Effect of two-level total disc replacement on cervical spine kinematics.

Area of Science:

• Spine Biomechanics
• Orthopedic Surgery
• Biomaterials and Artificial Organs

Background:

• Cervical total disc replacement (TDR) is an alternative to fusion for multilevel disease, offering potential benefits like motion preservation and reduced adjacent segment stress.
• Limited biomechanical data exists for multilevel cervical TDR.

Purpose of the Study:

• To biomechanically characterize the kinematics of human cadaveric cervical spines after two-level TDR implantation.
• To assess range of motion (ROM) at implanted and adjacent cervical spine segments.

Main Methods:

• Six human cadaveric cervical spine specimens (C3-C7) were tested.
• Testing included intact states, single-level TDR (C5-C6), and two-level TDR (C5-C6 and C6-C7).
• Specimens underwent flexion/extension, lateral bending, and axial rotation under a +/-1.5 Nm load; ROM was measured using optoelectronic instrumentation and fluoroscopy.

Main Results:

• Two-level TDR maintained ROM at implanted segments to near-intact levels across all motion types.
• TDR implantation did not significantly alter ROM at adjacent spinal levels (C4-C5).
• A slight increase in lateral bending ROM was observed at C4-C5 with two-level TDR.

Conclusions:

• Two-level cervical TDR effectively preserves mobility at the treated levels without destabilizing the spine or compromising adjacent segments.
• These findings support the use of single or multilevel cervical TDR as a potentially advantageous alternative to spinal fusion.