Abstract
Landes CA, Weichert F, Steinbauer T, Schroder A, Walczak L, Fritsch H, Wagner M. New details on the clefted uvular muscle: analyzing its role in histological scale by model-based deformation analyses. Cleft Palate Craniofac J. 2012;49:51–59.
The study by Landes et al. (2012) is well conducted and the article is well written. The authors reported on their findings involving 18 aborted embryos and fetuses. We take issue not with their methodology but with the following statements, which are quoted from the article. We believe that the stated conclusion is spurious for the reasons explained after the quote.
“The findings in the present publication should be seen in light of the fact that the MU [musculus uvulae] may be hypotrophic or even completely absent later in life (Landes et al., 2010). Therefore, it may be concluded that the role of the MU is at its zenith in prenatal and early postnatal periods of life rather than adulthood.” (p. 57–58)
The article by Landes et al. (2010) in this quote is referenced in the Landes et al. (2012) article as an “online publication ahead of print, August 16, 2010.” That article has now been published (Landes et al., 2011). We believe that reference to the 2010 reference (now 2011) is misleading in that the authors did not study adult specimens, but rather embryos and fetuses. Thus, the reader might misinterpret their reference to Landes et al. (2011) as evidence that the authors actually found examples of hypotrophic or absent MU later in life (i.e., in adult specimens). We know of no study in which investigators reported finding absent MU in normal adult specimens. On the contrary, in our own studies we have found that, although the expression of MU is variable across normal noncleft adult specimens (single versus paired structures, for example), the muscle is actually quite robust and is definitely present (Azzam and Kuehn, 1977; Kuehn and Kahane, 1990; Kuehn and Moon, 2005). Huang et al. (1997) reported similar findings in all 18 of their normal adult specimens. The argument that we are presenting is not aimed at adult individuals with cleft palate in whom the MU may indeed be hypotrophic or absent, given that it is normally a midline structure. Rather, we are arguing only in relation to normal noncleft adult individuals.
The logic of the conclusion that “the role of the MU is at its zenith in prenatal and early postnatal periods of life rather than adulthood,” is questionable. What possible reason could there be for the most important role of the muscle occurring early in life, even prenatally, versus later in life? One might argue that the function of MU might be involved in a primitive infantile reflex, such as the Moro reflex, which disappears early in life. Particularly, MU might be involved in the gag reflex. However, it is well known that the gag reflex does not disappear early in life but persists over the life span. Therefore, to the degree that MU may be involved in the gag reflex, its importance would persist in adulthood as well as in early life.
What is the role of MU? Several authors have suggested that MU functions as a space occupying structure and may stiffen the soft palate to increase responsiveness. We agree with these possible roles. In addition, we have suggested that MU might function in rotating the posterior half of the soft palate toward the posterior pharyngeal wall thereby working in concert with the levator veli palatini muscle to achieve tighter velopharyngeal closure (Kuehn et al., 1988). In this regard, we believe that MU might serve as a failsafe mechanism to ensure tight velopharyngeal closure in normal individuals for speech and swallowing. In individuals with cleft palate, for whom MU might be hypotrophic or absent, greater reliance would have to be placed on the levator veli palatini muscle (assuming that it has been surgically repaired properly) in achieving adequate velopharyngeal closure.
A final comment pertains to the name of MU, i.e., musculus uvulae. This is an unfortunate label given that the bulk of the muscle is not located within the uvula itself, but rather superior to it in an area overlying the levator sling (Azzam and Kuehn, 1977; Kuehn and Kahane, 1990; Ettema and Kuehn, 1994; Huang et al., 1997; Kuehn and Moon, 2005). Very few muscle fibers, if any, are found in the uvula proper. In their discussion of the functional relevance of MU prenatally versus in adults, Landes et al. (2011) seem to perpetuate the misconception of the primary location of MU given their statement that “Uvular ablation in snorers can be carried out without considerable detriment to speech or swallowing” (Landes et al., 2011, p. 644). That is probably a true statement, but it has little to do with MU given that the major bulk of the muscle is not in the uvula.
We wish to end on a positive note indicating that we applaud the careful and very informative work of Landes and colleagues. We simply feel that it is important to clarify the points that we have raised here.