Tacrolimus as an adjunct to autologous minced muscle grafts for the repair of a volumetric muscle loss injury

Abstract

Background: Volumetric muscle loss (VML) following extremity orthopaedic trauma or surgery results in chronic functional deficits and disability. A current translational approach to address the devastating functional limitations due to VML injury is the use of an autologous minced muscle graft (~1 mm³ pieces of muscle tissue) replacement into the injured defect area, although limitations related to donor site morbidity are still unaddressed. This study was designed to explore adjunct pharmacological immunomodulation to enhance graft efficacy and promote muscle function following VML injury, and thereby reduce the amount of donor tissue required.

Findings: Using a validated VML porcine injury model in which 20% of the muscle volume was surgically removed, this study examined muscle function over 3 months post-VML injury. In vivo isometric torque of the peroneus teritus (PT) muscle was not different before surgery among sham, non-repaired, non-repaired with tacrolimus, graft-repaired, and graft-repaired with tacrolimus VML groups. Bi-weekly torque analysis of the VML injured musculature presented a significant strength deficit of ~26% compared to pre-injury in the non-repaired, non-repaired with tacrolimus, and graft-repaired groups. Comparatively, the strength deficit in the graft-repair with systemic tacrolimus was marginally improved (~19%; p = 0.056). Both of the minced graft repaired groups presented a greater proportion of muscle tissue in full-thickness histology specimen.

Conclusions: We demonstrate that adjunctive use of tacrolimus with an ~50% minced muscle graft replacement resulted in modest improvements in muscle function 3 months after injury and repair, but the magnitude of improvement is not expected to elicit clinically meaningful functional improvements.

Keywords: Neuromuscular strength; Orthopaedic trauma; Porcine; Skeletal muscle injury.

Fig. 1

Representative histologic micrographs of Masson’s Trichrome stained (connective tissue is blue; nuclei are purple; skeletal muscle fibers are red) porcine peroneous tertius (PT) muscle following VML injury and repair. While all PT muscles indicate gross fibrosis following VML injury, only the muscle graft-repaired displayed areas of likely regenerated fibers. There were no apparent differences due to treatment with tacrolimus. (a) Each sample represents a full thickness sample through the muscle. Scale bar is 2 mm; all images are at the same magnification. (b) Representative inserts from the remaining muscle, border, and defect area of the samples are displayed. Scale bar is 100 μm; all images are at the same magnification

Fig. 2

Peroneus teritus (PT) muscle function was determined by peroneal nerve stimulation in vivo. The percent torque deficit to the pre-injury torque was determined for the (a) non-repaired and (b) muscle graft (MMG) repaired groups following VML injury and the effect of adjunctive tacrolimus was investigated across these groups. The strength of the sham operated group was consistent over time (duplicated in each panel) and all VML injured groups were less than sham operated. All data analyzed by two-way ANOVA (group p < 0.001; time p = 0.104; interaction p = 0.999). * Significant main effect of group, sham > all other surgical groups. Data are mean ± standard error