The Future of Cervical Spine Surgery

and Uwe Spetzger1



(1)
Department of Neurosurgery, Klinikum Karlsruhe, Karlsruhe, Baden-Württemberg, Germany

 



On the basis of recent spine research, the manufacturing of individualised implants is possible. Using patient-specific computed tomography or magnetic resonance imaging data, an individual spine model can be rendered. With the help of such a model, an implant can be individually configured. Furthermore, it might be possible to test virtually the biomechanical behaviour of the cervical spine after implantation when using the finite element method. Another field of research is biological disc replacement by autologous transplantation of chondrocytes. At the thoracic and lumbar spines, the augmentation of screws with polymethylmethacrylate in cases of severe osteoporosis has been established for many years. Thus, this technique could be used for the cervical spine, too.


11.1 Benefit of Total Disc Replacement


Despite the numerous prostheses for total disc replacement available on the market, there is still ongoing discussion about and controversy over the benefit of these relatively expensive implants (Bae et al. 2015; Radcliff et al. 2015). In particular, the avoidance of adjacent degeneration is still the focus of research (Richards 2012). Furthermore, the follow-up intervals of most studies are relatively short, since most implants have been on the market for less than 10 years.


11.2 Autologous Chondrocyte Transplantation for Disc Replacement


In the future there will be probably a trend towards biological replacement using autologous chondrocytes. This might be an alternative to mechanical prostheses in total disc replacement. However, no valid data are available for this procedure. Case reports and experiences have been gleaned from a phase I study of the lumbar spine. These results may lead to a useful and safe alternative to mechanical total disc replacement. However, valid results will likely not be available for years.


11.3 Augmentation of Screws in Fusion Cases


The use of augmented screws has been established in lumbar spine surgery for osteoporosis or revision cases. A pre-condition is the use of cannulated screws to enable the application of fluid polymethylmethacrylate (PMMA) into the cancellous bone. After the PMMA hardens, a tight junction between screws and the bone emerges.

Reports of PMMA augmentation in screwing the dens axis (Kohlhof et al. 2013) and in anterior plating of the cervical spine (Jo et al. 2012; Waschke et al. 2013) are available from small patient populations undergoing cervical surgery. We used PMMA augmentation for secondary breakout after anterior plating in patients with osteoporosis (Fig. 11.1). With increasing life expectancy, more and more patients with osteoporosis will likely have to be treated, and thus the number of cases with an indication for PMMA augmentation of screws will increase.

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Fig. 11.1
Sagittal computed tomography (CT) scan showing a burst fracture of the C7 vertebra after a fall in an 80-year-old female patient (a). Postoperative sagittal CT scan 1 day after surgery showing the correct position of all implants (b). Sagittal CT scan showing the secondary breakout of screws in the C6 vertebral body (c). Situation after revision surgery with a shorter anterior plate and polymethylmethacrylate (PMMA) augmentation of the screws in C6 and T1 as well as posterior fusion of C6 to T1, as seen on sagittal (d) and axial (e, f) CT scans. Good visualisation of the PMMA material in lateral (g) and anteroposterior (h) radiography studies

As mentioned in Chap. 7.​2.​2 page 67, the use of spreading screws did not win recognition since reports are available of increased breakout rates after using that kind of screw, even in patients without osteoporosis (König and Spetzger 2014).

The use of PMMA has also disadvantages, such as an exothermal hardening process and the release of toxic remnant monomers. Therefore the use of alternative substances and materials has been investigated (Hollstein 2003), but to date there are no noteworthy alternatives to PMMA.


11.4 Manufacturing and Implantation of an Individualised 3-Dimensional Printed Titanium Cage for Cervical Fusion



11.4.1 General Considerations


At present, anterior cervical discectomy and fusion (ACDF) with implantation of cages made of various biocompatible materials, with or without anterior plating, is the standard surgical treatment for spondylotic cervical myelopathy and/or radiculopathy (Cabraja et al. 2012; Kolstad et al. 2010; Wu et al. 2012; Yamagata et al. 2012).

The numerous cervical cages offered by the industry more or less mimic the anatomy of the intervertebral disc space, whereas the size and design of the cages are adapted to match the average shapes and sizes of a patient’s intervertebral discs. The strategy of standalone cages without an additional plate reduces the invasiveness of the procedure and is gaining overall acceptance.

The philosophy of our innovative project was to adapt a cage to a patient’s individual anatomy and not – as usual – adapt the patient’s anatomy to a commercially available cage. This development aims to create an implant that perfectly fits the individual endplates of the adjacent vertebral bodies in order to avoid fusion complications such as secondary dislocation or subsidence of the cage. Together with our industrial partners, we created a patient-specific and individualised cervical cage for ACDF.

This report summarises our interdisciplinary scientific industrial cooperation with computer-aided planning (virtual reality interactive simulation), manufacturing by 3-dimensional (3D) printing (selective laser melting) and surgical implantation of an individualised cervical cage. Simulation and planning were performed with 3D Systems, Rock Hill, SC. The manufacturing and 3D printing of the cage were performed by Emerging Implant Technologies GmbH (EIT), Tuttlingen, Germany. The surgical procedure was performed at the Department of Neurosurgery, Städtisches Klinikum Karlsruhe (SKK), Karlsruhe, Germany.

The first surgical procedure implanting such a customised 3D-printed cervical cage was performed in May 2015. A report of the whole project was published in 2016 in the European Spine Journal as a technical innovation (Spetzger et al. 2016).


11.4.2 Computer-Aided Planning and Virtual Reality Simulation


Using a DICOM CT data set (1.0-mm slice thickness), a 3D model of the patient’s cervical spine is rendered (‘rendered anatomy of the cervical spine’; Fig. 11.2 ). After analysing the 3D model with a focus on deformities, any kyphosis is virtually corrected by repositioning the C6 and C7 vertebrae (‘repositioned anatomy’; Fig. 11.3 ). With this procedure the individualised cage obtains the ideal lordotic angle for restoring the sagittal balance of the cervical spine.
Nov 14, 2017 | Posted by in NEUROSURGERY | Comments Off on The Future of Cervical Spine Surgery
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