The Journal of Bone and Joint Surgery (American). 2010;92:1754-1764.
doi:10.2106/JBJS.I.00984
© 2010 The Journal of Bone and Joint Surgery, Inc.
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Arthrodesis of the First Metatarsophalangeal Joint: A Robotic Cadaver Study of the Dorsiflexion Angle

Ahmad F. Bayomy, BS1, Patrick M. Aubin, MS1, Bruce J. Sangeorzan, MD1 and William R. Ledoux, PhD1

1 Department of Veterans Affairs Rehabilitation Research and Development Service Center of Excellence for Limb Loss Prevention and Prosthetic Engineering, VA Puget Sound Health Care System, MS 151, 1660 South Columbian Way, Seattle, WA 98108. E-mail address for W.R. Ledoux: wrledoux{at}u.washington.edu

Investigation performed at the Department of Veterans Affairs Center of Excellence for Limb Loss Prevention and Prosthetic Engineering, VA Puget Sound Health Care System, Seattle, and the Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington

Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants of less than $10,000 from the Department of Veterans Affairs Rehabilitation Research and Development Service (#A2661C and #A4843C) and the University of Washington Medical Student Research Training Program. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.

Background Arthrodesis of the first metatarsophalangeal joint is indicated for severe osteoarthritis or as a revision of failed treatment for hallux valgus. The literature suggests that an optimum fused dorsiflexion angle is between 20° and 25° from the axis of the first metatarsal. The purpose of this study was to investigate the relationship between dorsiflexion angle and plantar pressure in the postoperative gait. We assumed that there is a fused dorsiflexion angle at which pressures are minimized under the hallux and the first metatarsal head.

Methods Six cadaver foot specimens underwent incremental changes in simulated fused metatarsophalangeal joint dorsiflexion angle followed by dynamic gait simulation. A robotic gait simulator performed at 50% of body weight and one-fifteenth of physiologic velocity. In vitro tibial kinematics and tendon forces were based on normative in vivo gait and electromyographic data and were manually tuned to match the in vitro ground reaction force and tendon force behavior. Regression lines were calculated for peak pressure and pressure-time integral under the hallux and the metatarsal head by dorsiflexion angle.

Results Peak pressure and pressure-time integral under the hallux were negatively correlated with dorsiflexion angle (p < 0.004), while peak pressure and pressure-time integral under the metatarsal head were positively correlated with dorsiflexion angle (p < 0.004). The intersection of the regression lines that represented the angle at which peak pressure and pressure-time integral were minimized was 24.7° for peak pressure and 21.3° for pressure-time integral.

Conclusions Our findings support the hypothesis that an angle-pressure relationship exists following arthrodesis of the first metatarsophalangeal joint and that it is inversely related for the hallux and the metatarsal head. Our results encompass the suggested range of 20° to 25°.

Clinical Relevance This investigation provides a basis for assessing clinical decisions surrounding operative technique and hardware utilization that may improve gait, quality of life, and functional performance in patients undergoing operative treatment of osteoarthritis of the first metatarsophalangeal joint.


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