General Session: Biomechanics
Presented by: Y-P Lee - View Audio/Video Presentation (Members Only)
Y.-P. Lee(1), N. Bhatia(1), M. McGarry(1), T. Lee(1)
(1) UC Irvine Medical Center, Orthopaedic Surgery, Orange, CA, United States
Study Design: Biomechanical, cadaveric study.
Objectives: To compare the relative stiffness of unilateral C1 lateral mass-C2 intralaminar fixation to intact specimens and bilateral C1 lateral mass-C2 intralaminar contructs.
Methods: The biomechanical integrity of a unilateral C1 lateral mass-C2 intralaminar screw construct was compared to an intact specimens and bilateral C1 lateral mass-C2 intralaminar screw constructs. 5 human cadaveric specimens were used. Range of motion and stiffness were tested to determine the stiffness of the constructs.
Results: Unilateral fixation significantly decreased flexion/extension range of motion compared to intact (P < 0.001) but did not significantly affect axial rotation (P = 0.3) or bending range of motion (P = 0.3). The bilateral fixation significantly decreased axial rotation compared to the intact condition (P = 0.01) and flexion/extension and lateral bending range of motion compared to both intact (P < 0.001 and P 0.01, respectively) and the unilateral fixation (P < 0.001 and P = 0.002, respectively). There was a significant decrease in stiffness in extension for both unilateral and bilateral fixation techniques compared to intact (P = 0.04 and P = 0.03, respectively). There was also a significant decrease in stiffness for ipsilateral rotation for the unilateral construct compared to intact (P = 0.007) whereas the bilateral construct significantly increased ipsilateral rotation stiffness compared to both intact and unilateral fixation (P < 0.001). There were no other significant differences in stiffness between intact and both fixation techniques (P > 0.05).
Conclusion: The bilateral constructs did show improved biomechanical properties compared to the unilateral constructs. However, unilateral C1-C2 fixation using a C1 lateral mass and C2 intralaminar screw-rod construct decreased range of motion and improved stiffness of the destabilized C1-C2 segments to the intact state with the exception of extension and ipsilateral rotation. Hence, a unilateral construct may be acceptable in clinical situations in which bilateral fixation is not possible. However, an external orthosis may be necessary to provide enough stability to achieve a fusion.