General Session: Biomechanics
Presented by: P. Grunert - View Audio/Video Presentation (Members Only)
P. Grunert(1,2), P.M. Reyes(3), A.G.U.S. Newcomb(3), B. Kelly(3), R. Härtl(1)
(1) Weill Cornell Medical College, Neurosurgery, New York, NY, United States
(2) Medical University of Vienna, Neurosurgery, Vienna, Austria
(3) Barrow Neurological Institute, Neurosurgery, Phoenix, AZ, United States
Background: Multilevel lumbar stenosis where one level requires stabilization due to spondylolisthesis is routinely treated with multilevel open laminectomy and fusion. We hypothesized that a minimally invasive (MIS) decompression is biomechanically superior to open laminectomy and may allow decompression of the level adjacent the spondylolisthesis without additional fusion.
Objective: Study the mechanical effect of various decompression procedures adjacent to instrumented segments in cadaver lumbar spines.
Methods: Conditions tested: 1) L4/L5 instrumentation; 2) L3/L4 minimally invasive decompression; 3) addition of partial facetectomy at L3/L4; and 4) addition of laminectomy at L3/L4. Flexibility tests were performed for range of motion (ROM) analysis by applying nonconstraining, pure moment loading during flexion-extension, lateral bending, and axial rotation. Compression flexion tests were performed for motion distribution analysis with a constant compressive preload of 400 N. Motion was assessed stereophotogrammetrically.
Results: Instrumentation at L4/L5 decreased motion of the entire lumbar spine by about 20% (p< 0.001) and caused a significant redistribution of motion in all segments (p< 0.05). After instrumentation, MIS decompression increased flexion-extension ROM at L3/L4 by 13% (p=0.034) and axial rotation by 23% (p=0.003). Partial facetectomy further increased axial rotation by 15% (p=0.032). After laminectomy, flexion-extension ROM further increased by 12% (p=0.05), a 38% increase from baseline, and axial rotation by 17% (p= 0.023), a 58% increase from baseline. MIS decompression yielded no significant increase in segmental contribution of motion at L3/L4, in contrast to partial facetectomy and laminectomy (< 0.05).
Discussion: When compared to other biomechanical studies, MIS decompression adjacent to instrumented segments increased segmental ROM similar to MIS decompression without adjacent instrumentation. Compared to MIS decompression, laminectomy also leads to significant biomechanical alteration at further cranial lumbar segments (L2/L3 and L1/L2).
Conclusion: Minimally invasive tubular decompression is biomechanically superior to open laminectomy adjacent to instrumented segments. Facet joint preservation is crucial to avoid additional hyper mobility when performing MIS decompression. Our results lend support to the concept that in patients where a multilevel MIS decompression is performed, the fusion might be limited to the segments with actual instability.