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. 2019 Sep 3;11(Suppl 2):S260–S264. doi: 10.1016/j.jcot.2019.09.002

Early outcomes and complications of obese patients undergoing shoulder arthroplasty: A meta-analysis

Ashley Klein a, Julio J Jauregui a, Edward Raff b,c, R Frank Henn 3rd a, S Ashfaq Hasan a, Mohit Gilotra a,∗
PMCID: PMC7067985  PMID: 32189951

Abstract

Objective

The prevalence of obesity and shoulder arthroplasty have both been increasing in the United States. Although lower extremity arthroplasty literature suggests higher complication rates in these patients, there is a paucity of studies evaluating the outcome of shoulder arthroplasty in obese patients. Our purpose was to perform a meta-analysis to determine clinical outcomes and complications of these patients.

Methods

Following the PRISMA guidelines, the MEDLINE (PubMed), Embase, and Ovid libraries were used to perform a comprehensive literature review to compare complications and outcomes following shoulder arthroplasty between obese and non-obese patients. Our initial search returned 143 publications. Our inclusion criteria included full-text reports, minimum follow-up of 1 year, minimum of 10 patients, no cadaveric or biomechanical studies, only studies published in English, studies involving obese patients undergoing either anatomic or reverse shoulder arthroplasty. A total of 13 studies met the inclusion criteria. These studies were then evaluating using a methodological index for non-randomized studies (MINORS) score. Ultimately, 6 studies met our criteria and were included in the final analysis.

Results

A total of 978 patients were identified from the 6 studies. Patients with a BMI <30 kg/m2 had a complication rate of 9.7% and American Shoulder and Elbow Surgeons score (ASES) increased from 37.4 to 76.7. Patients with a BMI >30 kg/m2 had a complications rate of 6.5% and ASES increased from 34.4 to 76.2. Patients with a BMI >40 kg/m2 ASES increased from 29.5 to 68.6. The postoperative ASES score of 68.6 for patients with a BMI >40 kg/m2 was significantly lower than the ASES score of 76.8 in patients with a BMI <40 kg/m2 (p = 0.007). There were an insufficient number of patients and an insufficient number of complications to perform any meaningful statistical test on complication rates in patients with a BMI >40 kg/m2.

Conclusion

No significant difference was observed in number of complications and follow-up ASES scores following shoulder arthroplasty between obese and non-obese patients. Morbidly obese patients (BMI > 40 kg/m2) have a significantly lower ASES follow-up score than non-morbidly obese patients; however, this difference may not be clinically significant. Future studies are needed to investigate outcomes and complications associated with morbidly obese patients undergoing shoulder arthroplasty.

Keywords: Obesity, Shoulder arthroplasty, Meta-analysis

1. Introduction

The prevalence of obesity in the United States has been increasing in recent years with the Center for Disease Control (CDC) reporting 35% of adults are obese [body mass index (BMI) > 30 kg/m2)].1,2 Obesity may increase patient morbidity and mortality.3 This increased prevalence can lead to a greater utilization of health-care services with a yearly cost of >$100 billion.4 Obesity prevalence is even higher in the elderly population (>60 years old) with more than 70% estimated to be either overweight or obese.1 In regard to shoulder pathology, obesity has been shown to lead to an increased incidence of rotator cuff tendinitis, arthropathy, rotator cuff tear size, and eventual need for arthroplasty.5, 6, 7

From 2000 to 2008, there has been a 2.5 fold increase in annual total shoulder arthroplasty (TSA) and reverse shoulder arthroplasty (RSA) procedures in the US.8,9. Reasons for arthroplasty include rotator cuff tear arthropathy, massive rotator cuff tears, proximal humerus fractures, revision surgery, and glenohumeral osteoarthritis (OA).10,11 While these procedures are widely used, complications rates are higher than desired. Most commonly reported complications include instability, infection, fracture, and nerve injury.12,13

Lower extremity arthroplasty literature suggest that increasing BMI has an adverse effect on complications, infections, and revision rates.14, 15, 16 In the last several years, many studies have evaluated the effect of obesity on shoulder arthroplasty outcomes. However, these studies have yielded mixed results possibly due to variability in study design and small cohorts. The purpose of this study was to evaluate the complications and outcomes of TSAs and RSAs in obese patients.

2. Methods

A systematic literature search of clinical studies was performed to identify outcomes and clinical complications of TSAs and RSAs in the obese population using the search engines MEDLINE (PubMed), Embase, and Ovid. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used to ensure the study was completed properly.17 Two authors (AK and JJ) independently performed the comprehensive search and evaluated all studies published until January 2018 using the following search terms: “shoulder,” “replacement,” “BMI,” “obesity,” “arthroplasty.” In total, 146 studies were identified.

The titles and abstracts for each of the 146 studies were assessed for eligibility using the following inclusion criteria: (1) full-text reports; (2) minimum follow-up of 1 year; (3) minimum of 10 patients; (4) no cadaveric or biomechanical studies; (5) only studies published in English; (6) studies involving obese patients undergoing TSAs and RSAs (7) no patient data from national databases.

A total of 13 studies and 1064 patients were identified that met the inclusion criteria. These were then read in full and cross-referenced to make sure all relevant studies were included. Cross-referencing identified no additional studies (Fig. 1.). These studies were then designated a methodological index for non-randomized studies (MINORS) score.18 Two studies were excluded due to a MINORS score < 12 and 3 studies were excluded due to collecting patient data from a national database. Two studies were excluded due to lack of control groups.

Fig. 1.

Fig. 1

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Flow diagram describing inclusion-exclusion criteria.

Complications recorded in these studies included infections, dislocations, loosening, fractures, nerve injury, and revisions. The American Shoulder and Elbow Surgeons score (ASES) was also recorded. The ASES score was created to standardize outcome measures after shoulder and elbow surgery. The total score (out of 100) is composed of 50% pain and 50% function and includes both a physician-rated and patient-rated section.19 We investigated a potential difference in the number of complications and ASES follow-up scores for patients with a BMI < 30 kg/m2 compared to those > 30 kg/m2, as well as those with a BMI < 40 kg/m2 compared to those with a BMI > 40 kg/m2.

To perform the comparisons in all cases, we used the standard fixed-effect model to perform a meta-analysis across studies.20 We used the fixed effect model for all tests primarily due to the small number of studies that have looked at this problem. For a BMI threshold of 30 kg/m2, there are only 6 that provide the needed information for a meta-analysis for the complication rate and 5 studies that provide ASES scores. When we consider a BMI threshold of 40 kg/m2, only two studies were available. Due to the small number of studies, a random effects model would not be appropriate due to the need to estimate a larger number of parameters in the random-effect model.

To compare the differences between each population, we used Cohen's d as the effect size, which is the difference in means divided by the total population standard deviation.21 This measures the effect in terms of difference in standard deviations. We used a level of significance with an alpha error of less than 5%, and computed p-values as well as confidence intervals. We also performed Cochran's Q tests for heterogeneity to determine if the fixed-effect results may be misleading due to a significant deviation from a normal distribution.22

3. Results

Nine hundred seventy-eight adult patients that underwent shoulder arthroplasty, including 76 TSA and 592 RSA, were identified (total number does not add to 100% as a study did not specify the type of shoulder arthroplasty). The study included 393 males and 585 females. The patients had a mean age of 68.8 years (range, 18–95 years) at the time of the index procedure. Patient follow-up in these studies ranged from 12 months to 204 months. These patients were divided into a cohort of patients who have a BMI less than 30 kg/m2 (n = 607 patients, 607 shoulders) and a cohort with patients with BMI greater than 30 kg/m2 (n = 371 patients, 371 shoulders). The cohort of patients with BMI greater than 30 kg/m2 included those with a BMI greater than 40 kg/m2. A third cohort included patients with BMI greater than 40 kg/m2 (n = 43 patients, 43 shoulders) so that we could further evaluate outcomes in the morbidly obese population. This cohort had a mean BMI of 45.3 kg/m2. The indications for surgery included rotator cuff tear/arthropathy (53%), acute fracture (3%), arthritis (20%), and unspecified (24%).

In Table 1, we briefly summarize the results from the ASES comparisons for BMI >30 and >40, showing the number of studies that contributed to the meta-analysis, the p-value that there is a statistical difference between the populations tested, and the p-value associated with Cochran's Q test for heterogeneity (Table 1). In all cases, the result of the Cochran Q's test reassures us that the fixed-effect model is appropriate.

Table 1.

ASES comparisons for BMI >30 and >40, the number of studies, the p-value for statistical difference between the populations tested, and the p-value for Cochran's Q test for heterogeneity.

Test # Studies Cohen-d d, p-value Cochran Q Q, p-value
ASES, BMI ≥30 5 −0.09 0.435 7.284 0.122
ASES, BMI ≥40 2 −0.45 0.007 0.093 0.760
Complication Rate, BMI ≥30 6 0.01 0.958 10.81 0.055
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No significant difference was observed in number of complications between the cohort of patients with BMI less than 30 kg/m2 and BMI greater than 30 kg/m2 (CI -0.21–0.22, Fig. 1). The low BMI cohort has a complication rate of 9.7% (20 infections, 18 fractures, 8 dislocations, 12 loosening, and 1 nerve complication), and the BMI greater than 30 kg/m2 had a complication rate of 6.5% (8 infections, 10 fractures, 3 dislocations, 3 loosening, and 0 nerve complications).

No significant difference was observed in the ASES follow-up scores between these two groups (CI -0.33–0.14). The less than 30 kg/m2 cohort had a mean ASES that improved from 37.4 points to 76.7 points, while the more than 30 cohort has a mean ASES score that improved from 34.4 points to 76.2 points. Forest plots showing the confidence intervals for each study, as well as the confidence interval produced by the fixed-effect model's estimate, are shown in Fig. 2.

Fig. 2.

Fig. 2

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Forest plots for the effect size of average complication rate (left), and ASES (right) with BMI > 30 kg/m.2.

The forest plot comparing the ASES score between those with a BMI greater or equal to 40 kg/m2 and those with a BMI less than 40 kg/m2 is given below in Fig. 3. Both studies are at the edge of having significant and non-significant scores, but when combined in the fixed-effect model, there is a statistically significant difference (CI -0.78 to −0.12, p = 0.007, Fig. 3). For patients with a BMI >40 kg/m2, there were an insufficient number of patients and an insufficient number of complications to perform any meaningful statistical test.

Fig. 3.

Fig. 3

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Forest plot for the effect size of follow-up ASES scores with BMI >40 kg/m.2.

4. Discussion

Obese people account for approximately 35% of the United States population.1,2 Obese patients have an associated increase in morbidity and mortality compared to non-obese patients.3 They are at an increased risk of rotator cuff tendinitis, arthropathy, rotator cuff tear size, and shoulder arthroplasty.5, 6, 7 Previous research has shown that obese patients have worse outcomes after undergoing lower extremity arthroplasty.14, 15, 16 There is currently no consensus whether this pattern holds true for shoulder arthroplasty with current studies showing mixed results. Werner et al. utilized the Pearl Diver Patient Record Database in a study evaluating 144,239 patients reported that obesity was associated with significantly increased rates of complications including infection, dislocation, loosening and venous thromboembolism.23 Griffin et al. queried the National Inpatient Sample database and reported that obese patients tended to have longer hospital stays and an increased risk of post-operative respiratory complications.24 In contrast, Watermen et al. utilized the NSQIP database and reported that obesity was not associated with any specific complications after controlling for other variables.25 Similarly, Jiang et al. sampled the NSQIP database and found no association between BMI and 30-day complication rate. They did report an increased surgical time in the increased BMI group.26

Database studies are inherently limited by the inability to include outcome measures. When looking at the literature from case series, obesity does not appear to have a detrimental effect on functional outcomes although the magnitude of functional improvement in the obese patient can be less than in the non-obese patient.27, 28, 29, 30 Savin et al. in a retrospective study demonstrated no difference in post-operative ROM, patient-reported outcomes or complication rate between 5 different BMI groups after shoulder arthroplasty.31

The current study compared complications rates and outcomes after shoulder arthroplasty between non-obese and obese patients. Overall, the results show no difference in the number of complications and ASES follow-up scores between patients with a BMI less than 30 kg/m2 and BMI greater than 30 kg/m2. Interestingly, there was trend for a lower complication rate in the group with BMI greater than 30 kg/m2.

While the result comparing ASES follow-up scores with a BMI 40 kg/m2 cut-off was statistically significant, the low number of studies gives us cautionary pause. There are not enough studies to perform robust estimation of parameters even for the fixed-effect model. Statistically we would recommend that this provides a strong indication that a difference at BMI >40 kg/m2 exists, but further studies are still warranted to verify the veracity of this claim. Furthermore, the difference of less than 10 points on the ASES is below the minimum clinically important difference, suggesting that the observed difference may not be clinically important.32

Increased complications and less robust outcomes after total knee and total hip arthroplasty have led to some centers and surgeons to not offer arthroplasty to patients over a BMI threshold. Therefore, it is very important to determine if obese patients are at increased risk of complications and less robust outcomes after shoulder arthroplasty. The current data does not support elevated BMI as a contraindication for shoulder arthroplasty.

Like every other meta-analysis, there are several limitations. The main limitation is the small number of cohorts which limits the power of this study. In addition, the literature in lower extremity arthroplasty shows a larger increase in complications when BMI >40 kg/m2.14 There is a paucity of literature describing obesity and shoulder arthroplasty. Those studies most often look for differences using a BMI of 30 kg/m2 as a cut off. The results of this analysis show a potential difference in shoulder arthroplasty outcomes in patients with a BMI greater than 40 kg/m2 and future studies are warranted to explore this possibility.

5. Conclusion

Obesity has been associated with increased morbidity and mortality in most fields of medicine. No significant difference was observed in number of complications and follow-up ASES scores following shoulder arthroplasty between obese and non-obese patients. Morbidly obese patients (BMI > 40 kg/m2) have a statistically significant lower ASES follow-up score than non-morbidly obese patients. However, only two papers used BMI 40 kg/m2 as a cut-off for comparison. Future studies are needed to investigate outcomes and complications associated with morbidly obese patients undergoing shoulder arthroplasty.

Conflicts of interest

AK/JJ/ER: No disclosures.

RFH: Research support from Arthrex Inc.

SAH: Board or committee member for AAOS.

MG: Paid presenter or speaker for Arthrex Inc.

Funding

This study was unfunded.

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