Teriparatide treatment increases Hounsfield units in the lumbar spine out of proportion to DEXA changes

OBJECTIVE: The authors sought to assess whether Hounsfield units (HU) increase following teriparatide treatment and to compare HU increases with changes in bone mineral density (BMD) as measured by dual-energy x-ray absorptiometry (DEXA). METHODS: A retrospective chart review was performed from 1997 to 2018 across all campuses at our institution. The authors identified patients who had been treated with at least 6 months of teriparatide and compared HU and BMD as measured on DEXA scans before and after treatment. RESULTS: Fifty-two patients were identified for analysis (46 women and 6 men, average age 67 years) who underwent an average of 20.9 ± 6.5 months of teriparatide therapy. The mean ± standard deviation HU increase throughout the lumbar spine (L1-4) was from 109.8 ± 53 to 133.9 ± 61 HU (+22%, 95% CI 1.2-46, p value = 0.039). Based on DEXA results, lumbar spine BMD increased from 0.85 to 0.93 g/cm² (+9%, p value = 0.044). Lumbar spine T-scores improved from -2.4 ± 1.5 to -1.7 ± 1.5 (p value = 0.03). Average femoral neck T-scores improved from -2.5 ± 1.1 to -2.3 ± 1.0 (p value = 0.31). CONCLUSIONS: Teriparatide treatment increased both HU and BMD on DEXA in the lumbar spine, without a change in femoral BMD. The 22% improvement in HU surpassed the 9% improvement determined with DEXA. These results support some surgeons' subjective sense that intraoperative bone quality following teriparatide treatment is better than indicated by DEXA results. To the authors' knowledge, this is the first study demonstrating an increase in HU with teriparatide treatment.