Cervical Artificial Disc Replacement Using the Bryan

Rationale


Anterior cervical fusion surgery has been performed for over 40 years and is a safe and accepted part of neurosurgical care of cervical spinal disorders. Cervical anterior interbody fusion is widely accepted as leading to a reduction in normal cervical spine motion and increasing the stress at adjacent levels (1, 9, 14). Hilibrand et al confirmed a 2.9% per year of developing adjacent segment disease after anterior interbody fusion requiring cervical intervention (7). This coupled with unacceptably high incidences of bone graft harvest-related problems (8) has lead the search for an intervention that does not alter cervical motion and still allows for complete disc removal without needing iliac crest autografting or leaving an empty disc space prone to collapse. Consequently, replacement of the anterior cervical disc with a prosthesis that is easy to place, does not require bone grafting, maintains motion and balance and has longevity has been the goal of cervical arthroplasty.

History
Spinal arthroplasty has a relatively short history. Despite the ease of access in the cervical spine, spinal disc replacement surgery has historically concentrated on the lumbar spine (2-4). Fernstrom (5) in 1966 introduced an intracorporal endoprosthesis (artificial disc)that consisted of a stainless steel ball inserted into the center of a lumbar disc after laminectomy. Although Fernstrom focused on lumbar discs prostheses, he also placed these prostheses in the cervical spine. Cummins more recently has described his experience with the Cummin's artificial cervical joint (2). This prosthesis was basically a stainless steel ball-and-socket joint. A major shortcoming of this design has been the inability to instrument more than one level. It is currently being marketed as the Prestige® cervical disc replacement (Medtronic Sofamor Danek, Memphis, TN).

The Bryan® cervical disc prosthesis (Spinal Dynamics Corp., Mercer Island, WA) was first reported as being used for the management of cervical spondylotic disease in 2002 by Goffin et al (6) and subsequently by Sekhon (11). This cervical disc prosthesis consists of a polyurethane nucleus designed to fit between two titanium alloy shells (see Figure 1).

cross section of Bryan® cervical artificial disc
Figure 1: Cross-section of the Bryan® cervical disc prosthesis
(courtesy of Spinal Dynamics Corp., Mercer Island, WA and Medtronic Sofamor Danek, Memphis, TN)

Each shell has an outer titanium porous coating to encourage bony ingrowth and long-term stability. A polyurethane sheath surrounds the nucleus and is attached to the shells with titanium wire, forming a closed compartment. Sterile saline is placed into the prosthesis and titanium alloy seal plugs provide for its retention. This prosthesis requires precise milling for its placement and the technique aims at meticulous centering of the prosthesis. The prosthesis is held in place in a "press fit" fashion with bony ingrowth occurring into the porous outer shells (see Figure 2).

Bryan® cervical artificial disc between two endplates
Figure 2: The Bryan® disc prosthesis sits between the two milled
end plates and is held in place by being placed under distraction.
No screw or plate fixation is needed (courtesy of Spinal Dynamics Corp.,
Mercer Island, WA and Medtronic Sofamor Danek, Memphis, TN).

Multiple levels can be instrumented but must be visualized on fluoroscopy (13). The technique has also been used in the face on nonunion where previous arthrodesis (fusion) has been attempted but failed (12).

Technique
The criteria for selection for placement of the Bryan® disc prosthesis are more strict than that for anterior cervical fusion surgery. Patients with hypermobility (excessive motion), instability, gross degenerative disease, primarily facet joint pathology, and severe osteoporosis are excluded. The precise role in discogenic neck pain is unclear. Typically C4-5 and C5-6 are instrumented but C3-4 may be done if there is adequate access and C6-7 can be performed if it is able to be visualized on lateral fluoroscopy.

The case is performed with fluouroscopic guidance throughout for real time feedback (see Figure 3).

patient set up for surgery
Figure 3: Typical set up for Bryan cervical arthroplasty.
The patient is postioned supine with slight neck extension.
The fluoroscope is draped in and used for the entire case.

The apparatus for milling and placement of the Bryan® disc allows for precise centering of the prosthesis into the center of the disc space with a precise angle calculated before the skin incision is made (see Figure 4).

apparatus used to prepare the disc space and endplates
Figure 4: The apparatus used for milling and prosthesis placement is
technically more refined and exacting than that used for anterior cervical fusion surgery.

Once the prosthesis is placed, no collar is required and the prosthesis sits with a low profile in the pre-vertebral space (see Figure 5).

surgeon's eye view of the Bryan® cervical artificial disc implanted
Figure 5: Surgeon's eye view of the final
placement of the implant prior to wound closure.

A typical case is shown in Figure 6.

central C5-C6 disc protrusion

postoperative x-ray, front to back, Bryan® cervical artificial disc postoperative x-ray, lateral (side) view, Bryan® cervical artificial disc postoperative x-ray, neck flexion, Bryan® cervical artificial disc postoperative x-ray, neck extension, Bryan® cervical artificial disc

Figure 6: A typical case of myelopathy secondary to central C5-6 disc protusion (top). The postoperative AP, lateral, flexion and extension x-rays are shown in the bottom row confirming total disc arthroplasty with preservation of normal motion.

Results


lllustration of Cervical SpineGoffin et al (6) described the use of cervical arthroplasty in an attempt to maintain cervical motion and avoid arthrodesis (fusion) after decompression. In their study, 60 patients underwent single level anterior cervical decompression and placement of an artificial disc prosthesis. Of note is that 93% of Goffin's patients had predominantly radiculopathy. They reported follow-up at 12 months with clinical success reported at between 85 and 90%. No subsidence of the devices was noted and possibly 2 patients had device migration. No spondylotic bridging occurred at the implanted disc space. Range of motion was preserved and no device had been explanted or surgically revised. Sekhon has reported on the use of the Bryan® disc in cervical myelopathy with good results. (11)

The main questions with regard to this procedure relate to longevity of the implant and whether issues such as particle and wear debris will surface as new complications in the future. Between 500 and 1000 implants have been placed worldwide with none removed because of implant failure. A single case of fusion over the implant has been reported (10). The purported protective effect for adjacent levels is not yet known because of the short period of follow up to date and demonstration of the superiority of this technique in terms of reduced adjacent segment disease as compared to arthrodesis (fusion) is still to be shown. Experimentally, the prosthesis has been tested to the equivalent of 47 human years of movement with little wear.

Conclusion
The pitfalls of anterior cervical decompression and fusion have been discussed and the risks of adjacent segment disease have fueled the search for alternative interventions. It is hoped that by combining arthroplasty with anterior cervical decompression the traditionally good outcomes attained by anterior decompressive procedures can be married to the known advantages of maintenance of normal motion.

The Bryan® cervical disc prosthesis is at the forefront of cervical arthroplasty and is available today, allowing for anterior decompression of the spinal cord and nerve roots without the need for plating and fusion, bone grafting or cervical immobilization in a collar. The longevity and long term benefits of cervical arthroplasty remain to be seen.

 

Updated on: 11/29/18
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Artificial Disc Replacement

Orthopaedic surgeons have been engaged in research to offer an alternative to lumbar spinal fusion surgery; artificial spinal disc replacement.
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