title: StabilimaxNZ) versus simulated fusion: evaluation of adjacent-level effects.
abstract: Rationale behind motion preservation devices is to eliminate the accelerated adjacent-level effects (ALE) associated with spinal fusion. We evaluated multidirectional flexibilities and ALEs of StabilimaxNZ and simulated fusion applied to a decompressed spine. StabilimaxNZ was applied at L4-L5 after creating a decompression (laminectomy of L4 plus bilateral medial facetectomy at L4-L5). Multidirectional Flexibility and Hybrid tests were performed on six fresh cadaveric human specimens (T12-S1). Decompression increased average flexion-extension rotation to 124.0% of the intact. StabilimaxNZ and simulated fusion decreased the motion to 62.4 and 23.8% of intact, respectively. In lateral bending, corresponding increase was 121.6% and decreases were 57.5 and 11.9%. In torsion, corresponding increase was 132.7%, and decreases were 36.3% for fusion, and none for StabilimaxNZ ALE was defined as percentage increase over the intact. The ALE at L3-4 was 15.3% for StabilimaxNZ versus 33.4% for fusion, while at L5-S1 the ALE were 5.0% vs. 11.3%, respectively. In lateral bending, the corresponding ALE values were 3.0% vs. 19.1%, and 11.3% vs. 35.8%, respectively. In torsion, the corresponding values were 3.7% vs. 20.6%, and 4.0% vs. 33.5%, respectively. In conclusion, this in vitro study using Flexibility and Hybrid test methods showed that StabilimaxNZ stabilized the decompressed spinal level effectively in sagittal and frontal planes, while allowing a good portion of the normal rotation, and concurrently it did not produce significant ALEs as compared to the fusion. However, it did not stabilize the decompressed specimen in torsion.
authors.affiliation: Biomechanics Laboratory, Yale University, Orthopaedics and Rehabilitation, New Haven, CT 06510, USA. manoharpanjabi@gmail.com
authors.forename: Manohar M
authors.initials: MM
authors.lastname: Panjabi
authors.forename: Gweneth
authors.initials: G
authors.lastname: Henderson
authors.forename: Yue
authors.initials: Y
authors.lastname: James
authors.forename: Jens Peter
authors.initials: JP
authors.lastname: Timm
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D019299:Decompression, Surgical / Q000009:adverse effects; D005260:Female; D006801:Humans; D016268:Internal Fixators / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D011183:Postoperative Complications / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control*; D016059:Range of Motion, Articular / Q000502:physiology; D013122:Spinal Diseases / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control*; D013123:Spinal Fusion / Q000295:instrumentation*; D013131:Spine / Q000033:anatomy & histology / Q000502:physiology / Q000601:surgery*; D054159:Torsion, Mechanical