• Eur Spine J · Jun 2023

    Biomechanics after spinal decompression and posterior instrumentation.

    • Marco D Burkhard, Anna-Katharina Calek, Marie-Rosa Fasser, Frédéric Cornaz, Jonas Widmer, José Miguel Spirig, Florian Wanivenhaus, and Mazda Farshad.
    • Department of Orthopaedic Surgery, University Spine Center Zürich, Balgrist University Hospital, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland. marco.burkhard@balgrist.ch.
    • Eur Spine J. 2023 Jun 1; 32 (6): 187618861876-1886.

    PurposeThe aim of this study was to elucidate segmental range of motion (ROM) before and after common decompression and fusion procedures on the lumbar spine.MethodsROM of fourteen fresh-frozen human cadaver lumbar segments (L1/2: 4, L3/4: 5, L5/S1: 5) was evaluated in six loading directions: flexion/extension (FE), lateral bending (LB), lateral shear (LS), anterior shear (AS), axial rotation (AR), and axial compression/distraction (AC). ROM was tested with and without posterior instrumentation under the following conditions: 1) native 2) after unilateral laminotomy, 3) after midline decompression, and 4) after nucleotomy.ResultsMedian native ROM was FE 6.8°, LB 5.6°, and AR 1.7°, AS 1.8 mm, LS 1.4 mm, AC 0.3 mm. Unilateral laminotomy significantly increased ROM by 6% (FE), 3% (LB), 12% (AR), 11% (AS), and 8% (LS). Midline decompression significantly increased these numbers to 15%, 5%, 21%, 20%, and 19%, respectively. Nucleotomy further increased ROM in all directions, most substantially in AC of 153%. Pedicle screw fixation led to ROM decreases of 82% in FE, 72% in LB, 42% in AR, 31% in AS, and 17% in LS. In instrumented segments, decompression only irrelevantly affected ROM.ConclusionsThe amount of posterior decompression significantly impacts ROM of the lumbar spine. The here performed biomechanical study allows creation of a simplified rule of thumb: Increases in segmental ROM of approximately 10%, 20%, and 50% can be expected after unilateral laminotomy, midline decompression, and nucleotomy, respectively. Instrumentation decreases ROM by approximately 80% in bending moments and accompanied decompression procedures only minorly destabilize the instrumentation construct.© 2023. The Author(s).

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