Intramuscular Neural Arborization of the Latissimus Dorsi Muscle: Application of Botulinum Neurotoxin Injection in Flap Reconstruction

Abstract

Postoperative pain after breast reconstruction surgery with the latissimus dorsi flap is a common occurrence. Botulinum neurotoxin (BoNT) injection during surgery is effective in reducing postoperative pain. This study aimed to determine the most appropriate locations for BoNT injection. A modified Sihler's method was performed on the latissimus dorsi muscles in 16 specimens. Intramuscular nerve arborization was noted under the landmark of the medial side surgical neck of the humerus to the line crossing the spinous process of T5 and the middle of the iliac crest. The latissimus dorsi muscles were divided into medial, middle, and lateral segments with 10 transverse divisions to give 10 sections (each 10%). Intramuscular nerve arborization of the latissimus dorsi muscle was the largest from the medial and lateral part of the muscle ranging from 40 to 60%, middle part from 30 to 60% and medial, middle and lateral part from 70 to 90%. The nerve entry points were at the medial and lateral part with 20-40% regarding the medial side of surgical neck of the humerus to the line crossing spinous process of T5 to the middle of iliac crest. These outcomes propose that an injection of BoNT into the latissimus dorsi muscles should be administered into specific zones.

Keywords: Sihler’s method; botulinum neurotoxin; latissimus dorsi abdominis muscle; myocutaneous flap.

Figure 1

A Sihler’s stained latissimus dorsi muscle with enlarged panels showing intramuscular arborizations.

Figure 2

Intramuscular nerve arborization of the latissimus dorsi muscle was the largest from medial and lateral part with 40–60%, middle part with 30–60% and medial, middle and lateral part with 70–90% (blue shaded) and nerve entry point were at the medial and lateral part with 20–40% (red shaded) regarding the medial side of the surgical neck of the humerus to the line crossing spinous process of T5 to the middle of iliac crest.

Figure 3

Specimens were harvested from the medial side of the surgical neck of the humerus (SN) to the line crossing spinous process of T5 (T5-SP) to the middle of the iliac crest (MIC).

Figure 4

The latissimus dorsi muscle underwent modified Sihler’s method. The method consists of stages of fixation (FX), maceration and depigmentation (MD), decalcification, staining (ST) and clearing (CL).