SEGMENTAL VARIATIONS OF IN-VITRO MECHANICAL-PROPERTIES IN EQUINE SUPERFICIAL DIGITAL FLEXOR TENDONS

Objective-To determine the local variations of mechanical properties o f the equine superficial digital flexor tendon (SDFT). Sample Populati on-10 SDFT of adult horses, selected for absence of abnormality. Proce dure-Needles (with a dark marker at both ends) pinned perpendicularly through each tendon to delimit 7 segments. Each tendon was tested in t raction until rupture; lest was filmed, using an 8-mm video camera. Fo r 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 (E(max)) of each segment was evaluated as the maximum of the derivative of this po lynomial. Results-Mean rupture load of the 10 SDFT was 12,356 +/- 1,33 3 N. The strain at tendon rupture and E(max) varied, respectively, fro m 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 strai n corresponding to E(max) were remarkably similar along the SDFT (appr ox 5%). Conclusions-E(max) appeared fairly homogeneous along an SDFT, although being slightly higher in the metacarpal region. The 5% strain corresponding to E(max) could be the limit strain beyond which microl esions of the tendinous fibers begin to appear, this threshold being f irst reached during the traction test by the metacarpal segments.