Evaluation of support bandaging during measurement of proximal sesamoidean ligament strain in horses by use of a mercury strain gauge

Liquid mercury strain gauges were implanted in the forelimb proximal sesamoidean ligaments (PSL) of 8 adult horses. The gauges measured PSL strain while horses were standing with or without external support. In 6 of the horses, the gauges also measured PSL strain in horses at a walk, with or without external support. Gauges were enclosed within sliding polypropylene tubes to prevent nonaxial deformation. Each gauge was placed in 1 arm of a low-resistance half-bridge circuit. To provide temperature compensation, a dummy gauge was placed in the adjacent arm of the bridge circuit and was implanted next to the active gauge in the surrounding fascial tissue. External support included fiberglass cast support (CAST), dorsal fetlock splint support (DFS), support wraps of 3 bandage materials (SW1, SW2, and SW3), and support wrap with caudal splint (SW4). The cast was applied, with the fetlock and foot in weightbearing position, from the proximal portion of the metacarpus distal to and including the foot. The DFS was applied by placing the cranial half of the fiberglass cast on the dorsal aspect of the instrumented limb. The SW1, SW2, and SW3 were applied in a figure-8 pattern around the fetlock, using 50% of the linear stretch capacity of the bandage material, with the horse standing squarely on all 4 limbs. The SW4 was applied identically to the other support wraps, with the exception of addition of a flexible caudal splint incorporated in the support wrap. Mean maximal strain while standing without external support for 8 horses was 6.0% (range, 3.8 to 7.5%). Mean maximal strain at a walk without external support for 6 horses was 5.9% (range, 4.1 to 8.2%). Only cast and DFS significantly reduced mean maximal strain while standing. Cast support reduced mean maximal strain while standing to a mean +/- SEM 1.4 +/- 0.2%, 77% reduction in total strain (P < 0.0001). Use of DFS reduced mean maximal strain while standing to a mean 4.2 +/- 0.3%, 30% reduction in total strain (P < 0.0001). The SW1, SW2, and SW3 did not significantly reduce mean maximal strain while standing (power > 0.8, delta = 20%). Conclusions cannot be made for reduction of mean maximal strain while standing with SW4 (power < 0.8, delta = 20%) because of low sample size. Only CAST and DFS significantly reduced mean maximal strain while walking. Cast support reduced mean maximal strain while walking to a mean 2.0 +/- 0.3%, 67% reduction in total strain (P < 0.0001). The DFS reduced mean maximal strain while walking to a mean 4.4 +/- 0.4%, 25% reduction in total strain (P < 0.008). The SW1, SW2, and SW3 did not significantly reduce mean maximal strain while walking (power > 0.8, delta = 20%). Conclusions cannot be made for reduction of mean maximal strain while walking with SW4 (power < 0.8, delta = 20%) because of low sample size.