Fig. 2

Trephination was terminated when the trephine tip was located at the posterosuperior border of C6 (a and b). The bone plug (c) could be removed by moving the trephine gently in all directions. Some residual bone (d) could be seen after inserting the endoscopic system due to the non-parallel plane of the trephine relative to the posterior edge of C6. A hook (e) was applied to determine the posterior border of C6, after which the hernia was removed. The dural sac re-expansion (f) became apparent when sufficient decompression was achieved