The Implications of Obesity on Total Hip Arthroplasties: A Literature Review of the Associated Complications

Abstract


Introduction
Obesity is a global pandemic and public health crisis with a prevalence that has tripled since 1975 and a current estimation of 650 million adults suffering from obesity worldwide 1 . Medical costs of obesity in the United States were nearly $173 billion in 2019, accounting for approximately $1,861 higher medical costs annually in obese adults compared to people of healthy weight 2 . The definition of 'obesity' is a body mass index (BMI) ≥ 30 kg/ m 2 , with 'severe obesity' characterized as a BMI≥ 35 kg/m 2 and 'morbid obesity' defined as a BMI ≥ 40 kg/m 2 . 3 Osteoarthritis (OA) of the hip is a degenerative disease; causing disability, pain, and loss of function 5 . OA is considered a multifactorial disease and increases in prevalence with concurrent obesity, advanced age, female gender, low socioeconomic status, and genetics 6 . Although there has yet to be a precise relationship between obesity and osteoarthritis, the two conditions are strongly correlated, and the etiology is believed to be biomechanical, proinflammatory, and immunomodulatory 6 . Obesity is associated with a wide range of comorbidities, including osteoarthritis, leading to a significantly younger age at the time of primary total hip arthroplasty (THA) compared to nonobese individuals 4 . As our population continues to get older, combined with an increasing rate of obesity, an increased rate of consultations for total hip arthroplasty is expected.
This has led to concerns regarding the implications of obesity on the need for THA itself and the associated complications, especially for arthroplasty surgeons. Unfortunately, few articles provide an all-encompassing review of different complications surrounding obesity within orthopedic surgery, and even fewer specifically address complications associated with total hip arthroplasty. This literature review aims to provide a comprehensive review of the implications obesity has on total hip arthroplasties, its associated complications, and how we can potentially modify these risks.

Methods and Materials
Sources and research articles were identified by searching the databases of PubMed, Google Scholar, and the National Center for Biotechnology Information (NCBI) from 2000 to July 2022. Our search used the specific terms located within the abstract/title, including: "total hip arthroplasty" AND "complications," AND "obesity, OR obese." Inclusion criteria for research articles were the English language and peer-reviewed articles that were either observational studies, randomized controlled trials, systematic reviews, literature reviews, or metaanalyses published from inception to July 2022. Articles not directly examining the effect of obesity on the incidence of complications following primary THA were excluded. The first author (RB) performed study selection and data analysis unblinded. Multiple reviewers did not independently assess the articles, and inter-rater reliability was also not evaluated. Studies with outcomes of interest included the incidence of postoperative complications, primary THA in obese patients, and clinical outcome measures. A total of 265 studies were identified upon initial search. After reviewing abstracts, removing articles that met exclusion criteria, and removing duplicate articles, 58 remained under consideration. Full-text articles were then read, and 31 articles were selected for reference in this literature review. A PRISMA flow diagram was not created for this literature review.

Age at primary THA
Four studies directly examined the degree of obesity on the timing of primary THA, which showed a clear inverse relationship between the two variables 4,7-9 . Abdulla et al.

Duration of surgery
The impact of obesity on operative time is crucial to understand for surgeons optimizing patient care and resource allocation. A meta-analysis that included seven studies totaling 2608 hips by Liu et al. showed a positive correlation between degrees of obesity and operative time. Specifically, obese patients with a BMI greater than 30 kg/ m 2 experienced a mean deviation of 10.67 minutes longer operative time than patients with a BMI less than 30 kg/ m 2 (95% CI [3.00, 18.35], p = 0.005). When performing a subgroup analysis of these operative times, for those with a BMI greater than 40 kg/m 2 , the mean operative time was 37.6 minutes longer when compared to patients with a BMI less than 30 kg/m 2 (p < 0.0001) 10 . However, in Liu et al.'s meta-analysis, it was found that out of the seven studies compared, six exhibited non-significance with 95% confidence intervals, as indicated by negative lower bounds. Figure 2 demonstrates the positive correlation between operative time and BMI to enhance the clarity and visual representation of these results.

Infection
The association between total hip arthroplasty in obese patients and surgical wound/prosthetic joint infections has been supported by several studies [10][11][12][13][14] . When stratified, this data shows increased infection rates in higher BMI categories of > 40 and > 50 kg/m 2 compared to other obese categories 11,12 . Onggo et al. performed a meta-analysis including more than 2 million patients. In this metaanalysis, obese patients were found to have a higher risk of deep infections (OR = 2.71, P < 0.001) and superficial infections (OR = 1.99, P < 0.001) when compared to nonobese patients 13  Orthopedic surgeons have been exploring strategies to mitigate the increased infection risks observed in obese patients undergoing arthroplasty. One such approach is the administration of extended oral antibiotics as a postoperative prophylactic measure. However, accepting this practice as the standard of care remains to be determined due to inconclusive results reported in the current literature. Carender et al. recently examined the efficacy of extended oral antibiotic prophylaxis in morbidly obese patients undergoing total joint arthroplasty. Their findings did not show a significant difference in wound complications (11% vs. 8%; P = .41) or prosthetic joint infection (PJI) rates (1.7% vs. 0.6%; P = .35) between the group receiving antibiotic prophylaxis and the group without prophylaxis 16 .
In contrast, Inabathula et al. reported a 2.2% reduction in the risk of postoperative THA infections within 90 days among obese patients who received prophylactic oral antibiotics 17 . Furthermore, they found that obese patients not receiving prophylaxis had an odds ratio of 4.0 (p = 0.037) for developing PJI following THA 17 . While the data regarding using extended oral antibiotics prophylactically in obese patients remains controversial, Lipson et al. argue that the practice is cost-effective. Their study reported that prophylactic antibiotics post-operatively in obese patients were associated with an absolute reduction risk of 0.151%, although, in the setting of a relatively large number needed to treat (NNT = 662) 18 .

THA Dislocation Rate
Dislocation following THA has been consistently higher than in obese patients, regardless of surgical approach 10,13,14 . Onggo et al. noted obese patients had a higher rate of postoperative dislocations with an odds ratio of 1.72 (p < 0.001) 13 . Other meta-analyses, such as Liu et al., and Haverkamp et al., showed similar findings with a relative risk of 2.08 (p < 0.0001) and an odds ratio of 0.54, respectively, demonstrating higher rates of dislocation in obese individuals following THA as well 10,14 . The rate of dislocation also significantly increases incrementally in super-obese individuals when compared to patients with a BMI < 40 kg/m 2 (3.3%, six-month risk, p < 0.001), as demonstrated in Werner et al. 11 .

Periprosthetic fracture
The correlation between periprosthetic fracture in obese patients undergoing THA is not as defined, as well as infection and dislocation rates in this population. In a retrospective cohort study, Jeschke et al. analyzed 131,576 THAs and   21 . In a retrospective cohort study including more than 14,000 THAs and more than 300 periprosthetic fractures, BMI was not associated with a periprosthetic fracture 22 . Given these conflicting results and relatively little data, the risk of periprosthetic fractures in obese patients following THAs requires further study.

Venous Thromboembolism
Evidence also suggests obese individuals are likelier to experience VTE [12][13][14] . A prospective study of 1231 consecutive patients treated for VTE found that 96% had at least one recognized risk factor, and 37.8% were obese 23 . Despite this prevalence, studies have found no association of VTE based solely on excess weight, and etiology is likely multifactorial 24 . Haverkamp et al. analyzed seven studies totaling 3,716 patients noting an odds ratio of 0.56 (p = 0.04) [14]. Others have noted a much higher rate of VTE following THA (5.8%) in super-obese individuals (BMI > 50 kg/m 2 ) when compared to nonobese, obese, and morbidly obese patients (p < 0.0001 for all categories) 12 .

Role of preoperative bariatric surgery
Given the high rates of complications following THA in obese patients, there has been significant interest in researcher methods for reducing the risk of postoperative complications, such as bariatric surgery. However, the literature surrounding the role of preoperative weight loss via bariatric surgery prior to THA remains controversial 25,26,27 . In a meta-analysis review totaling 23,348 patients who underwent either THA or TKA (657 patients who had undergone bariatric surgery), there were no statistically significant differences in outcomes in superficial or deep wound infection(s), VTE, or need for revision surgery, between the two groups 25 . These findings suggest complication rates in obese patients are not solely due to BMI and are multifactorial. Further study indicated that analysis of postoperative complications in this metaanalysis was assessed as a 'very low' quality of evidence using the GRADE approach. Therefore, confidence remains low due to inconsistency, imprecision, and risk of bias 25 .
Other published literature surrounding bariatric surgery before THA include Parvizi et al., which looked at 20 patients with a mean BMI of 49 kg/m 2 who underwent bariatric surgery followed by total hip or knee joint arthroplasty. The mean BMI decreased to 29 kg/m 2 following bariatric surgery, and for the eight patients who underwent THA, their mean HHS score improved from 40 to 67.5 (p < 0.05) 28 . Although significant, Y H Chee et al. reported the mean increase in HHS following THA in obese individuals who did not undergo bariatric surgery was higher than reported in Parvizi et al.'s published data (see below) 29 . Furthermore, Parvizi reported one incidence of aseptic loosening at five years, requiring revision, which created a complication rate of 12.5% within the study.

Long-term outcomes
Surgeons aim to improve long-term functional mobility and pain when performing THA; therefore, examining such outcomes in obese is essential. In Haverkamp's meta-analysis, post-operative Harris Hip Scores (HHS) were compared, and nonobese patients had a mean difference of 5 points higher than obese patients, a statistically significant mean

Discussion
This literature review sheds light on the implications of obesity on total hip arthroplasties (THA) and its associated complications. The findings consistently demonstrate that obese patients undergoing primary THA for osteoarthritis tend to do so at an earlier age compared to nonobese patients 5,6 . Furthermore, obesity is associated with a significantly higher risk of perioperative complications, including infections, dislocations, and venous thromboembolism [10][11][12][13][14][15][16]23,24 . Regarding infection, many theories exist on why they tend to occur more often in obese individuals. One hypothesis seen in the direct anterior approach (DAA) is a combination of immune dysfunction and proximity of the anterior incision to the inguinal crease and genitalia with overlying abdominal pannus 15 . Other theories suggest an increased risk of infection due to exposure difficulty, increased operation duration, denutrition, and micro-inflammation status 10 .
Further examining dislocation risk, Elkins et al.
performed a biomechanical analysis examining the laterally directed forces during hip adduction owing to thigh-to-thigh contact and how factors under the surgeon's control (head size, neck offset, cup geometry, cup abduction) would affect stability under these conditions. The analysis attributed thigh soft tissue impingement as a mechanism that lowered resistance to dislocation for those with a BMI > 40 kg/m 2 , as increased thigh soft tissue impingement created an increased cup abduction angle and independently increased the risk for impingement 19 . Results suggested that reduced cup abduction, high neck offset, and full-cup coverage would likely reduce the risk of dislocation events, which could be considered for arthroplasty surgeons performing THA on obese patients 19 .
Despite the increased rate of perioperative complication risks in obese individuals undergoing primary THA, the long-term survival of prostheses is similar to nonobese patients 29 . Additionally, the degree of improvement in HHS scores is similar to nonobese patients, although nonobese patients tend to have higher scores pre-and postoperatively 28 . Given these findings, the decision to perform THA on obese patients should not be solely based on BMI, and other factors, such as management of comorbidities, surgical exposure, and nursing care, should be considered when deciding on surgical candidacy.
Providing obese patients counseling regarding their heightened risk of perioperative complications is paramount for a completely informed decision. While some arthroplasty surgeons may continue to advise preoperative weight loss before undergoing total hip arthroplasty, surgeons should acknowledge bariatric surgery before surgery in hopes of sustaining fewer complications has failed to be proven. However, data on this topic remains controversial [25][26][27][28][29][30] . Although controversial, all studies examining bariatric surgery concerning total joint arthroplasty have been retrospective and observational. Further studies with randomization of patients receiving preoperative bariatric surgery before THA with more standardization of study follow-up times could better answer this question.
It is also important to note using a hard cut-off based on a patient's BMI remains controversial among surgeons. While BMI is a commonly used metric to assess obesity, it does not capture the full complexity of an individual's health status. The decision to perform total hip arthroplasty (THA) should involve a thorough evaluation of various factors, including the patient's overall health, comorbidities, surgical risk, and potential benefits of the procedure. By developing more nuanced and personalized criteria for surgical candidacy, surgeons can consider individual patient characteristics outside of their BMI, which may lead to better outcomes for obese patients undergoing THA. However, this highlights the need for  further research to establish evidence-based guidelines and optimize decision-making in the obese population.
Considering the limitations of this literature review, it is important to note that the correlations between obesity and THA complications are primarily derived from retrospective studies and meta-analyses that may contain overlapping datasets. While the repetition of findings does not diminish their strength, it is essential to exercise caution when interpreting these results to avoid potential misrepresentation. Additionally, the study selection process was not conducted systematically, restricting this comprehensive analysis of the current literature to a review. The first author was the only one to complete the review process and interpret study data, potentially creating a selection bias. Furthermore, multiple reviewers did not independently assess the articles, and inter-rater reliability was also not evaluated.
Despite these limitations, the existing body of literature strongly supports increased complication rates in obese patients undergoing THA. This phenomenon is not solely attributable to biomechanical forces but is multifactorial, involving inflammatory and genetic predispositions that warrant further investigation. Continued research efforts are necessary to gain a more comprehensive understanding of the underlying mechanisms and to develop evidencebased interventions to mitigate the risks associated with obesity in the context of THA. By addressing these gaps in knowledge, we can strive for improved outcomes and better patient care in this population.

Funding
No funding was obtained to support this article.

Conflicts of Interest
The authors have no conflicts or competing interests to disclose.

Ethics Approval
Not applicable

Consent for Publication
Not applicable

Availability of Data and Material
All data generated or analyzed during this study are included in this published article (and its supplementary information files).

Authors' Contributions
Ryan Bialaszewski, PA-C, contributed to the literature review article in its entirety, including conceiving the presented idea, performing a literature review, writing the manuscript, and calculating of average relative risks between studies presented in the article. Robert H. Ablove, MD, provided critical feedback and helped shape the research, analysis, and manuscript.