Digital Resistance and Tendon Strength During the First Week After Flexor Digitorum Profundus Tendon Repair in a Canine Model In Vivo

After flexor tendon repair, the strength of the repair and the resistance to digital motion are important considerations in deciding when to initiate postoperative rehabilitation. Our objective was to assess these factors in a short-term in vivo canine model of flexor tendon repair.Forty-eight dogs were randomly allocated to four groups based on the duration of postoperative follow-up (one, three, five, or seven days). In each group, two flexor digitorum profundus tendons of one forepaw were exposed. One tendon (the repair tendon) was sharply transected and repaired with a modified Kessler suture, and the other one (the sham tendon) was simply exposed without laceration. The involved paw was immobilized until the animal was killed on the designated day. Three tendons from each dog, including the repair tendon, the sham tendon, and a control tendon from a corresponding normal digit on the contralateral side, were tested.The mean peak total digital resistance force in the repair group was lowest at five days (p < 0.01 compared with seven days; p > 0.05 compared with one and three days). The mean peak force needed to overcome the internal gliding resistance between the repaired tendon and sheath was significantly higher than that in both the sham and control groups at all time-points (p < 0.001); however, this value was also smallest at five days. There was no significant difference in suture strength at any time-point (p > 0.05).When we evaluated tendon-gliding and suture strength after flexor tendon repair, the least favorable ratio of repair strength to force needed to overcome the resistance to digital motion was noted on Day 7, whereas the best combination of tendon strength and low peak resistance force was noted on Day 5.