Studies using DXA have demonstrated that age is a major predictor of bone fragility and fracture risk, independent of BMD. This has been attributed to poorer bone “quality.” To investigate this issue, we used high resolution peripheral quantitative computed tomography (HRpQCT) to evaluate bone microarchitecture in young and old women and men matched for BMD by DXA. There were no differences between the young and old subjects for parameters related to trabecular microarchitecture, but older women and men had significantly greater cortical porosity for the same BMD by DXA. In a collaborative study with Drs. Zebaze and Seeman in Melbourne, we extended this analysis to compare trabecular and cortical microarchitecture in postmenopausal women with or without a history of distal forearm fractures. Again, cortical porosity emerged as a significant independent predictor of fracture risk, but only in women with osteopenia.
Patients with type 2 diabetes (T2D) similarly have an increase in fracture risk for the same BMD by DXA as compared to non-diabetic subjects. This has been postulated to be due to alterations in bone material properties as a result of chronic hyperglycemia. We formally tested this hypothesis in 60 normal postmenopausal women, 30 with T2D and 30 age-matched, non-diabetic controls. An index of bone material properties (bone material strength index, BMSI) at the midshaft of the tibia was obtained using the Osteoprobe, a hand-held microindentation instrument. BMSI was significantly lower in the T2D patients as compared to the non-diabetic controls. Of interest, the mean glycated hemoglobin over the previous 10 yrs was significantly correlated with the BMSI. These findings thus represent the first demonstration, using a direct in vivo index of bone material strength, of compromised bone material properties in patients with T2D. Thus, the skeleton should be recognized as another important target tissue subject to diabetic complications.