Biopsies from patients with sacral insufficiency fracture are characterized by low bone matrix mineralization and high turnover.

Sacral insufficiency fractures are known to occur primarily in older women without adequate trauma. While an association with low bone mineral density (ie, osteoporosis) has been reported, more detailed information on local bone quality properties in affected patients is not available. In the present study, core biopsies were obtained from the S1 sacral ala in patients with a bilateral sacral insufficiency fracture (type IV according to the fragility fractures of the pelvis classification) who required surgical stabilization. Dual energy X-ray absorptiometry (DXA) and laboratory bone metabolism analyses were performed. For comparison, control biopsies were acquired from skeletally intact age- and sex-matched donors during autopsy. A total of 31 biopsies (fracture: n = 19; control: n = 12) were evaluated by micro-computed tomography, histomorphometry on undecalcified sections, and quantitative backscattered electron imaging (qBEI). DXA measurements showed mean T-scores in the range of osteoporosis in the fracture cohort (T-score_min −2.6 ± 0.8). Biochemical analysis of bone metabolism parameters revealed high serum alkaline phosphatase and urinary deoxypyridinoline/creatinine levels. In the biopsies, a loss of trabecular microstructure along with increased osteoid values were detected in the fracture patients compared with controls (osteoid volume per bone volume 5.9 ± 3.5 vs. 0.9 ± 0.5%, p <.001). We also found evidence of microfractures with chronic healing processes (ie, microcallus) as well as pronounced hypomineralization in the biopsies of the fracture cohort compared with the controls as evidenced by lower CaMean measured by qBEI (22.5 ± 1.6 vs. 24.2 ± 0.5 wt%, p =.003). In conclusion, this high-resolution biopsy study provides evidence of local hypomineralization in patients with sacral insufficiency fractures, pointing to reduced fracture resistance but also a distinct phenotype other than the predominant loss of trabeculae as in postmenopausal osteoporosis. Our data highlight the importance of therapies that promote bone mineralization to optimally treat and prevent sacral insufficiency fractures. Lay Summary: Sacral insufficiency fracture is a type of fracture occurring particularly in older women after low-energy trauma or repetitive physiologic loads. While it is suspected that diminished bone quality plays a causal role, it has not yet been investigated which aspects of bone quality are affected by means of a biopsy study. Here, the microstructure, turnover, and mineralization were investigated in biopsies obtained from patients with bilateral sacral insufficiency fractures during surgery. Compared with a control group of skeletally intact donors, the most striking finding in the biopsies of the fracture patients was impaired bone mineralization. Namely, high proportions of unmineralized osteoid and low bone matrix mineralization were detected by undecalcified histology and quantitative backscattered electron imaging, respectively. In addition, the trabeculae of some biopsies showed signs of chronic microfracture. Collectively, these results not only show that sacral insufficiency fractures belong to a spectrum different from classical osteoporosis-related fractures but also underline the importance of therapies that promote bone mineralization, for instance vitamin D and calcium supplementation. [ABSTRACT FROM AUTHOR]