Paralysis of the arm after posterior decompression of the cervical spinal cord. II. Analyses of clinical findings.

Paralysis of the arm with radicular distribution occurring after posterior decompression of the cervical spinal cord included C5, C6, C7 and C8 roots, in isolation or combined. The most frequent patterns of paralysis were C5 and C6 root involvements of the motor-dominant type. The overall frequency of occurrence in our series was 11% (20 cases of postoperative paralysis in 188 surgical cases), but the frequency varied with the posterior decompression method. The higher frequency of postoperative paralysis was noted in the group in which the surgical procedures selected were considered as enabling the expanded dura to exert its traction power more easily on the extradural portion of the roots. Radiographical analyses showed that C5 roots which satisfied the following two conditions were more prone to sustain postoperative paralysis: first, location at the level of the highly expanded dural tube and, second, lying in the foramina with a higher degree of anterior protrusion of the superior process. In the majority of cases with C5 motor-dominant paralysis, the postoperative cord-root pouch distances of the C5 anterior roots were unchanged or even decreased compared with the preoperative ones, but the extradural portions of the C5 roots were elongated in all cases. These findings support the validity of mechanisms of postoperative paralysis which were deduced from the anatomical investigations.