Background For patients with single-level cervical radiculopathy, various types of motion preservation surgeries, such as total disc replacement (TDR), posterior cervical foraminotomy (PCF) and posterior percutaneous endoscopic foraminotomy and discectomy (PECF), are available. In addition to motion preservation, the quality of motion is an important issue. The aim of the present study was to evaluate the influence of these surgeries on cervical motion by comparing the instantaneous axis of rotation (IAR) among PECF, TDR and PCF at the index and superior/inferior adjacent segments. 

Methods A retrospective review was performed of patients who underwent index surgery at C5-6 for cervical single-level foraminal disc herniation or foraminal stenosis. Patients with minimal degeneration at the index and other cervical spinal levels and flexion/extension cervical lateral radiographs both preoperatively and 6 months postoperatively were included (PECF, 11 patients; TDR, 11 patients; PCF, 12 patients). The IARs were calculated at the index segment and segments above and below the index segment from the flexion and extension cervical lateral radiographs, which were obtained preoperatively and 6 months postoperatively. A standardized cervical normogram was referenced to qualify shifts in the IAR. 

Results Postoperatively, neck pain was significantly decreased, with no difference among the surgical methods. The IARs were not significantly changed after the PECF. Although significant inferior shift occurred at C6-7 after TDR (p = 0.02), the shift occurred within the normal range in the cervical normogram. However, significant inferior shifts in the IARs occurred after PCF at C5-6 (p = 0.02) and C6-7 (p = 0.02), and the IARs moved out of the normal range. 

Conclusions The IARs were significantly changed after PCF at either the index segment or the adjacent segment below. The shifts in IAR at the index and adjacent segments were not significant after PECF and TDR. The sample size was too small to allow definitive conclusions, but the present study showed that PECF may be another alternative to motion preservation surgeries.