Impact of Frailty and Other Factors as Estimated by HU to Predict Response to Anabolic Bone Medications

<b>Introduction:</b> Bone health optimization is a key component of the preoperative management of spine surgery patients, as poor bone quality increases the odds of mechanical complications. The present study aimed to achieve the following: (1) compare the relative efficacy of current osteoporosis medications in improving bone quality; (2) identify factors influencing treatment response in preoperative spine surgery patients. <b>Methods:</b> Patients treated at a single, multisite institution who received osteoporosis treatment were identified. Data were gathered on pre- and post-treatment lumbar spine Hounsfield Unit (HU) measurements, patient demographics, frailty scores (modified Frailty Index/mFI, risk analysis index/RAI), and pharmacologic treatment details. The primary outcome was a ≥7 point improvement in lumbar HU, and baseline and logistic regression models were utilized to identify factors associated with this improvement. Medications were grouped as anabolic (teriparatide, romosozumab) and antiresorptive (denosumab, alendronate) therapies. <b>Results:</b> A total of 267 patients were included (median age: 74 years; IQR [66-81]; 67.3% female), with 127 (47.6%) improving by ≥7 HU. The treatment agents used were alendronate (95), denosumab (113), romosozumab (31), and teriparatide (28). Univariable comparisons revealed significant differences across medication groups in age (<i>p</i> < 0.001), sex (<i>p</i> < 0.001), mFI (<i>p</i> < 0.001), RAI (<i>p</i> = 0.004), BMI (<i>p</i> < 0.001), pre-treatment HU (<i>p</i> = 0.022), and treatment duration (<i>p</i> < 0.001). The highest HU improvement rates (ΔHU ≥ 7) were observed in patients receiving the anabolic medications romosozumab (67.7%) and teriparatide (60.7%). Univariable logistic regression identified male sex (OR 0.54, <i>p</i> = 0.019), higher pre-treatment HU (OR 0.99, <i>p</i> = 0.006), and longer treatment duration (OR 0.97, <i>p</i> = 0.003) as factors associated with lower odds of HU improvement. Only romosozumab was associated with significantly higher odds of HU improvement relative to alendronate (OR 3.02, <i>p</i> = 0.012). In our multivariable analysis, male sex (OR 0.53, <i>p</i> = 0.028) and higher pre-treatment HU (OR 0.99, <i>p</i> = 0.002) remained significant predictors of HU improvement. However, medication type was not significant in the multivariable analysis. <b>Conclusions:</b> Our study highlights that male sex and higher pre-treatment HU were independently associated with lower odds of HU improvement, while medication type was not a significant predictor. Additionally, anabolic agents offered superior improvement relative to antiresorptive therapies.