The PDN prosthetic disc-nucleus device.

The health of an intervertebral disc is based on a complicated interplay between physiology and biomechanics. The nucleus pulposus must remain well hydrated, and the surrounding anulus fibrosus must be competent in order for the disc to function properly. If either of these components fail, the disc will begin to degenerate, and clinically relevant symptoms may appear. Disc degeneration has traditionally been treated by either discectomy or immobilization of the affected vertebrae, and though these treatments can be effective, they also have their limitations. To help fill the therapy gap that exists for treating moderate degenerative disc disease, the PDN device has been developed. The device consists of a hydrogel core and a polyethylene jacket that are designed to assume the cushioning function of a healthy disc, while restoring/maintaining disc height and allowing normal range of motion. To receive the device, patients must have a preoperative disc height of at least 5 mm and the vertebral endplates must be free of significant defects such as Schmorl's nodules or fractures. Two approaches can be used for implanting PDN devices: a hemilaminotomy approach, where the disc is accessed through the back, or an Anterior-Lateral transPsoatic Approach (ALPA), where the disc is accessed from the side. In either case, the nucleus material is removed from the disc, and the devices are placed transversely within the nucleus cavity. The amount of research and development currently taking place in the field of disc arthroplasty gives hope that the treatment of degenerative disc disease will soon become multifaceted, with numerous choices being available to surgeons and their patients.