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  • Author: Neil A. Sharkey x
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Andrew R. Fauth, Andrew J. Hamel and Neil A. Sharkey

This study involved a biomechanical examination of the first and second tar-sometatarsal (TMT) joints. In the in vitro testing protocol, physiologic joint moments were applied to the first and second TMT joints of 10 cadaver specimens, which had been dissected to yield only the midfoot components comprising the tarsals, metatarsals, and associated ligaments. The isolated joints were placed in a 37 °C water bath and were independently cycled into and out of dorsiflexion, while angular displacement and resultant joint moments were collected. The specimens were sequentially cycled between zero and peak moment levels of 2.5, 5.0, 7.5, and 10 Nm, after which mean moment-angle curves were plotted for each TMT joint at each loading condition. Least-squares curve-fitting procedures, employing a root mean square error threshold of 0.005 Nm, were used to describe the average overall moment vs. angle relationship of each joint. Curves for the first and second TMT joints exhibited similar behavior. The joints displayed reasonably constant stiffness at low angles of dorsiflexion, followed by rapidly increasing stiffness at higher angles of dorsiflexion. These data provide new insight into the behavior of the TMT joints under load and are valuable for use in numerical models of the foot, as well as in the understanding and treatment of certain foot pathologies.

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Jay Hertel, Craig R. Denegar, W.E. Buckley, Neil A. Sharkey and Wayne L. Stokes

Objective:

To identify changes in sagittal- and frontal-plane center of pressure (COP) excursion length and velocity during single-leg stance under 6 orthotic conditions.

Design:

1 × 6 repeated-measures.

Setting:

University biomechanics laboratory.

Participants:

Fifteen healthy young adults without excessive forefoot, arch, or rear-foot malalignments.

Measurements:

Selected variables of COP length and velocity were calculated in both the frontal and sagittal planes during three 5-second trials of quiet unilateral stance.

Methods:

Postural control was assessed under 6 conditions: shoe only and 5 orthotics.

Results:

The medially posted orthotic caused the least frontal COP length and velocity, and the Cramer Sprained Ankle Orthotic® caused the greatest frontal-plane sway. No significant differences were found between the different orthotic conditions in sagittal-plane measures.

Conclusions:

Differently posted rear-foot orthotics had various effects on frontal-plane postural control in healthy participants. Further research is needed on pathological populations.