Effects of increased in vivo excursion on digital range of motion and tendon strength following flexor tendon repair

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Abstract
Postoperative rehabilitation is an important factor in determining functional outcome following intrasynovial flexor tendon repair. We hypothesized that a rehabilitation protocol that produced increased in vivo excursion would lead to increased digital range of motion and tendon strength and decreased adhesion formation in a canine model. Ninety‐six flexor digitorum profundus tendons from 48 dogs were cut transversely and repaired by a multistrand suture technique. Postoperative rehabilitation was performed daily with a low excursion‐low force (1.7‐mm average excursion: < 10 N force) or a high excursion‐low force (3.6 mm excursion: < 10 N force) protocol. After death of the dogs at 10, 21, or 42 days, specimens were evaluated for digital range of motion, tensile mechanical properties, elongation of the repair site, and adhesion formation. Our data indicate that the range of motion of digits whose tendons were at low or high excursion was similar to that of controls. Increased in vivo tendon excursion due to synergistic wrist motion did not significantly affect ex vivo flexion of the distal and proximal interphalangeal joints or tendon displacement (p > 0.05). Similarly, tensile properties (ultimate load, repair site rigidity, and repair site strain at 20 N and at failure) and length of the gap at the repair site were not significantly affected by increased excursion (p > 0.05). Severity of adhesion formation was reduced slightly by increased excursion (p = 0.04). Our findings indicate that 1.7 mm of tendon excursion is sufficient to prevent adhesion formation following sharp transection of the canine flexor tendon and that additional excursion provides little added benefit.