March 2013

OFFLOADING: Walkers’ effect on proximal biomechanics varies depending on design characteristics

Tibial inclination appears significant

By Jordana Bieze Foster

Orthotic walkers have significant effects on proximal joint mechanics during gait, the extent of which appear to depend on individual device design, according to research from the University of Central Lancashire in the UK.

Investigators analyzed the kinetic and kinematic effects of two different orthotic walkers on hip and knee function in 11 healthy volunteers. The two devices differed from one another primarily with regard to positioning of the heel rocker and inclination of the tibial component: Device A featured a slightly more anterior heel rocker and a slightly anterior tibial inclination; Device P featured a slightly more posterior heel rocker and a slightly posterior tibial inclination.

Compared to walking in normal footwear, both walkers were associated with significantly greater knee flexion angle during stance phase, but only Device P was also associated with a significantly increased knee flexion moment. Knee extension moment was significantly higher for both rockers than for normal footwear, but was also significantly higher for Device P than for Device A.

At the hip, both walkers were associated with significantly greater hip extension angles and significantly decreased hip extension moments compared to normal footwear. In both cases, the deviations were more pronounced with Device P than Device A.

These effects are likely related to the relatively posterior positioning of the heel rocker and the posterior tibial inclination in Device P, said James Richards, BEng, MSc, PhD, professor of biomechanics at the University of Central Lancashire, who presented his group’s findings at the ISPO World Congress in Hyderabad, India.

The concept of an association between tibial inclination and gait mechanics was also discussed during several ISPO sessions by Elaine Owen, MSc, SRP, MCSP, superintendent and clinical specialist pediatric physiotherapist at the Child Development Centre in Bangor, North Wales, UK.

In her work with children with cerebral palsy, Owen consistently advocates that the shaft of an ankle foot orthosis be slightly inclined relative to vertical, with inclinations varying in degrees depending on the patient’s natural inclination, stiffness, and any observed shank reversal. Owen described these evidence-based concepts in a 2010 paper published in Prosthetics & Orthotics International.

“An optimal alignment is always one where they can incline the thigh,” Owen said. “It’s the inclined alignment that will give the optimal performance.”

Richards believes that similar biomechanical concepts may be at work with regard to the proximal effects of orthotic walkers.

“A better tibia inclination angle seems to be a dominant factor in knee and hip mechanics, although the rockers are also very important,” he said.

Richards emphasized, however, that manufacturers are constantly redesigning devices and probably have done so since the launch of his group’s study.

“The take-home message is that not all walkers are the same,” he said. “Further research is needed on the effects of orthotic walkers on knee and hip joint mechanics with a focus on the effects of changing the tibial angle and rocker profiles. This should help to inform future designs of walkers, with a greater focus on obtaining a more normal gait pattern.”

And, when it comes to at least one variable, an orthotic walker’s effect on the knee may actually be positive. The Central Lancashire group found that both devices were associated with significant reductions in knee adduction moment, which is commonly used as a surrogate for medial knee loading in studies of patients with medial compartment knee osteoarthritis, compared to normal footwear.

Source:

Richards J, Payne K, Myatt D, Chohan A. Do orthotic walkers affect knee and hip function during gait?  Presented at International Society of Prosthetics and Orthotics 2013 World Congress, Hyderabad, India, February 2013.

Owen E. The importance of being earnest about shank and thigh kinematics especially when using ankle-foot orthoses. Prosthet Orthot Int 2010;34(3):254-269.

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