Foot Complications of Obesity

LOUIS J. ARONNE

ANTHONY CASPER

REKHA KUMAR

LEON IGEL

ALPANA SHUKLA

Obesity is recognized as a chronic disease state that affects multiple organ systems, and is closely associated with type 2 diabetes, cardiovascular disease, sleep apnea, and osteoarthritis. The World Health Organization defines a person with a body mass index (BMI) of 30 or more as obese, and a person with a BMI between 25 and 30 as overweight. According to 2009 to 2010 data from the National Health and Nutrition Examination Survey published in 2012, US prevalence of obesity remains high, with greater than one-third of US adults and one-sixth of US children and adolescents affected. In 2008, the annual medical costs associated with obesity in the USA were estimated at $147 billion. Once thought to be a problem solely in affluent countries, overweight and obesity are now on the rise globally in many developing countries.

Increasing BMI has a negative impact on the foot in several areas, ranging from dermatologic complications to orthopedic, vascular, and neurologic conditions as well. Increasing BMI, specifically abdominal fat mass, is strongly associated with foot pain and disability stemming from metabolic complications such as inflammation, as well as mechanical consequences because of increases in pressure, gait alterations, and problems with balance. Although these issues are prevalent in the adult community, as evidenced by the approximate 51% of adults with obesity who reported their foot health as being in fair to poor condition according to the 2012 National Foot Health Assessment, it is now recognized that weight-related disorders of the foot affect the adolescent population as well.¹ A 2009 Dutch national survey of family practices concluded that children aged 2 to 17 years with overweight and obesity reported considerably more ankle and foot complications compared to those with normal weight. The results also revealed that there was no significant difference between the two groups with respect to reported upper extremity issues, which suggests that the increase in fat mass may be directly correlated to the lower extremity complications.²

The goal for patients with overweight or obesity is modest weight reduction, which is known to improve several medical complications of obesity. Producing any change in weight for an individual must begin with a difference in energy expenditure and energy intake. Therefore, to specifically attain weight loss, one must achieve a net negative energy balance where energy expenditure exceeds energy intake. The two major components of creating a negative energy balance are a calorie-restricted diet and physical activity. The activity level of an individual is not only a contributing factor for obesity and diabetes but has also proven to influence cardiovascular health, bone and joint diseases, as well as depression.³ An obvious hindrance to physical activity is lower extremity pain or injury, which can lead to weight gain, thus creating a vicious cycle that leads to increased immobility and further weight gain. The opposite is also true, where primary weight gain from increased caloric intake and the development of an obesogenic environment leads to decreased activity and worsening of the primary complication. The overweight and obese populations are consequently at an increased risk of developing foot complications, leading to the lowering of one’s quality of life.¹,⁴

Dermatologic Obesity Complications

Obesity is associated with a number of dermatologic conditions. Much of the pathophysiology of these dermatologic complications is unknown, but demonstrates strong correlation with elevated weight. Obesity can affect many pathways that disrupt the normal function of the integumentary system such as temperature control, skin barrier function, lymphatic drainage, and wound healing capabilities.⁵ Obesity’s effect on the lymphatic system is demonstrated by the direct relationship seen between the increased weight of a patient and the increased risk of that patient developing lymphedema⁶ in the postoperative setting. In addition, patients with BMI > 50 kg/m² are at risk of developing primary lymphedema. Currently, the mechanism by which obesity increases the incidence of lymphedema is unclear; however, it is believed that the overgrowth of adipose tissue impedes the flow of lymphatic fluid.⁶ The obstruction of flow results in the accumulation of fluid in the lower extremities, beginning with the feet and spreading proximally.⁷ Eventually, this progresses into a chronic inflammatory state.⁷ Weight reduction has exhibited some benefit in relieving the burden of lymphedema, further demonstrating the effect obesity and overall weight gain has on the lower limbs.⁷

Another common dermatologic issue frequently linked to obesity is the development of skin infections. Obesity’s effect on the skin barrier function as well as the lymphatic system has been shown to increase the incidence of skin infections and cellulitis.⁷,⁸ The presence or growth of erythematous plaque, which appears commonly in skin folds and other intertriginous areas, increases the development of abrasions
and results in moisture retention, creating an optimal environment for bacterial and fungal growth.⁷ Obesity is one of the most prevalent factors predisposing individuals to fungal infections of the feet and nails.⁵ The Achilles Project, which was a large-scale assessment conducted across Europe in patients with normal, overweight, and obese BMI classifications, revealed that of patients who conveyed having fungal foot disease, 35.1% reported having at least some discomfort in walking and 17.6% reported experiencing limitations in activities of daily living.⁹ These results demonstrate that fungal foot infections are debilitating to all patients, regardless of BMI. Fungal foot diseases in patients with obesity may be even more debilitating because of a potential impairment of the wound healing function of the integumentary system.⁷,¹⁰ Impaired wound healing is a consequence of an excess accumulation of adipose tissue, which subsequently causes reduced perfusion at the injured site, limiting the delivery of oxygen and essential nutrients.⁷,¹⁰

Lower extremity pressure ulcers have also been observed more frequently in individuals with obesity because of difficulty with mobilization and decreased sensitivity to pressure.⁵ Increased weight also has the ability to produce physical changes to foot shape. These musculoskeletal changes, coupled with decreased pressure sensation, increase exposure to unalleviated pressure.⁵,¹⁰ Particularly damaging in feet, the unalleviated pressure leads to ischemia and tissue necrosis.¹⁰ The main factors leading to the development of pressure ulcers are high amounts of force (typically over bony prominences within the soft tissue), high levels of friction, and prolonged contact, all of which would be amplified in patients with obesity.¹⁰ According to a cross-sectional study on the association of pressure ulcers and BMI classification, participants who were classed as morbidly obese had twice as many pressure ulcer occurrences compared to those with BMIs below 40.¹¹

Orthopedic Complications from Obesity

The burden of extra stress on the foot as a result of obesity impacts the mechanics of activity, such as an individual’s gait. Obesity affects gait in two predominant ways: changes in foot structure (increased thickness of the plantar fat pad) and changes in motor operations (compensatory movements due to lack of muscular strength and power).¹² Excess weight places additional pressure on the foot, which can lead to a variety of biomechanical concerns. A 2012 study showed that there is a correlation between obesity and foot pain, and that those with a higher fat mass were more likely to suffer from foot pain.¹² This correlation remained even after being adjusted for skeletal muscle mass.¹² A possible explanation for this association is that as a patient’s weight increases, the strain placed on muscles and tendons of the foot to function at a basic capacity will also increase, giving patients with overweight and obesity a high likelihood of developing foot disorders like tendonitis. Tendonitis, a condition in which a tendon becomes inflamed and irritated, is an anticipated disorder because of the altered gait patients with obesity experience. This was demonstrated by a separate 2012 study, which determined that patients with obesity are twice as likely to experience tendonitis of the foot compared to those with a normal BMI.¹³ Tendonitis can severely limit function of the inflamed area, and, in this case, would decrease the mobility of the patient with obesity.

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