Single-unit artificial intervertebral disc

Area of Science:

• Biomedical Engineering
• Orthopedic Surgery
• Spinal Mechanics

Background:

• Artificial disc replacement aims to restore spinal motion and alleviate pain.
• Current devices often require complex fixation systems.
• A novel single-unit artificial disc (SUAD) design eliminates the need for fixation.

Purpose of the Study:

• To evaluate the stability and integrity of the single-unit artificial disc (SUAD) under simulated physiological loading.
• To assess the ability of the SUAD to maintain its position within the disc space without an anchoring device.

Main Methods:

• Kinematic fatigue testing of various SUAD designs (flat discs and custom-designed discs) with different durometers (30D and 85D) placed between cadaveric C-5 and C-6 vertebral bodies.
• Simulated physiological movements (flexion-extension, lateral bending, coupled rotation) were applied using a robotic testing fixture.
• Cyclic loading up to 5 million cycles was performed, with analysis of disc integrity, position, and wear.

Main Results:

• Softer (30D) SUADs maintained their position in the disc space without fixation after 1 million cycles.
• Harder (85D) discs and some 30D discs experienced weight loss, while 30D custom-designed discs showed minimal weight gain or loss.
• One 85D flat disc was extruded, and one 85D recess-edged disc rotated, indicating potential issues with harder or specific designs.

Conclusions:

• A 30D SUAD can successfully maintain its position in the disc space without fixation.
• Softer SUADs appear to conform better to the disc space and exhibit less wear.
• Further long-term fatigue studies (10 million cycles) are warranted to confirm efficacy and assess particle generation.