We have observed that some osteoporotic vertebral compression fractures (VCFs) are mobile. The purpose of this report was to document the existence of dynamic fracture mobility, estimate the frequency of dynamic mobility in patients referred for vertebroplasty, define the magnitude and nature of dynamic mobility, and consider the implications of the dynamic mobility of osteoporotic VCFs. This was a prospective radiographic analysis of 41 consecutive patients with 65 VCFs who underwent vertebroplasty. Preoperative standing lateral radiographs of the fractured vertebrae were compared with supine cross-table lateral radiographs to determine the presence or absence of dynamic mobility. Postoperative standing lateral radiographs were evaluated to document fracture mobility and assess final vertebral height restoration. Radiographs were manually digitized to calculate vertebral body morphometrics. Dynamic fracture mobility was demonstrated in 44% of patients (35% of treated vertebrae) who underwent vertebroplasty. Postoperatively, in mobile fractures, average anterior vertebral height increased 106% compared with initial fracture height (absolute increase, 8.41 +/- 0.4 mm). Mean lateral vertebral area increased from 48% to 80% of normal, and kyphotic angle decreased 40%. Mobile fractures dominated at the thoracolumbar junction. Intravertebral clefts were defined and identified in every mobile fracture and were absent from every nonmobile (fixed) fracture. This radiographic series documents the previously unrecognized occurrence of dynamic fracture mobility in many osteoporotic VCFs. Fracture mobility can be substantial and clinically significant. Any intervention that claims vertebral height restoration must control for the occurrence of dynamic fracture mobility.