How many cases of spinal intramedullary ependymoma surgery are required to achieve stability? - Analysis using X-bar charts.

Abstract

Retrospective cohort study. To evaluate surgical consistency and clinical outcomes in intramedullary ependymoma (WHO grade II) cases by using X-bar charts as a tool to assess procedural stability. The single institution in Japan. This study included patients who underwent resection of intramedullary ependymomas between 2001 and 2023. All surgeries were performed by one of five board-certified spine surgeons. Operative time was analyzed for stability using X-bar charts. Neurological outcomes were assessed using the modified McCormick Scale (mMS), and regression analysis was performed to evaluate the relationship between operative time and mMS. The study included 144 patients (82 men, 62 women; average age 50.3 ± 14.6 years). Tumors were located at cervical (67.4%) or thoracic (32.6%) levels, averaging 3.0 ± 1.2 vertebrae. The surgeon who performed 71 cases was defined as the experienced surgeon, and the other surgeons performed 10-24 cases, respectively. The mean operative time was 380.6 ± 140.7 min, and 135 cases achieved gross total resection. The average follow-up duration was 6.9 ± 3.9 years. X-bar charts showed surgical stability once the average number of cases exceeded 17. No significant correlation was found between operative time and mMS for any surgeon. Perioperative complications were minimal. X-bar charts are a valuable tool for objectively evaluating surgical stability. In intramedullary ependymoma surgeries, consistency in operative time was achieved after 17 cases, and longer procedures did not adversely affect neurological outcomes. This method could be extended to monitor procedural reliability in other complex surgical interventions.