and Uwe Spetzger1
Department of Neurosurgery, Klinikum Karlsruhe, Karlsruhe, Baden-Württemberg, Germany
The current trend in cervical spinal surgery is affected by continuous optimisation of intervertebral cages and disc prostheses. The latter have been developed since the 1990s based on experiences with lumbar prostheses. The initial focus was put on different designs with titanium endplates and a plastic core. Nowadays, there is a development of single unit implants made of elastic polymeric material. To what extent these implants provide an approximation to physiological conditions in shape, function and bony anchorage is still unclear.
During the last decade, the number of surgeries for the treatment of degenerative diseases of the cervical spine has continuously increased. This development is based on an increasing life expectance as well as on the improvement of diagnostic and therapeutical options.
Furthermore, the number of available implants for the replacement of a removed intervertebral disc has exponentially increased. This development can be seen for dynamic implants (disc prostheses) as well as for non-dynamic implants (so-called cages). Because of the relatively short period since their introduction to the market, numerous implants have been evaluated on the basis of small patient populations and short follow-up times only. Furthermore, there are a relatively small number of studies with radiological and clinical comparison of fusion versus total disc replacement. In terms of choosing a certain implant, there are different algorithms depending on the surgeon’s preferences. Nevertheless, most surgeons include patient’s age, range of motion of the affected level, range of motion of adjacent levels and the number of affected levels in their decision-making process.
There is a similar situation for cervical vertebral body replacement in cases of confluent multilevel stenoses. The interposition of an iliac crest bone graft is still the gold standard, but there are also implants made of polyetheretherketone as well as of titanium on the market. The use of a certain material differs between institutions analogue to disc replacement.
Furthermore, different spine surgeons prefer different approaches and instrumentations at the cervical spine (anterior, posterior, combined) in cases of spinal instability.
The aim of this book is to explain the strategies in choosing a surgical approach and an implant for disc or vertebral body replacement based on the authors´ experiences and recent biomechanical and clinical studies.
1.2 History of Diagnostics and Therapy of Cervical Disc Herniation
The etiological relation between disc degeneration and spondylosis deformans was first described by Wenzel (1824). A cervical spondylosis as the reason for radicular symptoms was identified by Braun (1875). In the early twentieth century, a cervical disc herniation as a possible reason of paraparesis (thus myelopathic symptoms) was recognised (Hawk 1936). Küttner probably was the first surgeon removing a cervical disc herniation that compressed a nerve root (Frykholm 1969). In the 1930s and 1940s, numerous publications reported about the clinical significance of discogenic nerve root and spinal cord compression. At that time cervical disc herniations were removed using a laminectomy or hemilaminectomy. Since these methods did not result in radicular decompression in the intervertebral foramen, Scoville (1946) as well as Frykholm (1947) developed surgical techniques for foraminal nerve root decompression using a drill. Despite the modification of the posterior surgical techniques, it was not possible to achieve sufficient treatment of medial osteophytes or disc herniations. Therefore, Cloward (1958) developed an alternative method using an anterior approach. After anterior discectomy, a spondylodesis with a cylindric iliac crest bone graft was performed. Robinson and Smith (1958) introduced a similar technique that used a rectangular autologous bone graft. In the 1980s, the anterior plating was established to avoid local complications with the bone graft (Caspar et al. 1989).
Because of the morbidity at the site of harvesting the iliac bone graft, Grote and Rottgen (1967) introduced polymethylmethacrylate (PMMA) as an alternative to the autologous transplant. PMMA is still used at some institutions, but critics of this technique point to the increased rate of pseudarthrosis and heat during the polymerisation process. For this reason, the industry developed intervertebral cages that have become the standard implant worldwide. Usually these cages have a central hole that enables bony fusion especially when filled with osteoinductive material. The idea of using intervertebral cages came from veterinary medicine (DeBowes et al. 1984; Bagby 1988) because cervical fusion is indicated in horses suffering from the Wobbler syndrome which is a veterinary disease with gait ataxia due to spondylotic myelopathy.