Development of an equine groove model to induce metacarpophalangeal osteoarthritis: a pilot study on 6 horses

Abstract

The aim of this work was to develop an equine metacarpophalangeal joint model that induces osteoarthritis that is not primarily mediated by instability or inflammation. The study involved six Standardbred horses. Standardized cartilage surface damage or "grooves" were created arthroscopically on the distal dorsal aspect of the lateral and medial metacarpal condyles of a randomly chosen limb. The contralateral limb was sham operated. After 2 weeks of stall rest, horses were trotted 30 minutes every other day for 8 weeks, then evaluated for lameness and radiographed. Synovial fluid was analyzed for cytology and biomarkers. At 10 weeks post-surgery, horses were euthanized for macroscopic and histologic joint evaluation. Arthroscopic grooving allowed precise and identical damage to the cartilage of all animals. Under the controlled exercise regime, this osteoarthritis groove model displayed significant radiographic, macroscopic, and microscopic degenerative and reactive changes. Histology demonstrated consistent surgically induced grooves limited to non-calcified cartilage and accompanied by secondary adjacent cartilage lesions, chondrocyte necrosis, chondrocyte clusters, cartilage matrix softening, fissuring, mild subchondral bone inflammation, edema, and osteoblastic margination. Synovial fluid biochemistry and cytology demonstrated significantly elevated total protein without an increase in prostaglandin E2, neutrophils, or chondrocytes. This equine metacarpophalangeal groove model demonstrated that standardized non-calcified cartilage damage accompanied by exercise triggered altered osteochondral morphology and cartilage degeneration with minimal or inefficient repair and little inflammatory response. This model, if validated, would allow for assessment of disease processes and the effects of therapy.

Figure 1. (A) Modified arthroscopic probe in which the tip was hooked and sharpened to a 2 mm internal length. (B) The distal MC3: D = dorsal, P = palmar, L = lateral, and M = medial.

A woven pattern of 4 dorso-palmar and 4 radial grooves created on the weight-bearing area of the lateral and medial condyles. Blue arrows represent the direction the instrument was introduced. Red and green rectangles represent the dorsal histologic slices centered over the groove areas and the palmar histologic slices in the continuity of the dorsal slices.

Figure 2. Lameness evaluation with the inertial sensor-based system.

(A) Asymmetry of movement of the groove limb (red) as opposed to the sham limb (blue), measured by A1/A2. Mean ± SEM is shown. Asterisks represent significant differences between the groove and sham limbs (*P < 0.05, **P < 0.005). (B) Individual time-course of lameness measured by vector sum.

Figure 3. Radiographic views of the MP joint of an individual at week 0 (A, B, C) and week 10 (D, E, F).

A and D show the latero-medial view, B and E show the 45-degree oblique view, and C and F show the dorso-palmar view. Grade 1 to 2 osteophytes (white arrows) and grade 1 sclerosis (white triangles) are visible.

Figure 4. Macroscopic view of the articular cartilage surfaces at week 10 of the sham joints (left) and groove joints (right).

(A), (E) are the dorsal aspects of MC3; (B), (F) are the palmar aspects of MC3; (C), (G) are P1; and (D), (H) are PSB. Characteristic grade 2 wear lines (1), grade 3 erosions (2), grade 3 palmar arthrosis (OC lesions of the distal palmar aspect of MC3) (3), and surgical grooves (4).

Figure 5. (A and B) Representative light micrographs of the dorsal MC3 condylar cartilage (hematoxylin and eosin stained) obtained from a groove joint at week 10 showing lesions of the non-calcified cartilage (red), calcified cartilage (blue), and subchondral bone (green).