Partial lacerations of human digital flexor tendons: a biomechanical analysis

The biomechanical properties of human flexor tendons with partial lacerations have not been previously studied. To determine the loss of tensile strength with varying degrees of partial laceration, tensile tests were performed on 2 matched groups of human cadaver flexor tendons: One group had 50% while the other had 75% transverse volar lacerations of the anteroposterior diameter. The mean failure load of the 50%-lacerated tendons was 93% higher than that of the 75%-lacerated tendons. The forces tolerated by the lacerated tendons before failure were also compared to those measured in vivo during physiologic loading. The breaking loads of both 50%- and 75%-lacerated tendons far exceeded the in vivo forces measured in human flexor tendons during unresisted active finger movement (up to 34 N). Further, the breaking loads of 50% lacerations was higher than the in vivo forces during resisted active finger movement (up to 117 N). This study demonstrates that the threshold load levels to rupture of 50% and 75% lacerations are higher than physiologic load levels measured during active motion, suggesting that partial flexor tendon lacerations of up to 75% can withstand in vivo forces associated with active unresisted mobilization of the digital flexor tendon.