Histomorphometric analysis of fracture healing cascade in acute osteoporotic vertebral body fractures

Abstract

Background While fracture healing has been well characterised in long bones, there is scant data relating to this process in acute vertebral body fractures. Aim To characterise the histological process of fracture healing in acute osteoporotic vertebral body fractures using qualitative and quantitative bone histomorphometry. Subjects and methods Transpedicular bone biopsy was performed in patients undergoing percutaneous vertebroplasty. Undecalcified biopsy specimens were prepared from cores of cancellous bone harvested from vertebral bodies with MRI evidence of bone marrow oedema. These were analysed by light microscopy using grid analysis and defined using bone histomorphometry criteria. Normative data obtained from 5 age-matched volunteers without evidence of metabolic bone disease or osteoporosis was used for comparison. Results Adequate biopsy specimens were obtained in 72 of 90 patients (15 men and 57 women), mean age 75.6 years. All biopsies confirmed severe osteoporosis with reduced cancellous bone volume (mean of 13.5%; P < 0.001 compared to controls). The timing of biopsies varied from 1 to 24 weeks (median of 6 weeks) after the fracture event. There were 4 stages of fracture callus healing observed: Stage I in 17 (24%) patients, Stage II in 16 (22%), Stage III in 22 (30%) and Stage IV in 17 (24%). An overlap between the various stages was evident with 55 (76%) patients demonstrating at least 2 or more of the stages of fracture healing in the same biopsy specimen. The time interval since fracture event was the most important predictor of the stage of the fracture callus ( R = 0.32; P < 0.001). Conclusion Our data demonstrates a mixed fracture callus with overlapping of the various stages of fracture healing. This suggests that individual vertebra may be susceptible to multiple fractures over the course of the healing process.