Retrospective series reported excellent and good results based on patients’ clinical satisfaction with a success rate higher than 90% (3). Unfortunately there was no relevant clinical evaluation using the common scores such as Oswestry or SF-36 for functional activities. Even visual analogue scoring was not available. Griffith’s (4) series reporting Charité experience in 1994 showed only 66% clinical success. Two retrospective series are very interesting. The first one is reported by Putzier et al. (1) and is the original experience of Charité with 17-year follow-up. Seventy-one patients were treated with 84 Charité TDRs types I to III. Indication for TDR was moderate to severe DDD. Fifty-three patients (63 TDRs) were available for long-term follow-up of 17 years. Evaluation at revision only included Oswestry Disability Index (ODI), visual analogue scale (VAS), overall outcome score, and plain and extension-flexion radiographs. Implantation of Charité TDR resulted in a 60% rate of spontaneous ankylosis after 17 years. No significant difference between the three types of prostheses was found concerning clinical outcome. Reoperation was necessary in 11% of patients. Although no adjacent segment degeneration was observed in the functional implants (17%), these patients were significantly less satisfied than those with spontaneous ankylosis. The second paper reported Lemaire’s (2) experience using Charité III in 107 patients with 11-year follow-up. Of these 107, one hundred were followed for a minimum of 10 years (range 10–13.4
years). One hundred forty-seven prostheses were implanted with 54 one-level and 45 two-level procedures and 1 three-level procedure. Clinically, 62% had an excellent outcome, 28% had a good outcome, and 10% had a poor outcome, but this evaluation was not performed with Oswestry and SF-36 scores but only on patient satisfaction. Of the 95 eligible to return to work, 88 (91.5%) either returned to the same job as prior to surgery or to a different job. These included 63.2% (12) of those working in heavy labor employment returning to the same job. Mean flexion-extension motion was 10.3 degrees for all levels (12.0 degrees at L3–L4, 9.6 degrees at L4-L5, 9.2 degrees at L5-S1). Mean lateral motion was 5.4 degrees. Slight subsidence was observed in two patients, but they did not require further surgery. No subluxation of the prostheses and no cases of spontaneous arthrodesis were identified. There was one case of disc height loss of 1 mm. Five patients required a secondary posterior arthrodesis. The difference in between those two retro-spective series is amazing. Spontaneous fusion moves from 0% at 10 years in one series to 60% at 17 years. The difference needs to be analyzed. Patient selection is probably different but no data are available on this point in both series.

Some prospective series report experience with Prodisc and Maverick. Tropiano et al. (5) recently reported Marnay initial experience. Sixty-four patients had single- or multiple-level implantation between 1990 and 1993. The mean duration of follow-up was 8.7 years. Clinical results were evaluated by assessing preoperative and postoperative lumbar pain, radiculopathy, disability, and modified Stauffer-Coventry scores. At an average of 8.7 years postoperatively, there were significant improvements in the back pain, radiculopathy, disability, and modified Stauffer-Coventry scores. Thirty-three of the 55 patients with sufficient follow-up had an excellent result, 8 had a good result, and 14 had a poor result. Neither gender nor multilevel surgery affected outcome. An age of younger than 45 years and prior lumbar surgery had small but significant negative effects on outcome. Radiographs did not demonstrate loosening, migration, or mechanical failure in any patient.

Using Prodisc II, Bertagnoli et al. (6,7,8) recently reported their experience. This prospective analysis was performed on 118 patients treated with single-level lumbar disc arthroplasty (6). A total of 104 patients (88%) fulfilled all follow-up criteria. The median age of all patients was 47 years (range, 36–60 years). Statistical improvements in VAS, Oswestry, and patient satisfaction scores occurred 3 months postoperatively. These improvements were maintained at the 24-month follow-up. Radicular pain also decreased significantly. Full-time and part-time work rates increased from 10% to 35% and 3% to 24%, respectively. No additional fusion surgeries were necessary either at the affected or at the unaffected levels. Radiographic analysis revealed an affected disc height increase from 4 to 13 mm (p < 0.001) and an affected disc motion from 3 to 7 degrees (p < 0.004). The same author (7) also reported his experience regarding the safety and efficacy of single-level lumbar disc (ProDisc prosthesis) replacement in patients 60 years of age or older. Twenty-two patients presented with disabling discogenic LBP with or without radicular pain. The involved segments ranged from L2 to S1. Patients in whom there was no evidence of radiographic circumferential spinal stenosis and with minimal or no facet joint degeneration were included. Outcome was evaluated postoperatively at 3, 6, 12, and 24 months by administration of standardized tests (VAS, ODI, and patient satisfaction). The median age of all patients was 63 years (range 61–71 years). There
were 17 single-level cases, 4 two-level cases, and 1 three-level case. Statistical improvements in VAS, ODI, and patient satisfaction scores were observed at 3 months postoperatively and were maintained at 24-month follow-up. Patient satisfaction rates were 94% at 24 months. Radicular pain also decreased significantly. Patients in whom bone mineral density was decreased underwent same-session vertebroplasty following implantation of the ProDisc device(s). There were two cases involving neurologic deterioration: unilateral foot drop and loss of proprioception and vibration in one patient and unilateral foot drop in another patient. Both deficits occurred in patients in whom there was evidence preoperatively of circumferential spinal stenosis. There were two cases of implant subsidence and no thromboembolic phenomena. Although the authors’ early results indicate that the use of ProDisc lumbar total disc arthroplasty in patients older than 60 years reduces chronic LBP and improves clinical functional outcomes, they recommend the judicious use of artificial disc replacement in this age group in whom bone quality is adequate in the absence of circumferential spinal stenosis. The use of cement bone augmentation to avoid subsidence as proposed in this series is probably the limit to avoid and at the moment we definitively advise against this kind of indication as our experience is definitively different. Even if this author never reported complications related to the implant, Aunoble et al. (9) experienced two cases of polyethylene inlay dislocation after 30 cases operated. This was mainly related to some technical errors during implantation, but it is still a problem particularly at the level L5-S1 where the disc height is sometimes less than 9 mm and the sacral slope is important. In those cases this author recommends a fusion.