Antidegenerative effects of artificial disc replacement by low water content-poly (vinyl alcohol)

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Although some authors reported that partial disc replacements (PDR) have beneficial clinical outcomes, there are few controlled animal studies in which the therapeutic effects of this procedure have been demonstrated. The objective of this study was to establish an animal surgery model of PDR and to demonstrate its therapeutic effects. In vivo degenerative changes of rabbit intervertebral discs after PDR were evaluated radiologically and histologically in a controlled trial. The implants were made of poly (vinyl alcohol) hydrogel (35% water content) and rod-shaped. The L2/3 or L3/4 intervertebral discs of Japanese white rabbits were pierced with a 2.0 mm Kirschner wire and implants were inserted into the holes. For comparative purposes, the adjacent discs underwent sham treatments or control treatments in which the dish was pierced but no implant was inserted. Sixty discs from 30 rabbits were analyzed radiologically and histologically for degenerative changes at 1, 3, or 6 months postoperatively. Radiological analysis revealed that significantly less disc height was lost with the replacement treatment than with the control treatment. Change in disc height after the replacement treatment was not significantly different from that after the sham treatment. Histological degeneration of the replaced discs was delayed in comparison with that of the control discs but progressed with time. Even when implants with higher water content were used, no remarkable change was histologically observed in shape. In this study, a safe and reproducible animal model of PDR was established, and its antidegenerative effects were demonstrated by quantitative radiological and histological analyses. Degeneration of the AF after the replacement treatment was delayed by preserving disc height and occupying the NP space. Proper selection of material and design of implants are necessary for long-term success.