EFFECTS OF TENDON GRIP TECHNIQUE (FROZEN VERSUS UNFROZEN) ON IN-VITROSURFACE STRAIN-MEASUREMENTS OF THE EQUINE DEEP DIGITAL FLEXOR TENDON

Objective-To determine effects of tendon grip technique on in vitro su rface strain measurements of equine deep digital flexor tendon (DDFT) when loaded in tension. Sample Population-12 hind limb DDFT from 8 adu lt horses (mean age, 9.8 years [range, 4.5 to 17 years]; mean body wei ght, 472 kg [range, 450 to 509 kg]), with no clinical evidence of hind limb lameness. Design and Procedure-After calibration, liquid mercury strain gauges were sutured to plantar surfaces of the tendons at dist al (position 1), middle (position 2), and proximal (position 3) metata rsal regions. Each tendon was affixed to a materials testing machine ( distally by the distal phalanx, and proximally by a metal clamp), and loaded once in tension, at a strain rate of 2.8 to 3.0%/s, to 3% clamp displacement. Liquid nitrogen was used to freeze the proximal ends of 6 tendons before placement in the clamp. Proximal ends of the remaini ng 6 tendons were left unfrozen. Surface strains were determined with the aid of low-resistance bridge circuits. Data were analyzed at time points corresponding to 1, 2, and 3% clamp displacement. Results-Mean surface strains of tendons with frozen ends were significantly greater than those for tendons with unfrozen ends, and closer to strain measu red by clamp displacement, at 1 and 2% clamp displacement. This differ ence was present but not significant at 3% clamp displacement. Mean lo cal surface strain was not significantly different between the 3 gauge positions. Conclusions-Freezing tendon ends is a useful technique to increase measured surface strains in equine DDFT, thereby making them closer to universal strain as measured by clamp displacement, and, thu s, more likely to represent true surface strain.