Cervical Artificial Disc Replacement Using the Bryan
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.
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).
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).
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).