P39. Teriparatide treatment improves bone quality in the lumbar spine out of proportion to DEXA changes

BACKGROUND CONTEXT Teriparatide has been used to improve bone quality when considering spinal fusion surgery in patients with osteoporosis. Hounsfield units (HU), a standardized measurement for radiodensity, can be obtained on routine computed tomography (CT) scans, while dual energy X-ray absorptiometry (DEXA) is the common test for bone density. PURPOSE To compare changes in bone quality in the lumbar spine between Hounsfield unit measurements and dual energy X-ray absorptiometry (DEXA) following teriparatide treatment. STUDY DESIGN/SETTING Retrospective Chart Review. METHODS A retrospective chart review was performed from 1997 to 2018 across all campuses at our institution. We identified patients who had been treated with at least 6 months of teriparatide with a CT scan and DEXA scan before and after therapy. HU were measured from L1-L4 with three measurements per vertebral body. RESULTS Fifty-two patients (46 women, six men) were identified for analysis with an average age of 67 years who underwent an average of 20.9±6.5 months of teriparatide therapy. Mean (± standard deviation) HU improvement throughout the lumbar spine (L1-L4) was from 109.8±53 to 133.9±61 with a p-value of 0.039 and a 95% CI from 1.2 to 46.1. Each individual lumbar level also had an average improvement in HU but only L1 was statistically significant (L1 improved from 112.4 to 139.2 with a p-value of 0.013). Based on DEXA results, lumbar spine t-scores improved from -2.4±1.5 to -1.7±1.5 with a p-value of 0.03. Average femoral t-scores improved from -2.5±1.1 to -2.3±1.0 with a p-value of 0.31. CONCLUSIONS Teriparatide treatment improved BMD based on HU and DEXA in the lumbar spine, without a change in femoral BMD. The 22% improvement in HU surpassed the changes seen on DEXA. These results supports some surgeons’ subjective sense that intraoperative bone quality following teriparatide treatment is better than indicated by DEXA results. FDA DEVICE/DRUG STATUS Unavailable from authors at time of publication.