Attention is increasingly being drawn to risk factors that may affect patient outcomes in orthopaedic surgery. Frequently, modifiable risk factors such as smoking, alcohol use, and obesity are discussed and modified prior to elective orthopaedic surgery. Obesity is a recognized medical condition which is increasing in both the adult and child population. The prevalence of obesity has doubled in adults in the past 20 years, with 35 percent of the U.S. population with a body mass index greater than 30. However, recent findings indicate that obesity may not be as modifiable as other risk factors.

Social, behavioral, and biological determinants
Obesity is determined by social, behavioral, and genetic variables. A biologic predisposition to obesity may manifest itself through behavioral phenotypes. Environmental factors should be considered with respect to biologic factors, as should genetics. Obesity is a complicated disease process that involves metabolism, energy expenditure, energy balance, and neurobehavioral pathways involving the hypothalamic pathways.
Twin studies reveal the genetic makeup of an individual influences intake of nutrients as well as size and frequency of meals and intake of particular foods. It has been shown that 40 percent of the variance in resting metabolic rate, thermic effects of food, and energy cost of low-to-moderate intensity exercise may be explained by inherited characteristics. Obesity-related genes, which have been identified, contribute to phenotypes found in obese individuals. For example, Prader-Willi Syndrome and Bardet-Biedl Syndrome are both characterized by structural abnormalities, mental retardation, and obesity.

The state of obesity becomes an interaction between genes and the environment. It is a daunting task for an orthopaedic surgeon to simply tell someone to lose weight if genetics play a significant part.

Implications for genetic influence include predicting an individual's risk at a young age and then introducing strategies to prevent weight gain and the potential associated health conditions, such as diabetes, hypertension, heart disease, and arthritis. Other recognized pediatric orthopaedic conditions associated with obesity include slipped capital femoral epiphysis and Blount's disease. Biology and the genetic influence of DNA should be considered as key determinants of obesity in a preoperative orthopaedic patient. Behavioral phenotypes which result—influenced by biologic predispositions—manifest as excess caloric intake, sedentary behavior, and increased weight and obesity.

AAOS Position Statement on Obesity: A patient safety issue
Orthopaedic surgeons have publically recognized the risk of performing surgery on obese patients. The AAOS adopted a position statement on obesity as a patient safety issue. The notion that obesity affects bone and joint health has far-reaching consequences.  The position statement, "The Impact of Obesity on Bone and Joint Health," was developed by a Communications Cabinet workgroup formed after the AAOS Now Forum on "Obesity, Orthopaedics, and Outcomes." It states the following:

"The AAOS believes that orthopaedic surgeons and patients should maintain an open dialogue about the detrimental effects of obesity on musculoskeletal health, and the increased risks of obesity on orthopaedic pre- and postsurgical complications and inferior outcomes. In particular: Patients with obesity have a high incidence of altered nutritional status, and poor nutrition may contribute to comorbidities such as diabetes, in which blood sugar should be brought to reasonable levels to reduce risk."

Adult implications are numerous: Obesity affects elective surgeries such as total joint replacement by elevating the risks of wound infection, increased pain, and decreased mobility. Orthopaedic surgeons recognize preoperative medical maximization is imperative for successful surgery, appropriate clinical decision making, and healthcare delivery.  The position statement calls for orthopaedic surgeons to become engaged with patient behavior by encouraging increased activity and nutritional choices. Armed with knowledge of the influence of genetics and energy balance status, orthopaedic surgeons can realistically offer strategies to patients for successful weight loss prior to elective orthopaedic surgery.

Moral and ethical considerations
There is a recognized association between obesity and osteoarthritis in patients who seek consultation for joint replacement surgery. Opinion varies with respect to total joint replacement in the obese individual. One study reported 55 percent of patients who presented at a tertiary hospital were obese.

Despite the known comorbidities and risk of increased infection after total joint replacement, many researchers still support total joint replacement in the obese individual, as the implant survival remains high. According to one author, obesity itself is not a reason to deny a total joint replacement. With the prevalence of obesity increasing, obese patients will have increased needs for total hip and knee replacements.

As an important issue in orthopaedics, obesity was given moral and ethical consideration by Clint Wooten, MD, and Brian Curtin, MD, in a 2016 journal editorial, "Morbid Obesity and Total Joint Replacement: Is it Okay to Say 'No?'" Included in this editorial were the principles of non-maleficence, autonomy, beneficence, and justice. The orthopaedic surgeon, note the authors, should treat the whole patient, and has a duty to optimize modifiable risk factors especially when the risk of the surgery outweighs the benefit, and to say "no" if that is the correct answer.

The editorial concluded that obese patients must also be supplied with the resources to optimize their condition prior to surgical intervention. However, within this editorial, obesity was a presumed modifiable factor. This editorial did not address the nonmodifiable genetic predisposition of obesity, and consideration was not given to those who may be genetically predisposed.

Conclusion
Treatment of obesity as a neurobehavioral issue will benefit the orthopaedic surgeon's decision making and the preoperative preparation process. Advancements in neurobehavioral research, in addition to new discoveries in the crosstalk between bone and cartilage, may lead to novel answers on how best to prevent conditions such as arthritis in obese patients. Obesity, as an epidemic, is frequently seen in patients seeking orthopaedic care. The challenge for the orthopaedic surgeon is to be equipped to educate, encourage, and provide resources and treatment appropriate to the individual.

Laura M. Bruse, MD, chairs the AAOS Women's Health Issues Advisory Board. She can be reached at laura.bruse.md@gmail.com

References:

1. Tingle, Casey. Orthopaedics today August 2015 page 9 (MacDonald SJ Paper #32 Presented at Current Concepts in Joint Replacement Annual Spring Meeting; May 17-20, 2015; Las Vegas}
2. Philos Trans R Soc Lond B Biol 2006 Jul 29; 361(1471): 1095–1105.Published online 2006 Jun 15. doi: 10.1098/rstb.2006.1850 PMCID: PMC1642700 2006 Jul 29; 361(1471): 1095–1105. Published online 2006 Jun 15. doi: 10.1098/rstb.2006.1850. PMCID: PMC1642700 Genetics of obesity Stephen O'Rahilly and I.Sadaf Farooqi*
3. The AAOS Now Forum on "Obesity, Orthopaedics, and Outcomes." NOW March 2015
4. (Welton, KL, et al Orthopaedics. 2016; doi 10.3928/01477447-20151222-12)
5. "Morbid Obesity and Total Joint Replacement Is it Okay to Say No? "By Clint Wooten, MD and Brian Curtin, MD in The Blue Journal Orthopaedics Volume