Critical points and effectiveness of prophylactic C4/5 foraminotomy to prevent C5 palsy after posterior cervical spine surgery

The aim of this study was to clarify the cut-off values of the spinal canal parameters as risk factors for C5 palsy after posterior cervical spine surgery with and without foraminotomy.

One hundred three consecutive patients (67 males, 36 females; mean age = 66 years, age range = 27-87 years) with cervical myelopathy who underwent posterior cervical spine surgery at our institution were retrospectively reviewed and included in the study. The first consecutive 69 patients who underwent posterior cervical spine surgery with prophylactic bilateral C4/5 foraminotomy were designated as the F (+) group. The subsequent 34 consecutive patients who underwent posterior cervical spine surgery without prophylactic bilateral C4/5 foraminotomy were designated as the F (-) group. All patients were then divided into four subgroups. In the F (+) group, patients with C5 palsy were designated as the F (+) P (+) subgroup (n = 13), while those without C5 palsy were designated as the F (+) P (-) subgroup (n = 56). In the F (-) group, patients with C5 palsy were designated as the F (-) P (+) subgroup (n = 5), while those without C5 palsy were designated as the F (-)P(-) subgroup (n = 29). Receiver operating characteristic curves were used to investigate the cut-off values of the spinal canal parameters for the development of postoperative C5 palsy. The assessed spinal parameters were the gutter positions (GP), laminar inclination angles (LIA), and postoperative cross-sectional areas (CSA) of the dural sac. The risk ratios (RR) of the spinal canal parameters as risk factors for C5 palsy were evaluated.

The incidence of C5 palsy was similar between the F (+) group (18.8%) and the F (-) group (14.7%). The cut-off values for each spinal canal parameter in the F (+) group (GP: 0.82-0.84, LIA: 58.9-62.4°, and CSA: 189.5-200 mm2 ) were similar to those in the F (-) group (0.81-0.89, 61.7-62.5°, and 197.5-199.5 mm2, respectively). In the RR results for C5 palsy, the LIA was highest in both groups. The F (+) P (-) subgroup had significantly larger mean CSA at C4/5 and C5/6 (202.3 mm2 and 200.9 mm2, respectively) than the F (-)P(-) subgroup (177.3 mm2 and 178.9 mm2, respectively) (P = 0.0181 and P = 0.0277, respectively). Prophylactic C4/5 foraminotomy did not specifically prevent postoperative C5 palsy due to foraminal stenosis at C4/5.

C4/5 foraminotomy should not be recommended for avoidance of C5 palsy. Although the bony spinal parameters were similar between the F (+) and F (-) groups, the CSA in the F (+) group was significantly than that in the F (-) group in the patients without C5 palsy.