This basic science study attempted to evaluate the effect of the rehabilitation method and in vivo force on the healing of repaired flexor tendons. Two-hundred and fourteen profundus tendons in 107 adult dogs were acutely transected and repaired using two techniques; a four- and eight-strand modified Kessler 4-0 core suture and a 6-0 nylon running peripheral stitch. The dogs were randomized into two passive rehabilitation methods. A low-force method employed passive range of motion of the digits with the wrist in a flexed position and wrist extension only with composite digital flexion. The high-force group allowed for full composite wrist and digital extension. The low-force protocol had been shown to generate forces similar to a passive range-of-motion human protocol. The high-force protocol is believed to generate forces similar to human active unrestrained digital flexion. Two five-minute rehabilitation sessions were performed five days a week starting on post-operative day 1. Mechanical testing was performed on the flexor tendon repairs at 5, 10, 21, and 42 days post-operatively. Overall, tensile properties of the repaired tendon did not increase with increased levels of rehabilitation force. The investigators did observe a significant increase in repair-site rigidity (stiffness), a decrease in strain and no overall increase in ultimate force over the first 21 days. They also found a 35% increased rigidity and decreased gapping with the eight-strand suture repair method compared to the four-strand method.
Previous studies have shown an advantage of early passive motion on both the tensile properties and excursion of the repaired flexor tendon as well as in limiting adhesions. This study did not show any further advantage of increased force imparted to the healing flexor tendon with respect to its tensile properties. As has been shown previously, the number of core sutures significantly increased the repair site strength and decreased gapping. Importantly, the use of a greater number of core sutures did not have an adverse affect on healing.