The Charité artificial disk was the first available total disk replacement (TDR) system. Three different types have been developed so far. While type I and II Charité artificial disks were manufactured in the former German Democratic Republic (GDR) and, therefore, was never commercially available, the type III Charité disk was distributed by DePuy Spine (Raynham, Massachusetts, USA) until spring 2010.

The Charité type I was developed in East Berlin by Kurt Schellnack and Karin Büttner-Janz in the Charité Hospital in 1982. The idea was based on the biomechanically proven “low friction” principle, which had already been successful in total joint replacement. It consisted of two highly polished metal end plates with teeth for bony anchorage and an ultra-high-molecular-weight polyethylene (UHMWPE) sliding core. The device was intended to imitate the movement of the nucleus pulposus of the intervertebral disk within its annular containment. It is therefore considered to be an unconstrained type of total disk replacement. An unconstrained design incorporates a mobile-bearing core and provides independent rotation and translation about three axes. The so-called SB Charité Artificial Disk Mark I was implanted at the Charité Hospital in the years 1984–1985 [21, 22].

Due to axial plane migrations, the device was modified to the SB Charité II.

It was used between 1985 and 1987. In contrast to type I, end plates were enlarged and exhibited bilateral wings to avoid subsidence. Finally, problems of migration and metal fatigue fractures led to the abandonment of type II also [22].

From 1987 on, the Link SB Charité III was manufactured by Waldemar Link GmbH in Hamburg, West Germany. The end plates were changed to cobalt-chromium-molybdenum alloy (CoCrMo) and received a porous coating of plasma-sprayed titanium and calcium phosphate to enhance osteointegration. The free-floating biconvex sliding core is still made of ultra-high-molecular-weight polyethylene (UHMWPE), encased by a metal wire for radiological marking. Primary stability is achieved by press-fit implantation through the teeth on the end plate which anchor into the subchondral bone. Different sizes and angulations were developed later [21].

After being taken over by DePuy Spine (Johnson & Johnson) in 2003, the SB Charité III was called Charité artificial disk until its abandonment (Fig. 41.2).

One of the earliest and most comprehensive clinical review regarding the Charité III was published by LeMarie in 1997. After 51 months follow-up of 105 patients, he found 79 % excellent results and a return to work rate of 87 % [23].

The American Food and Drug Administration (FDA) approved the Charité artificial disk in October 2004, the first of its kind, for use in treating pain associated with degenerative disk disease (DDD). The device is intended to replace a diseased or damaged intervertebral disk at either the L4–L5 or L5–S1 level.

In a multicenter study, the artificial disk was performed in 205 patients who had been diagnosed with DDD and had failed to have their pain relieved after 6 months of nonsurgical therapy and compared them to 99 patients who received the control device (stand-alone BAK spinal fusion cage using bone graft).

The study showed that 2 years after surgery, patients treated with the artificial disk did no worse than patients treated with intervertebral body fusion. However, patient satisfaction was higher in the artificial disk group. The rates of adverse events from use of the artificial disk were similar to those from treatment with fusion. In addition, the study showed that there was no statistically significant relationship between motion at the level where the disk was implanted and the patient’s relief from pain [24, 25]. To conclude, the patients treated with the Charité artificial disk were as good as the patients treated with a stand-alone cage. However, the latter is considered to be an obsolete treatment in Europe due to unsatisfactory clinical results.

The SB Charité III has the longest clinical follow-up of any TDR. It has been implanted more than 17.000 times worldwide. Following the implantation, most of the authors stated 60–90 % satisfactory to excellent results [26–28].

Despite the good results published otherwise, Michael Putzier from the Charité Berlin published long-term results after an average follow-up of 17 years. The deflating results revealed spontaneous ankylosis in 60 % and a reoperation rate of 11 % [29].

Interestingly, the last Charité artificial disk was already implanted in the Charité hospital in Berlin in 1989. Despite the fact that the implant carried the name of the biggest university hospital in Germany, it has not been used there since then. In the USA, criticism increased over time, and numerous patients started to sue Johnson & Johnson alleging the pharmaceutical company knew or should have known about the serious complications of the artificial disk surgery. As mentioned above, the Charité artificial disk is not available anymore.

Another early type of artificial disk was the AcroFlex (DePuy Spine), designed by Arthur Steffee. The first implant type consisted of a hexen-based polyolefin rubber cushion attached to two titanium end plates. A pilot study with six patients was published in 1993. Due to concerns regarding potential carcinogenicity of parts of the implant, the clinical trials were suspended. The next generation was proposed by Steffee, Fraser and co-workers. Debris and implant failure were the typical problems of the AcroFlex series [30, 31]. A prospective non-randomised study with almost 10 years follow-up revealed a cumulative survival of only 61 %. The authors concluded that further use of this implant is not justified [32].

Two other types of TDR were developed in the 1990s and showed promising results: the ProDisc and the Maverick artificial disk.

The first ProDisc (Aesculap, Tuttlingen, Germany) was developed by Thierry Marnay in Montpellier in the late 1980s [33].

The ProDisc has two metal (titanium) end plates which are plasma sprayed with titanium and have two vertical fins for fixation to the end plates. The core is made of high-density polyethylene and fits firmly to the inferior end plate. The superior surface of the core is formed convex. The resulting centre of rotation is fixed and located inferior to the disk space. This semiconstrained design includes a fixed axis of rotation that limits translation. This leads to increased stress within the device and at the device-bone interface, resulting in a potentially increased risk of implant loosening.

The first series of 64 patients were operated by Marnay between 1990 and 1993 with promising results. Follow-up ranged between 7 and 11 years with over 75 % excellent or good results. There was no outcome difference between 1 and 2 level implantations. All implants were still intact and functioning without signs of subsidence or migration [34].

The second generation of the ProDisc called ProDisc-L (Fig. 41.3) is distributed by Synthes (Paoli, Pennsylvania, USA). It was introduced to the market in 2000. Different end plate sizes and lordosis angles, different core heights and only one keel per end plate were the main design changes. It has been approved by the American FDA in August 2006 for one- or two-level implantation. The FDA IDE trial compared the ProDisc II with an anteroposterior fusion using femoral ring allografts anteriorly and pedicle screw fixation with autograft posteriorly. The clinical results in the ProDisc group were slightly better than in the fusion group [35].

In uncontrolled clinical series, success rates up to 90 % are reported [27, 36]. Long-term data are sparse. In a prospective, single-centre investigation, 181 patients (90 % follow-up rate) could be examined after a mean follow-up of 7.4 years. Clinical results improved significantly after surgery and 87 % of patients were (highly) satisfied at final follow-up. Complication rate was 14 %, about half of which were device related. Reoperation rate was 16 %. The authors concluded that for a carefully selected cohort of patients, results compare favourably to results achieved with fusion [37]. Similar mid- to long-term results have been published by other authors [38–40].

Mathews, Le Huec and co-workers conceived the semiconstrained Maverick artificial disk (Fig. 41.4) (Medtronic Sofamor Danek, Memphis, Tennessee, USA), a metal-on-metal (chrome cobalt) interface implant with a posterior rotation axis [41].

Metal-on-metal disk prostheses have been developed to eliminate polyethylene wear and its potential risks. Although polyethylene debris and osteolysis have not been proven to be significant clinical issues with TDR, the long-term effects remain unclear. As known from hip surgery, metal-on-metal surfaces produce far lesser debris than polyethylene-on-metal surfaces [27].

The Maverick artificial disk is fixated to the end plates with a midline sagittal fin like the ProDisc. The end plates are hydroxyapatite coated. The overall biomechanical profile is similar to the ProDisc. However, the convex caudal component has a slightly smaller radius of curvature compared with the concave superior component.

Like in the other TDR, different sizes, heights and angles are available.

The first implantation was performed in 2002 and a randomised FDA clinical trial was begun in 2003, comparing the Maverick artificial disk to a fusion using cage combined with BMP. LeHuec and co-workers published a prospective study reporting the outcome of 64 Maverick devices implanted between January 2002 and November 2003. The Oswestry score improved for 75 % of patients [42]. Published midterm data 4 years after surgery showed 85 % of patients were again working and 79 % took up their normal sports activities [43].

In the last 6 years, a variety of new implants and techniques have been developed so that nowadays nearly all companies offer implants for disk arthroplasty. Despite extensive biomechanical studies, it currently remains unclear which type of constraint offers the most advantages in total disk replacement. Constrained implants offer stability but lead to high stress on fixation, while unconstrained implants are sensitive to surgical positioning. The normal axis of rotation of the lumbar spine is not fixed but varies. Although a constrained device in good position may provide more controlled motion and consecutive preservation of the facet joints, an unconstrained device may provide greater range of motion and be more forgiving in terms of surgical positioning.