Comparison of Cervical Sagittal Alignment and Kinematics after Posterior Full-endoscopic Cervical Foraminotomy and Discectomy According to Preoperative Cervical Alignment

Background: The progression of cervical kyphosis due to injury to the facet joints and musculature is a major concern for posterior foraminotomy especially for patients with cervical lordosis of less than 10 degrees. However, cervical hypo-lordosis (cervical lordosis < 10 degrees) may be improved with the alleviation of pain and muscle spasms, which corresponds with the disappearance of a positive Spurling's test. When surgery is necessary, the spontaneous recovery of cervical curvature may be minimally offset using minimally invasive surgical techniques, such as posterior percutaneous endoscopic cervical foraminotomy (P-PECF). Objectives: The primary objective was to compare the changes in cervical kinematics between patients with cervical lordosis (>= 10 degrees, group I) and hypo-lordosis (< 10 degrees, group II) after P-PECF. Study Design: This study was a retrospective nested case-control study with the IRB No. H-1210-078-434. Setting: University Medical Center, Seoul, Korea. Methods: P-PECFs were performed for patients with a radiculopathy due to single-level unilateral cervical foraminal soft-disc herniations or foraminal stenosis with minimal degeneration of the disc/facet joints and a positive Spurling's test. A retrospective nested case-control study was performed for 23 patients with cervical lordosis of >= 10 degrees (group I; M:F = 15: 8; age, 52.3 +/- 9.8 years) and 23 patients with cervical lordosis of < 10 degrees(group II; M: F = 15: 8; age, 46.3 +/- 12.7 years). P-PECFs were performed using the methods previously reported, and all patients were discharged the next day without limitations on neck motion. The patients were followed at one, 3, 6, and 12 months postoperatively and yearly thereafter. The follow-up period was 25.8 +/- 19.6 months. Clinical outcomes were assessed using the visual analogue pain score of arms. The cervical angles (C2-7, tangential method) were measured on neutral (CA), flexion (CAF), and extension (CAE) lateral radiographs, and range of motion (C-ROM) was calculated by conducting a radiological analysis. A linear mixed model was used to assess the linearity of the changes in cervical curvatures during the postoperative 12 months between the groups. Results: Significant reductions in arm pain and negative results on Spurling's test were initially achieved in 21/23 patients in group I and in 23/23 patients in group II with means of 1.7 +/- 0.31 months and 1.09 +/- 0.09 months, respectively. Using the mixed effect models, the interactions between group and time were significant for the CA (P = 0.004), CAE (P < 0.001), and C-ROM (P < 0.001) but not the CAF (P = 0.392). The CA (adjusted-P < 0.001), CAE (adjusted-P < 0.001), and C-ROM (adjusted-P = 0.046) exhibited significant between-group differences at the pre-operation. However, during the follow-up, these parameters were significantly changed in group II, especially during the postoperative 3 months. The CA, CAE, and C-ROM changed by - 11.7 degrees, - 19.87 degrees, and 20.32 degrees, respectively. Postoperatively, 17/23 patients in group II and 22/23 patients in group I exhibited cervical lordosis of = 10 degrees. Limitations: This study was retrospective in design, and the inherent selection bias and limited statistical power should be considered. Conclusions: Cervical hypo-lordosis less than 10 degrees may not be a contra-indication for P-PECF when the change of cervical curvature is not a structural change. A larger study is necessary to identify prognostic factors.