Effect of flexor sheath integrity on tendon gliding: a biomechanical and histologic study

The effect on tendon gliding of flexor sheath excision versus incision/closure following primary flexor tendon repair was examined biomechanically and histologically in forty-one chickens. There was no significant difference in either the tendon excursion required to fully flex the digit or in the work of flexion (the integration of the forces that resist tendon gliding during excursion) between the sheath excised and sheath closed groups. The results were unaffected by postoperative immobilization or intermittent passive motion. Histologically, it was noted that at 3 weeks the healing tendon was surrounded by a layer of granulation tissue that was nearly identical in both the sheath excised and the sheath closed digits. Of note was the finding that a synovial lining could not be identified in those digits that had previously undergone sheath closure. However, at 6 weeks postoperatively, a new gliding surface could be identified surrounding the tendon in both the sheath excised and the sheath closed digits. This study indicates that closure of the flexor sheath after primary tendon repair does not improve tendon gliding as measured biomechanically. Despite its repair, the flexor sheath does not maintain its synovial characteristics as demonstrated histologically, and a new sheath must subsequently be formed.