Canal and intervertebral foramen encroachments of a burst fracture - Effects from the center of rotation

Study Design. The neural spaces of thoracolumbar burst fractures were inves tigated in an in vitro biomechanical study. Objective. To evaluate encroachments of spinal canal diameter and intervert ebral foramen area as functions of where the center of rotation is located during flexion and extension. Summary of Background Data. Decompression of the neural spaces is important for the recovery of neural function in a patient with a burst fracture inj ury. A few biomechanical studies have documented the decompression of the n eural elements by adjustment of posterior fixation devices. However, the de vice adjustments have been device specific and ill defined. No study has in vestigated the neural decompression phenomenon with precisely defined multi ple adjustments. Methods. Burst fractures were produced at L1 vertebra in nine T11-L3 human spinal segments. Specimens were flexed and extended around five different c enters of rotation located in the mid-L1 plane. The spinal canal diameter a nd intervertebral foremen area encroachments were quantified in maximum fle xion and extension around each center of rotation using lateral radiographs . Results. The average canal encroachment of 42.6% changed in flexion (32.2-4 8.5%) and extension (36.3-44.2%) by location of the center of rotation. The average intervertebral foramen area encroachment was decreased to a greate r extent more often in flexion than in extension because of where the cente r of rotation was located. Conclusions. Both flexion and extension can decompress canal and foramina, depending on the choice for the location of the center of rotation. If lord otic posture is preferred clinically, then the optimal choice may be extens ion around the center of rotation located at the tip of the spinous process of the burst vertebra.