Canal and intervertebral foramen encroachments of a burst fracture: effects from the center of rotation.
METHODS
The neural spaces of thoracolumbar burst fractures were investigated in an in vitro biomechanical study.


OBJECTIVE
To evaluate encroachments of spinal canal diameter and intervertebral foramen area as functions of where the center of rotation is located during flexion and extension.


BACKGROUND
Decompression of the neural spaces is important for the recovery of neural function in a patient with a burst fracture injury. A few biomechanical studies have documented the decompression of the neural elements by adjustment of posterior fixation devices. However, the device adjustments have been device specific and ill defined. No study has investigated the neural decompression phenomenon with precisely defined multiple adjustments.


METHODS
Burst fractures were produced at L1 vertebra in nine T11-L3 human spinal segments. Specimens were flexed and extended around five different centers of rotation located in the mid-L1 plane. The spinal canal diameter and intervertebral foramen area encroachments were quantified in maximum flexion and extension around each center of rotation using lateral radiographs.


RESULTS
The average canal encroachment of 42.6% changed in flexion (32.2-48.5%) and extension (36.3-44.2%) by location of the center of rotation. The average intervertebral foramen area encroachment was decreased to a greater extent more often in flexion than in extension because of where the center 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 lordotic posture is preferred clinically, then the optimal choice may be extension around the center of rotation located at the tip of the spinous process of the burst vertebra.
Panjabi
M M
MM
Biomechanics Laboratory, Department of Oorthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT 06520-8071, USA. monahar.panjabi@yale.edu
Kato
Y
Y
Hoffman
H
H
Cholewicki
J
J
D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000293:injuries*; D008297:Male; D008875:Middle Aged; D011859:Radiography; D012399:Rotation; D013115:Spinal Canal / Q000000981:diagnostic imaging / Q000503:physiopathology*; D016103:Spinal Fractures / Q000000981:diagnostic imaging / Q000503:physiopathology*; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000293:injuries*