Neurectomy Preserves Fast Fibers When Combined With Tenotomy Of Infraspinatus Muscle Via Upregulation Of Myogenesis

Introduction: We evaluated the contribution of denervation-related molecular processes to rotator cuff muscle degeneration after tendon release. Methods: We assessed the levels of myogenic (myogenin and myogenic differentiation factor [myoD]) and proadipogenic (peroxisome proliferator-activated receptor gamma) transcription factors; the denervation-associated proteins tenascin-C, laminin-2, and calcium/calmodulin-dependent kinase II (CaMKII); and cellular alterations in sheep after infraspinatus tenotomy (TEN), suprascapular neurectomy (NEU), or both (TEN-NEU). Results: Extracellular ground substance increased at the expense of contractile tissue 16 weeks after surgery, correlating with CaMKII isoform levels. Sheep undergoing NEU and TEN-NEU had exaggerated infraspinatus atrophy and increased fast fibers compared with TEN sheep. The beta MCaMKII isoform levels increased with TEN, and myoD levels tripled after denervation and were associated with slow fibers. Discussion: In sheep, denervation did not affect muscle-to-fat conversion after TEN of the infraspinatus. Furthermore, concurrent NEU mitigated the loss of fast fibers after TEN by inducing a fast-contractile phenotype. Muscle Nerve 59:100-107, 2019