December 2009

For those about to rock, we caution you

by Cary Groner

Shoes with rocker-bottom soles have long been used to alleviate plantar pressures in diabetes patients and others susceptible to forefoot pain or ulceration. The soles move the apex of the toe rocker behind the metatarsal heads, reducing pressure as the patient’s weight transfers forward over the ball of the foot.

“Rocker soles provide assistance to diabetes patients who lose the active phase of propulsion,” said David Levine, DPM, CPed, who practices in Frederick, MD. “Those patients lose some of the musculature in their feet, and if they have forefoot ulcers, rocker soles help transfer the pressure from the heel to the toe more rapidly.”

Levine uses rocker soles extensively in such patients, and is surprised that more clinicians do not.

“A lot of conservative care modalities are getting left behind as podiatric training moves more toward surgery,” he said. “I’m a big proponent of rockers, but you have to design the sole to make it work with the individual patient.”

However, recent findings that rocker-bottom soles may decrease stability strike a cautionary note for clinicians whose patients experience diminished foot sensation due to diabetic neuropathy.

The research was conducted by Bruce Albright, PT, PhD, a professor at East Carolina University, and published in the July issue of Gait Posture. The paper showed that rocker soles had a destabilizing effect to perturbed stance in healthy young subjects.

“Plenty of research has shown the effectiveness of reducing pressures with rocker-bottom soles,” Albright said. “But for a population with peripheral neuropathy, could this design lead to a problem? I feel that it could. The message to the therapist is that if you’re working with a patient who has a high risk for falls because of peripheral neuropathy, you need to address balance training with them.”

All such soles are not created equal, as it turns out. Researchers at the Medical College of Wisconsin reported in the January 2004 issue of Archives of Physical Medicine and Rehabilitation that different rocker-bottom sole designs transfer weight in distinct ways. As a result, practitioners should choose a design carefully depending on the pathologies and needs of the individual patient.

Dennis Janisse, CPed, president and CEO of National Pedorthic Services in Milwaukee, is an author of that study and a clinical assistant professor at the college.

“When you design a rocker sole, you have to look at the entire foot, not just the forefoot,” he said. “You can relieve pressure in different parts of the foot by varying the design.”

Subjects in the study wore one of three basic rocker-bottom designs: a toe-only rocker (the variant most commonly prescribed in general practice); a negative-heel rocker (similar to an Earth shoe); and a double rocker, the profile of which looks as if the area under the midfoot has been scooped out.

There were often tradeoffs involved in choosing a sole type.

“The toe-only rocker gave us the best forefoot relief—the great toe had as much as an 89% reduction in pressure compared to an unmodified shoe,” Janisse said. “But we saw a dramatic [pressure] increase at the base of the fifth metatarsal. By unloading the forefoot, we were loading the midfoot.”

Such redistribution of force doesn’t necessarily present a problem, but the clinician needs to be aware of it.

The double-rocker sole was especially helpful in subjects with a prominent fifth metatarsal base or a rocker-bottom foot deformity; it decreased midfoot pressure significantly, though it wasn’t as good at lowering forefoot pressures. The negative heel shoe functioned similarly to the toe-only rocker, though some subjects reported anecdotally that they felt more stable in the negative heel design.

“These shoes dramatically improve ambulation,” Janisse said. “But when people have peripheral neuropathy, their balance and proprioception are compromised. The rocker sole has to be very individualized.”

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