Pedicle screw adjustments affect stability of thoracolumbar burst fracture.
METHODS
An in vitro biomechanical study of the stabilizing effect of pedicle screw instrumentation on experimental thoracolumbar burst fractures.


OBJECTIVE
To evaluate the effects of different adjustments applied by the pedicle screw fixation device on the stability of the spine-device construct.


BACKGROUND
Pedicle screw devices are widely used to accomplish spinal reduction and provide stability to an injured spine. In previous biomechanical studies the stability of the spine-device constructs has been examined for many devices. However, no study has quantitatively assessed the associations between the device adjustments and the stability of the construct.


METHODS
Five-vertebrae human cadaveric specimens with burst fracture at L1 vertebra were studied. Pedicle screw fixation device was attached to the T12 and L2 vertebrae. Five device adjustments (pure compression, pure distraction, pure extension, a combination distraction-extension, and neutral posture) were studied. Multidirectional flexibility test was performed when intact, after burst fracture, and after each device adjustment to document spinal stability.


RESULTS
The construct stability had a complex association to the device adjustment. For example, the maximum flexion and extension stabilities were achieved by pure compression and distraction-extension combination adjustments, respectively. Pure distraction and pure extension adjustments decreased the construct stability.


CONCLUSIONS
The device adjustments affected the spinal construct stability differently in different directions. Although pure compression provided the most stability in most directions, the combined distraction-extension adjustment may be more suitable considering the neural decompression also.
Oda
T
T
Department of Orthopaedics, Yamaguchi University School of Medicine, Ube, Japan.
Panjabi
M M
MM
D000328:Adult; D000368:Aged; D001863:Bone Screws; D002102:Cadaver; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000293:injuries / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D018583:Pliability; D011859:Radiography; D016059:Range of Motion, Articular / Q000502:physiology; D016103:Spinal Fractures / Q000000981:diagnostic imaging / Q000503:physiopathology*; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000503:physiopathology*