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Abstract

Objective

To determine the local variations of mechanical properties of the equine superficial digital flexor tendon (SDFT).

Sample Population

10 SDFT of adult horses, selected for absence of abnormality.

Procedure

Needles (with a dark marker at both ends) pinned perpendicularly through each tendon to delimit 7 segments. Each tendon was tested in traction until rupture; test was filmed, using an 8-mm video camera. For each image, the coordinates of the center of mass of each marker and the corresponding force were registered. The third-degree polynomial that best fits the stress-strain curve thus obtained was calculated by a least squares approximation. The modulus of elasticity (Emax) of each segment was evaluated as the maximum of the derivative of this polynomial.

Results

Mean rupture load of the 10 SDFT was 12,356 ± 1,333 N. The strain at tendon rupture and Emaxvaried, respectively, from 8.1 ± 1.3% and 1,002 ± 161 MPa (sesamoidean region) to 12.5 ± 1.7% and 1,189 ± 63 MPa (metacarpal region). The values of the strain corresponding to Emax were remarkably similar along the SDFT (approx 5%).

Conclusions

Emax appeared fairly homogeneous along an SDFT, although being slightly higher in the metacarpal region. The 5% strain corresponding to Emax could be the limit strain beyond which microlesions of the tendinous fibers begin to appear, this threshold being first reached during the traction test by the metacarpal segments. (Am J Vet Res 1996;57:1111–1117)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To assess histologic variations of the equine superficial digital flexor tendon (SDFT) according to site and to horse age and activity, and to correlate these data with reported segmental mechanical results.

Sample Population

Superficial digital flexor tendons isolated from 42 horses 0.5 hour to 23 years old.

Procedure

7 segments of each SDFT were delimited and submitted for conventional histologic examination. Each segment was examined and graded for fiber undulation, cellularity, number and size of interfascicular connective spaces (ICS), presence or absence of focal and diffuse chondroid metaplasia, and differentiation of the dorsal (DB) and palmar (PB) borders of the tendon.

Results

Fiber undulation and cellularity significantly decreased with age. The proximal and middle metacarpal segment fibers were significantly less undulated and their ICS were smaller than those of the other segments, especially in old horses. Focal chondroid metaplasia developed from 5 years onward, mainly in the sesamoidean segments. Diffuse chondroid metaplasia was characteristic of the digital region in horses > 6 years old. The DB of the metacarpodigital region tended to differentiate into fibrocartilage in association with age. The PB was generally differentiated as nonfascicular dense connective tissue. Activity induced a decrease in the number and size of the ICS.

Conclusions

The lesser undulation of the proximal and middle metacarpal segments fibers can be correlated to their mechanical behavior (stress-strain curve) and relative weakness within the SDFT. Focal chondroid metaplasia and fibrocartilage on the DB are normal features, related to the compression stresses undergone by the sesamoidean region of the tendon. (Am J Vet Res 1998;59:969–977)

Free access
in American Journal of Veterinary Research