We measured the gliding resistance of canine and human tendons of intrasynovial origin and tendons of extrasynovial origin with and without paratenon, and investigated the structure of paratenon using scanning electron microscopy. In the canine study, seven intrasynovial flexor digitorum profundus (FDP) tendons, seven extrasynovial fibularis (peroneus) longus (FL) tendons with paratenon, and seven FL tendons without paratenon were used. In the human study, seven intrasynovial FDP tendons and seven extrasynovial palmaris longus (PL) tendons cut in half (one half with paratenon, the other half without paratenon) were used. The gliding resistance of each tendon was measured at 1, 5, 10, 20, 50, and 100 flexion/extension cycles. The canine and human FDP tendons maintained a gliding resistance significantly lower than that of the other tendons at all observation points (P < 0.05). In the canine, the gliding resistance of the FL tendon with paratenon was significantly lower than that of the FL tendon without paratenon up to 50 flexion/extension cycles (P < 0.05), but the two were not significantly different at 100 cycles. In the human, the gliding resistance of PL tendons with paratenon was significantly lower than that of the PL tendons without paratenon at all measuring points (P < 0.05). Preservation of paratenon thus appears to decrease the gliding resistance of extrasynovial tendons after repetitive motion in vitro.
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