title: Hoof position during limb loading affects dorsoproximal bone strains on the equine proximal phalanx.
abstract: Sagittal fractures of the proximal phalanx (P1) in the racehorse appear to be associated with turf racing surfaces, which are known to restrict forward slide of the foot at impact. We hypothesized that restriction of forward foot slip would result in higher P1 bone strains during metacarpophalangeal joint (MCPJ) hyperextension. Unilateral limbs from six equine cadavers were instrumented with strain gauges and bone reference markers to measure dorsoproximal P1 bone strains and MCPJ extension, collateromotion and axial rotation during in vitro limb loading to 10,500 N. By limiting movement of the distal actuator platform, three different foot conditions (forward, free, and restricted) were applied in a randomised block design. Bone reference markers, recorded by video, were analyzed to determine motion of P1 relative to MC3. Rosette strain data were reduced to principal and shear magnitudes and directions. A mixed model ANOVA determined the effect of foot position on P1 bone strains and MCPJ angles. At 10,000 N load, the restricted condition resulted in higher P1 axial compressive (p=0.015), maximum shear (p=0.043) and engineering shear (p=0.046) strains compared to the forward condition. The restricted condition had higher compressive (p=0.025) and lower tensile (p=0.043) principal strains compared to the free condition. For the same magnitude of principal or shear strains, axial rotation and collateromotion angles were greatest for the restricted condition. Therefore, the increase in P1 principal compressive and shear bone strains associated with restricted foot slip indicate that alterations in foot:ground interaction may play a role in fracture occurrence in horses.
authors.affiliation: Department of Musculoskeletal Biology, Institute of Aging and Chronic Disease, School of Veterinary Medicine, University of Liverpool, Leahurst, Chester High Road, Neston CH64 7TE UK. Electronic address: e.r.singer@liverpool.ac.uk.
authors.forename: Ellen
authors.initials: E
authors.lastname: Singer
authors.affiliation: JD Wheat Veterinary Orthopedic Research Laboratory, School of Veterinary Medicine, University of California, One Shields Avenue, Davis, CA, USA.
authors.forename: Tanya
authors.initials: T
authors.lastname: Garcia
authors.affiliation: JD Wheat Veterinary Orthopedic Research Laboratory, School of Veterinary Medicine, University of California, One Shields Avenue, Davis, CA, USA.
authors.forename: Susan
authors.initials: S
authors.lastname: Stover
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001842:Bone and Bones; D005121:Extremities; D005552:Forelimb / Q000502:physiology*; D050723:Fractures, Bone / Q000662:veterinary; D006724:Hoof and Claw / Q000502:physiology*; D006736:Horses; D007596:Joints / Q000502:physiology*; D011312:Pressure; D011897:Random Allocation; D012399:Rotation; D033081:Shear Strength; D013180:Sprains and Strains / Q000503:physiopathology*; D013314:Stress, Mechanical; D013718:Tensile Strength; D016474:Weight-Bearing
keywords: Bone strain; Foot slip; Horse; Metacarpophalangeal joint kinematics; Proximal phalanx