#365 Biomechanical Analysis of a Single-level 360o Lumbar Spine Arthroplasty: An in vitro Cadaveric Study

General Session: What's New in Biologics and Biomechanics

Presented by: B.G. Santoni

Author(s):

A. Nayak (1)
M. Doarn (2)
R.B. Gaskins (2)
C.R. James (1)
A. Cabezas (1)
B.G. Santoni (1)
A.E. Castellvi (3)

(1) Foundation for Orthopaedic Research and Education, Tampa, FL, Orthopaedic Biomechanics Research, Tampa, FL, USA
(2) University of South Florida, Department of Orthopaedic Surgery and Sports Medicine, Tampa, FL, USA
(3) Florida Orthopaedic Institute, Center for Spinal Surgery and Disorders, Tampa, FL, USA

Abstract

Study Objective: Total spine arthroplasty may be an alternative to fusion by eliminating pain generators in both the disc and facets while affording motion at the affected level. Purpose of this study was to quantify the motion-preserving effect of a total facet replacement system alone and combination with a total posterior disc replacement at a single lumbar level.

Methods: Six (n=6) human cadaveric lumbar spines (L1-S1) were biomechanically evaluated using a pure-moment flexibility protocol (±7.5 Nm) in flexion-extension (FE), lateral bending (LB) and axial rotation (AR). Each specimen was tested in the following order: (1) intact; (2) unilateral facet replacement (FR); (3) unilateral FR + posterior total disc (PTDR); and (4) bilateral FR + PTDR (360° arthroplasty).

Index and adjacent level ROM (hybrid protocol) were determined optoelectronically. Interpedicular travel (IPT) at the index level was also measured as a function of condition. The instantaneous center of rotation (ICR) was derived for each condition on ± 7.5 Nm flexion-extension images. ROM, ICR, and IPT measurements were compared (repeated measures ANOVA) between the four conditions.

Results:

ROM: In FE and AR, there was no significant difference in index level ROM (p=0.158 and p=0.159, respectively) between test conditions. No changes in adjacent level motion were detected in FE (p>0.087) or AR (p>0.195). In LB, motion significantly increased at L4-L5 (16.8° ± 8.0°) in the bilateral FR+PTDR condition compared to intact (12.0°±6.0°; p=0.014) and unilateral FR (12.6°±6.0°; p=0.025) conditions, respectively. No changes in adjacent level ROM were detected in LB (p>0.113).

IPT: No significant differences in IPT were identified between conditions in FE (p=0.058) or AR (p=0.334) at L4-L5. However, IPT in LB for the bilateral FR+PTDR condition (15.4 ± 5.9 mm) was significantly higher (p=0.027) than intact (9.6 ± 3.3 mm) at L4-L5.

ICR: ICRs were qualitatively similar for the intact vs. unilateral FR cases and appeared to follow placement (along the AP direction) of the PTDR in the disc space.

Conclusion: Index and adjacent level ROM were unaffected by the facet and total disc arthroplasty systems in FE and AR. 3600 arthroplasty at the L4-L5 level resulted in increased LB ROM, which was corroborated by increased LB IPT. ICRs between test conditions seemed to qualitatively lie very close to intact ICRs and positioning of the PTDR (AP placement) within the disc space. Results confirm the motion preserving effects of total spine arthroplasty using the facet and disc replacement devices.

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