268 - Biomechanical Assessment of Anterior Thoracolumbar Instrumentation: A...

#268 Biomechanical Assessment of Anterior Thoracolumbar Instrumentation: A Comparison between a Low Profile Dual Rod System and a Dual Rod System

Oral Posters: Deformity

Presented by: M. Moldavsky

Author(s):

M. Gehrchen (1)
S.K. Hegde (2)
M. Moldavsky (3)
S.R. Chinthakunta (4)
M. Gudipally (4)
K. Salloum (4)
B. Bucklen (4)
S. Khalil (4)

(1) Rigshospitalet, National University Hospital of Copenhagen, Copenhagen, Denmark
(2) Apollo Hospitals, Chennai, India
(3) Globus Medical, Research, Audubon, PA, USA
(4) Globus Medical, Audubon, PA, USA

Abstract

Introduction: Anterior lateral fixation of the thoracolumbar spine is used for stabilization after a corpectomy. Dual rod systems have been used successfully for treating patients after a thoracolumbar corpectomy and placement of an expandable cage for anterior column support. Two dual rod anterior thoracolumbar fixation systems (ATF) are compared biomechanically following corpectomy in thoracolumbar calf specimens. The effect of cross connectors is also investigated.

Methods: Fourteen T12 to L3 mature calf spines were separated evenly into two groups and tested in a six degree of freedom spine testing machine. A load control protocol of ±7.5Nm at a rate of 1.5º/sec was applied in flexion-extension (FE), lateral bending (LB), and axial rotation (AR). An expandable cage, XPand® (Globus Medical; Audubon, PA) was implanted in both groups after corpectomy at L1. A low-profile anterior dual rod system, REVERE® CROSSTOP™ (Globus Medical) was used in Group 1 (LP DRS) and a dual rod system, REVERE® Anterior Staples (Globus Medical) was tested in Group 2 (DRS). The profile height from the vertebral bodies of LP DRS is 11mm compared to 18.5mm for DRS. Titanium rods were used in both groups (5.5mm diameter).

The following constructs were tested in both groups;

1) intact;

2) ATF from T13-L2 with two cross connectors (ATF + 2 CC);

3) ATF from T13-L2 with 1 cross connector (ATF +1 CC); and

4) ATF from T13-L2.

Overall range of motion (ROM) was measured only from T13 to L2. A one-way ANOVA and post hoc Student-Newman-Keuls test was used to determine statistical significance.

Results: In FE, ROM for LP DRS and its equivalent cross connector constructs are significantly less compared DRS and its equivalent cross connector construct (p≤0.05). ROM for LP DRS + 2 CC and LP DRS + 1 CC are significantly (p≤0.05) reduced compared to intact ROM. All DRS constructs significantly (p≤0.05) reduced ROM compared to intact.

In LB, LP DRS ROM is greater than DRS, but not statistically. All LP DRS and DRS systems significantly reduced ROM compared to intact (p≤0.05).

In AR, LP DRS ROM is less than DRS without a significant difference between similar cross connector configurations (p≥0.05). LP DRS + 2 CC ROM is greater than intact but without significance (p≥0.05). ROM of all other constructs are significantly greater compared to intact (p≤0.05).

Conclusion: Anterior thoracolumbar fixation with cross connectors significantly reduces motion below the intact specimens in flexion-extension and lateral bending. Axial rotation motion is greater than the intact specimens after a corpectomy and fixation. The addition of cross connectors increases thoracolumbar stability in all loading modes. The low-profile dual rod system is 7.5mm less in profile, and reduces flexion extension motion with significance compared to an equivalent dual rod system. In axial rotation, plates of an increased profile plates showed a trend of higher stability.

ROM at T12-L1 of all tested constructs