Letter to the Editor Regarding: “Supercharge End-to-Side Nerve Transfer: A Systematic Review,” by Dunn et al.

To the editor,

We read with interest the recent article entitled “Supercharge End-to-Side Nerve Transfer: A Systematic Review” by Dunn et al.¹ They evaluated 73 papers, eventually including 4 papers. After analysis of the 78 patients from the 4 studies, they concluded that the supercharge end-to-side transfer (SETS) of the anterior interosseous nerve (AIN) to the motor branch of the ulnar nerve (MUN) had yielded a high return of intrinsic function of 91.7 % at an average of 3.7 months.¹ These results must be interpreted with caution. Such a rapid and complete recovery is typical of incomplete lesions or aberrant median-to-ulnar intrinsic innervation. The patients included have a mixed etiology of compressive, inflammatory, and traumatic lesions of the ulnar nerve, as well as a variety of adjunctive procedures.^1-4 This would make interpretation of the results difficult, and we feel that traumatic lesions should be a separate subgroup from compressive lesions. A further concern is that 2 of the 4 papers included in the systematic review were not papers about SETS transfers, but used a standard end-to-end (ETE) transfer technique.^2,3 The first of these is by Haase and Chung² in 2002. Haase and Chung detail the procedures used in the 2 reported cases, and they describe division of the MUN for direct coaptation with the pronator quadratus (PQ) branch of the AIN in one case and via a sural nerve graft in another case. These are standard ETE transfers and not end-to-side (ETS) or SETS transfers as determined by the authors of this review. This is further confirmed by intraoperative photographs and diagrams that demonstrate an ETE repair. For further clarification, in their discussion, Haase and Chung² comment on the limitation of their technique as to not being able to tell whether a patient has a Martin-Gruber (MG) anastomosis, but go on to state that any return of function is definitely through the transfer as the MUN was divided distal to any potential MG anastomosis. The second paper in their review that should not be there is by Novak and Mackinnon³ in 2002. This similarly is a cohort of patients who underwent standard ETE transfers and not SETS transfers. Barbour et al⁵ detailed their results of SETS transfers in 2012, which was soon followed by a letter to the editor by Jonathan Isaacs⁶ in 2013, stating he first described this technique as a reverse ETS in a rat model in 2005. Susan Mackinnon⁷ herself replies to this comment, stating she first performed the SETS transfer in 2009, and hence both the 2002 studies^2,3 included in the systematic review of SETS transfers by Dunn and colleagues were 7 years before this procedure was performed in clinical practice and should be excluded from the review.^1-3,7 Future robust research is needed to ascertain the efficacy of the SETS AIN transfer to elucidate the source of axonal regeneration resulting in functional muscle recovery in these patients before it can become a widespread practice among nerve surgeons.