In vivo analysis of cervical range of motion after 4- and 5-level subaxial cervical spine fusion.

Study Design. A cohort study analyzing the cervical range of motion (ROM) of subjects with 4- or 5-level posterior laminectomy and fusion or anterior and posterior decompression and fusion operation. Objective. The purpose of this study was to evaluate the effect of extending a C3-C7 fusion to C3-T1 on subject's ROM and level of disability. Summary of Background Data. Cadaveric studies show a reduction in the ROM of C3-C7 cervical fusion spines. In vivo, surgeons treat symptomatic cervical subaxial spine with either a C3-C7 fusion or C3-T1 fusion. While in some cases extending the fusion level to T1 is merited due to pathology, most cases are due to surgeon's preference to avoid future degeneration and reoperation of the C7-T1 junction. Methods. This study involved 44 4-level fusion and 20 5-level fusion subjects along with 18 nonoperative controls. Operative subjects were divided according to early or late postoperative clinical visit. Subjects were asked to complete the neck disability index survey and their maximum ROM during flexion/extension, axial rotation, and lateral bending was measured using a virtual reality assisted electromagnetic tracking system. In addition, the helical axis of motion was calculated for flexion and extension motions. An analysis of variance statistical test was used to determine significant differences between study groups. Results. Five-level subjects had significantly less ROM than 4-level subjects and both groups were significantly less than control group during all motions. There was no effect of postoperative time on subject's ROM. In addition, there was no difference in the center of helical axis of rotation across the 3 groups. Finally, both operative groups exhibited similar levels of mild disability as measured by the neck disability index. Conclusions. Extending the subaxial fusion from C3-C7 to include C7-T1 resulted in a significant loss of ROM, while postoperative time healing, center of rotation, and level of disability were similar across groups. This finding merits further investigation of the intersegmental motions of the cervical spine.