Time-dependent conditioning effects are important when evaluating the gliding resistance of flexor tendon repairs
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Tensile strength and gliding resistance are key factors influencing the outcome of flexor tendon repairs. In contrast to estimates of tensile strength, little is known about the effect of cyclic conditioning on the gliding resistance of tendon. This study evaluated the effect of pre-conditioning on the internal-work-of-flexion (WOF), a measure of gliding resistance, of Flexor Digitorum Profundus (FDP) tendons when intact and following standard zone 2 repair both with and without repair of the accompanying sheath. Twenty one fresh porcine trotters were dissected the flexor tendon–pulley system of the central rays exposed. The distal FDP insertion was divided and a custom force transducer inserted at the tendon-bone interface. The proximal tendon was secured to the load cell of a uniaxial load-frame, which resulted in an excursion of 30mm, at a rate of 2mm/s, before returning to the rest position. Proximal and distal tendon force was recorded for three flexion-extension cycles under each of the following conditions: (1) tendon and sheath intact, (2) incised tendon sheath, (2) 4–strand surgical tendon repair in zone II, (3) closure of the sheath post repair. WOF was calculated by numerically integrating differential force with respect to tendon excursion. Potential differences in WOF were investigated using a general linear modeling approach with repeated measures. Surgical repair resulted in a significant increase in WOF (56%) when averaged across all test cycles (F=787, P<0.05). Preconditioning, in contrast, resulted in a significant reduction in WOF across all repair states during cycle 2 (12%) and 3 (4%, F=29, P<0.05). The effect was greatest following surgical repair (F=11, P<0.05). In contrast to surgical repair, preconditioning reduced WOF of surgically repaired FDP tendons. It is recommended, therefore, that research evaluating the gliding resistance of repaired tendons employ a preconditioning protocol. These findings also have important clinical implications for rehabilitation protocols.
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