Tendon autografts for bridging nerve defects

A new method, where a tendon segment – a tendon autograft – was used as graft material for peripheral nerve reconstruction, was developed. Defects, 10-15 mm long, in rat sciatic nerves were bridged by various modifications of tendons. A piece of an intact tendon and a tendon, that had been teased into a membrane and then rolled to form a loose “collagen roll”, supported axonal regeneration over a nerve defect. After modification by forming a tube of the teased tendon, axonal regeneration started after an initial delay period of 6.8 days, and axons then grew at a rate of 1.0 mm per day. Schwann cells migrated into the grafts from the proximal and distal nerve segments, proximally ahead of the regenerating axons. Macrophages were initially present at the periphery of the grafts but gradually increased in numbers inside the grafts. The tendon autograft was vascularized and the blood vessels entered the grafts from both the proximal and distal nerve segments. The tendon autograft supported recovery of muscle function measured as tetanic force of the gastrocnemius muscle, to the same extent as nerves reconstructed by a freeze-thawed muscle graft. Morphometrical analysis of the tibial nerve distal to the graft showed a correlation between the number of regenerating nerve fibers and recovery of muscle force. Initial experiments indicated that a teased and rolled tendon, which had been pretreated by attachment of nerve segments to allow migration of Schwann cells into the tendon, improved regeneration. To refine the tendon autograft and to enhance regeneration, cultured Schwann cells were added to grafts that were used to bridge a 10 mm long nerve defect. Addition of cultured Schwann cells resulted in a higher rate of axonal regeneration compared to untreated control rats. Analogous observations were made in the pretreated freeze-thawed muscle grafts. To address clinical demands of a faster procedure for production of Schwann cells, acutely dissociated Schwann cells from a previously injured nerve were added to tendon autografts bridging nerve defects. Addition of dissociated Schwann cells resulted in a longer axonal outgrowth seven days after nerve reconstruction compared to untreated control grafts. The use of tendon autografts with added acutely dissociated Schwann cells may be an alternative in bridging nerve defects in a clinical setting