Comparison of clinical performance, histology and single-fiber contractility in free neurovascular muscle flaps

The aim of this study was to obtain further insights about muscle regenerat ion processes in free neurovascular flaps. In cases of insufficient functio nal return of muscle strength, several factors, such as diminished axonal i ngrowth, fatty degeneration, or connective tissue proliferation are discuss ed. In the study, free neurovascular latissimus dorsi (LD) Flaps were exami ned after a regeneration period of 2 to 6 years. Clinical function (M1 to M 4) and histopathologic characteristics of the muscle grafts were correlated . The rare instances of secondary procedures, such as tenolysis or scar cor rection, were used for biopsies of the muscle graft. Free neurovascular LD flaps were examined after a regeneration period between 2 and 6 years. The grafted LD was compared to normal, healthy LD muscle. Normal LD muscle show ed a typical homogeneous pattern of types 1 and 2 fibers in a ratio of almo st 1:1. No significant differences concerning fiber distribution and fiber diameters in three anatomic areas of the LD (proximal, medial, caudal) coul d be detected. After regeneration, the authors found the following. type gr ouping of muscle fiber types, fiber splitting, and groups of hypertrophic a nd atrophic fibers. Most of the muscle Fibers were not reinnervated by axon s and were atrophic or degenerated. The essential proliferation of connecti ve and fatty tissue was absent. Normal and hypertrophic fibers were found m ainly in the muscle grafts with good clinical results. In muscle grafts wit h good contraction force (M4), 46 percent of reinnervated muscle fibers wer e found; M3 contractility was correlated with 31 percent of reinnervated mu scle fibers; M2 with 24 percent; and M1 with 21 percent of reinnervated fib ers. The force of a free muscle graft seems to depend mainly on the quality of nerve regeneration. Characteristics of the muscle fiber itself were not examined extensively, because the single-fiber contractility of the regene rated fibers was similar to the contractility of normal, healthy fibers.