Improvements in vertebral body strength under teriparatide treatment assessed in vivo by finite element analysis: Results from the EUROFORS study

Monitoring of osteoporosis therapy based solely on DXA is insufficient to assess antifracture efficacy. Estimating bone strength as a variable closely linked to fracture risk is therefore of importance. Finite element (FE) analysis-based strength measures were used to monitor a teriparatide therapy and the associated effects on whole bone and local fracture risk. In 44 postmenopausal women with established osteoporosis participating in the EUROFORS study, FE models based on high-resolution CT (HRCT) of T₁₂ were evaluated after 0, 6, 12, and 24 mo of teriparatide treatment (20 μg/d). FE-based strength and stiffness calculations for three different load cases (compression, bending, and combined compression and bending) were compared with volumetric BMD (vBMD) and apparent bone volume fraction (app. BV/TV), as well as DXA-based areal BMD of the lumbar spine. Local damage of the bone tissue was also modeled. Highly significant improvements in all analyzed variables as early as 6 mo after starting teriparatide were found. After 24 mo, bone strength in compression was increased by 28.1 ± 4.7% (SE), in bending by 28.3 ± 4.9%, whereas app. BV/TV was increased by 54.7 ± 8.8%, vBMD by 19.1 ± 4.0%, and areal BMD of L₁-L₄ by 10.2 ± 1.2%. When comparing standardized increases, FE changes were significantly larger than those of densitometry and not significantly different from app. BV/TV. The size of regions at high risk for local failure was significantly reduced under teriparatide treatment. Treatment with teriparatide leads to bone strength increases for different loading conditions of close to 30%. FE is a suitable tool for monitoring bone anabolic treatment in groups or individual patients and offers additional information about local failure modes. FE variables showed a higher standardized response to changes than BMD measurements, but further studies are needed to show that the higher response represents a more accurate estimate of treatment-induced fracture risk reduction.