Fig. 2

a–d Observation of bone cement distribution and classification of vertebrae. a The vertebrae in which the bone cement located unilaterally (restricted by the midline) comprised group I. b The vertebrae in which the bone cement diffused across the midline but not to the contralateral vertebral pedicle comprised group II. c The vertebrae in which bone cement diffused over the contralateral pedicle comprised group III. d Existence of bone cement extravasation was recorded