Control of bone cement volume (PMMA) may be critical for preventing complications in vertebroplasty, the percutaneous injection of PMMA into vertebra. The purpose of this study was to predict the optimal volume of PMMA injection based on CT images. For this, correlation between PMMA volume and textural features of CT images was examined before and after surgery to evaluate the appropriate PMMA amount. The gray level run length analysis was used to determine the textural features of the trabecular bone. Estimation of PMMA volume was done using 3D visualization with semi-automatic segmentation on postoperative CT images. Then, finite element (FE) models were constructed based on the CT image data of patients and PMMA volume. Appropriate material properties for the trabecular bone were assigned by converting BMD to elastic modulus. Structural reinforcement due to the changes in PMMA volume and BMD was assessed in terms of axial displacement of the superior end plate. A strong correlation was found between the injected PMMA volume and the area of the intertrabecular space and that of trabecular bone calculated from the CT images (r=0.90 and -0.90, respectively). FE results suggested that vertebroplasty could effectively reinforce the osteoporotic vertebra regardless of BMD or PMMA volume. Effectiveness of additional PMMA injection tended to decrease. For patients with BMD well lower than 50mgjml, injection of up to 30% volume of the vertebral body is recommended. However, less than 30% is recommended otherwise to avoid any complications from excessive PMMA because the strength has already reached the normal level.

Since the spine is one of the most complex joint structures in the human body, its surgical treatment requires careful planning and high degree of precision to avoid any unwanted neurological compromises. In addition, comprehensive biomechanical analysis can be very helpful because the spine is subject to a variety of load. In case for the osteoporotic spine in which the structural integrity has been compromised, it brings out the double challenges for a surgeon both clinically and biomechanically. Thus, we have been developing an integrated medical image system that is capable of doing the both. This system is called 'orthopedic surgical analyzer' and it combines the clinical results from image-guided examination and the biomechanical data from finite element analysis. In order to demonstrate its feasibility, this system was applied to percutaneous vertebroplasty. Percutaneous vertebroplasty is a surgical procedure that has been recently introduced for the treatment of compression fracture of the osteoporotic vertebrae. It involves puncturing vertebrae and filling with polymethylmethacrylate (PMMA). Recent studies have shown that the procedure could provide structural reinforcement for the osteoporotic vertebrae while being minimally invasive and safe with immediate pain relief. However, treatment failures due to excessive PMMA volume injection have been reported as one of complications. It is believed that control of PMMA volume is one of the most critical factors that can reduce the incidence of complications. Since the degree of the osteoporosis can influence the porosity of the cancellous bone in the vertebral body, the injection volume can be different from patient to patient. In this study, the optimal volume of PMMA injection for vertebroplasty was predicted based on the image analysis of a given patient. In addition, biomechanical effects due to the changes in PMMA volume and bone mineral density (BMD) level were investigated by constructing clinically relevant finite element models. In conclusion, we were able to demonstrate the feasibility of our orthopedic surgical analyzer in a case for percutaneous vertebroplasty.