Does loading velocity affect failure strength after tendon repair?

Tensile testing of repaired tendons has been used to assess the efficacy of repair techniques. However, individuals flex and extend fingers at rates higher than those typically used for testing. This study characterized the effect of loading rate on the failure strength of repaired canine flexor tendons. Thirty-six canine flexor digitorum profundus tendons were lacerated, repaired, and tested at three displacement rates: 0.33 mm/s; 84 mm/s; and 590 mm/s. Peak force and stiffness of the repairs were evaluated. Peak force was significantly greater (p<0.05) for tendons distracted at 590 mm/s than at 0.33 mm/s. Crosshead stiffness was significantly greater for tendons distracted at 590 mm/s than at either 84 mm/s or 0.33 mm/s. The predominant failure mode was core suture knot untying. Distracting tendons at slow loading rates provides a conservative assessment of tendon repair strength. Additionally, an estimate of the failure load of this repair for different clinical events has been identified.