Surgical and clinical results with the PDN prosthetic disc-nucleus device.

The PDN prosthetic disc-nucleus device has been in use for 6 years, both in clinical trials and through commercial sale. Surgical and clinical data for the device have been collected and analyzed to help determine the strengths and limitations of the implant. The shape of the device has been found to be an important element in predicting surgical success, with wedge and rectangular devices being the most stable. The patient's disc dimensions are also critically important. Data indicate that patients with a disc height of less than 5 mm should be excluded from surgery. Moreover, the anterior-posterior (AP) diameter of the disc endplates must be 37 mm or more in order to properly situate two devices within the disc--patients with a smaller AP diameter should receive only a single device. Body mass and overall patient weight are also good predictors of surgical success. If the patient's body mass index is 30 or greater, then the patient should not receive the implants. Complications related to the PDN implant have included migration of the device and endplate remodeling in some patients. This endplate remodeling has usually been mild, and has occurred in response to the change in load distribution. In a few cases there has been more pronounced remodeling with a loss of disc height. To minimize endplate remodeling, the PDN hydrogel has been reformulated to be softer, absorbing 80% of its weight in water. Subsequent to implementing changes in device design and patient selection, and with the introduction of the ALPA (Anterior-Lateral transPsoatic Approach) technique for implanting the devices, there has been an increase in surgical success with a concomitant reduction in the number of revision surgeries. The current surgical success rate for patients implanted from 1999 through 2001 is 88%. Clinical results are also very encouraging, with marked decreases in Oswestry and visual analog scale pain levels, and disc height also shows improvement and stabilization.