Biomechanics after spinal decompression and posterior instrumentation

Area of Science:

• Orthopedics
• Spine Surgery
• Biomechanics

Background:

• Lumbar spine surgery aims to decompress neural elements and stabilize the spine.
• Understanding the impact of surgical interventions on spinal biomechanics is crucial for patient outcomes.

Purpose of the Study:

• To quantify the changes in segmental range of motion (ROM) of the lumbar spine.
• To evaluate ROM alterations following common decompression and fusion procedures.

Main Methods:

• Biomechanical testing of 14 human cadaver lumbar spine segments (L1/2, L3/4, L5/S1).
• Assessment of ROM in six loading directions (flexion/extension, lateral bending, etc.).
• Evaluation of ROM in native state, after unilateral laminotomy, midline decompression, nucleotomy, and with posterior instrumentation.

Main Results:

• Unilateral laminotomy and midline decompression significantly increased segmental ROM.
• Nucleotomy led to substantial ROM increases, particularly in axial compression/distraction (153%).
• Pedicle screw fixation drastically reduced ROM (e.g., 82% in flexion/extension), with minimal impact from concurrent decompression.

Conclusions:

• Posterior decompression techniques significantly influence lumbar spine ROM.
• A simplified rule of thumb: expect ~10% ROM increase after laminotomy, ~20% after midline decompression, and ~50% after nucleotomy.
• Spinal instrumentation markedly decreases ROM, with decompression procedures having minor effects on construct stability.