In vitro biomechanical study to quantify range of motion, intradiscal pressure, and facet force of 3-level dynamic stabilization constructs with decreased stiffness.
METHODS
An in vitro biomechanical study.


OBJECTIVE
To perform in vitro biomechanical testing on a lumbar spine using a 6-degree-of-freedom machine. To compare the range of motion (ROM), intradiscal pressure, and facet force of different 3-level dynamic stabilization constructs with traditional rigid constructs. To determine the effect of decreasing the stiffness of the dynamic construct on the various parameters.


BACKGROUND
Dynamic stabilization systems are a surgical option that may minimize the development of adjacent segment disease.


METHODS
Seven T12-S1 specimens were tested at ± 7.5 Nm in flexion-extension, lateral bending, and axial rotation. The testing sequence was (1) intact, (2) intact with facet sensors, (3) L3-S1 rigid (3R), (4) L3-L4 dynamic and L4-S1 rigid (1D-2R A), (5) L3-L5 dynamic and L5-S1 rigid (2D-1R A), and (6) L3-S1 dynamic (3D A). Constructs 1D-2R A, 2D-1R A, and 3D A were tested again with the specialized designs of B and C of decreased stiffness. ROM, intradiscal pressure, and facet force were measured.


RESULTS
In all loading modes there was a trend of increasing motion with decreased stiffness. Significant differences were seen with more dynamic stabilization levels but no significance was seen with only decreasing the stiffness. 3R facet force at the caudal instrumented level significantly decreased compared with intact and dynamic stabilization constructs during axial rotation.


CONCLUSIONS
Biomechanical testing resulted in a trend of increased ROM across instrumented levels as the stiffness was decreased. Dynamic stabilization increased the ROM across instrumented levels compared with rigid rods. These results suggest that decreasing the stiffness of the construct may lessen the probability of adjacent-level disease. Although the specialized devices are not commercially available, clinical data would be necessary for a clearer understanding of adjacent level effects and to confirm the in vitro biomechanical findings.


METHODS
N/A.
*New York Presbyterian Hospital/Columbia University Medical Center, New York, NY; and †Globus Medical Inc., Audubon, PA.
Joseph K
JK
Lee
Jaime
J
Gomez
Christopher
C
Michelsen
Yongjung
Y
Kim
Mark
M
Moldavsky
Suresh Reddy
SR
Chinthakunta
Saif
S
Khalil
D000328:Adult; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000503:physiopathology* / Q000601:surgery; D008159:Lumbar Vertebrae / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009038:Motion; D011312:Pressure; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D012447:Sacrum / Q000503:physiopathology* / Q000601:surgery; D016474:Weight-Bearing / Q000502:physiology; D021801:Zygapophyseal Joint / Q000503:physiopathology*