Muscle regeneration and fiber-type transformation during distraction osteogenesis

The successful outcome of distraction osteogenesis depends in part on the a dequate adaptation of the surrounding soft tissue. We characterized the ada ptation of the tibialis anterior during distraction osteogenesis at differe nt rates (0.7 and 1.4 mm/day) and amounts (15 and 30%) of lengthening. We d ocumented the increased expression of neonatal and slow myosin heavy chain in the tibialis anterior of skeletally immature rabbits. There was neither expression of neonatal myosin heavy chain in the experimental soleus or in the slow muscle fibers of the tibialis anterior nor increased expression of slow myosin heavy chain in the soleus or gastrocnemius. The increased amou nt of neonatal myosin heavy chain was concentrated in the distal half of th e muscle, whereas the increase in the number of fibers that were labeled wi th antibodies to slow myosin occurred to the same extent throughout the tib ialis anterior. Electrophysiological methods showed that the tibialis anter ior was functionally intact during and after distraction osteogenesis. We c oncluded that in the tibialis anterior of young, skeletally immature animal s, distraction osteogenesis seems to induce a recapitulation of the develop mental process without leading to functional changes. In addition, during d istraction osteogenesis, a fiber-type transformation occurs similar to that observed in models of muscle overloading.