Update on the Split Muscle Technique for Breast Augmentation
The subpectoral technique  and systematic analysis of soft tissue characteristics  have resulted in a more predictable approach to breast implant surgery, yet certain problems receive scant attention. Among these problems are animation distortions and shape issues such as "double-bubble" deformity.
In 2004, I reported the split-muscle technique as an option that balances factors such as the need for coverage in thin or athletic women who want to avoid breast distortion with physical activity . Use of the split-muscle technique in a large series also has been reported by Khan , with good outcomes and no significant animation problems. Conversely, a recent survey by Spear et al.  found an overall incidence of 77.5% for some degree of distortion with subpectoral augmentation, rated as moderate or severe by 15% of patients. Considering that more than 350,000 augmentation cases occur annually in the United States , most of which are subpectoral, this becomes a significant issue.
Another problem, the ‘‘double-bubble’’ deformity, may be related. Although this contour defect generally corresponds to the original inframammary fold, particularly in cases with a short preoperative distance from the areolar margin to the inframammary fold, I have routinely observed termination of the pectoralis muscle into the anterior capsule at the level of the external groove, which defines the abnormality. This may be coincidental where the preoperative inframammary fold is high, but the double-bubble contour occasionally develops when the areolar margin-to-fold distance is normal. This can easily be ascertained by asking the patient to flex and then observing upward pull at the level of the external groove, a phenomenon called "windowshading" (Fig. 1a, b). When the patient is at rest, this external indentation is manifest externally as the ‘‘double bubble’’ and corresponds to the edge of the muscle where it transitions into the capsule.
The aforementioned problems occur because the portion of the muscle originating from the rib cage typically is attached at or cephalad to the inframammary fold. Therefore, it must be divided in most cases, allowing its retraction superiorly (Fig. 2a, b). By definition then, the divided edge of the muscle settles somewhere between the nipple– areolar complex and the inframammary fold, where it fuses with the anterior capsule as it develops. Contraction of the muscle unavoidably exerts pull on the capsule (Fig. 3), tethered only at its medial transition to the sternal attachment. For this reason, conversion to the split-muscle plane can be a useful option in cases of double-bubble deformities with animation.
One of the primary indications for subpectoral placement is upper pole coverage, afforded by the portion of the pectoralis major originating from the sternum. The costal portion provides central coverage, in which a subfascial or subglandular plane very often is adequate because of breast tissue, even when upper pole muscle coverage is desirable.
For primary augmentation using the split-muscle technique, the prepectoral fascia is elevated using electrocautery under direct vision up to a line from the axilla to the point at which the pectoralis transitions from the sternum to the rib cage. The muscle fibers then are separated along this line to elevate the superior portion of the muscle while leaving the inferior portion undisturbed (Fig. 4).