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

This research studied the effects of two different techniques for gripping tendons during experiment — having the ends frozen or not — on the recorded surface strain measurements in horse muscles. The findings suggested that freezing the tendon ends before clamping them leads to higher measured surface strains, making these measurements closer to the true strain on the muscles.

Methodology

• The researchers for this study selected 12 hind limb deep digital flexor tendons (DDFT) from 8 adult horses with an average age of 9.8 years. Their mean body weight was roughly 472 kg. None of these horses showed any clinical signs of hind limb lameness.
• The tendons were then fitted with liquid mercury strain gauges that had undergone calibration. These gauges allowed the researchers to measure the strain at different parts of the tendons, specifically their distal, middle, and proximal sections.
• The tendons were loaded on a materials testing machine in a specific way. The distal end was attached via the distal phalanx, while the proximal end was secured by a metal clamp.
• A key aspect of their experimental design was that half the tendons had their proximal ends frozen using liquid nitrogen before being placed in the clamp. The remaining tendons were left untreated, so they may serve as a comparison group.

Results

• The tendons were loaded in tension once at a strain rate of 2.8 to 3.0%/s to a 3% clamp displacement. The researchers closely monitored surface strains with the use of low-resistance bridge circuits, and quantitatively analyzed the data at 1%, 2%, and 3% clamp displacement.
• Comparisons revealed that the tendons with frozen ends recorded higher average surface strain than their unfrozen counterparts. This disparity, however, became less significant at the 3% clamp displacement.
• Local surface strain was not significantly different across the three gauge positions.

Conclusions

• From the data, it’s clear that freezing the tendon ends beforehand does increase the measured surface strains in horse DDFT. The fact that these readings are closer to the strain measured by clamp displacement suggests that they are in fact more representative of the true surface strain.
• This technique might be useful in future studies or medical procedures that require a more accurate measurement of surface muscle strain.