In this study we surveyed California orthopaedic surgeons who regularly perform THA and/or TKA about BMI cutoffs for these procedures. This preliminary survey was only circulated among members of the California Orthopaedics Association, so surgeons practicing THA and TKA in California that were not part of this organization may not be properly represented. Additionally, these responses may not represent the policies and decision making of surgeons outside of California. The survey received a small number of responses compared to the number of orthopaedic surgeons in California. However, the COA website lists 295 “total joint” surgeons in their member directory, leading us to believe our 32 responses is a large enough proportion of relevant surgeons (> 10%) to glean important information regarding BMI cutoffs for these surgeries. Through their responses, we were able to assess the prevalence and specific cutoff numbers for these procedures. We also identified four categories for BMI cutoff justifications including (1) increased risk of complications, (2) logistics for performing surgeries, (3) concerns about facilities or resources, and (4) surgeon perception.

Our resulting average values (BMI cutoffs of 40.5 and 41 for THA and TKA, respectively) are in line with another survey distributed nationally to the American Association of Hip and Knee Surgeons Research Committee members, though the western/Pacific northwest portion of their respondents had a markedly lower BMI cutoff than present in our data [19]. The Western/Pacific northwestern portion makes up just 13% of their total study population, so their aggregated findings may not represent Californian surgeons.

Justifications for denying a THA or TKA due to a high BMI pertaining to surgery-related complications represent possible areas for future research (Fig. 5A). Medical complications can arise during surgery, perioperatively, and post-operatively with varying levels of severity. Database studies frequently compare the rate of complications as a function of BMI category (underweight, normal weight, overweight, and the obesity classes). Complications that correlate with increased BMI can include cardio-respiratory issues, infection, and the need for revisions [21]. Surgery-related issues can lead to longer hospital stays and increased resource utilization and cost of care [22, 23], but not in all cases [23, 24]. Additionally, the literature currently has no consensus on the prevalence of these issues after THA and TKA in different BMI categories. Certain clotting conditions, such as pulmonary embolism, exhibit a higher likelihood in individuals with elevated BMI, whereas others, like deep vein thrombosis, remain unaffected by variations in patient weight [25]. Readmission and infections, including surgical site infections and perioperative joint infections, are one of the most identified risks of high BMI individuals [23, 26,27,28,29], though the correlation of BMI and infection risk is not clear for all surgeons or operations [30]. There is also no consensus as to the impact of BMI on THA and TKA on overall functional outcomes [23, 31,32,33]. The pro-inflammatory state in an high BMI patient puts them at a higher risk of Perioperative cardiac and respiratory complications [34]. Due to the metabolic syndrome seen in bariatric patients, there is an increased risk of cardiac morbidity and mortality, in general, but this has not been defined in the joint arthroplasty population due to the extremely low mortality rates. Similarly, respiratory challenges in high BMI patients during and after surgery include hypoxia, need for higher positive end-expiratory pressure (PEEP), higher incidence of obstructive sleep apnea (OSA) and higher risk of intensive care unit (ICU) admissions [35]. There is some evidence to suggest that operative times are also increased in patients with higher BMI [21, 36].

Orthopaedic research may be able to close several knowledge gaps that prevent safe surgeries on high BMI individuals including infection rate, blood clot/DVT risk, and adverse effects of anesthetics. Understanding the mechanisms that increase these issues in people with higher body weight, whether biological or procedure based, will help advance translational research that benefits patients of all sizes. As the average BMI of Americans increases, new research should be conducted to apply treatments of past studies to larger body sizes. Future medical studies and clinical trials should include a range of BMIs to reflect the impact of these treatments on a representative sample of patients that represent all patient populations.

Perceived difficulty of surgery, increased length of surgery, and adverse effects of anesthetics on high BMI patients may be addressable by increased and specific training on caring for patients with larger body sizes (Fig. 5B) [34]. With practice, surgery difficulty and length can be reduced, and anesthesia application can be improved. Additionally, the negative correlation between years of experience and percentage of surgeons implementing BMI cutoffs for joint arthroplasty could represent a variety of training-related issues. These concerns could indicate that medical schools and residency programs are not adequately preparing trainees for operating on high BMI individuals, requiring years of post-graduation and post-residency experience to adequately serve these patients. This is consistent with research about bias in medical schools and those training in healthcare fields [37]. Additionally, it is a possibility that the more experienced surgeons can handle the complexities of the surgery better than their younger counterparts or that they are just not aware of the AAOS guidelines (or chose to ignore them because of lived experience).

Hospitalization time, lack of proper equipment, and rehabilitation/physical training availability were less influential on a surgeon’s chosen BMI cutoff (Fig. 5C). However, these factors are still a systemic concern for hospitals around the US [38,39,40]. Developing a system to share equipment between orthopaedic surgery and bariatric surgery centers could help address any concerns related to access to appropriate facilities and equipment.

In some cases, surgeons being unable or unwilling to operate on higher BMI individuals may be influenced by implicit or explicit anti-fat bias. Concerns about lifestyle and assumed non-compliance after surgery indicate an unspoken moral standard has been applied to high BMI patients (Fig. 5D). These prejudices heavily impact patient wellbeing beyond denial of care [41,42,43,44]. Patients that experience weight stigma have worse outcomes and morbidities compared to high BMI patients that have not experienced this stigma [44]. Increased body size may add difficulty or length to surgery, but these concerns would likely be mitigated with proper training and resources. Length of surgery as a justification to avoid high BMI joint arthroplasty patients may also reflect anti-fat bias. A metadata analysis of over 5 million patients found that mean surgery times were increased for high BMI patients by just 6 min for all surgeries (from 83 to 89 min) and 7 min for orthopaedic surgeries (from 76 to 83 min) [21]. THA and TKA surgeries carry a much shorter operation time than other elective orthopaedic procedures, and length of surgery can be impacted by many factors beyond weight, including inter-surgeon variability, available support staff, and even day of the week [45,46,47]. Inadequate training, education, and facilities, as well as provider bias, all impact the ability of high BMI individuals to receive life-changing healthcare. This is a growing issue in many medical fields. As the population weight increases, so will the medical costs associated with delayed or avoided medical care. A scarcity of orthopaedic surgeons that are able and willing to perform surgeries on larger individuals will increase these issues unless policies and medical training are modified to be more accommodating of high BMI patients.

There is currently no consensus about the impact of BMI on implant failure based on implant survival and surgery outcomes [10, 31, 48,49,50,51]. Studies have found that there is no difference in knee prosthesis failures or outcomes regarding BMI or total body weight [10, 50, 51]. Others suggests that high BMI demonstrate increased infection rates in THA and TKA, and that reduced outcomes may be due to higher BMI at younger ages [52, 53]. Research has demonstrated increased dislocations of hip arthroplasty related to BMI [48, 49], but that mechanical failure and aseptic loosening were not correlated with BMI [49]. Several implant manufacturers include high BMI as a contradiction for the use of their products, though some researchers have shown that the forces on an implant reduce with height more so than weight, so BMI based cutoffs may be unjustified with respect to implant failure [31]. Despite these conflicting studies, the majority acknowledge that joint arthroplasty surgeries still provide a vast improvement to the quality of life of high BMI patients. THA and TKA surgeries carry extremely high success and satisfaction rates compared to other elective surgeries, so while many factors go into a surgeon’s decision about whether to operate on a patient, concerns about implant failure should not be primary factor affecting this decision.

We found that less than 1 out of 4 California orthopaedic surgeons considered the national American Association of Orthopaedic Surgeons (AAOS) guidelines as a key factor for their BMI cutoff selection. Current AAOS guidelines cite reduced clinical outcomes for individuals with high BMI based on “strong evidence”. However, a review of the few provided publications cited on the AAOS OrthoGuildelines website at the time of publication [54, 55] demonstrated conflicting evidence. BMI/Obesity received their highest risk factor recommendation of “Strong Recommendation” for TKA based on the articles cited on these pages. However, several of these publications stated that outcomes are not correlated with BMI [10, 50, 54,55,56]. For example, Judge et al. determined that there were no reduced outcomes in higher BMI individuals, and that BMI should not be an access to care barrier given the benefits of TKA [50, 51]. The main risk factors listed for high BMI individuals were wound complications, such as surgical site infections, and reduced functional outcomes. However, outcomes such as Knee Society scored were still higher for high BMI patients post-TKA than their pre-clinical range and function scores [11], demonstrating that this surgery still provided an improvement in function for these individuals. The AAOS and similar professional organizations should consider revisiting their BMI cutoff guidelines and justifications to better mirror current understandings in the field, such as those cited by this study, which some Californian surgeons are currently using to inform their own BMI cutoffs.