Obese and overweight patients have a lot to lose: their cartilage, their muscle tone, their quality of life, their limbs. Few patient populations have more to gain from orthotic and prosthetic therapy. But no other group of patients poses a bigger clinical challenge.
by Cary Groner
It’s no longer news that Americans are getting fatter; two-thirds of adults are now overweight, up from 45% in 1960. One-third are obese—defined as a body-mass index (BMI) ≥30—as are 17% of children.1 Such numbers tell only the beginning of the story, however, because all that extra weight affects overall health and has repercussions for orthopedic, orthotic, and prosthetic treatment of the lower extremities.
Obesity is a risk factor for a host of medical problems including diabetes, heart disease, stroke, and osteoarthritis (OA), according to the National Institutes of Health. As a result, it may affect the lower extremities directly—say, via OA of the knees—or indirectly, by increasing the risk of amputation, which occurs in diabetes patients at rates 10 times those of people without diabetes.2
A recent study found that obesity also increases the risk of overuse injuries such as tendinitis, plantar fasciitis, and osteoarthritis.3 This makes sense when you realize that every pound of body weight puts three pounds of force through the foot while walking, and seven pounds when running.
One of that study’s authors, Carol Frey, MD, said that extra weight can even affect injury type.
“When people of normal weight suffer inversion injuries and roll over the side of the foot, they tend to injure their ligaments and have a sprain,” she said. “In an overweight person, the same movement often breaks the fifth metatarsal.”
Metabolic Syndrome Affects Healing
Frey, director of foot and ankle surgery and an assistant clinical professor at UCLA, as well as the fellowship director of the West Coast Sports Medicine Foundation in Manhattan Beach, CA, said the situation is more complicated than simple biomechanics, however. Even in nondiabetic people, obesity is associated with a metabolic syndrome that can slow the healing process—which means heavier patients might need to log considerably more time in an orthotic device than their lighter counterparts would before seeing a positive effect.
“The syndrome has to do with fat percentage, because fat produces an estrogen-like hormone and also interferes with insulin production, which in turn affects healing,” she said.
Weight and pathology
Regardless of these complex metabolic effects, scientists have found a few straightforward correlations between obesity and lower extremity pathology. For example, one study reported that severe obesity affected the foot mechanics of adult women.4 Another found that obesity and pronated foot posture were associated with chronic heel pain.5
Similarly, researchers concluded that reduced ankle dorsiflexion and obesity were independent risk factors for plantar fasciitis,6 and one paper reported that patients with posterior tibial tendon dysfunction often had such comorbidities as obesity, hypertension, and diabetes.7
Finally, scientists in Germany found a possible correlation between childhood obesity and foot development. They also speculated that the pain associated with the resulting abnormal morphology may lead to decreased activity levels, creating a vicious cycle of inactivity and obesity.8
Children and clinical choices
The extent to which obesity affects children and adolescents in developed nations is one of the biggest shockers in the literature. The correlation with diabetes is stark; in those age 10–19 years, type 2 diabetes now accounts for about a third of all new diabetes cases, and in some ethnic groups (e.g., Asian/Pacific Islanders and Native Americans) its incidence is significantly higher than type 1 diabetes.1
Such considerations affect the decisions practitioners make regarding treatment with O&P devices, as well as their outcomes. Robert Lin, CPO, said that children constitute roughly 60% of his practice, and that weight and diabetes status are often a factor.
“Clinical obesity has different implications for children,” said Lin, who is the chief orthotist for Hanger Orthopedic Group at Connecticut Children’s Medical Center and an associate clinical instructor at the University of Connecticut. “Children don’t have years of wear and tear on the joints. But if the patient has diabetes, you have to think carefully about the viscoelastic properties of the materials you use, because diabetes increases the risk of ulceration. When I’m making a thermoplastic ankle-foot orthosis [AFO] for those patients, I line the interior of the plantar surface with a diabetic-sensitive viscoelastic material.”
High-temperature polymers such as polypropylene remain Lin’s first choice of orthotic materials for obese patients.
“Some people think you need to go with carbon fiber or metal and leather, but that’s not really true if you use the appropriate design, corrugations, and reinforcements with the polypropylene,” he said.
One factor that can affect therapeutic decisions is plain old youthful metabolism. Obese children typically respond much more dramatically to weight-loss programs than older adults do, which offers both hope and challenges. If an overweight 14-year-old drops 40 pounds in six months, he may get healthier, but he may also need a new orthosis—or none at all.
Lin sees differences in the type of injury suffered by adults and pediatric patients, as well.
“In adults, I tend to see more degenerative issues, insidious intra-articular pain,” he explained. “In children, problems express more acutely. Their knee may be tender, so they have a workup and you find that things are structurally sound but there is additional strain due to their weight.”
Ironically, such strains caused by obesity are often similar to the overuse syndromes common to adolescent athletes. Lin noted that many kids play sports year round now, so their bodies never get a chance to rest and heal. It may be better than obesity from the perspective of general health, but knee pain is knee pain, and clinicians have to address it whether it’s due to too much soccer or too many orders of fries.
Lin believes that practitioners need to pay more attention to results.
“People think you need million-dollar computerized gait analysis tools to look at outcomes, but it isn’t true,” he said. “We can look at performance outcomes—does this AFO affect your vertical leap, your forty-yard dash?—and we can also evaluate physiologic cost index.”
PCI is a simple way to assess walking efficiency. The patient walks, and the clinician measures the patient’s pulse over certain cadences, velocities, and distances. Then they repeats the exercise with the patient wearing the AFO.
“You hope that you’ve improved the efficiency of the gait with the AFO,” Lin said. “I teach my students that tools like this are available to them on a daily basis.”
Some studies suggest that certain devices don’t work as well in obese patients. In patients with unicompartmental knee OA, researchers found that braces were least effective in obese patients.10,11
The coauthor of one of those studies, Douglas Dennis, MD, is president and executive director of the Rocky Mountain Musculoskeletal Research Laboratory in Denver and an adjunct professor in the Department of Biomedical Engineering at the University of Tennessee.
“In patients with the common pattern—deterioration of the medial compartment—an offloading brace can move the knee out of a bowlegged or varus position into a more valgus one, but you have to be able to transmit the brace’s force down to the bone,” Dennis said. “If the femur is surrounded by too much muscle and fat, as it is in obese patients, the forces are dissipated and the brace can’t transmit enough load to change the alignment.”
In other cases, particularly with AFOs, some clinicians believe little or no adaptation is needed to make the orthosis suitable for the overweight.
“The forces going through the foot, ankle, and lower leg are not as dependent on body mass as they are on the deformity itself,” said Doug Richie, DPM. “It’s not that you shouldn’t take body weight into account, but it isn’t directly proportional to the stresses transmitted through a foot orthosis.”
Richie, in private practice in Seal Beach, CA, is the inventor of the Richie Brace as well as an adjunct associate professor of applied biomechanics at the California School of Podiatric Medicine (CSPM) at Samuel Merritt College in Oakland.
When a walking person puts three times their weight through their foot as they step, it’s called the ground reaction force, Richie explained. Such forces are important and related to pathology; however, torques on joints—or joint moments—are a bigger concern.
“Joint moments depend on the patient’s velocity, direction, and the muscular force they generate in the lower extremity,” Richie said. “A healthier patient, who walks faster and with stronger muscular contractions, gets higher joint moments than an obese patient shuffling along more slowly.”
As a result, Richie said, his fabricators don’t make significant adjustments for body weight unless a practitioner specifically asks for them.
“We look at the foot deformity and modify the prescription accordingly, whether we add extra correction in the cast or the phalanges, but it doesn’t have that much to do with the patient’s weight,” he said. “We have fabricated and dispensed braces to thousands of patients, and we are confident that weight or height do not directly affect the quality of our outcomes. No objective standard justifies modification of AFO braces based upon weight.”
Others disagree in certain cases, however. According to Paul Scherer, DPM, distinct lower extremity pathologies require a range of flexibility in the orthoses or braces designed to address them, and patient weight is a consideration. Scherer, founder of ProLab Orthotics in Napa, CA, is also immediate past chair of the department of applied biomechanics at CSPM. “Flexibility is determined by the weight of the patient in relation to the thickness of the material,” he said. “When patients put weight on materials such as polypropylene, they become more flexible.” Scherer explained that a foot orthosis made of 3mm polypropylene would be rigid in a 120-pound female but extremely flexible in a 220-pound man.
“If you want to control a foot with plantar fasciitis, for example, you need a relatively rigid device to prevent metatarsal joint motion, and it’s the same with AFOs and dorsiflexion-assist devices,” Scherer said. At least one of ProLab’s AFOs is specially designed for patients who weigh more than 200 pounds, and the company’s custom order form contains a chart of rigidity guidelines for both vacuum-formed and directed-milled polypropylene shells. A 4 mm direct-milled shell, for example, is listed as “very rigid” for a patient <100 pounds, “rigid” for someone 100 to 150 pounds, “semirigid” for those 151 to 200 pounds, “flexible” for a 201- to 250-pound patient, and “very flexible” for anyone heavier than 250 pounds. The clinician must determine which level of flexibility is appropriate for a given patient and pathology, of course, but the message is clear. Psychological issues
Active people of any age, overweight or not, typically become frustrated when an injury prevents them from working out, according to Lin. This leads to the kind of debilitating cycle described earlier, where disability leads to weight gain, which exacerbates the condition that caused the disability in the first place.
“The caloric intake doesn’t change, they start getting bigger, they get frustrated, and sometimes they get depressed,” Lin said. “So they eat. It’s a common cycle.”
Clinicians should pay close attention to the psychological aspect of such syndromes, according to M. Jason Highsmith, DPT, CP. Highsmith is an assistant professor of physical therapy and rehabilitation at the University of South Florida in Tampa.
“People want to have a good body image, but often it’s a circular problem, because you’re less likely to go to a gym, or even go walk at the mall, if you don’t have that,” Highsmith said. “Then activity declines and problems increase.”
Highsmith notes, however, that studies show many highly active people aren’t that different in their daily habits than the sedentary, once you remove the factor of their workouts. This could help explain the bizarre phenomenon of people vying for parking places close to the front door of the gym, so they can walk as short a distance as possible before they go inside and get on the treadmill.
Prostheses have to adapt
Highsmith has found that prostheses for obese amputees need to be built of strong materials such as graphite and carbon fiber. To assess the appropriate choice for a given patient, he considers the potential for both “cycles to failure” and threshold of “ultimate failure.” The former describes how many times a device can sustain a lower peak load before it fails, whereas the latter refers to the maximum force it can take. Cycles to failure is often a concern in highly active patients, while ultimate failure pertains more to the obese.
“We have to consider high activity and heavy duty as two separate camps, though there is overlap,” Highsmith said. “In terms of the material makeup of an artificial limb, you may need to make it thicker, bigger, stronger, or more strategically engineered so it doesn’t fail either ultimately or under high cyclic loading.”
In either case, Highsmith added, patients who exceed the mass or activity levels recommended by manufacturers may require custom components.
Nevertheless, prosthetists are much better at building components for heavy patients than they were a decade ago, according to Kevin Carroll, MS, CP, who is vice president of prosthetics for Hanger in Bethesda, MD.
“There is a lot you can do, even for someone who weighs five hundred pounds,” Carroll said. “With a very heavy person, there’s a lot of force going onto a small area of skin where it meets the prosthetic device. There are numerous types of gel liner, some with a little stiffer durometer, that will help prevent skin breakdown. But it’s important to see these individuals regularly so you can continually evaluate the materials.”
Prosthetists face an additional challenge because daily limb volume changes significantly in amputees, due to the loss of the skeletal muscle in the amputated extremity that would normally help regulate the pumping of fluid back toward the heart. Conditions such as obesity and cardiovascular disease compound the problem.
“We have seen people with as much volume fluctuation as 20 plies of socks in a day,” Highsmith said. In other words, the residual limb may lose roughly 4 cm in circumference between morning and evening, and the amputee may need 20 layers of socks to maintain an adequate fit.
In such cases, atmospheric suspension (suction) designs won’t work, and the practitioner must rely on pin or lanyard-strap models. It also means that if a patient loses weight, they may need a new socket sooner than their insurance will pay for it. In such cases, Highsmith said, prosthetists can make a new flexible interface for the existing socket, change the liner size, or employ other tricks to help the patient get through until reimbursement is available.
“It’s very important that you never let a socket-fitting headache be the reason that the patient doesn’t lose weight,” Highsmith emphasized. “In addition to the health benefits, they may become suitable for standard catalog products, so the cost drops because they no longer need custom components. There are psychological, health, and fiscal benefits to the person losing weight.”
At the end of the day, practitioners should become involved in helping patients manage weight, Frey said.
“A lot of them don’t want to get into counseling about diet, but it’s important and we need to give basic recommendations,” she explained. “And patients who are morbidly overweight should be referred to an obesity specialist.”
Quality of life initiatives for obese patients are important, Richie added.
“We are trying to get them more active, rehabbed, and reduce pain so that obesity can be minimized,” he said. “We want to improve their lives, and that should be the ultimate bracing strategy.”
Cary Groner is a freelance writer based in Northern California
1. NIH. Statistics related to overweight and obesity, Accessed at: http://www.win.niddk.nih.gov/STATISTICS/.
2. AAOP. O&P trends and statistics. Accessed at: http://www.opcareers.org/assets/pdf/TrendsFINAL.pdf
3. Frey C, Zamora, J. The effects of obesity on orthopaedic foot and ankle pathology. Foot Ankle Int 2007;28(9):996–999.
4. Messier SP, Davies AB, Moore DT, et al. Severe obesity: effects on foot mechanics during walking. Foot Ankle Int 1994;15(1):29–34.
5. Irving DB, Cook JL, Young MA, Menz HB. Obesity and pronated foot type may increase the risk of chronic plantar heel pain: a matched case-control study. BMC Musculoskelet Disord 2007;8:41.
6. Riddle DL, Pulisic M, Pidcoe P, Johnson RE. Risk factors for plantar fasciitis: a matched case-control study. J Bone Joint Surg Am 2003;85(5):872-877.
7. Lake C, Trexler G, Barringer, W. Posterior tibial tendon dysfunction: a review of pain and activity levels of twenty-one patients. JPO 1999;11(1):2-5.
8. Mauch M, Grau S, Krauss I, et al. Foot morphology of normal, underweight, and overweight children. Int J Obes 2008;32(7):1068–1075.
9. Haboubi NH, Heelis M, Woodruff R, Al-Khawaja I. The effect of body weight and age on frequency of repairs in lower-limb prostheses. J Rehab Res Devel 2001;38(4):375–377.
10. Dennis DA, Komistek RD, Nadaud MC, Mahfouz M. Evaluation of off-loading braces for treatment of unicompartmental knee arthrosis. J Arthroplasty 2006;21(4 Suppl 1):2–8.
11. Komistek RD, Dennis DA, Northcut EJ, et al. An in vivo analysis of the effectiveness of the osteoarthritic knee brace during heel-strike of gait. J Arthroplasty 1999;14(6):738–742.