CT-derived bone density as an adjunct predictor of sacral fracture complexity in older adults.

Background: Bone mineral density (BMD) is a known risk factor for fragility fractures, yet its relationship with specific sacral fracture morphologies, particularly H-type fractures, is not well understood.

Objectives: To evaluate whether CT-derived Hounsfield Units (HU) correlate with the complexity of sacral fractures, focusing on H-type fracture patterns.

Methods: A retrospective study was conducted involving 164 elderly patients (≥60 years) with sacral fractures. HU values were measured at the L5 vertebral body using CT imaging. Fractures were classified by Fragility Fractures of the Pelvis (FFP) classification and Denis zones. Logistic regression models were developed to identify predictors of H-type fractures. Model performance was evaluated using accuracy, AUC, precision, and recall.

Results: Among 164 patients, 59 (36 %) had H-type fractures. FFP classifications were distributed as follows: FFP II (n = 68), FFP III (n = 18), and FFP IV (n = 78). HU did not significantly differ across FFP categories. A weak but significant negative correlation was observed between HU and age (r = -0.22, p = 0.0039). In multivariate logistic regression, FFP classification (OR = 10.03, p < 0.001), Denis zone involvement (OR = 8.58, p < 0.001), and HU (OR = 1.14, p = 0.63) were evaluated for their predictive value. The model achieved 92 % accuracy (AUC = 0.93).

Conclusion: HU alone is not a strong standalone predictor of H-type sacral fractures but improves multivariate model performance when combined with anatomical and clinical variables. HU's inverse relationship with age supports its utility as a surrogate marker for bone quality, especially when DXA is unavailable.