Segmental variations of in vitro mechanical properties in equine superficial digital flexor tendons.

The research paper focuses on investigating the local variations in the mechanical properties of horse’s superficial digital flexor tendons.

Research Methods

• The study observed 10 superficial digital flexor tendons (SDFT) of adult horses, specially selected without any abnormality.
• Needles marked with a dark marker at both ends were pinned perpendicularly through each tendon, dividing them into 7 segments.
• A traction test was performed on each tendon until rupture and each test was recorded using an 8-mm video camera.
• The coordinates of the center of mass of each marker and the corresponding force were registered diligently for each image.
• A third-degree polynomial that best fits the stress-strain curve thus obtained was calculated using a least squares approximation.
• The modulus of elasticity (Emax) of each segment was evaluated as the maximum of the derivative of this polynomial.

Findings

• The average rupture load for the 10 SDFTs was found to be 12,356 +/- 1,333 N.
• The strain at tendon rupture and Emax showed variations. In the sesamoidean region, the values were recorded to be 8.1 +/- 1.3% and 1,002 +/- 161 MPa respectively. In the metacarpal region, the values were observed to be 12.5 +/- 1.7% and 1,189 +/- 63 MPa respectively.
• The strain values corresponding to Emax were found to be remarkably similar along the length of the SDFT, approximately 5%.

Conclusions

• Emax was found to be almost homogeneous along an SDFT, though it was slightly higher in the metacarpal region.
• The study suggests that the 5% strain corresponding to Emax could be the critical strain level beyond which microlesions in the tendinous fibers may begin to appear. This threshold seemed to be first reached during the traction test by the metacarpal segments.