Effects of Shoe Heel Height on Biologic Rollover
Andy Hansen PhD and his colleagues at Northwestern recently published the latest in their ongoing research into the functional parameters of prosthetic ankle-foot mechanisms. [Hansen AH, Childress DS. Effects of heel height on biologic rollover characteristics during walking. JRRD 2004; 41(4): 547-554] This subset of their ongoing investigation into the concept of rollover shapes looked at the effect of varying heel heights on the gait of ten non-disabled females. This simple study is noteworthy, because it helps builds the foundation for future outcomes studies by establishing baseline data that can be compared to the mechanical function of prosthetic and orthotic components.
Like Dr. Hansen's prior work, these results are relevant to clinical practice because they provide objective information that is directly related to assumptions we make based on collective subjective experience with patient fittings. Hansen et al note early in the article that recent literature does NOT support the commonly held clinical belief that lumbar lordosis increases to compensate for higher heels. They hypothesized that the compensation for different heel heights occurs primarily at the ankle, and investigated this theory.
A convenience sample of ten female subjects was tested in the gait laboratory while walking in self-selected flat, mid-range, and high heeled shoes. Kinematic and kinetic data was gathered at a slow, normal, and fast walking pace for each shoe. They then calculated the rollover shape, as described in earlier research, which is a mechanical representation of the net sagittal plane motion as if the ankle-foot complex were a simple cam shape.
The results suggest that, during normal walking with different heel heights, the subject's gait adapts to maintain similar rollover characteristics, which results in very similar rollover shapes. In particular, the radius and forward shift of the rollover shapes did not change significantly with moderate changes in heel height, although the distance from the ankle marker to the floor increased with higher heels, reflecting the greater distance between the ankle and sole of the shoe.
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For the highest heels, particularly those exceeding 50 millimeters [2 inches], the rollover shapes began to shift posteriorly. The authors speculate that this could indicate a limit in the biological ability to accommodate marked plantar flexion at the ankle, noting that this heel height was associated with an increased energy cost in earlier research. This implies that the body may partially adapt to these more extreme heel heights at the knee, hip, or spine.
Hansen et al conclude by noting the limitations of this study, primarily due to small sample size and the limited scope of heel types tested [e.g., no stilettos, which presumable are less stable in the coronal plane]. These results demonstrated that the average radius for the rollover shape was 0.19 times the person's overall height for all low to moderate heel heights.
The invariance of the rollover shape, despite changes in heel height, implies that component designers could create ankle-foot devices that automatically compensated for heel heights while maintaining similar rollover shapes. I was struck by how similar this conclusion was to the design criteria for the Runway foot from Freedom Innovations, which were derived prior to the conduct of this research from subjective clinical observations.
The entire article is posted online at www.vard.org/jour/04/41/4/hansen.html .