Akira Arakaki

Effects of innervation on the distribution of acetylcholine receptors in regenerating skeletal muscles of adult chickens

In order to determine the roles of nerves in the formation of clusters of acetylcholine receptors (AChRs) during synaptogenesis, we examined the distribution of AChRs in denervated, nerve-transplanted (neurotized) muscles and in regenerated skeletal muscles of adult chickens by fluorescence microscopy using curaremimetic toxins. In the denervated muscles, many extrajunctional clusters developed at the periphery of some of the muscle nuclei of a single muscle fiber and continued to be present for up to 3 months. The AChR accumulations originally present at the neuromuscular junctions disappeared within 3 weeks. In the neurotized muscles, line-shaped AChR clusters developed at 4 days after transection of the original nerve, but no change in the distribution of AChRs had occurred even at 2 months after implantation of the foreign nerve. The line-shaped AChR clusters were found to be newly formed junctional clusters as they were associated with nerve terminals of similar shape and size. Some of both the line-shaped and extrajunctional clusters were formed at least partly by the redistribution of preexisting AChRs. Finally, based on the above observations, the regenerating muscle fibers in normal muscles and in denervated muscles were examined: The extrajunctional clusters appeared in both kinds of muscles at 2 weeks after injury. Afterward, during the innervation process, the line-shaped AChR clusters developed while the extrajunctional clusters disappeared in the innervated muscles. In contrast with this, in the absence of innervation, only the extrajunctional clusters continued to be present for up to 3 months. These results demonstrate clearly that the nerve not only induces the formation of junctional clusters at the contact site, but also prevents the formation of clusters at the extrajunctional region during synaptogenesis.

Limb Saving Surgery Without Endoprosthesis on Malignant Bone Tumors

Four cases of vascularized fibular graft and three cases of rotationplasty for reconstruction after wide resection in malignant bone tumors are presented. Since endoprosthetic reconstruction does not offer life-long durability and can cause limb discrepancy in growing patients dual vascularized fibular grafts should be considered for reconstruction of the diaphysis in the lower extremity. For reconstruction of the proximal humerus, the vascularized proximal fibula can be utilized, occasionally with the epiphyseal plate to minimize limb discrepancy in growing patients. Rotationplasty can be recommended because of good function even in lesions at the femoral diaphysis, neck, or proximal tibia.

Familial flexion-supination deformity at the PIP joint of the finger

The case of a 36-year-old female typist with familial bilateral flexion-supination deformity at the PIP joint of the long fingers is presented. This deformity was ascribed to hypoplasia of the radial lateral band and retaining structures of the long extensor tendon. The deformity was corrected by bridging the second dorsal interosseous muscle and the radial extensor lateral band with a free tendon graft and the reconstruction of retaining ligaments.