Cervical Disk Arthroplasty

Chapter Preview

Chapter Synopsis	The ability for cervical total disk arthroplasty (TDA) to treat specific cervical spine disorders while maintaining cervical motion is now feasible. Although unclear, it appears that cervical TDA may be an effective alternative to anterior cervical diskectomy and fusion (ACDF) for the management of cervical myelopathy or radiculopathy, or both, in selective cases. Careful patient selection and surgical technique are vital to maintaining good patient outcomes. Concerns and challenges regarding proper patient selection, developing effective salvage procedures, and managing implant wear-related disease remain. Long-term outcome studies should continue to provide answers to many of these questions. The purpose of this chapter is to review the indications, contraindications, surgical techniques, complications, and results of cervical TDA.
Important Points	Cervical TDA is indicated for patients with single-level disease that is causing cervical radiculopathy or myelopathy, or both. One TDA design has received approval for two-level placement. Cervical TDA is not indicated for diskogenic neck pain. Careful attention to patient selection remains vital for maintaining favorable patient outcomes. In selected cases, cervical TDA may be an effective alternative to ACDF and is designed to maintain motion at the disk space. Early short-term results suggest that cervical TDA may be equivalent to ACDF in terms of neck disability index and visual analog scores. The ability of cervical TDA to prevent adjacent segment disease is not yet conclusively proven. Patients scheduled for cervical TDA should be informed preoperatively of the possibility for conversion from TDA to ACDF, depending on intraoperative findings.
Clinical and Surgical Pearls	The patient is placed in a position that encourages cervical lordosis, but the surgeon must remember that excessive lordosis may exacerbate myelopathy. Performance of adequate neurologic decompression relieves the patient of symptoms before end plate preparation. The anteroposterior (AP) fluoroscopic view is key to proper positioning of the cervical TDA. The spinous process is oriented equidistant between the pedicles on the AP radiograph. The sagittal fluoroscopic view is checked during trials to ensure proper lordotic alignment.
Clinical and Surgical Pitfalls	Lack of meticulous hemostasis has been implicated in the formation of heterotopic ossification. Overdistraction of the disk space may create facet pain. Placing the disk prosthesis off center and not fitting the disk completely in the medial lateral orientation can adversely affect outcomes. Implant malpositioning and improper sizing can be reduced by careful intraoperative trials and the use of fluoroscopy.

The most common surgical procedure for the treatment of cervical disk disease resulting in radiculopathy or myelopathy is the combination of anterior cervical diskectomy and fusion (ACDF). Although it is effective for relieving symptoms of neural compression, questions still remain about the effect of cervical fusion on cervical biomechanics and subsequent adjacent segment disease. Therefore, the main goal for the development of a cervical total disk arthroplasty (TDA) system is to preserve motion while maintaining spinal stability to minimize adjacent segment disease. Other advantages of TDA over other conventional surgical procedures may include quicker return to activities of daily living and improved acceptance by patients. Other motion-preserving procedures such as cervical laminoplasty and anterior and posterior cervical foraminotomies are discussed elsewhere in the textbook.

The history of current cervical TDA can be linked back to the development of lumbar spine arthroplasty systems. The original purpose for the development of lumbar TDA was to address lumbar axial diskogenic pain while providing the benefit of motion preservation. In selected cases, when conservative measures have failed, lumbar TDA may be of benefit in the management of lumbar degenerative disk disease. Since their development, the lumbar disk systems have been extensively studied biomechanically. However, as lumbar TDA has become more extensively used and investigated, several questions remain unanswered, including questions about in vivo wear rates, revision strategies, and payer acceptance.

Several differences exist between cervical and lumbar TDA systems, however. Biomechanically, the load demand on TDA in the cervical spine is less than in the lumbar spine. Furthermore, identifying acceptable motion of the instantaneous axis of rotation may be more important and position sensitive in cervical TDA design in comparison with lumbar TDA. Perhaps most fundamentally different is that the indication for cervical TDA is the management of radiculopathy and myelopathy and not axial diskogenic pain, in contrast to the indication for lumbar disk arthroplasty. Therefore, as for all surgical procedures, the best results of cervical TDA require careful patient selection and precise surgical technique.

Indications and Contraindications

Currently, cervical TDA is indicated and approved in the United States, depending on the implant selected for patients with single-level or two-level disease causing cervical radiculopathy or myelopathy, or both. Unlike in lumbar arthroplasty, cervical diskogenic pain is not an indication.

Patients should be evaluated with a minimum of a cervical spine radiographic series including flexion and extension views to assess for radiographic evidence of instability. Magnetic resonance imaging should be obtained to help confirm the surgical level and to correlate with the clinical examination. In some cases, a computed tomography scan may also be of benefit to determine the extent of facet arthropathy and cervical spondylosis and the presence or absence of ossification of the posterior longitudinal ligament. A bone mineral density scan may help in assessing patients with suspected osteoporosis.

Although several contraindications to placement of cervical TDA exist, particular attention should be paid to both clinical and radiographic evidence of moderate to severe facet arthropathy. The presence of facet arthropathy is believed to be a contraindication to cervical TDA because motion preservation at the operated level may aggravate or even result in pain within the arthritic facet joints. Other contradictions include cervical instability, osteoporosis, and a history of cervical spine infections. A complete list of contraindications is listed in Box 32-1 .

BOX 32-1

Cervical instability
- >11 degrees of angulation
- >3 mm of segmental translation
Multilevel disease
Radiographic evidence of severe facet joint degeneration
Radiographic evidence of severe osteoarthritis with loss of normal disk space height >80%
“Hard disk” disease
Lack of motion of target disk space on preoperative radiographs
Postlaminectomy status with kyphotic deformity
Osteoporosis
Metabolic bone disease
Rheumatoid arthritis, ankylosing spondylitis
Ossification of the posterior longitudinal ligament or diffuse hyperostosis
Infection (past or present)
Malignant disease
Known hypersensitivity to cobalt, chromium, molybdenum, titanium, or polyethylene
Traumatic injury
Pregnancy or possible pregnancy within 3 years of implantation