Vascular and stimulation delays in dynamic musculoplasty

Dynamic musculoplasty is increasingly being used to replace severely damaged muscle. Electrical stimulation induces a change in muscle composition from type II to type I muscle fibers. The aim of this study was to assess the optimal time to start stimulation and the beneficial effect of a vascular delay.

Both gracilis muscles in rabbits (n = 3 x 6) were wrapped around a double polyurethane tube, and leads were implanted together with a neurostimulator. Right muscles were electrically stimulated for 11 weeks, and left muscles served as controls. In group 1 the muscle was stimulated immediately after transposition, in group 2 it was stimulated after 6 weeks, and in group 3 a vascular delay was performed and stimulation was started immediately after transposition.

During stimulation the percentage of type 1 muscle fibers increased from a mean of 4.6% to 41.9%. In group 1 there was significantly more change in muscle tissue. There were no significant differences in recorded pressures between groups. In group 1 the increase in amplitude during stimulation was significantly elevated (p < 0.05). The fatigue index in group 1, 259 (SE 130) seconds, was significantly lower than that of group 2, 515 (SE 102) seconds (p < 0.05).

Compared with the methods used in groups 2 and 3, immediate stimulation (group 1) gives more change in muscle tissue, demanding a higher increase in amplitude to achieve sufficient contraction. The fatigue index is also impaired. Thus vascular delay, as presently applied, does not improve muscle function.