Effects of tendon grip technique (frozen versus unfrozen) on in vitro surface strain measurements of the equine deep digital flexor tendon

Abstract

Objective - To determine effects of tendon grip technique on in vitro surface strain measurements of equine deep digital flexor tendon (DDFT) when loaded in tension Sample Population - 12 hind limb DDFT from 8 adult horses (mean age, 9.8 years [range, 4.5 to 17 years]; mean body weight, 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 distal (position 1 ), middle (position 2), and proximal (position 3) metatarsal 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 remaining 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 measured by clamp displacement, at 1 and 2% clamp displacement. This difference was present but not significant at 3% clamp displacement. Mean local 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, thus, more likely to represent true surface strain.