Artificial Disc Placement for Cervical Myelopathy

History
This 45-year-old man has had increasing difficulty walking and using his hands. He also noted numbness in both hands and on neck flexion occasionally had electric shock-like symptoms through his whole body. He is a non-smoker. On examination he had evidence of a moderately severe cervical myelopathy, with hypertonia, hyperreflexia, positive Hoffman's signs bilaterally, upgoing toes and poor fine-finger movements. There was no weakness. Neck movements were within normal limits. His initial preoperative imaging is shown below (Figures 1-3):

Figure 1: Sagittal T2-weighted

Figure 2: Axial T2-weighted MRI at the C5-6 level

Figure 3: CT Scan at the C5-6 level

All images confirm severe compression predominantly from anterior osteophyte and disc causing cord flattening with signal changes in the spinal cord. Cervical lordosis is reasonable. The adjacent levels appear reasonable.

In view of the symptomatic myelopathy with signal change surgical intervention was recommended.

Operative Details
Initial surgical positioning was similar to that for a standard anterior cervical decompression and fusion. A roll was placed behind the shoulders and the head placed on a foam donut. The neck was extended slightly to facilitate exposure and an image intensifier was draped into the field. A transverse cervical incision was made in the neck over the C5-6 disc space and a standard extensile exposure of the C5-6 disc space was performed. Similarly routine diskectomy was performed. The Bryan Cervical Disc System was utilized. The size of the implant (14 mm) and angle of the disc space was calculated precisely prior to placement of the implant. Using custom drill bits, and a milling wheel, a reciprocal concavity was cut into the endplates of C5 and C6. This is shown in Figures 4 and 5.

Figure 4
Figure 4: Shows intraoperative fluoroscopic images during surgery. Distraction pins are in place and a depth gauge is measuring the maximal depth of milling.

Figure 5
Figure 5: A view of the decompression prior to insertion of the prosthesis. A total discectomy has been affected and a trough approximately 10 mm in height created. A larger decompression is attained through endplate milling than through a standard anterior cervical decompression for disc.

After the endplates were precisely drilled and the decompression effected, the correct size prosthesis was placed into the defect (see Figure 6-9).

Figure 6
Figure 6: Shows the artificial disc prosthesis being primed with saline prior to insertion.

Figure 7
Figure 7: Shows the implant on the implant holder prior to insertion into the disc space.

Figure 8
Figure 8: Shows intraoperative fluoroscopic images during surgery after implantation of the prosthesis into the disc space.

Figure 9
Figure 9: Shows a "surgeon's eye" view of the anterior surface of the prosthesis as it appears placed.

At the completion of this stage closure was affected over a suction drain. The patient was transferred to the intensive care unit and extubated uneventfully.

Postoperative Course
Postoperatively, the patient was mobilized on the first day postop without a collar. Dynamic x-rays of the cervical spine this stage showed maintenance of motion at the level of the decompression (see Figure 10).

Figure 10
Figure 10: Postoperative flexion extension x-rays show satisfactory placement of the prosthesis with motion maintained at the instrumented segment.

The patient was discharge on the 2nd day after surgery. He had no neck pain or discomfort and returned to work the following week. The patient was reviewed 6 weeks postoperatively and had improved symptomatically from his myelopathy. His hand function had improved and he no longer had a positive Lhermitte's phenomenon. There was no neck discomfort and he had returned to work. Imaging at this stage was satisfactory. He has been followed for 3 months and continues to improve.

Discussion
This case illustrates the management of single level cervical myelopathy through anterior decompression and disc replacement. This patient has had an excellent short-term result with improvement in myelopathic symptoms, maintenance of motion, and reduced surgical morbidity.

Cervical myelopathy is a relatively common spinal condition and is generally managed either from an anterior or posterior approach. Single level disease is usually caused by anterior osteophytic compression or disc protrusion. The current standard of care for this is anterior cervical discectomy, usually with an iliac crest autograft, with or without plating. Some surgeons use cages or allograft but the overall goal is aimed at achieving arthrodesis at the involved level. Because anterior cervical fusion has been performed for many years, it is now being realised that there is an incidence of adjacent segment disease, with accelerated wear and tear at levels above and below. The risk of requiring surgery at those adjacent levels may be as high as 30% at 10 years. Consequently the placement of a disc prosthesis is attractive from the point of view of maintaining motion and trying to prevent adjacent segment disease. Coupled with this, no orthosis is required, and iliac crest grafting, which has a morbidity of up to 20%, is avoided.

When looking at a patient as a potential candidate for disc replacement, patient selection, as in most surgical interventions, is the key. This case, and subsequent cases we have performed, have illustrated that the thought processes are different when deciding to use this new technology, from standard surgical procedures. Cervical disc replacement is currently only appropriate for single level disease and trials are underway on 2 level disease. It is not appropriate if there is significant dorsal disease. It is not appropriate for correcting deformity, and indeed may lead to accelerated prosthesis wear if used in kyphotic patients. Also, the foramina are not distracted by the surgery and meticulous foraminal decompression must be performed at the time of surgery, as distraction is not typically prominent.

Cervical disc replacement is becoming available throughout the world, and is currently available in Belgium and Australia. Trials are beginning in the North America. Not all patients are suitable for this technology. The procedure is technically more demanding and more time consuming than current surgical options. The long-term sequelae of these implants are not known although at 25 million cycles in vivo, little wear is seen, the equivalent of 25 years of neck movements.

This case illustrates a new and exciting technique used in the management of cervical myelopathy. It is gratifying to see the patient leave hospital with no collar and no hip grafting. Just as in large joint surgery, fusion is giving way to joint replacement and this procedure may become commonplace in the management of cervical spine disease in the near future.