Quantification of axonal ingrowth and functional recovery in a myocutaneous flap model in rats with strong clinical implications.

The process of reinnervation, an important component of functional restoration after flap transfer, is understudied, making it necessary to carry out a further investigation for delineation of the exact timeline. Seventy-six Sprague-Dawley rats were used as the experimental animals. An anatomic study was first conducted to clarify the pattern of nerve distribution in the dorsal skin of 16 rats. Afterward, a myocutaneous flap was harvested on the right flanks of 40 rats, which were then assigned into seven time points. At each time point, skin samples were harvested and immunofluorescent staining was performed using α-Bungarotoxin, and antibodies against NF-200, p75, α-SMA, and TH. One-way analysis of variance was adopted for comparison of nerve density after surgery. For evaluation of functional return, cutaneous trunci muscle reflex (CTMr) test was performed on 10 additional rats, and the Chi-square test was used for comparison of reflex intensity among six time points after surgery. The outcomes revealed that the cutaneous branches from the intercostal nerves and the dorsothoracic nerve from the brachial plexus could be found entering the dorsal skin, distributed in the skin proper and the panniculus carnosus, respectively. After flap surgery, full spontaneous reinnervation of the skin proper and vessels within the flaps could be achieved at day 180. However, if the stumps of cutaneous branches of the intercostal nerves were damaged, the nerve density in the skin proper underwent a 2/3 decline. The panniculus carnosus in the cranial part had a much better reinnervation than that in the caudal part. The CTMr test showed that the flap could regain most of its sensate and motor activity. Our study shows that strong spontaneous reinnervation could be expected after flap surgery. The pattern of the original nerve distribution in both the recipient and donor sites may have a big impact on the reinnervation of the flap.