Simulation of the Effects of Minimum Case Volume Thresholds on the Geographic Accessibility of Inpatient Neurosurgical Facilities in Germany.

Background/Objectives: The aim of this study was to simulate the impact of different minimum case volume thresholds, introduced under Germany's Hospital Care Improvement Act, on the geographic accessibility of inpatient neurosurgical care. The Act introduces minimum case volume thresholds per service group, potentially leading to closures of low-volume neurosurgical units and reduced accessibility within 40 min of driving time (A2N40, Accessibility to a Neurosurgical Facility within 40 min). Methods: Inpatient case volumes of neurosurgical facilities were extracted from the Structured Quality Reports for reporting years 2023 and 2024, published by the Federal Joint Committee. Facilities were geocoded, 40-min driving time isochrones were generated, and the population within each isochrone was calculated. Results: At baseline in 2024, 66.6% of Germany's area and 84.7% of the population were within the A2N40. Each one-percentile-point increase in the case volume threshold reduced A2N40 area coverage by an average of 0.70 percentage points, corresponding to approximately 305,000 additional people losing access, with the largest reductions observed in rural, less densely populated regions of the eastern federal states. Conclusions: Minimum case volume thresholds may substantially reduce the geographic accessibility of neurosurgical facilities, revealing a measurable trade-off between quality assurance through centralisation and geographic access to care, particularly in rural regions. The presented simulation approach can support evidence-based, geographically informed planning of future minimum case volume regulations.