Shoe configuration effects on third phalanx and capsule motion of unaffected and laminitic equine hooves in-situ

Abstract

Equine shoes provide hoof protection and support weakened or damaged hoof tissues. Two hypotheses were tested in this study: 1) motion of the third phalanx (P3) and hoof wall deformation are greater in laminitic versus unaffected hooves regardless of shoe type; 2) P3 displacement and hoof wall deformation are greatest while unshod (US), less with open-heel (OH), then egg-bar (EB) shoes, and least with heart-bar (HB) shoes for both hoof conditions. Distal forelimbs (8/condition) were subjected to compressive forces (1.0x102-5.5x103 N) while a real-time motion detection system recorded markers on P3 and the hoof wall coronary band, vertical midpoint, and solar margin. Magnitude and direction of P3 displacement and changes in proximal and distal hemi-circumference, quarter and heel height and proximal and distal heel width were quantified. Hoof condition and shoe effects were assessed with 2-way ANOVA (p<0.05). P3 displacement was greater in laminitic hooves when US or with OH, and EB and HB reduced P3 displacement in laminitic hooves. P3 displacement was similar among shoes in unaffected hooves and greatest in laminitic hooves with OH, then US, EB and HB. EB and HB increased P3 displacement from the dorsal wall in unaffected hooves and decreased it in laminitic hooves. OH and EB increased P3 motion from the coronary band in laminitic hooves, and HB decreased P3 motion toward the solar margin in unaffected and laminitic hooves. In laminitic hooves, HB reduced distal hemi-circumference and quarter deformation and increased heel deformation and expansion. Proximal hemi-circumference constriction was inversely related to proximal heel expansion with and without shoes. Overall, shoe configuration alters hoof deformation distinctly between unaffected and laminitic hooves, and HB provided the greatest P3 stability in laminitic hooves. These unique results about P3 motion and hoof deformation in laminitic and unaffected hooves inform shoe selection and design.

Fig 1. Study design schematic.

Unaffected and laminitic hooves (n = 8/condition) were stabilized in fixtures on a materials testing system at the metacarpophalangeal joint proximally and the toe distally. Infrared markers of an active motion detection system were attached to the third phalanx (P3) through a window in the hoof capsule and the hoof wall at the level of the coronary band and the solar margin of the lateral and medial quarters and heels. Additional markers were placed at the vertical midpoint of the hoof wall at the toe and the medial quarter, at the dorsal toe at the level of the coronary band, and on the testing fixture at point of the toe. Motion data was recorded during loading up to 5.5x10³ N in a pattern representing a forelimb step cycle with hooves unshod and with open-heel, egg-bar, and heart-bar shoes applied in random order. DW: dorsal wall coronary band, CB: lateral quarter coronary band, SM: lateral quarter solar margin.

Fig 2. Specimen preparation steps.

Photographs depicting a forelimb digit (A) with soft tissues removed except the deep digital flexor tendon (DDFT, white arrow, A, B); fixation of the DDFT to the first phalanx (B); a 3-hole plate (white arrow, C, E, F) immobilizing the proximal interphalangeal joint (C); a specimen stabilized with screws (black arrows, D) within two PVC pipes viewed from proximal (D) and dorsal (E) perspectives; and a construct with resin surrounding the specimen and between two PVC pipes (black arrow, F).

Fig 3. Equine hoof instrumented for data acquisition.

Representative specimen with infrared markers attached and stabilized between the receiving cup (proximally) and the toe piece (distally) fixtures (A) and a corresponding stick figure diagram showing individual segments between markers used to quantify proximal and distal hemi-circumferences, heel and quarter lengths, and proximal and distal heel widths (B). The spheres in the stick figure diagram correspond to the infrared markers, and the lateral surface of the hoof is to the left in each image. DW: dorsal wall coronary band, CB: lateral quarter coronary band, SM: lateral quarter solar margin.

Fig 4. Measures on a mediolateral equine hoof radiograph.

Representations of the radiographic measures used in the study including the coronary band to P3 extensor process distance (CE), proximal and distal horn lamellar zone (HL), the dorsal wall and P3 parietal surface angles, and sole depth (S).

Fig 5. Three-dimensional hoof landmark displacement.

Displacement curves (mean ± SEM) of the third phalanx (P3), lateral quarter coronary band (CB), lateral quarter solar margin (SM), and dorsal wall coronary band (DW) of unaffected (A-D) and laminitic (E-H) hooves during application of a compressive load cycle (~350N/s) from 1.0x10²–5.5x10³ N (n = 8/condition) while unshod (A, E) or while shod with open-heel (B, F), egg-bar (C, G), or heart-bar (D, H) shoes. Significant differences in hoof marker displacement between unaffected and laminitic hooves for each shoeing condition are indicated by asterisks above the associated points in the load cycle (p ≤ 0.05). Asterisk color corresponds to marker location.

Fig 6. Three-dimensional P3 displacement.

Three-dimensional P3 displacement (mean ± SEM) in unaffected (A) and laminitic (B) equine hooves during application of a compressive load cycle (~350N/s) from 1.0x10²–5.5x10³ N (n = 8/condition) while unshod (blue) or while shod with open-heel (gray), egg-bar (orange), or heart-bar (purple) shoes. Significant differences among shoes within hoof condition at distinct loading cycle percentages are indicated by different color letters above data points (p≤0.05).

Fig 7. P3 displacement direction.

Three-dimensional displacement (mean ± SEM) of P3 relative to the lateral quarter coronary band (CB), lateral solar margin (SM) and dorsal wall coronary band (DW) in unaffected (A) and laminitic (B) equine hooves during application of a compressive load cycle (~350N/s) from 1.0x10²–5.5x10³ N (n = 8/condition) while unshod or while shod with open-heel, egg-bar, or heart-bar shoes. Significant differences in landmark displacements among shoeing conditions at the indicated percentage of the load cycle are indicated by distinct letters above data points (p≤0.05).

Fig 8. 3-D hoof wall deformation.

Three-dimensional change (mean ± SEM) of the proximal (A & E) and distal (B & F) hemi-circumference, and proximal (C & G) and distal (D & H) lateromedial heel width in unaffected (A-D) and laminitic (E-H) hooves while unshod (blue) or shod with open-heel (gray), egg-bar (orange), or heart-bar (purple) shoes during a compressive load cycle (1.0x10²–5.5x10³ N). Significant differences among shoeing types within hoof at specific points in the load cycle are indicated by distinct letters (p≤0.05).

Fig 9. 3-D quarter and heel length change.

Three-dimensional change (mean ± SEM) of the quarter (A & C) and heel (B & D) length in unaffected (A-B) and laminitic (C-D) hooves while unshod (blue) or shod with open-heel (gray), egg-bar (orange), or heart-bar (purple) shoes during a compressive load cycle (1.0x10²–5.5x10³ N). Significant differences among shoeing types within hoof at specific points in the load cycle are indicated by distinct letters (p≤0.05).

Fig 10. Mediolateral radiographs of unaffected and laminitic hooves with representative measures.

Radiographs of an unaffected (upper) and laminitic (lower) equine hoof during compressive loading at 1x10² (A, D), 2.75x10³ (B, E), and 5.5x10³ N (C, F). Representative measures are indicated on each image.