Cervical degenerative diseases are chronic, progressive conditions evolving to anchyloses of the motion segment. These pathological conditions are characterized by an initial loss of elasticity of the disc and its progressive alteration of the ability to reduce and distribute the pressure forces on the vertebral endplates. The loss of compactness of the disc also causes the decrease of vertebral heights and thickening of the ligamentum flavum. The process of bone rearrangement due to an incorrect alignment can cause the formation of osteophytes too. Consequence of these structural alterations can be hypo and/or hypermobility of the cervical spine, spondylolisthesis and spinal stenosis. The frequent injuries to which the spinal cord is subject, can cause inflammatory and/or ischemic phenomena and, finally yield myelopathy. Although in the early stages these alterations can also be asymptomatic, however the presence of disc herniation, osteophytes and hypertrophied ligaments may compress the spinal cord with the result of onset of cervical pain, radiculopathy, or myelopathy [6].
The surgical treatment must aim to decompress the nerve structures, to restore the correct alignment of the vertebrae and, if necessary, allow the stabilization of the vertebral spine. In planning surgical treatment, neuro-radiological studies are extremely important. The radiographic study with dynamic tests of the cervical spine allows us to evaluate the degree of movement of the affected segment. As a result, in our cases history, we observed in all patients a significant reduction of the degree of movement of the concerning segment. Finally, the MRI provides information on the extent of compression, on the presence of any malacic areas and if the discopathy is soft or hard.
Many procedures have been proposed for the surgical treatment of cervical degenerative diseases such as anterior decompression, laminectomy, laminoplasty and instrumented anterior and posterior fusion by plates or screws. Anterior approaches are effective for neural decompression, showing better clinical outcomes with less surgical trauma compared to posterior approaches. Anterior plating has been used to increase fusion rates and reduce subsidence and postoperative kyphosis. Husag et al., reported in our series of patients undergone anterior cervical discectomy, an excellent overall benefit in 95% of cases. However, at the same time, the merger rate of 70%, after the procedure, led to an increase segmental motion, subsidence and cervical kyphosis leading to instability and degenerative disc disease in adjacent levels [7].
The microsurgical ACDF through placement of auto or etero graft in the intersomatic space represents the operative procedure of choice for degenerative disc disease and cervical spondylosis associated with radiculopathy or myelopathy. The term “total removal” means that disc must be taken away up to the cortex of the vertebral body, paying special care to the preparation of the endplates for the lodging of the cage. With this procedure it is possible to overcome the limitations associated with anterior plates and screws [8]. This procedure has the potential to improve fusion, correct vertebral alignment and significantly reduce the incidence of subsidence. The objective of ACDF is to eliminate motion between adjacent vertebrae by forming a bony amalgamation which is obtained by minimizing intervertebral motion during the fusion phase. The position of any interbody spacer should be maintained to prevent its extrusion, irritation of surrounding tissues, and to allow union with the adjacent vertebrae. Nevertheless, ACDF is burdened by a series of possible complications such as dysphagia and, especially in multilevel procedures. Breakage, loosening of screws, screw penetration to endplate and fractures are possible complication too [9].
Although ACDF represents a well-established technique in the treatment of degenerative cervical pathology, to date, there are still doubts about the most suitable technique of fusion to adopt. The use of autologous grafts from the iliac crest represented the ideal treatment for many years. However, this technique is burdened by a series of complications such as graft collapse, disc space height loss, kyphosis and possible morbidity of the donor site such as pain, hematoma, and infections [10–11]. In order to overcome these limitations, intersomatic fusion cages of various shapes and compositions have been developed. Cages are characterized as cubical implants that are thought to restore physiological disc height and allow bone growth through the implant with osseous fusion [12]. Thus structured the cages favor a faster fusion allowing the correct realignment of the cervical spine. Moreover. the presence of dislocation and subsidence appears significantly reduced [13]. Different types of cages, of various shapes and materials, are available to perform ACDF, including titanium cages, carbon fiber reinforced polymer cages, PEEK cages, and cages integrated with and without synthetic bone grafts [13–16]. However, Meier et al., in 2004 comparing six different spacers for spondylosis of the cervical spine in a series of 267 patients, reported a higher tendency of dislocation of PEEK cages as compared to other implants such as plasmaphore coated titanium cages [17].
The Plasmapore® pore sizes range from 50 to 200 micrometers with a microporosity of 35% and thickness of 0.35 mm, leading to a large surface area and providing an optimal surface for bone growth. Moreover, Plasmapore® is a very rough surface and should support the primary stability of the cage, consequently, the cages are not filled with any form of bone or other form of material. At the end of the discectomy, the choice of cage dimensions must be made by means of a special measuring device which is housed in the now empty interbody space of the disc. It is necessary to choose the right height measurement, to avoid both the over-size, which would risk stretching the nerve roots causing iatrogenic damage, and the down-size, which could result in a kyphosis of the motion segment with loss of the spinal balance.
Krayenbuhl et al., in their series of patients affected by cervical myelo-radiculopathies, described a 98% fusion rate with only 2% of subsidence [18]. Arregui et al., implanted Cespace in a series of 104 patients. Bone fusion rate was 66.3% six months after the surgical procedure, while it was 91% at the end of the first year of follow-up [14]. Recently, Takeuchi et al., have shown that the use of PPC promotes faster bone formation after ACDF. In this study, the bone fusion defined as the formation of bone bridges between the fixed vertebral bodies was total [19]. Our data appear in line with reported literature. Bone fusion rate was 97% while subsidence cases were only 8 (4.4%).