Volume matters: a review of procedural details of two randomised controlled vertebroplasty trials of 2009

Two recent randomised controlled trials (RCT) published by the New England Journal of Medicine (NEJM) in 2009 comparing vertebroplasty to sham procedures have concluded that vertebroplasty is no more effective than injection of local anaesthetic at the pedicle entry point. This finding contradicts previously published clinical series on vertebroplasty which have shown clinical efficacy. The procedural details of the two RCTs are analysed specifically with regard to vertebral levels treated and injected polymethylmethacrylate (PMMA) volumes in an attempt to combine the data for assessment against the available basic science underpinning the effect of vertebral augmentation procedures. Neither investigation provides a breakdown of the vertebral levels treated in the original publication or in supplementary online material. Only one investigation provides information on fill volumes with an overall average fill volume of 2.8 ± 1.2 ml SD. The available basic science indicates a minimum fill volume of 13–16% of the vertebral body volume to be necessary for a relevant biomechanical effect on restoration of vertebral strength. The most commonly treated vertebrae of the thoracolumbar junction have an anatomical vertebral body volume of ~30 ml. An effective fill would require a minimum of ~4 ml PMMA. Anatomical volumes and required fill volumes increase towards the lower lumbar spine. According to the available basic science, only vertebrae of the upper to mid thoracic spine could reasonably have received a biomechanically effective fill with the declared average volume of 2.8 ± 1.2 ml SD. The available data of the NEJM publications strongly indicates that the treatment arm includes patients who were not treated in a reasonably effective manner. The technical information provided by the NEJM publications is insufficient to conclusively prove or disprove the clinical efficacy of vertebroplasty.