L5 - s1 segmental kinematics after facet arthroplasty

Area of Science:

• Spine surgery
• Biomechanics
• Orthopedic implants

Background:

• Facet arthroplasty is a motion-preserving alternative to rigid fixation after posterior lumbar decompression.
• Previous studies show success at L3-L4 and L4-L5, but lumbosacral (L5-S1) joint kinematics present unique challenges.
• The L5-S1 segment's distinct anatomy and kinematics necessitate specific evaluation for facet replacement viability.

Purpose of the Study:

• To evaluate the kinematics of facet arthroplasty at the lumbosacral (L5-S1) joint.
• To assess the ability of the Lumbosacral Total Facet Arthroplasty System (TFAS-LS) to restore stability and motion after destabilizing procedures.

Main Methods:

• Six human cadaveric lumbar spines (L1-S1) underwent testing: intact, laminectomy-facetectomy at L5-S1, and TFAS-LS implantation at L5-S1.
• Motion was assessed in flexion, extension, lateral bending, and axial rotation under controlled loads.
• Statistical analysis used Bonferroni correction to compare motion across conditions.

Main Results:

• Laminectomy-facetectomy significantly increased L5-S1 range of motion (ROM) in all planes.
• TFAS-LS implantation reduced ROM compared to the destabilized state, restoring it to intact levels for lateral bending and axial rotation.
• Flexion-extension ROM after TFAS-LS was less than intact but within physiologic norms, with sigmoidal load-displacement curves indicating graded resistance.

Conclusions:

• The TFAS-LS effectively restores stability to the lumbosacral segment post-decompression.
• The system allows for near-normal kinematics across all tested planes at L5-S1.
• Facet arthroplasty technology is adaptable to the lumbosacral joint, offering functionality comparable to superior lumbar levels.