Upper cervical lordosis compensates lower cervical kyphosis to maintain whole cervical lordosis after selective laminectomy

After lower-cervical-level spinal-cord tumor resection, compensatory upper cervical lordosis with lower cervical kyphosis was observed. However, no studies examined this compensation following posterior decompression surgery for cervical compressive myelopathy (CCM). The purpose of this study was to evaluate the compensatory mechanism after muscle-preserving selective laminectomy (SL) and to assess the clinical outcomes following such compensation. Enrolled in the study were 125 CCM patients who underwent C6 single-level SL, C5–C6 two-level SL, C4–C6 three-level SL, and C3–C6 four-level SL. Cervical spine lateral radiography was taken before surgery and during the final followup. The C2–C5, C5–C7, and C2–C7 angles were measured and presented respectively as the patients’ “upper,” “lower,” and “whole” cervical alignments. Patients were divided into two groups according to their postoperative C5–C7 alignment changes. We then divided the C5–C7 kyphotic-change group according to the patients’ postoperative C7 slope changes. Postoperative cervical sagittal balance and surgical outcomes were compared within the groups. Postoperative C5–C7 kyphotic change was compensated for by C2–C5 lordotic change, maintaining the preoperative C2–C7 angle. Although postoperative C5–C7 kyphotic change alone did not affect cervical sagittal balance or surgical outcomes, patients with C5–C7 kyphotic changes and C7 slope increases showed greater increases in the C2–C7 sagittal vertical axis and lower recovery rates in Japanese Orthopaedic Association scores. The patients’ postoperative lower cervical kyphotic changes were compensated for by upper cervical lordotic changes. Despite this compensation, increases in patients’ C7 slopes adversely affected sagittal balance and functional recovery.