Determinants of Intraoperative Radiation During Single-Level Tubular Lumbar Decompression

Background Minimally invasive tubular lumbar decompression requires intraoperative fluoroscopy for retractor docking, yet dosimetry data beyond the learning curve is poorly characterized. Most studies report fluoroscopy time rather than a dose index. We identified patient- and case-level determinants of intraoperative reference air kerma (Kar) during single-level tubular lumbar decompression by a surgeon far into the surgical proficiency learning curve. Methods 114 consecutive patients undergoing single-level unilateral tubular lumbar decompression were retrospectively reviewed between January 2023 and January 2026. The primary outcome was fluoroscopic Kar (mGy). The influence of body mass index (BMI), operative level, age, sex, American Society of Anesthesiologists (ASA) physical status class, laterality, and concurrent discectomy was measured on univariate and multivariable analysis. Results Median Kar was 2.13 mGy (IQR 1.28 to 3.50) over 4.0 seconds (IQR 3.0 to 6.0) of fluoroscopy. In the multivariable model BMI was the only independent predictor with a 6.9% increase per unit of BMI (1.069 per kg/m², 95% CI 1.036 to 1.104, p=0.0001). Operative level was not independently significant. Higher BMI was associated with both longer fluoroscopy time (ρ=0.214, p=0.022) and greater Kar per second (ρ=0.388, p<0.001). Secondary analysis suggested higher Kar at upper lumbar levels (L2–3, L3–4) than at lower levels. Conclusions BMI is the dominant determinant of intraoperative radiation during tubular lumbar decompression, acting through increased fluoroscopy time and greater C-arm power output rather than surgical complexity. These findings support preoperative radiation planning and dose-reduction strategies targeting automatic exposure control parameters.