Clinical study of dissociated motor weakness following anterior cervical decompression surgery

C5 segment motor loss (deltoid muscle) after a cervical spinal operation, either anterior decompression or posterior decompression, has rarely been reported. However, most such cases are diagnosed immediately after surgery, and they appear to be due to inadequate surgical technique or insufficient decompression. Recently, the authors have experienced three cases in which weakness of the deltoid muscle started several days following anterior cervical decompression surgery. On the basis of postoperative plain films, myelography, and computed tomography (CT) myelography, the cause of the motor weakness was considered to be C5 root disturbance due to postoperative malalignment of the cervical spine, which gradually increased. The malalignment of the cervical spine seemed to be due to weakness of iliac bone grafts, inadequate design of the bone graft and recipient site, and insufficient postoperative fixation. To prevent this malalignment, eg, lateral inclination of the bone graft to axial rotation deformity, adequate bone graft design is required. The authors have been performing internal fixation using sapphire screws on cases in which fusion extending over four vertebral bodies is required.