482 - Biomechanical Evaluation of a Unilateral, Minimally Invasive Approach...

#482 Biomechanical Evaluation of a Unilateral, Minimally Invasive Approach for Decompression in the Lumbar Spine: A Cadaver Study

Oral Posters: MIS

Presented by: Z. Smith


Z.A. Smith (1)
G. Vastardis (2)
G. Carandang (2)
R.M. Havey (2)
S. Hannon (2)
L. Voronov (2)
A. Patwardhan (2)
R.G. Fessler (1)

(1) Northwestern University, Neurological Surgery, Chicago, IL, USA
(2) Loyola University Chicago, Edward Hines, Jr.; Veteran's Hospital, Hines, IL, USA


Study Design: A biomechanical cadaver study of the human lumbar spine.

Objective: To evaluate post-procedure effects on segmental motion in the lumbar spine following a minimally invasive, unilateral approach as compared to traditional facet sparing and non-facet sparing decompressions.

Summary of Background Data: Minimally invasive lumbar decompression, using tubular retractors and a unilateral approach for bilateral decompression, has become a common modern approach for lumbar stenosis. In addition to known advantages for this technique (that include improvements in peri-operative outcome measures) this approach may potentially mitigate post-operative increases in segmental motion.

Methods: Six human complete lumbar cadaveric specimens were used. With the use of a 400 N follower-load, each specimen was tested in the following conditions: flexion, extension, left and right axial rotation, and left and right lateral bending. Each testing condition was evaluated following three separate interventions at a single-level (L4/L5):

1) Minimally invasive decompression (MI-D),

2) Facet-sparing, bilateral decompression, and

3) Bilateral decompression with a wide-factectomy.

Range of motion following each testing condition was compared to intact specimens.

Results: Both a minimally invasive and traditional decompression create significant increases in ROM in all conditions. With flexion-extension testing, ROM at the operative level (L4/L5), increased with each intervention. With flexion-extension testing, ROM at L4/L5 for intact, MI-D, traditional decompression, and wide-decompression was 9.2, 9.6, 10.7, and 12.3 degrees, respectively. Similar serial increases in segmental motion were found with other testing conditions. When compared to the MI approach, traditional decompression produces a significantly greater increase in ROM in flexion-extension (p < 0.005) and axial rotation (p < 0.05). When compared to the intact spine, the MI-D approach may cause increased ROM with lateral bending on the approach side (p < 0.05). Lateral bending on the non-approach side is not significantly changed when compared to intact specimens. Lastly, wide bilateral medial facet removal (40-50%) causes a statistically significant increase in segmental motion. This increase in motion is especially notable with axial rotation.

Conclusions: While both minimally invasive and traditional lumbar decompressions may increase post-operative ROM in all conditions, a minimally invasive approach causes significantly less segmental mobility. With an MI approach, increased movement with lateral bending is only toward the approach side. Further, non-facet sparing decompression is further destabilizing in all conditions, especially axial rotation.