-
Mean age at surgery, y-61-64-
P (age at TKA)-.001-.0001-
≥50No.101---1042
Mean age at surgery, y60---60
P (age at TKA).37---.0001
Survivorship93%----
Authors

The authors are from the Center for Joint Preservation and Replacement (JJJ, RKE, TPP, JJC, MAM), Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore, Baltimore, Maryland; and the Department of Orthopaedic Surgery (SFH), Beth Israel Medical Center, New York, and the Department of Orthopaedic Surgery (QN), SUNY Downstate Medical Center, Brooklyn, New York.

Dr Harwin was not involved in the peer review of this manuscript.

Drs Jauregui, Elmallah, Pierce, and Naziri have no relevant financial relationships to disclose. Dr Harwin is a paid consultant for and is on the speaker's bureau of Stryker and Convatec and holds stock in Stryker. Dr Cherian is a paid consultant for DJ Orthopaedics. Dr Mont receives grants and personal fees from Stryker, Wright Medical Technology, Inc, DJ Orthopaedics, Joint Active Systems, Sage Products, Inc, and TissueGene and personal fees from Medical Compression Systems and Medtronic.

Correspondence should be addressed to: Michael A. Mont, MD, Center for Joint Preservation and Replacement, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore, 2401 W Belvedere Ave, Baltimore, MD 21215 ( mmont@lifebridgehealth.org).

Received: June 09, 2015
Accepted: June 26, 2015
Posted Online: May 20, 2016

10.3928/01477447-20160513-05

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