Is the Planus Foot Type Associated With First Ray Hypermobility?

Oliver J Morgan; Rajshree Hillstrom; Robert Turner; Jonathan Day; Ibadet Thaqi; Kristin Caolo; Scott Ellis; Jonathan T Deland; Howard J Hillstrom

doi:10.1177/24730114221081545

Is the Planus Foot Type Associated With First Ray Hypermobility?

Foot Ankle Orthop. 2022 Mar 4;7(1):24730114221081545. doi: 10.1177/24730114221081545. eCollection 2022 Jan.

Authors

Oliver J Morgan¹, Rajshree Hillstrom^{2

3}, Robert Turner³, Jonathan Day⁴, Ibadet Thaqi³, Kristin Caolo⁴, Scott Ellis⁴, Jonathan T Deland⁴, Howard J Hillstrom³

Affiliations

¹ Medical Engineering Research Group, Faculty of Science and Engineering, Anglia Ruskin University, Chelmsford, Essex, United Kingdom.
² Biomed Consulting, Inc, New York, NY, USA.
³ Leon Root, MD Motion Analysis Laboratory, Hospital for Special Surgery, New York, NY, USA.
⁴ Department of Foot and Ankle Surgery, Hospital for Special Surgery, New York, NY, USA.

Abstract

Background: Many foot pathologies have been associated with foot type. However, the association of first ray hypermobility remains enigmatic. The purpose of this study was to investigate first ray hypermobility among participants with planus and rectus foot types and its influence on static measures of foot structure.

Methods: Twenty asymptomatic participants with planus (n = 23 feet) and rectus (n = 17 feet) foot types were enrolled. Several parameters of static foot structure (arch height index, arch height flexibility, first metatarsophalangeal joint flexibility, and first ray mobility) were measured. Participants were further stratified into groups with nonhypermobile (n = 26 feet) and hypermobile (n = 14 feet) first rays. First ray mobility ≥8 mm was used to define "first ray hypermobility". Generalized estimating equations, best-fit regression lines, and stepwise linear regression were used to identify significant differences and predictors between the study variables.

Results: Overall, 86% of subjects categorized with first ray hypermobility exhibited a planus foot type. Arch height flexibility, weightbearing first ray mobility, and first metatarsophalangeal joint flexibility showed no significant between-group differences. However, weightbearing ray mobility and first metatarsophalangeal joint laxity were associated with partial weightbearing first ray mobility, accounting for 38% of the model variance.

Conclusion: The planus foot type was found to be associated with first ray hypermobility. Furthermore, weightbearing first ray mobility and first metatarsophalangeal joint laxity were predictive of partial weightbearing first ray mobility, demonstrating an interaction between the translation and rotational mechanics of the first ray.

Clinical relevance: Association of first ray hypermobility with foot type and first metatarsophalangeal joint flexibility may help understand the sequela to symptomatic pathologies of the foot.

Keywords: biomechanics; first metatarsophalangeal joint flexibility; first ray hypermobility; first ray mobility; foot; foot type.