Remodeling of the gliding surface after flexor tendon repair in a canine model in vivo

Maintaining a smooth lubricated surface between the flexor tendon and sheath after tendon repair is very important for restoration of digit function. We studied the tendon surface after tendon repair mechanically in a canine model in vivo by measuring frictional force. One hundred and twenty flexor digitorum profundus (FDP) tendons were lacerated to 80% of their cross-section and repaired with either a modified Kessler (MK) or Becker (MGH) repair. The postoperative therapeutic regimen was either synergistic wrist and digit motion (SWM) or passive digit flexion and extension with the wrist fixed in 45° of flexion (FIX). The dogs were sacrificed at one, three, or six weeks postoperatively. Thirty six FDP tendons from normal paws served as the control group, with each control tendon tested in two different conditions: intact and immediately after partial laceration and repair (0 time), making a total of five different timing points (intact, 0 time, one week, three weeks, and six weeks) for each repair type and each postoperative therapy. Frictional force between tendon and proximal pulley was evaluated after breaking any adhesions. Compared to intact tendons, friction was significantly increased immediately after tendon repair. The friction of the MK repair was significantly less than that of the MGH repair at all time and therapy groups, except at six weeks in the SWM group. For the MGH repair, at six weeks friction in the SWM group was significantly less than friction in the FIX group. This study showed that postoperative tendon gliding depends on the method of tendon repair and the postoperative therapy regimen. Furthermore, we have demonstrated that the gliding surface after tendon repair remodels with time.