Mechanical properties of the tendinous equine interosseus muscle are affected by in vivo transducer implantation.

The research investigates how the insertion of liquid metal strain gauges (LMSGs) into the tendinous interosseous muscle (or suspensory ligament, SL) in a pony’s forelimbs affects its mechanical properties. The study emphasizes that strain measurements should be taken as quickly as possible post-implantation, as local changes in the tendon’s mechanical properties can occur within three to four days.

Methodology

• LMSGs were implanted in the SL of six ponies to measure in vivo strains and forces.
• Movement and ground reaction forces were recorded in conjunction with LMSG signals before implantation and then three and four days after.
• All ponies were euthanized, after which tensile and failure tests were carried out on both the instrumented tendons and the tendons in the other limb, where instruments were introduced after death.
• The strain from the origin to the insertion (OI) of the SL was calculated from the movements recorded before and after the operation, using a 2D geometrical model.

Results and Discussion

• The peak strain recorded while the ponies walked was 5.4±0.9%, and that while they trotted was 9.1±1.3%.
• Failure of the SL occurred at a strain of 15.4±2.1% (mean±S.D.).
• The strain measured by the LMSG was larger than the simultaneously recorded OI strain both during walking (0.5±0.7%) and trotting (2.2±1.1%).
• The strain from the origin to the insertion point (OI strain) taken after the implantation was only slightly greater than the pre-operation values.
• The strain at which failure occurred in the in vivo instrumented SLs was 2.0±1.2% hotter, and the failure forces were slightly lesser, than those in the opposite SLs in which instruments were introduced after death.
• The strains appearing in the SLs seemed to be significantly larger than those observed in previous, acute experiments.
• The disparities between in vivo LMSG and OI strains, which were justified by lower failure strains when comparing in vivo and post mortem instrumented SLs, suggested that the tendon’s mechanical properties altered locally within three to four days following the insertion of the transducer.

Conclusion

The researchers concluded that to accurately measure normal physiological tendon strains, the measurements should be taken as soon as possible after transducer implantation to account for any changes in the tendon’s mechanical properties.