Fibrosis impairs the formation of new myofibers in the soft palate after injury.

Muscle repair is a crucial component of palatoplasty but little is known about muscle regeneration after cleft palate repair. We hypothesized that the formation of new myofibers is hampered by collagen accumulation after experimental injury of the soft palate of rats. One-millimeter excisional defects were made in the soft palates of 32 rats. The wound area was evaluated after 3, 7, 28, and 56 days using azocarmine G and aniline blue to stain for collagen and immunohistochemistry to identify myofibroblasts and to monitor skeletal muscle differentiation. To evaluate age effects, 16 unwounded animals were evaluated at 3 and 56 days. Staining was quantified by image analysis, and one-way ANOVA was used for the statistical analysis. At day 56, the area percentage of collagen-rich tissue was higher in the injured palatal muscles (46.7 ± 6.9%) than in nonwounded controls (15.9 ± 1.0%, p < 0.05). Myofibroblasts were present in the injured muscles at days 3 and 7 only. The numbers of proliferating and differentiating myoblasts within the wound area were greater at day 7 (p < 0.05), but only a few new myofibers had formed by 56 days. No age effects were found. The results indicate that surgical wounding of the soft palate results in muscle fibrosis. Although activated satellite cells migrated into the wound area, no new myofibers formed. Thus, regeneration and function of the soft palate muscles after injury may be improved by regenerative medicine approaches.