In biomechanical kinematic studies, it has been shown that the sliding core of the CHARITÉ mimics the instantaneous axis of rotation of the normal intervertebral disc. Simply, as one flexes, the center of the nucleus moves posteriorly. In extension, the center of the nucleus moves anteriorly. In comparison to normal intervertebral discs, the CHARITÉ’s motions are nearly identical. Additionally, the wear characteristics of the CHARITÉ are favorable compared to metal and polyethylene prosthesis for the hip and knee. At 10 million cycles, the core showed 0.11 mm of wear per million cycles tested. Ten million cycles is the equivalent of lifting 20 kg 125,000 times per year for 80 years (1).

Compared to fusion, total disc arthroplasty offers potential advantages including motion preservation, avoidance of the morbidity associated with a posterior exposure, and potential decrease in adjacent segment breakdown. Both short- and long-term clinical studies have addressed these issues and have yielded promising results. Lemaire et al. (2) reported on the initial patients who underwent the procedure in Europe. They implanted 147 CHARITÉ devices in 100 patients at a mean follow-up of 11.3 years (range 10 to 13.4 years). The mean range of motion was 10.3 degrees in flexion/extension and
5.4 degrees in lateral bending. Ninety-two percent of the patients returned to work. No difference in clinical outcome was found between one- and two-level disc arthroplasty. Their failure rate was 3.3% and these patients were treated with posterior fusions. No migration or spontaneous fusions were noted.

Yoon et al. (3) studied their results on a series of 800 patients with the majority at 5-year follow-up. Their series consisted of 704 single-level, 92 two-level, and 4 three-level disc arthroplasties for a total of 825 artificial discs. The mean age was 44.8 years (range 21–81 years). Disc height increased 52% on postoperative radiographs. Visual analogue scale (VAS) pain measurement decreased 5.4 points in leg pain and 4.7 points in back pain (on a 0 to 10 scale). The authors determined that poor prognosis was directly related to poor positioning, violation of the endplate, and obesity.

Recently, in the United States, the results of the FDA IDE clinical trial have been published (4,5). These two studies are the landmark articles comparing artificial disc to stand-alone anterior fusion for the treatment of single-level discogenic degeneration in the lumbar spine. A prospective, randomized, controlled, FDA-regulated trial was conducted at 15 centers across the United States. The study included 375 patients randomized in a 2:1 ratio of CHARITÉ to BAK cages (205:99) plus 71 nonrandomized “training cases.” In March 2000, the first artificial disc was implanted in the United States. An additional 635 disc implantations were performed under a continued access protocol from May 2002 to October 2004. Primary inclusion and exclusion criteria are described in Table 16.1. Two-year follow-up clinical and radiographic data were submitted to the FDA, leading to subsequent approval (October 26, 2004).

The data from these studies demonstrate the CHARITÉ Artificial Disc is safe and effective for symptomatic degenerative disc disease at one level (L4-5 or L5-S1) compared with stand-alone ALIF with BAK cages. It provides superior early clinical improvement (p < 0.05) with a shorter hospitalization period and higher patient satisfaction. The authors concluded that results directly correlate to placement of the device. Ideal placement is within 3 mm of midline in both planes. Criticisms of the study include corporate sponsorship, the exclusion of the nonrandomized data in the statistical analysis, and the quoted clinical success rate of 64%. Notwithstanding, the authors’ rebuttal with the fact that funding is arbitrary, the clinical success and complication rate of the nonrandomized cases were comparable to the randomized cases, and the success rate is understated secondary to FDA criterion of success.

The Texas Back Institute has one of the largest series of CHARITÉ Artificial Disc patients in the United States. From March 2000 through June 2005, 303 discs have been implanted in 283 patients. In our population, the mean operative time was 68.5 minutes for a single-level TDR with an additional 20 minutes for an additional level. The mean blood loss was 134.3 mL. Patients were generally discharged on the first or second postoperative day with a soft corset. Return to normal activity was allowed after 2 weeks with extreme extension limited for 3 months. Normal activity was allowed after 3 months. At 2-year follow-up, VAS scores decreased from 69.1 to 29.5 and the Oswestry Disability Index (ODI) decreased from 49.5 to 24.0. Complications included major neurologic deficit in two patients (foot drops, one of which was transient), minor neuropraxia in five patients, and vascular injury in three patients. The reoperation rate was 3.1%. There were seven posterior fusions and two of the discs were revised. One patient had an intraoperative conversion to a fusion. Subsidence was not clinically significant. None of the devices failed.