The authors review the literature concerning end-to-side nerve repair to determine the current state of clinical practice and applicability. The paper is divided into sections discussing: Terminology, End-to-Side Coaptation with Deliberate Donor Nerve Axotomy, End-to-Side Coaptation without Deliberate Donor Nerve Axotomy, Experimental Studies of TLN without Deliberate Axotomy, Clinical Experience Utilizing TLN without Deliberate Axotomy, and Controversy Regarding the Source of Axons Populating and End-to-Side Nerve Coaptation. For the purposes of their discussion, the terms terminolateral neurorrhaphy (TLN), latero-terminal neurorrhaphy, end-to-side nerve coaptation, and side-to-end nerve coaptation are used interchangeably. The techniques of TLN with and without deliberate interruption of donor nerve axons are thoroughly described and the mechanisms by which they affect distal reinnervation are postulated. After carefully reviewing and summarizing the available data and clinical experience with the two techniques, the authors conclude that TLN without deliberate axotomy does indeed produce measurable distal reinnervation in both sensory and motor end-unit models. The mechanism by which this occurs is hypothesized to be either: 1) a disruption of donor nerve axons (despite deliberate efforts to prevent this at the time of the TLN) which stimulates axonal sprouting and repopulation of the lateral graft; or 2) trophic substances from the degenerated distal lateral nerve which stimulate collateral internodal sprouting from the intact donor axons to repopulate the lateral graft. Their conclusion is that at the current time, there is little evidence to support the clinical use of TLN without deliberate donor nerve axotomy, as TLN with deliberate donor nerve axotomy is more effective. In fact, they hypothesize, TLN without axotomy may work at all only because there is indeed some degree of axotomy that is unintentionally taking place at the time of coaptation.
This interesting review of the available literature regarding TLN, or end-to-side nerve repair, helps clarify the differences and similarities between the two experimental methods. Their clear message is that TLN without deliberate axotomy is currently neither well understood nor clinically recommended, despite other recent encouraging reports and the obvious theoretic advantage of minimizing donor nerve end-organ deficits. The review is a useful tool for the nerve researcher, outlining the techniques, mechanisms, study methods, and conclusions from current literature. They cautiously recommend future lines of investigation to further resolve the continued controversy regarding the true mechanism of reinnervation, including their own theory that there really is no true difference in the mechanism of axonal sprouting with the two methods. One wonders then, why they go to such lengths to support one method over the other. Clinically, their review shows that the efficacy of reinnervation in TLN does appear to correlate with the degree of damage to the donor nerve, which is the most important point of this review for the practicing peripheral nerve surgeon.
Journal of Reconstructive Microsurgery