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The Effects of Dynamic Tension and Reduced Graft Size on Muscle Regeneration in Rabbit Free Muscle Grafts

In a study of 28 adult New Zealand White rabbits, the influence of tension and size on muscle regeneration in tibialis anterior free muscle grafts (without vascular anastomoses) was examined 6 months after transplantation. Three laboratory models were studied: (1) whole dynamic (WD) graft (allowing ankle excursion and, therefore, variable dynamic physiologic tension), (2) whole static (WS) graft (constant, fixed length and, thus, only isometric tension), and (3) longitudinally sliced (reduced radius) dynamic (SD) model. Bilateral orthotopic grafts of the tibialis anterior muscle were performed in 24 rabbits (eight animals in each of the three different model groups). Controls consisted of normal tibialis anterior muscle from four age-matched rabbits. All tibialis anterior muscle grafts were examined histologically (fiber counts) and functionally (determined by in situ contractile properties under maximal stimulation conditions). The WD grafts demonstrated a significantly higher number of regenerated fibers per muscle cross section (4819 ± 589) than the WS (2221 ± 603) or SD (1919 ± 732) grafts. The amount of tetanic tension in the WD grafts was 35 percent of the control and twice as much as that of the WS grafts (WD 1.0 ± 0.2 kg versus WS 0.5 ± 0.4 kg; p < 0.05). The SD grafts produced approximately one-third as much maximum tetanic tension as the WD grafts (0.3 ±0.1 kg versus 1.0 ± 0.2 kg), demonstrating that the amount of recovery was similar in these two dynamic models, since only the longitudinal middle third of the muscle was grafted in the SD model. Free muscle grafts under dynamic tension, which allows excursion, have shown a greater amount of muscle-fiber regeneration and restoration of function compared with a graft with fixed length. The positive effect of dynamic mechanical tension on small autogenous free muscle grafts (without vascular anastomoses) is clinically significant in the reconstruction of facial and hand neuromuscular deficits when blood vessels are not available for reanastomosis. Future studies using the tibialis anterior WD and SD transplant models will strengthen our understanding of the events of spontaneous revascularization and skeletal muscle regeneration.