Defining the bone morphometry, micro-architecture and volumetric density profile in osteopenic vs non-osteopenic adolescent idiopathic scoliosis.

PURPOSE: Osteopenia has been widely reported in about 30 % of girls with adolescent idiopathic scoliosis (AIS). However, the bone quality profile of the 70 % non-osteopenic AIS defined by areal bone mineral density (BMD) with conventional dual-energy X-ray absorptiometry (DXA) has not been adequately studied. Our purpose was to verify whether abnormal volumetric BMD (vBMD) and bone structure (morphometry and micro-architecture) also existed in the non-osteopenic AIS when compared with matched controls using both DXA and high-resolution peripheral computed tomography (HR-pQCT).
METHODS: This was a case-control cross-sectional study. 257 AIS girls with a mean age of 12.7 (SD = 0.8) years old and 187 age- and gender-matched normal controls with an average age of 12.9 (SD = 0.5) years old were included. Areal BMD (aBMD) and bone quality were measured with standard DXA and HR-pQCT, respectively. The parameters of HR-pQCT could be categorized as bone morphometry, vBMD and bone micro-architecture. The results were compared between the osteopenic AIS and osteopenic control, and between the non-osteopenic AIS and non-osteopenic control.
RESULTS: In addition to the lower aBMD and vBMD, osteopenic AIS showed significantly greater cortical perimeter and trabecular area than the osteopenic control even after adjustments of age (P < 0.05). Non-osteopenic AIS also showed significantly lower aBMD together with lower cortical area, thickness and vBMD than the non-osteopenic control (P < 0.05). After adjustments of age, cortical area and vBMD, and trabecular number and separation continued to show statistical significance (P < 0.05). Both the osteopenic and non-osteopenic AIS subgroups revealed significant abnormal bone quality parameters from that in the control group after adjustments of age and aBMD with multi-linear regression analysis (P < 0.05).
CONCLUSIONS: The present study specifically defined the abnormal profile of bone quality in the osteopenic and non-osteopenic AIS for the first time. Both the osteopenic and non-osteopenic AIS were likely to have relatively lower bone mineral status and abnormal bone morphometry, micro-architecture and volumetric density profile compared with their normal matched controls. The observed abnormalities were suggestive of decreased endocortical bone apposition or active endocortical resorption that could affect the mechanical bone strength in AIS. The underlying pathomechanism might be attributed to abnormal bone modeling/remodeling that could be associated with the etiopathogenesis of AIS.