If a soft-disc herniation or osteoligamentous spinal stenosis at the level of the intervertebral disc is responsible for the patient’s clinical symptoms, then neural structures can be adequately decompressed by doing a discectomy. After discectomy, the height of the intervertebral space has to be maintained to achieve an adequate height of the neuroforamina. Despite of that, it is remarkable that some departments in the 1980s did not use any implant but achieved clinical results that were comparable to other surgical methods (Bertalanffy and Eggert 1988).

Another aim of surgery, especially in younger patients, is the maintenance of motion in the affected level (Cardoso and Rosner 2010; Goel et al. 2012; Richards et al. 2012; Svedmark et al. 2011). Furthermore, the reestablishment of the physiological cervical lordosis after total disc replacement has become of interest for many spine surgeons (Bryan 2002; Le et al. 2004; Park et al. 2012). There is a general consensus about the fact that physiological motion at C2/3 and C7/T1 is relatively little and that it is not reasonable to implant a prosthesis (see Table 3.1). The level C3/4 is in an intermediate position – it is at the discretion of the surgeon to indicate total disc replacement or fusion depending on the patient’s age and preoperative range of motion at the affected level.

In the last two decades, numerous cervical disc prostheses have been developed (Figs. 7.1, 7.2, 7.3, 7.4, and 7.5). Main criteria for the implantation of these relatively expensive implants are a good range of motion at the affected level in preoperative functional X-ray images and a biological age of less than 55 years. Furthermore, the level of osteochondrosis in preoperative CT scans and MRIs is taken into account.

A historical overview about the development of cervical disc prostheses is given in Sect. 1.​2. The most widespread model of the first generation was the Prodisc-C prosthesis (Synthes, Umkirch, Germany). Numerous spine surgeons criticised the difficult implantation procedure due to the big keels in the endplates. This fact was taken into account by the manufacturer of this implant as well as by other manufacturers (Fig. 7.1). In some cases, keels were downsized, in others, pins or teeth were added to the endplates and the prosthesis was implanted under distraction. After taking back distraction, the implant jams between the endplates of the vertebral bodies.

A widely used implant in Europe and the USA is the M6C prosthesis (Spinal Kinetics, Sunnyvale, USA; Fig. 7.2). It consists of a polyurethane core, a woven annulus made of polyethylene and endplates made of titanium, whereas the endplates have a porous surface and keels for a safe anchoring in the adjacent vertebral bodies. The handling during implantation is assessed as very good by most surgeons, and the surgical morbidity is very low. Nevertheless, the height of the prosthesis is at least 6 mm which does not always correlate with physiological conditions, especially at the anterior aspect of the vertebral bodies. The average height of the anterior intervertebral disc space is about 4 mm (see Sects. 2.​1 and 2.​2). Thus, it might be possible to induce overdistraction of the facet joints that can lead to persisting neck pain after surgery. Furthermore, segmental lordosis is abandoned due to the parallel titanium endplates. This fact is a disadvantage from a biomechanical point of view.

The normal anatomical shape of the intervertebral disc space with a curvature in the middle of the cranial endplate is taken into account by the latest generation of cervical disc prostheses. One example for this development was the Cadisc-C implant (Ranier, Cambridge, UK; Fig. 7.2b) with a polycarbonate polyurethane elastomere composition for the simulation of a natural disc. The biomechanical properties with six degrees of freedom and a mobile centre of rotation were similar to physiological conditions. The minimum anterior height of this implant was 4.7 mm, but it went out of production in late 2015 due to economical problems of the manufacturer. Nevertheless, it is likely that there will be more prostheses with a single-unit design in the future (Fig. 7.5).

If the patient does not meet the criteria for total disc replacement, then the implantation of an intervertebral cage is given (Fig. 7.6a and 7.7). Nowadays, many surgeons use cages made of polyetheretherketone (PEEK). The main disadvantage of this material is that it does not have osseointegrative potential. To achieve a safe fusion in the medium term, most cages have a central hole for filling it with osteoinductive substance such as tricalcium phosphate. Besides PEEK cages, numerous institutions use titanium cages that have a micro-porous surface for better osseointegration and thus a better healing. A disadvantage of these cages is the severe artefacts in postoperative MRI studies that are sometimes necessary in patients with unsatisfying clinical result of surgery. Chen et al. (2013) could show in a prospective randomised control study that PEEK cages show a better maintenance of intervertebral height and lordosis as well as clinical outcome compared to titanium cages. Nevertheless, there is a recent trend to titanium cages to avoid the filling of the cage with osteoinductive substances and because of their excellent osseointegration.

The implantation of intervertebral cages without additional anterior plating in one-level and two-level case is the most frequent method to achieve cervical fusion at most European neurosurgical departments. However most orthopaedic spine surgeons tend to use additional anterior plating on a regular base. The authors’ use anterior plating after cage implantation at three or more levels only.

Besides the use of cages or prostheses, there is the possibility of an intermediate solution with the so-called dynamic cervical implant DCI (Paradigm Spine, Wurmlingen, Germany) which allows motions in the sagittal plane (flexion and extension; Figs. 7.6b and 7.8).

In cases of two-level and three-level surgeries, it is possible to establish a hybrid solution with a combination of cage and prosthesis (Fig. 7.9). This method achieved very good clinical and radiological results in several studies (Barbagallo et al. 2009; König et al. 2015; Shin et al. 2009; Spetzger et al. 2013).

In the last three decades, numerous cervical fusions after discectomy have been done by using PMMA. Early experimental and clinical evaluations of PMMA interposition were published by Roosen (1982). It could be shown that despite the heat generation during the hardening of the PMMA, there is no necrosis in the surrounding soft tissue including the neural tissue.

By using this technique with grouting of the intervertebral disc space, the surgeon creates an optimum, patient-individualised surface. Nowadays, PMMA is occasionally used when even the smallest cages are too high to fit in a very narrow disc space. Compared to cages and prostheses the use of PMMA is very low-priced.

In the long term after PMMA application, good clinical results with either fusion (Fig. 7.10) or persisting minimum pseudarthrosis have been observed. The supporter of PMMA use refers to the low clinical relevance of the pseudarthroses (Fig. 7.11).

The classical surgical technique with implantation of a cylindrical bone graft from the iliac crest was established by Cloward (1958). Additional anterior plating was introduced to avoid secondary subsidence of the bone graft (Caspar et al. 1989; Hermann 1975). This classical surgical technique is still used in cases of osteochondrosis and/or disc herniation without instability in the Anglo-American countries.

Besides that, it is still a safe procedure in cases of degenerative instability with rupture of the intervertebral disc (Fig. 7.12). For the treatment of traumatic instability, a discectomy with interposition of an iliac crest bone graft and anterior plating is still the therapeutical gold standard.

Besides the numerous stand-alone cages with or without pins at the endplates that are implanted into the disc space under distraction, there is a solution with fixing of the cage by angled screws called Zero P (Synthes, Oberdorf, Switzerland; Fig. 7.13). In the authors’ opinion, its implantation is indicated if there is degenerative instability next to a previous anterior fusion in adjacent levels (Fig. 7.13b). In this case, the use of this fixable cage is of advantage because the previous anterior plate can be left in place which avoids surgical morbidity due to removal of the plate.

A 49-year-old patient was admitted to our department with a history of neck pain and brachialgia for 3 months. These clinical complaints were progressive despite conservative treatment. The past medical history included fusion at C6/7 with PMMA 10 years ago. In the clinical examination, paresthesia in the right C6 dermatome and a slight palsy of the right biceps muscle (grade 4 of 5) were verified. The biceps reflex was weak on the right side and normal on the left side. Coordination tests (Unterberger’s stepping test, tightrope walking test) were normal. The sensation of vibration as well as the reflexes of the lower limbs showed physiological findings as well. There were no signs of disorders of the pyramidal tracts; thus, we could not find clinical signs of spinal cord compression.