Discussion: Revisiting the Abdominal Donor Site

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Whether it is Linnaeus describing biological taxonomies of flora and fauna or clinicians using the tumor, node, metastasis (TNM) system, classification schemes have long been recognized as a way of better describing—and comprehending—natural phenomena. In plastic surgery, and breast reconstruction in particular, an example of a widely used and practical classification system has been Nahabedian’s seminal muscle-sparing (MS) system. In its original iteration, Nahabedian identified patterns of rectus muscle preservation from none (MS-0) to lateral muscle preservation (MS-1) to lateral and medial muscle preservation (MS-2) to full muscle preservation [MS-3 or a formal deep inferior epigastric perforator (DIEP) flap].1 Lee et al. subsequently modified this by integrating nerve preservation into the MS terminology.2
Weissler et al. have further elaborated on these predicate classification formats by introducing more robust descriptors for percentage and location of muscle harvest, type of fascial closure, mesh placement, and segmental nerve division. The authors provide a rationale for this new scheme with the argument that the previous Nahabedian and Lee formulations do not fully describe the anatomical variability of rectus abdominis harvest. As they note, “Given the heterogeneity in flap dissection techniques and definitions, we must interpret surgical outcomes judiciously.” Wu and colleagues point out that although the location of the muscle harvested (and concomitant muscle preserved) is important, how much of that muscle is preserved may also be an important factor. To this end, their proposed system factors in the percentage of the width of the muscle divided coupled with location of the divided muscle. The literature provides measured justification of this concept of abdominal muscle strength correlating with muscle preservation in the most polarized comparisons (MS-0 versus DIEP flaps): Blondeel noted a significant difference in abdominal wall strength at 1 year, whereas Schaverien et al. did not find significant differences in functional activities as measured by 36-Item Short-Form Health Survey scores.3,4
Furthermore, Weissler et al. note that a dichotomy between muscle preservation and fascia preservation may exist. That is, occasions may arise in which fascia preservation may not coincide with muscle preservation. The authors’ pragmatic solution to the issue of how much fascia is preserved is to simply equate fascia preservation with the ability to close primarily or not. Not only does this make eminent sense, but it allows us to consider the subtle implications of partial muscle–full fascia preservation vis-à-vis other permutations (e.g., full muscle-full fascia preservation, or varying muscle-mesh closures).
Sensitive to adapting their new classification system to modern breast reconstructive practice, the authors also include a category for mesh placement. Especially for MS-0 to MS-2 flaps, the use of mesh may impact bulge and hernia. The caveat here is that the proposed mesh subtype simply delineates its presence or absence, whereas there is some support in the literature that type of mesh (biological versus synthetic) and inset strategy (onlay versus inlay) may also impact abdominal wall integrity.5–7 With respect to denervation of the rectus abdominis, several studies suggest the importance of preservation of the lateral intercostal nerves.8,9 Accordingly, the authors’ classification scheme incorporates this concept of lateral nerve preservation into the scheme as N0 to N2. Although the authors do not specifically point this out, the utility of their system is that from a functional perspective, even pedicled transverse rectus abdominis myocutaneous (TRAM) flaps could be largely encompassed by their schema (a pedicled TRAM flap could be construed as a MuCLM100% F0MN2).
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