March 2016

The importance of obesity in foot pain management

3footObesity-shutterstock_76797145Increasing numbers of studies suggest that a high body mass index can significantly affect foot structure and function, increasing the risk of painful conditions. But questions remain as to how foot health specialists can best address foot pain in their obese and overweight patients.

By Barbara Boughton

Many scientific studies have documented the link between body mass index (BMI) and foot pain, and research has now shown conclusively that being overweight also increases the risk of abnormal plantar pressures, foot function, and foot structure. Obese individuals (defined by the World Health Organization as having a BMI of 30 kg/m2 or higher) and overweight individuals (BMI between 25 and 29 kg/m2) also are more likely than their normal-weight counterparts to develop foot complications such as osteoarthritis, tendinitis, and plantar fasciitis, which can be disabling enough to compromise quality of life.

Yet, how these findings translate to the clinical management of overweight and obese patients with foot pain is still not entirely clear. Although some studies have documented that losing weight by calorie restriction or bariatric surgery may reduce plantar pressures on the foot, no research has shown conclusively that either of these solutions significantly reduces foot pain or the risk of abnormal foot conditions.

Still, foot specialists and researchers interviewed by LER said they make adaptations in clinical practice for overweight and obese individuals to maximize treatment efficacy and safeguard patient health.

Obesity is strongly associated with low-arched foot posture, dynamic pronation, and increased plantar pressures during gait; all of these can contribute to foot pain.

The increased plantar pressures seen in overweight and obese patients, as well as their decreased tolerance for high-impact exercise, may change a clinician’s prescription for foot orthoses, exercise, and even recovery after surgery, for instance. Foot specialists may be more likely to prescribe nonaerobic exercise and stiffer and thicker orthotic devices for a patient with a high BMI. After foot surgery, specialists are also less likely to utilize early weightbearing during recovery in heavier patients.

“There’s only so much weight a foot can take before overuse sets in—affecting the muscles, ligaments, and bones,” said Alex Kor, DPM, clinical associate at Johns Hopkins Bayview Medical Center in Baltimore, MD. “Yet, it’s not the only factor to consider in treating a foot condition. The structure of the foot, the shoes worn by the patients, and activity level are all important contributors to foot pain.”

Kor prescribes exercise and proper shoe wear for all his patients with foot pain and foot disorders, no matter their weight, and sometimes orthotic devices, as well.

“While I’ll prescribe exercise for all my patients with foot conditions, there are some patients—including those with high BMI and diabetes—for whom running, jumping, or even walking long distances is inappropriate,” he added.

Experts say it’s crucial for all clinicians—not just foot specialists—to be aware of the increased potential for foot pain and foot damage in overweight and obese individuals of all ages. Clinicians should also use strategies to prevent the development or progression of foot pain in overweight and obese patients, since foot pain and damage in these patients tends to increase over time, said Catherine Bowen, PhD, a researcher, podiatrist, and associate professor in the faculty of Health Sciences at the University of Southampton in the UK.

“Treating foot joint pain early in high BMI patients could possibly prevent longer-term loss of mobility,” she said.

The evidence

Recent systematic reviews have found that obesity is strongly associated with low-arched foot posture, pronated dynamic foot function, and increased plantar pressures when walking—all of which can contribute to foot pain.1-2 High BMI causes increased loading on the foot during standing and walking, which in turn puts additional stresses on the soft tissues that support the joints within the foot, Bowen said.

“Over time these stresses cause the joints of the feet to collapse when the soft tissues are no longer able to support the foot joints. As the joints collapse, the joint capsules swell—causing pain and eventual remodeling of pain and cartilage,” she said.

In a study published in Arthritis Care & Research in December 2014, Bowen and colleagues reviewed data regarding foot joint pain over a five-year period in 639 middle-aged women, who were part of a community cohort for the Chingford Women’s Study.3 Both BMI and foot joint pain increased significantly from year 10 to year 15 of the 20-year study, and BMI at year 10 was significantly associated with incidence of foot joint pain five years later (odds of foot pain increased by 5% for each BMI unit). This association was independent of age, diabetes mellitus, and rheumatoid arthritis.

“The fact that foot joint pain was independent of age was a surprising finding to us,” Bowen said. ”We did expect that women would have more foot joint pain as they aged, but our findings imply that foot health should be considered and monitored in patients with high BMI at any age.”

Another large epidemiological study also found that foot pain was significantly increased in overweight (BMI 25-30 kg/m2) and obese (BMI greater than 30 kg/m2) patients older than 60 years, and these patients were also more likely than normal-weight individuals to exhibit diminished foot strength, stride length, and walking speed.4 High BMI was associated with disabling foot pain and alterations in foot function that negatively affected patients’ quality of life, according to Karen Mickle, PhD, research fellow at the College of Sport and Exercise Science at Victoria University in Footscray, Australia.

In the study, 312 Australian men and women aged between 60 and 90 years completed a questionnaire that assessed foot pain, as well the 36-item Short Form Health Survey (SF-36). The researchers assessed musculoskeletal foot structure using a 3D foot scanner, and soft tissue thickness at the heel, midfoot, and first and fifth metatarsal heads using ultrasound. They recorded maximum isometric dorsiflexion strength, hallux strength, and lesser toe flexor strength using pressure platforms. They also assessed ankle dorsiflexion flexibility with a modified lunge test, and gait while the patients walked at a comfortable pace.

Foot muscle strengthening exercises may reduce foot pain in overweight and obese patients, and may decrease the risk of falling in individuals who are also elderly.

Obese participants had a significantly higher prevalence of disabling foot pain (40%) than overweight patients (23.4%) or normal-weight participants (11.4%). Obese and overweight patients also had greater disability as measured by the SF-36. Compared with normal-weight subjects, obese participants had greater tissue thickness at all sites except the first metatarsal head, and overweight patients had thicker soft tissue and fat pads at the fifth metatarsal head and at the heels. Obese patients also had significantly reduced flexor strength of the hallux and lesser toes compared with overweight and normal-weight participants. As well as having shorter stride length and reduced walking speed, the obese patients spent more time in stance and double support phases and less time in swing phase than their leaner counterparts. They also generated greater plantar pressures across the foot when walking.

Foot strength as a factor

“High plantar pressures in overweight and obese people have been reported in both children and younger adults, so this study confirmed that altered foot loading patterns are also seen in obese older adults,” Mickle told LER Foot Health. “The foot muscle weakness we reported was a novel finding—and may contribute to altered loading patterns during walking.”

The observed gait alterations also suggest that the participants’ ability to perform activities of daily living was inhibited by their excess mass and confounded by the presence of foot pain, Mickle and colleagues wrote in the paper.

The high prevalence of disabling foot pain in obese patients most likely contributed to reduced function and quality of life, Mickle noted. The decreased muscle strength combined with the increased plantar pressures in obese patients were probably the most important contributors to excess foot strain and foot pain, the researchers concluded.

Foot muscle strengthening exercises may reduce foot pain in overweight and obese patients, and may decrease fall risk in those who are also elderly, according to Mickle and other researchers.

Focused exercises that build strength in the forefoot benefit both overweight and obese patients, but walking and other weightbearing exercises have even more advantages—helping to strengthen the muscle groups that affect ankle and hindfoot motion and function, according to Bowen.

For overweight and obese patients with decreased foot muscle strength, Kor advises specific exercises that target the foot’s intrinsic muscles, including the abductor hallucis, flexor hallucis brevis, and flexor digitorum, he said. Physical and aquatic therapy can also be effective for strengthening the muscles of the feet in overweight and obese patients, he added.

What about weight loss?

Large epidemiological and review studies contribute to our understanding of the increased prevalence of foot pain, and suggest the benefits of muscle strengthening exercise for obese and overweight patients. Yet, these studies have other clinical implications.

“From many biomechanical studies, we know that three to six times body weight is transmitted through the foot with normal cadence and gait,” said Zachary Vaupel, MD, assistant professor of orthopedic surgery at Oakland University William Beaumont School of Medicine in Royal Oak, MI. “So I tell my patients that just by losing five pounds, they will potentially be transmitting thirty pounds less through the foot and ankle.”

Researchers and clinicians like Vaupel acknowledge that the medical literature has yet to prove the benefits of weight loss for obese patients with foot pain.

“In the peer-reviewed literature, weight loss has not been consistently linked with a reduction in foot pain, although research studies do show that it reduces back and knee pain,” said Todd Davenport, PT, DPT, MPH, OCS, an associate professor in the Department of Physical Therapy at the University of the Pacific in Stockton, CA.

A systematic review published in Obesity Reviews in 2012,2 for instance, concluded that greater BMI was strongly associated with increased risk of chronic plantar heel pain. Yet there was only limited and weak evidence showing that weight loss resulted in any improvements or changes in plantar heel pain.

Still, Davenport and other physical therapy experts felt strongly enough about the benefits of weight loss for obese patients to include it as a treatment recommendation for heel pain in the 2014 American Physical Therapy Association guidelines.5

The guidelines suggest clinicians should educate and counsel obese patients with heel pain to use low-impact exercise strategies that can maintain optimal lean body mass. The guidelines also note that obese individuals with heel pain should be referred for nutritional counseling. Davenport, however, noted that weight loss and exercise recommendations also need to take into account individual patient’s body structure, foot diagnoses, and goals.

When prescribing exercise for his patients, Kor often advises very obese patients or those with diabetes to start out with low-impact or nonweightbearing exercise. Walking 30 minutes each day may be too much for these patients, so swimming or using a seated stationary bicycle may be better choices. But, once the patient’s foot-related symptoms or overall fitness improve, weightbearing exercise such as walking or running can play a part in their continued treatment, he said.

Tailoring treatment

Whether an obese or overweight patient should receive different treatments than normal-weight individuals for foot-related symptoms is also a question that has not been resolved—nor has it received much attention in the scientific literature. Yet, in small studies, researchers have begun to consider the efficacy of different treatment modalities for obese patients with foot pain and other symptoms.

In a small study on 10 normal-weight individuals, for instance, published in the Journal of Foot and Ankle Surgery in 2014, researchers studied the effect of adding weights with anterior and posterior body packs to mimic the BMI of overweight and obese individuals.6 As more weight was added, the mean peak plantar pressures in the heel, midfoot, and forefoot also increased in a linear fashion. The researchers also tested the effects of using three different off-loading devices—a surgical shoe, a controlled ankle motion walker, and a total contact cast.

“The walking boot and the total contact cast were the best at reducing plantar pressures in the foot,” said lead researcher Andrew Meyr, DPM, associate professor in the Department of Surgery at Temple University in Philadelphia. “The surgical shoe provided some improvement—but the plantar pressures with these shoes were not dramatically different than those seen with sneakers.”

Although some obese patients, such as those with diabetes, would benefit from these types of off-loading devices, many overweight patients need less-intensive interventions. Most patients with foot-related symptoms—whether or not they are obese—benefit from sturdy shoes with stiff soles to provide support and symptom relief, Kor said.

“My shoe recommendations really don’t vary based on a patient’s weight,” he added.

Overweight and obese patients, however, are more likely to benefit from thicker and more rigid orthoses, such as those made of polypropylene, than from softer or less durable devices.

“These types of orthotics will be more durable and last longer, because they can withstand the heavier weight of an overweight and obese individual,” Kor said.

By contrast, a graphite orthosis would be a poor choice for an overweight or obese patient, because it is less able to withstand excess weight, he said.

Although some studies have suggested obese patients have higher risks of complications than normal-weight patients after ankle surgery,7,8 other studies have not,9,10 and there is limited evidence that such risks also extend to foot surgery. In 2007, Pinzur et al reported that obesity was one of five variables associated with a high risk of complications following midfoot arthrodesis in patients with Charcot arthropathy.11 And researchers from Singapore found that obese (BMI of 30 or higher) patients undergoing hallux valgus surgery were significantly more likely than nonobese patients to need repeat surgery for complications.12

A patient’s weight, however, is likely to make little difference in the type of physical therapy or surgery they receive for foot disorders and ailments, clinicians said.

“Whether or not a patient is overweight or obese does not change my surgical plan,” Vaupel said. “But I would be more cautious in recommending early weightbearing after surgery for a patient who is obese. In heavier patients, early weightbearing has greater potential to jeopardize surgical results.”

Yet, no matter what the surgery or treatment plan is for an obese or overweight patient, Vaupel always recommends weight loss and makes a referral for nutrition and exercise counseling.

“Even if we don’t have scientific proof that there are worse outcomes with obesity, we also have to consider that weight loss can have a beneficial impact on the whole patient—on the patient’s overall health and well-being,” he said.

Barbara Boughton is a freelance writer based in the San Francisco Bay Area.

REFERENCES
  1. Butterworth PA, Landorf KB, Gilleard W, et al. The association between body composition and foot structure and function: A systematic review. Obes Rev 2014;15(4):348-357.
  2. Butterworth PA, Landorf KB, Smith SE, Menz HB. The association between body mass index and musculoskeletal foot disorders: A systematic review. Obes Rev 2012;13(7):630-642.
  3. Gay A, Culliford D, Leyland K, et al. Associations between body mass index and foot joint pain in middle-aged and older women: A longitudinal population-based cohort study. Arthritis Care Res 2014;66(12):1873-1879.
  4. Mickle KJ, Steele JR. Obese older adults suffer foot pain and foot-related functional limitation. Gait Posture 2015;42(4):442-447.
  5. Martin RL, Davenport TE, Reischl SF, et al; American Physical Therapy Association. Heel pain-plantar fasciitis: revision 2014. J Orthop Sports Phys Ther 2014;44(11):A1-A33.
  6. Pirozzi K, McGuire J, Meyr AJ. Effect of variable body mass on plantar foot pressure and off-loading device efficacy. J Foot Ankle Surg 2014;53(5):588-597.
  7. Werner BC, Burrus MT, Looney AM, et al. Obesity is associated with increased complications after operative management of end-stage ankle arthritis. Foot Ankle Int 2015;36(8):863-870.
  8. Burrus MT, Werner BC, Park JS, et al. Achilles tendon repair in obese patients is associated with increased complication rates. Foot Ankle Spec 2015 Oct 12. [Epub ahead of print]
  9. Gross CE, Lampley A, Green CL, et al. The effect of obesity on functional outcomes and complications in total ankle arthroplasty. Foot Ankle Int 2015 Sep 16. [Epub ahead of print]
  10. Bouchard M, Amin A, Pinsker E, et al. The impact of obesity on the outcome of total ankle replacement. J Bone Joint Surg Am 2015;97(11):904-910.
  11. Pinzur MS, Sostak J. Surgical stabilization of nonplantigrade Charcot arthropathy of the midfoot. Am J Orthop 2007;36(7):361-365.
  12. Chen JY, Lee MJ, Rikhraj K, et al. Effect of obesity on outcome of hallux valgus surgery. Foot Ankle Int 2015;36(9):1078-1083.

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