Biomechanical assessment of minimally invasive decompression for lumbar spinal canal stenosis: a cadaver study.

STUDY DESIGN: A biomechanical study on the cadaveric human lumbar spine.

OBJECTIVE: We focused on a biomechanical comparison of the changes wrought on motion segments after a minimally invasive decompression and after a conventional medial facetectomy.

SUMMARY OF BACKGROUND DATA: Minimally invasive posterior decompression using a microscope or an endoscope is becoming popular for elderly patients with lumbar spinal canal stenosis. An advantage of the technique is that the cauda equina and nerve roots are in clear view and the facet joints, paravertebral muscles, and spinous process are well preserved.

METHODS: Eight human lumbar motion segments were used in this study. Each specimen was tested according to the following loading protocol: axial compression, flexion, extension, lateral bending to the right and to the left, and axial rotation to the right and to the left. This loading protocol was applied to each motion segment after the following surgical interventions: (1) left fenestration, (2) bilateral decompression via unilateral approach, (3) medial facetectomy, and (4) total facetectomy. The relative stiffness of the motion segments was determined and compared with a normalized stiffness for the specimen when intact.

RESULTS: Bilateral decompression via unilateral approach produces less biomechanical effect in terms of stiffness changes as compared with medial facetectomy. Bilateral decompression leaves the spine more than 80% as stiff as the intact spine.

CONCLUSIONS: These results go toward supporting a minimally invasive bilateral decompression. Minimally invasive bilateral decompression, as opposed to a conventional medial facetectomy, preserves the facet joints as much as possible. Preserving the facet joints during the decompression should produce less postoperative instability.