Discussion: Redefining the Rectus Sheath
Those of us who commonly perform abdominal wall reconstruction know that the clinical location of the transversus abdominis muscle differs from what is taught in anatomy textbooks; this is the first study to confirm and reinforce our clinical observation with radiographic data. In the standard textbook illustration of the abdominal wall, the transversus abdominis muscle is located lateral to the semilunar line; its aponeurosis contributes to the posterior rectus sheath above the arcuate line and to the anterior rectus sheath below the arcuate line. However, the authors found, on the basis of computed tomographic imaging, that the transversus abdominis muscle itself is a component of the posterior rectus sheath above the arcuate line in the vast majority of patients (not only its aponeurosis). Specifically, the muscle was present in the posterior rectus sheath at the level of the costal margin in 100 percent of subjects, 98 percent at L1, and 85 percent at L2. Furthermore, the mean overlap of the rectus abdominis and transversus abdominis was 4.4 cm at the level of L1, 2.9 cm at L2, and 1.3 cm at L3. These findings are particularly germane to the transversus abdominis release procedure: to correctly perform the release, the transversus abdominis muscle must first be identified and released in the upper abdomen. Here, a plane can be developed between the transversus abdominis and the transversalis fascia. The transversus abdominis should then be followed inferiorly, as its medial border retreats laterally and posterior to the internal oblique muscle. Identification of the transversus abdominis muscle rather than the aponeurosis facilitates the entry and release of the correct plane. As the release proceeds inferiorly, the plane of release is maintained as the transversus abdominis muscle retreats laterally, leaving only the transversus abdominis aponeurosis to release.
Novitsky et al. and Krpata et al. provided the first clinical descriptions and case series of the transversus abdominis release/posterior component separation.1,2 Interestingly, they describe the necessity of identifying the transversus abdominis within the posterior rectus sheath in the upper abdomen and releasing the muscle inferiorly. However, although this anatomical relationship is well known to abdominal wall reconstruction surgeons, the fact that it is incorrectly depicted in the literature does our students and trainees a disservice. Possibly, this article will provide anatomists with a reliable source with which to revise the canon of human anatomy.
There are several aspects of the article that require emphasis. First, to completely perform a transversus abdominis release/posterior component separation, the transversus abdominis muscle and aponeurosis must first be identified and released in the upper abdomen. The surgeon can identify the correct plane in the upper abdomen and easily follow it inferiorly, providing a proper release.