Adjacent segment alterations were found only in cases where spontaneous ankylosis of the treated segments, spondylodesis, or fusion after implant failure occurred. In the nine cases without signs of ankylosis, spondylodesis, or implant failure (as mentioned above) no signs of adjacent segment degeneration were found. The different types of prostheses did not influence this parameter nor did the kind of fusion (spondylodesis vs ankylosis) as shown in Table .
Clinical evaluation at follow-up showed no significant difference of the ODI and the VAS between the different types of Charité artificial discs (Table ). Additionally, overall outcome of the patients in relation to the type of prosthesis showed no significant differences either (Table ).
In summary, implantation of Charité TDR resulted in a high rate (60%) of spontaneous ankylosis after an average follow-up of 17 years. There was no significant difference in the clinical outcome between the three types of prostheses. Although no adjacent segment degeneration was observed in the few functional implants (17%), these patients were significantly less satisfied with the long-term outcome of the surgery than the patients with spontaneously ankylosed motion segments or fusion after implant failure. Although the Charité TDR nowadays is an approved implant, the evidence that long-term results of TDR implantation in DDD are as good as or even better than fusion results is still missing.
Additionally, for a correct implantation of artificial disc prostheses a nearly complete removal of the remaining disc tissue is mandatory [, , , ]. This process implies the decortication of the vertebral endplates. Consecutively, osteoinductive substances are regularly released into the disc space due to the interruption of the integrity of the bone–cartilage border . In operative spondylodesis, this effect is intended to enhance and promote the osseous consolidation; however, it is unintended in TDR. This undesired process might also have contributed to the high rate of spondylodesis. Finally, since all of the reported patients suffered preoperatively from moderate to severe DDD, a progression of these processes after surgery can be assumed. This may be another cause of ongoing ossification as a result of degenerative changes of segment-related tissue such as bone and ligaments.
All operations were performed by senior spine surgeons experienced with the anterior approach including the designers of the prosthesis. Under protection of the great abdominal vessels, the intervertebral disc space was exposed using a pararectal extraperitoneal approach. The anterior longitudinal ligament was incised and the degenerated disc tissue was removed after radiological verification of the correct level. The size for each part of the prosthesis was measured, and after preparation of the endplates the artificial disc replacement was implanted. The anterior longitudinal ligament was then thoroughly sutured and afterwards the wound closure was performed in layers.
While type I and II Charité total disc prostheses were manufactured in the former German Democratic Republic (GDR) and never commercially available, type III is still in use, and in the meantime distributed by Johnson and Johnson.
After an average follow-up of 17.3 years (14.5–19.2 years) 53 patients (follow-up rate 74.6%) were available for clinical and radiological examination. Patient population consisted of 20 males and 33 females with an average age of 44 years (30–59 years). Overall 63 TDRs (follow-up rate 75.0%) had been performed in the patients available for follow-up. Treated levels included L3/4 in 2 patients, L4/5 in 25 patients, L5/S1 in 16 patients, and L4–S1 in 10 patients. Fifteen patients operated between 1984 and 1985 had been treated with 16 type I, 22 patients operated between 1985 and 1987 had received 25 type II and 16 patients operated between 1987 and 1989 had received 22 type III Charité total disc prostheses (Table ). In all 53 patients, indication for surgery was a mono- or bisegmental DDD of the lumbar spine with moderate to severe osteochondrosis of the treated segments. Eight patients had had previous disc surgery and three patients suffered from additional spondylolisthesis grade I according to Meyerding .
Type I Charité total disc prostheses consisted of two highly polished metal endplates and an ultra high molecular weight polyethylene (UHMWPE) sliding core articulating between these endplates. The endplates of this type were 1 mm thick, had 5 respectively later 11 teeth for bony anchorage and were made of URX2CrNiMoN 18.12 steel. The sliding core was manufactured from Chirulen UHMWPE .
A retrospective clinical–radiological study to evaluate the long-term outcome after artificial disc replacement was performed. The objective is to investigate long-term results after implantation of a modular type artificial disc prosthesis in patients with degenerative disc disease (DDD). Total disc replacement (TDR) is a surgical procedure intended to save segmental spinal function, and thus replace spondylodesis. Short-term results are promising, whereas long-term results are scarce. The Charité TDR is the oldest existing implant, therefore, the longest possible follow-up is presented here. Seventy-one patients were treated with 84 Charité TDRs types I–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 included Oswestry disability index, visual analog scale, overall outcome score, 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. TDR, nowadays, is an approved procedure. Proof that long-term results of TDR implantation in DDD are at least as good as fusion results is still missing.
Type II Charité total disc prostheses also consisted of two highly polished metal endplates and an UHMWPE sliding core. The endplates were made of stainless steel. In contrast to type I, endplates were enlarged resulting in bilateral wings with three anterior and two posterior anchoring teeth .
Type III Charité total disc prostheses followed the same technical principle as types I and II. The endplates were changed to cast CoCrMo alloy with three anterior and three posterior anchoring teeth. During the study period only three endplate sizes either in parallel or 5° angulation were available . A porous coating of the endplates consisting of titanium and calcium phosphate was introduced later on to promote osteointegration, but was not available at the time of surgery of the reported patients.