Gaps remain in literature on insoles and back pain
When it comes to the evidence-based use of foot orthoses to manage low back pain, clinicians and researchers point to a need for more comparisons of therapeutic devices and sham devices. Conducting such studies, however, is sometimes easier said than done.
Although foot orthoses are widely prescribed for low back pain, a 2016 review in the journal The Foot describes the state of research on this topic as having gaps still waiting to be filled.1
Gaps in the literature
Kinematic and kinetic changes associated with foot orthoses in patients with low back pain have been documented in clinical studies, but the changes are widely disparate, and the clinical implications are unclear, according to the review authors, M. Owen Papuga, PhD, and Jerrilyn Cambron, DC, PhD.
“Clinical studies lack the rigorous biomechanical analysis needed, while detailed biomechanical studies do not provide a longitudinal view of intervention and generally lack clinically relevant outcome measures. A truly translational approach is needed to address the evidence gaps that are currently present in this area of research,” the authors wrote.
One systematic review and meta-analysis discussed in the 2016 review was published in 2014 by BMC Musculoskeletal Disorders.2The authors identified five trials that assessed treatment of low back pain with foot orthoses and six other trials that assessed the use of foot orthoses to prevent low back pain.
“No statistically significant effect for the use of insoles or foot orthoses is seen for either prevention trials or treatment trials,” they wrote, but also noted that results are trending in a positive direction. “Future research for [low back pain] treatment should concentrate on variables from the patient history, physical examination, or simple diagnostic tests that may assist in classification of [low back pain] patients most suited to a foot orthosis or insole intervention, as there is some evidence that trials structured along these lines have a greater effect on reducing [low back pain].”
In their review, Cambron and Papuga offered five recommendations for filling the gaps:
Mechanistic studies that start with dynamic characterization of foot function at baseline,
Controlled and systematic alteration of foot orthoses based on dynamic assessment,
Using patient feedback in the foot orthosis customization processes,
Prevention studies of well-defined patient populations, and
Biopsychosocial classification of low back pain prior to treatment.
The proprietary nature of the custom foot orthosis field accounts for some of the missing evidence, Papuga, assistant professor at the New York Chiropractic College in New York City, told LER in a phone interview.
“If you go to someone who makes orthotics by hand, it’s a kind of art and skill that they rely upon in order to get their desired effect, and that needs to be quantified. There’s got to be some categorization of patients,” Papuga said. “What I think is lacking in a lot of prescription is the dynamic assessment of the foot—seeing what that pressure profile looks like while you’re walking rather than doing a static scan of the foot.”
The ability to relate those dynamic assessments to what a clinician thinks an orthosis should look like to have the desired effect would help tremendously, he said.
One recent study has shown some evidence that foot orthoses are beneficial for patients with low back pain.3 Led by Cambron, chair of the College of Health Sciences and Distance Education at the National University of Health Sciences in Lombard, IL, the study examined foot orthoses’ effects on patients with low back pain of three months or longer.
The researchers randomized 225 patients into one of three groups. An orthosis group received custom foot orthoses. A “plus” group received custom foot orthoses plus chiropractic manipulation, manual soft tissue massage, and hot or cold packs. A wait-list group received no treatment.
While at six weeks, all three groups showed significant improvement in average back pain, the orthosis group demonstrated significantly greater improvement in pain and function than the wait-list group. Adding chiropractic manipulation to foot orthosis treatment resulted in significantly greater improvement in function compared with the orthosis-only group. Group differences at 12 weeks were not statistically significant.
However, the study could have benefitted from the use of a sham insole in the control group, according to Papuga and Thomas C. Michaud, DC, author of the textbook Human Locomotion: The Conservative Management of Gait-Related Disorders4 and a practicing chiropractor in Newton, MA.
“I would like to have seen a control where they gave a sham orthotic, because whenever you throw a sham in, like a flat insole, the outcomes get blurred,” Michaud said. “I would like to have seen a control put in with a flat insole.”
Sham study struggles
Papuga and Cambron’s paper noted that a randomized controlled trial was launched in 2013 by researchers at the Canandaigua VA Medical Center in Rochester, NY, to compare custom foot orthoses and sham insoles in a population of veterans with low back pain. However, that trial was discontinued in June 2016, according to clinicaltrials.gov.5
Another group of researchers recently performed their own similar comparison,6but fell short of confirming the effectiveness of the custom devices—and they believe the design of the sham device they used may have been a limitation.
Anthony L. Rosner, PhD, a research and grant director and medical writer in Watertown, MA, teamed up with two chiropractic professionals, Katharine M. Conable, DC, and Tracy Edelmann, DC. Conable is associate professor at Logan University College of Chiropractice in Chesterfield, MO, where the trial was conducted, and Edelmann is in private practice in Wildwood, MO.
The double-blinded parallel-group randomized study investigated how four weeks of using custom foot orthoses or sham insoles affected pain, disability, recurrence of spinal fixation, and muscle dysfunction. Study participants had to have low back pain for at least a month.
The researchers randomized 46 low back pain patients (21 women, average age 59.5 years) to receive either custom orthoses (22 patients, 19 completing) or a flat sham insole (24 patients, 19 completing) as part of a monthlong intervention that included five clinic visits and limited chiropractic care.
Their primary outcome measures were self-reported pain and disability, the number of muscles scoring grade 4 or lower on manual muscle testing, and the number of spinal fixations (hypomobile areas) detected by motion palpation and vertebral challenge (application of force) at intake.
The Journal of Manipulative and Physiological Therapeutics published the findings in February 2014. Scores improved from baseline to the final assessment in both groups, though the improvements did not reach statistical significance, and there were no significant between-group differences with regard to degree of improvement. Preliminary analysis suggested that, in both groups, longer daily duration of orthosis wear was associated with greater improvement in outcome measures; however, these findings lost their significance once the analysis accounted for significant between-group differences at baseline. No major adverse events occurred during the trial.
“That’s just the luck of the draw. In a trial, you would hope for statistical significance. We didn’t see it, but there’s a definite tendency toward better outcomes with better compliance,” Rosner told LER in a phone interview.
The trial results had important implications in terms of blinding and the use of a sham, according to Rosner. Neither the treating chiropractor nor the patients knew which devices they were wearing, nor did other trial personnel (other than the research assistant who assisted with the insertion of the devices). A substantial majority of participants in both groups believed they had been issued custom devices (16/20 in the experimental group, 13/20 in the sham group), suggesting successful patient blinding.
“They didn’t know from Adam which they received. That is your test of blinding. That is supposed to eliminate a sense of bias,” Rosner said.
However, the researchers also noted that what’s good for blinding may not be so good for providing a true placebo control. Both devices were manufactured by the same orthotic laboratory, and the sham insole had a number of the same cushioning and contouring features as the custom orthosis.
“The sham really was a puckered insole and really had the characteristics of the orthotic device we were testing,” Rosner said. “As it turned out, in the trial, people responded positively to that. Since the puckered sham really wasn’t a placebo it diminished the effect we would’ve liked to see.”
Findings of improved pain and disability associated with sham devices as well as therapeutic devices in patients with low back pain suggest proprioception may play a role, Michaud said, particularly in light of studies challenging the theory that foot orthoses affect mechanics in the frontal plane.7-10
“Whenever you look at lower back pain and orthotics, that whole belief that the tibia internally rotates farther creating the anterior tilt to the pelvis, it doesn’t happen,” he said. “Orthotics don’t alter end ranges. They alter velocity;11 they can improve proprioception.12 I think if someone is going to get better with an orthotic, it’s because they have enhanced proprioception. They feel the ground better.”
Michaud advises against initially prescribing a custom orthotic device for simple low back pain.
“Give them an off-the-shelf orthotic and see how they do,” he said.
Searching for subgroups
According to Michaud, some low back pain patients are more likely to have a positive response to foot orthoses than others.
“I find the people who respond best to orthotics are nonspecific low back pain patients who have pain while standing for a long time. That subgroup tends to do well with orthotics, whether custom or over-the-counter,” he said. “But, if mechanical low back pain patients can stand all day without much of a problem but get a jolt when reaching for something, that type of person doesn’t respond as well to an orthotic, in my experience.”
Michaud likes the concept of teaming orthotic therapy with spinal manipulation, which has been studied since 1988.13
“When you couple chiropractic manipulation with orthotics you get better outcomes usually, even if it’s just short-term,” he said. “You decrease the vertical force traveling through the lower extremity, you enhance proprioception from the ground up, and the chiropractic care can improve spinal stability and increase range of motion and can increase proprioception in the lumbar spine.”
Larry Hand is a medical writer based in Massachusetts.