Multidirectional testing of one- and two-level ProDisc-L versus simulated fusions.
METHODS
An in vitro human cadaveric biomechanical study.


OBJECTIVE
To evaluate intervertebral rotation changes due to lumbar ProDisc-L compared with simulated fusion, using follower load and multidirectional testing.


BACKGROUND
Artificial discs, as opposed to the fusions, are thought to decrease the long-term accelerated degeneration at adjacent levels. A biomechanical assessment can be helpful, as the long-term clinical evaluation is impractical.


METHODS
Six fresh human cadaveric lumbar specimens (T12-S1) underwent multidirectional testing in flexion-extension, bilateral lateral bending, and bilateral torsion using the Hybrid test method. First, intact specimen total range of rotation (T12-S1) was determined. Second, using pure moments again, this range of rotation was achieved in each of the 5 constructs: A) ProDisc-L at L5-S1; B) fusion at L5-S1; C) ProDisc-L at L4-L5 and fusion at L5-S1; D) ProDisc-L at L4-L5 and L5-S1; and E) 2-level fusion at L4-L5 to L5-S1. Significant changes in the intervertebral rotations due to each construct were determined at the operated and nonoperated levels using repeated measures single factor ANOVA and Bonferroni statistical tests (P < 0.05). Adjacent-level effects (ALEs) were defined as the percentage changes in intervertebral rotations at the nonoperated levels due to the constructs.


RESULTS
One- and 2-level ProDisc-L constructs showed only small ALE in any of the 3 rotations. In contrast, 1- and 2-level fusions showed increased ALE in all 3 directions (average, 7.8% and 35.3%, respectively, for 1 and 2 levels). In the disc plus fusion combination (construct C), the ALEs were similar to the 1-level fusion alone.


CONCLUSIONS
In general, ProDisc-L preserved physiologic motions at all spinal levels, while the fusion simulations resulted in significant ALE.
Panjabi
Manohar
M
Biomechanics Research Laboratory, Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT 06520-8071, USA. manoharpanjabi@gmail.com
Henderson
Gweneth
G
Abjornson
Celeste
C
Yue
James
J
D006801:Humans; D066298:In Vitro Techniques; D007403:Intervertebral Disc / Q000502:physiology / Q000601:surgery; D007405:Intervertebral Disc Displacement / Q000503:physiopathology* / Q000601:surgery; D008159:Lumbar Vertebrae / Q000502:physiology* / Q000601:surgery; D019736:Prostheses and Implants; D016059:Range of Motion, Articular; D013123:Spinal Fusion; D014102:Torsion Abnormality; D016474:Weight-Bearing