Multidirectional flexibility analysis of cervical artificial disc reconstruction: in vitro human cadaveric spine model.

OBJECT: This in vitro experimental study was conducted to investigate the initial biomechanical effect of artificial intervertebral disc replacement in the cervical spine. The multidirectional flexibility of replaced and adjacent spinal segments were analyzed using a cadaveric cervical spine model. METHODS: The following three cervical reconstructions were sequentially performed at the C5-6 level after anterior discectomy in seven human cadaveric occipitocervical spines: anterior artificial disc replacement with a bioactive three-dimensional (3D) fabric disc (FD); anterior iliac bone graft; and anterior plate fixation with iliac bone graft. Six unconstrained pure moments were applied with a 6-df spine simulator, and 3D segmental motions at the operative and adjacent segments were measured with an optoelectronic motion measurement system. The 3D FD group demonstrated statistically equivalent ranges of motion (ROMs) when compared with intact values in axial rotation and lateral bending. The 45% increase in flexion-extension ROM was demonstrated in 3D FD group; however, neutral zone analysis did not reach statistical significance between the intact spine and 3D FD. The anterior iliac bone graft and iliac bone graft reconstructions demonstrated statistically lower ROMs when compared with 3D FD in all loading modes (p < 0.05). The adjacent-level ROMs of the 3D FD group demonstrated nearly physiological characteristics at upper and lower adjacent levels. Excellent stability at the interface was maintained during the whole testing without any device displacement and dislodgment. CONCLUSIONS: The stand-alone cervical 3D FD demonstrated nearly physiological biomechanical characteristics at both operative and adjacent spinal segments in vitro, indicating an excellent clinical potential for cervical artificial disc replacement

Multidirectional flexibility analysis of anterior and posterior lumbar artificial disc reconstruction: in vitro human cadaveric spine model.

The in vitro multidirectional flexibility analysis was conducted to investigate the initial biomechanical effect of biomimetic artificial intervertebral disc replacement from either anterior or posterior approach in a cadaveric lumbosacral spine model. Two designs of anterior total and posterior subtotal artificial discs were developed using bioactive three-dimensional fabric and bioresorbable hydroxyapatite/poly-l-lactide material (3DF disc). Both models were designed to obtain the stable interface bonding to vertebral endplates with maximum surface area occupation. Using seven cadaveric lumbosacral spines, the following three anterior reconstruction methods were sequentially performed at L4–5 level: anterior 3DF disc replacement; anterior BAK cages (BAK); and posterior pedicle screw fixation and anterior BAK cages combined (BAK + PS). The L2–3 level received two methods of posterior reconstructions: subtotal 3DF disc replacement (two implants), and posterior interbody cages and pedicle screw fixation (PLIF). Six unconstrained pure moments were applied and three-dimensional segmental motions were measured with an optoelectronic motion measurement system. The center of rotation (COR) calculation was conducted radiographically using flexion-extension films. Both anterior and posterior 3DF replacements statistically demonstrated equivalent range of motions (ROMs) in all loading modes compared to intact segment. Anterior BAK, BAK + PS, and PLIF demonstrated significantly lower ROMs when compared to intact and 3DF groups (P<0.05). The 3DF reconstruction tended to realign the COR to the posterior third or surrounding position at the operative disc level. The stand-alone lumbar 3DF disc replacement demonstrated biomechanical characteristics nearly equivalent to the intact spinal segments even through anterior or posterior approach in vitro, suggesting an excellent clinical potential