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Antidegenerative Effects of Partial Disc Replacement in an Animal Surgery Model

Study Design. In vivo degenerative changes of rabbit intervertebral discs after partial disc replacements were evaluated radiologically and histologically in a controlled trial. Objective. To demonstrate the therapeutic effects of partial disc replacement in an animal surgical model. Summary of Background Data. Although some authors reported that partial disc replacements have beneficial clinical outcomes, there are few controlled animal studies in which the therapeutic effects of this procedure have been demonstrated. Methods. The implants for partial disc replacements were made of poly (vinyl alcohol) hydrogel and rod-shaped. The L2–L3 or L3–L4 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 disc 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 after surgery. Results. Radiologic 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. Histologic degeneration of the replaced discs was delayed in comparison with that of the control discs but progressed with time. Conclusions. The antidegenerative effects of partial disc replacement surgery were demonstrated by quantitative radiologic and histologic analyses. Degeneration of the anulus fibrosus after the replacement treatment was delayed by preserving disc height and occupying the space of the nucleus pulposus. Properly designed implants and minimally invasive techniques are necessary for long-term success.