Development and evaluation of a simple CT-based DXA triage score for osteoporosis in candidates for lumbar spine surgery.

Abstract

STUDY DESIGN: Retrospective cohort study. PURPOSE: Requiring DXA testing before lumbar spine surgery can delay surgical scheduling and time to surgery and may be unnecessary for many candidates. We aimed to develop and evaluate a simple, bedside-calculable score using routinely available preoperative variables to decide, at the time of surgical evaluation, which patients should have a DXA ordered (prioritized) versus which patients may safely defer DXA (DXA triage). METHODS: In a single-center cohort (n = 182), osteoporosis was defined according to ISCD site criteria as a T-score ≤ − 2.5 at the lumbar spine, femoral neck, or total hip. Mean L1–L4 HU was derived from preoperative lumbar CT. A 4-item additive score (sex, age, BMI, and mean L1–L4 HU; range 0–15) was constructed using clinically interpretable cutpoints informed by multivariable logistic regression. Discrimination, calibration, and clinical utility were evaluated with bootstrap optimism correction. RESULTS: The cohort had a mean age of 72.3 ± 8.3 years and included 106 women (58.2%). DXA-defined osteoporosis was present in 61/182 (33.5%). Hip-only osteoporosis predominated (44/182, 24.2%), whereas lumbar-involved osteoporosis occurred in 17/182 (9.3%). Mean L1–L4 HU correlated with the DXA lowest site T-score (r = 0.516, p < 0.001). The point-based score demonstrated strong discrimination for osteoporosis (AUC 0.826), outperforming HU alone (AUC 0.722) and approaching a multivariable FRAX-lite model (age, sex, BMI, HU; AUC 0.810); optimism-corrected AUCs were similar (score 0.827; HU 0.726; FRAX-lite 0.796). Using Score ≥ 4 as a triage rule (order DXA if ≥ 4) selected 130/182 (71.4%) patients for DXA, reducing DXA utilization by 28.6% versus DXA-for-all, with sensitivity 96.7% (59/61) and specificity 41.3%. The two missed cases occurred exclusively in men and represented hip-only osteoporosis. Decision curve analysis supported score-based triage as a practical DXA prioritization strategy across clinically plausible threshold probabilities. CONCLUSIONS: A simple CT-enabled 4-item score can support DXA ordering decisions at surgical evaluation, prioritizing DXA for higher-risk patients and reducing unnecessary testing while preserving high sensitivity for DXA-defined osteoporosis. However, DXA should not be deferred when hip-predominant risk is suspected, particularly in men.