Calibration of the mercury-in-silastic strain gauge in tendon load experiments.

The research presents a method for calibrating strain gauges implanted in horse tendons, which helps measure the force applied to these tendons. The researchers focused on correcting for changes in the strain gauges’ readings due to movement of the gauge or changes in temperature.

Method of calibration of strain gauges

• The researchers introduce a calibration method for mercury-in-silastic strain gauges (MISS) which are implanted in tendons of equine hindlegs studied in vitro (outside the body).
• The calibration process involves conversion of signals from the MISS into quantifiable tendon loads.
• The relationship between the output signals from the MISS and the loads placed on the tendons was determined through tensile-force tests applied to the tendons. This means that the tendons were stretched under controlled conditions, and the corresponding readings from the MISS were recorded.

Addressing Shift Corrections

• Particular emphasis was paid to correct the MISS signals for amplitude shifts that might result from the internal repositioning of the MISS after the tendon has been isolated.
• Adjustments were also made to correct the variations in signals due to changes in temperature.
• The researchers found out that shift corrections equivalent to tendon strains up to 2.8% were necessary in their in vitro experiment.

Verification of Calibration

• The tendon loads deduced from the corrected MISS signals were further checked by torque analyses of the lower part of the limb.
• Differences between the computed and experimentally obtained values of the torque of the tendon loads with respect to the fetlock joint (joint equivalent to the human knuckle located on a horse’s hindleg) were measured.
• The range of these differences was between -4 to +13%, indicating a reasonable margin of error. This confirmed the accuracy and reliability of the calibration method for MISS implanted in tendons.