Increasing numbers of patients are finding relief from chronic low back pain with the use of foot orthoses, but the mechanism underlying the positive outcomes is largely unknown.
By Larry Hand
Robert Ferrari, MD, MSc, kept hearing from patients about how the foot orthoses he was prescribing for them were helping not only with their foot pain, but also with pain in their knees, hips, and backs. As a clinician, he wanted to know why. Naturally, he went on a literature hunt.
He didn’t find a lot of what he wanted to find.
“I looked into the literature and, although there are some reasons to believe that pain other than foot pain or other disorders of the leg could also respond to orthotics, there were very few adequate or appropriate studies directly addressing some of the issues that I see,” Ferrari told LER in a telephone interview.
A clinical professor of medicine and rheumatic diseases at the University of Alberta in Edmonton, Canada, Ferrari first trained in internal medicine, then took additional training in rheumatology. Many of the patients he treats suffer from common low back pain.
Ferrari performed two studies, both published in 2013, investigating how orthoses would affect two different patient populations with specific back pain problems.1,2 The researchers showed patients with low back pain resulting from accidents had greater improvement in short-term outcomes and pain scores if they used custom foot orthoses in addition to usual care.
“Many of the patients I see have low back pain and have knee and hip pain,” Ferrari said. “I used to prescribe orthotics for the obvious things, which are foot pain and foot disorders. Some patients came back to me telling me that they were surprised that their knees and their hips and their backs felt better. So I had an opportunity a few years ago in the clinical setting to conduct a study comparing the addition of orthotics to usual therapy for people with back pain either after a motor collision or after a work-related injury.”
In one study,1 physicians referred consecutive motor-vehicle-accident patients (62% men, mean age 39 years) to Ferrari during a three-month period in 2009. The patients were experiencing low back pain but no spinal pain above the T12 region. Of the 66 patients eligible for the study, 30 received usual care prescribed by their primary physician or physical therapist and 34 received usual care plus custom foot orthoses. No significant differences existed among participants’ age, sex, or duration of low back pain.
The orthoses were made from foam impressions, with patients sitting and the knee flexed at 90°. The semirigid orthoses featured vinyl reinforcement, polyurethane foam cushioning, and a large-profile metatarsal pad. For leg length discrepancies of at least 1.5 cm, patients received leg lifts of up to .75 cm.
At eight weeks follow-up, Oswestry Disability Index (ODI) scores had improved in both groups, but significantly more so in the orthoses group. Patients who received orthoses also used significantly fewer analgesics than the usual care group after eight weeks.
Ferrari used the same type of orthosis in a second study, this time of patients referred to him after a work injury. Of 62 patients (76% men, mean age 37.8 years), 28 received usual care and 32 received usual care plus orthoses. Again, there were significant differences in age, sex, or duration of low back pain and both groups improved, but the orthoses group had significantly lower ODI scores than the usual care group and used fewer prescribed analgesics after eight weeks.
“Chiropractors have long been saying that orthotics are beneficial for all sorts of conditions,” Ferrari pointed out. “Because studies haven’t been done, or not enough studies have been done, physicians don’t feel that they really know what, if anything, these devices are doing and they’re a bit skeptical. Physicians should be using them more, because that will reduce, if anything, medication requirements. If that’s the only thing orthotics did, that alone would be a benefit.”
He said his clinic charges between $250 and $350 (Canadian dollars) for orthoses that can last six months to a year or more, depending on a patient’s weight and usage and estimated that savings on prescription pain medications could add up to a few hundred dollars a month.
“It’s a struggle,” said Marian T. Hannan, DSc, MPH, an epidemiologist at the Institute for Aging Research, a Harvard Medical School-affiliated center in Cambridge, MA, and senior author of a paper published in September 2012 in Rheumatology3 that found pronated foot function, but not foot posture, was associated with low back pain.
“Here’s a condition that’s an incredibly common condition, low back pain. And here’s pronated foot function, which is also pretty common,” she said.
Yet studies addressing both conditions either have been done in younger or population-limited groups of people, such as military recruits in Europe or mail carriers in Israel.4-7
“If they’re young and healthy and they’ve got really good muscles, from a population level, they’re probably not where most of the outcomes are going to be. So we said, ‘Let’s look at older people, average age early 60s, and see what’s going on with them,’ because there should be a lot more outcomes and they’re still at a phase in life where orthotics are going to make a difference,” she told LER in a telephone interview.
Hannan said many other studies only include patients “who show up at a doctor’s office and say, ‘I’ll do anything. My back’s been killing me for a while,’ But a large portion of the population with back pain may be missing from those studies.”
Her recent study found pronated foot function carried a 51% higher risk of low back pain in women than in men, a difference that remained significant even after adjusting for age, weight, smoking, and depressive symptoms. Of 3378 participants in this Framingham Foot Study, an offshoot of the well-known Framingham Heart Study, 1930 (1067 women, mean age 64 years) had low back pain and foot pressure data in records at the time of analysis. About a third reported low back pain, aching, or stiffness on most days.
“What was surprising to me was that we see these results in women and not in men,” Hannan said. “It may be that there actually is something in men but we don’t have sufficient numbers of men to see that. But we think it may be due to known gender differences in alignment. Men and women have different ranges of motion and function in the spinal joints. Women have more pelvic tilt, and women have more hip rotation than men do. It also may be due to men having stronger spinal muscles than women do.”
Although Hannan and colleagues did not specifically evaluate the use of foot orthoses, they concluded that such interventions may have a role in the prevention and treatment of low back pain.
“If you can alter a patient’s foot function with an orthotic, which we know we can do clinically, it could be a way to lessen people’s low back pain,” Hannan explained.
Pronation as a player
Another recent study in Prosthetics and Orthotics International may provide information to help pinpoint how distal factors might contribute to lower back pain.8 The study cites literature that shows how, over time, excessive foot pronation relates to chronic low back pain and how the use of orthoses might help to alleviate the problem.10
“If subtalar joint hyperpronation plays a fundamental role in the pathomechanics of lower limb, and this can facilitate the development of low back pain, then controlling the abnormal mobility of subtalar joint by means of foot orthoses should improve this symptom,” the authors wrote.
Researchers in Seville, Spain, conducted a randomized double blinded clinical trial of 51 patients with chronic low back pain and excessive subtalar pronation. The investigators randomized participants into one of two groups: experimental (treated with custom foot orthoses) and control (treated with placebo). There were 22 controls (20 men, 19 to 64 years) and 29 patients in the experimental group (23 women, 18 to 64 years).
The researchers made foam molds of the feet under weight-bearing subtalar neutral conditions with the forefoot plantar plane parallel to the floor. All experimental foot orthoses had a base layer of 3-mm polypropylene from the heel to just behind the metatarsal heads, covered with 2-mm of polyethylene foam. The researchers also made adjustments after all orthoses were applied. The control orthoses were 1.9-mm insoles of polyester resin, fitted in patients’ shoes without conforming to the positive foot mold.
After four weeks of treatment, use of the orthoses was associated with significant reductions in low back pain (measured by visual analog scale) and disability (measured by ODI).
Coauthor Pedro V. Munuera, PhD, LicPod, of the department of podiatry at the University of Seville, said the results did not surprise him.
“Not at all, as this is a method I use frequently,” he wrote in an email to LER. “When we observed the results [low back pain improvement] obtained in patients, we decided to register those results and publish them.”
The researchers acknowledged in their paper that only excessive subtalar pronation was considered, and that other factors may lead to lower back pain.
Thomas C. Michaud, DC, author of the textbook Human Locomotion: The Conservative Management of Gait-Related Disorders, and a practicing chiropractor in Newton, MA, would agree about the other factors.
“I actually feel a pronated foot is a good shock absorber, and I have never felt there was a strong correlation between low back pain and excessive pronation,” he said. “A lot of our early research in the eighties and nineties suggested that a pronated foot caused more lower extremity internal rotation, which could produce an anterior tilt to the pelvis. The femur internally rotated, and the femoral heads would shift posteriorly, which would cause the pelvis to extend, which in turn would cause the lumbar spine to compress a little bit more. That was the theory. But I feel that people with pronated feet have more global ligamentous laxity,9 and it’s not the transfer of internal rotation that causes the trouble. It’s that they have more laxity.”
An accommodating approach
In 2011, researchers at the National University of Health Sciences in Lombard, IL, described a pilot randomized controlled trial of 50 patients with chronic low back pain that has since led to a much larger ongoing trial.10 They randomized 25 patients to wear custom foot orthoses for 12 weeks, while another 25 patients waited six weeks, then wore the same type of orthoses for another six weeks.
The flexible accommodative orthoses provided support for the medial longitudinal, lateral longitudinal, and transverse arches; had a shock-absorbing polymer in the heel and a springy polymer in the forefoot; and had a stiffer polymer for support in midstance. Back pain (VAS) and disability (ODI) improved significantly in the experimental group at six weeks but improved no further at 12 weeks.
For these patients, it was a combination of treatments that worked, according to coauthor Thomas Solecki, DC, who spoke to LER in a telephone interview.
“The biggest thing is that the orthotic is an additional aid in helping the healthcare provider with stability for the patient,” Solecki said. “It’s making a small change for the foot, giving it extra support that it doesn’t necessarily have from the musculature and the joint itself. It does not replace the rehabilitation and short foot training programs that one will need to undergo. There is still a great deal of self management and active participation that the patient must do to ultimately become healthy.”
The flexibility of accommodative foot orthoses makes them particularly useful for patients undergoing rehabilitation, he said.
“The devices have some give to them so the patient’s not so restricted, and it fits with the concept of adaptation while they’re training,” Solecki said.
Another recently published study evaluated the effects of prefabricated insoles in 25 workers at an aircraft assembly plant who experienced both back pain and lower extremity pain after four consecutive days of working 12-hour shifts without insoles. After a break of several days, the workers put in another four consecutive days of 12-hour shifts, wearing the insoles in their normal work shoes. In the 25 workers, low back pain scores after four shifts with the insoles was 40% lower than after four shifts without the insoles.11
Ferrari’s observations about the costs of orthoses and their offsetting of other costs in Canada reverberate in the US. When asked whether orthoses help to reduce spending on prescription medicines, Michaud said, “Absolutely yes. They even reduce the need for surgery. They’re very effective when prescribed for the right person. They last a long time and they decelerate the velocity of pronation. But the outcomes are unpredictable.12 It’s hard to say which patients will do well in advance and it’s also hard to explain why they get better.”
Michael T. Gross, PT, PhD, a professor of physical therapy at the University of North Carolina at Chapel Hill, agreed.
“Patients like to not have to spend money. Patients also don’t like to have pain with every step that they take,” Gross said. “I think they would like the latter rather than the former, although both are attractive.”
He said he probably prescribes orthoses 300 times a year, just practicing one or two days a week and teaching the rest of the time.
The US costs of orthotic devices for lower back pain, according to multiple sources, range from $5 to $10 for a heel lift to help with leg-length discrepancies, $20 to $450 for an accommodating orthosis, and to $250 to $500 for a custom orthosis, depending on such factors as who does the work and whether office visits are included.
The costs, combined with therapeutic effect, can be a motivating factor for good patient compliance, said Bruce Williams, DPM, who recently became director of gait analysis studies at the Weil Foot and Ankle Institute in Chicago. When patients seeking relief from a long-time problem finally find a solution, they comply, he said.
“Once they find it they don’t want to switch out of it,” Williams said. “These are the patients that I refer to as my orthotic junkies because they won’t go without them if I tell them that’s what they need to do. When they do go without them, they know they’re going to end up right back in the office because they’re going to end up back in pain.”
Larry Hand is a writer in Massachusetts.
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