By Emily Delzell
New approach supports orthotic care
In contrast with previous findings based on peak pressure values, an abstract presented at July’s International Society of Biomechanics (ISB) meeting in Brussels used a new method of measuring dynamic plantar pressure distribution to confirm that custom orthoses improve distribution of peak pressure during dynamic foot loading in patients with painful pes cavus.
“Custom foot orthoses are thought to work by reducing plantar pressure magnitudes of the foot by redistributing them, said abstract author Bijan Najafi, PhD, associate professor of applied biomechanics at the Center for Lower Extremity Ambulatory Research at Rosalind Franklin University in Chicago. “Our study suggests painful pes cavus alters the distribution of plantar loading during walking and that custom orthoses are an effective therapeutic solution that can significantly improve it.”
Najafi noted that much literature assessing benefits of orthotics have assessed magnitude of peak plantar pressure (MPP) to measure efficacy.
A September 2007 study in the Clinical Journal of Sports Medicine found no link between pressure effects and symptom improvement. The authors evaluated pain, function, and plantar pressure values in 66 participants who received custom foot orthoses and 67 persons given sham orthoses (latex foam insoles). All had painful pes cavus and wore the intervention for three months.
Investigators found no significant differences between groups in pain or function (44 improved in the orthotic group, 34 in improved in the sham group). Although there were differences in foot pressure between groups (sham group, 5.5% reduction in peak pressure; orthotic group, 15% reduction), these did not correlate with other improvements.
“Shock absorption provided by functional and sham orthotics may reduce peak pressure. This measurement, however, doesn’t quantify improvements in pressure distribution,” Najafi said. “In addition, MPP is confounded by gait velocity and body mass index [BMI].”
A 2010 Gait and Posture study by Najafi et al identified a technique for characterizing abnormalities in dynamic plantar loading before and after reconstructive surgery for Charcot neuroarthropathy. They theorized this same measurement, called a regression factor (RF) index, could address some shortcomings of using MPP to assess efficacy of orthotics in patients with painful pes cavus.
RF is dynamic plantar loading measure that looks at the statistical distribution of MPP in individuals and compares it with a customized distribution curve representing normal loading.
In the ISB study, investigators randomized 154 persons with painful pes cavus to a group given custom orthoses or a control group that received sham orthoses. Outcomes for characterizing plantar loading were MPP; RF index; and the relative location of second peak pressure as a percentage of stance phase.
The active treatment group significantly improved in all three outcomes compared with the controls. However, MPP was significantly reduced in both control and active groups, with a significantly higher reduction (average, 8%) in the active group.
“RF index results suggest custom orthoses contribute to better distribution of peak pressure during dynamic loading, significantly improving pressure distribution compared with sham orthoses,” Najafi said. “Although sham orthoses significantly reduce peak pressure, they have no impact on RF, suggesting peak pressure may be biased by effects of the sham while RF index is not.”
Tom McPoil, PT, PhD, professor in the School of Physical Therapy at Regis University in Denver, CO, said he found the results intriguing but not surprising.
“It’s clear that one of the best things for pes cavus patients is increasing total contact area on the bottom of the foot to relieve heel and forefoot pressure,” McPoil said.
He noted, however, that pes cavus is associated with a unique plantar pressure pattern while other foot conditions, such as plantar fasciitis, are not.
“I’d like to see if RF is useful in patients without characteristic pressure patterns,” he said.