Cervical Total Disc Replacement, Part I: Rationale, Biomechanics, and Implant Types
Section snippets
Anatomy and pathophysiology
The cervical spine is composed of seven vertebral bodies with intervening intervertebral discs. These discs are critical for normal motion and biomechanics of the cervical spine. Discs function to provide load bearing and to optimize motion at intervertebral segments. The intervertebral disc is composed of an outer anulus fibrosis and a central nucleus pulposus, separated by a transitional zone. The anulus fibrosis is composed primarily of an organized network of type I collagen, contributing
Rationale for cervical total disc replacement
Treatment for herniated cervical discs in patients without neurologic deficit consists initially of nonoperative management consisting of anti-inflammatory medications, physical therapy, and epidural steroid injections in some cases. When conservative measures fail or when a neurologic deficit exists, surgical decompression is indicated.
Traditionally, ACDF has been performed for cases of cervical radiculopathy or myelopathy resulting from disc herniation. This technique involves anterior
Indications
Symptomatic cervical disc disease and herniation without neurologic deficit should initially be treated with a trial of nonoperative management. In fact, approximately 90% of symptomatic cervical disc disease responds to a combination of nonsteroidal anti-inflammatory drugs and physical therapy with traction. Cervical TDR provides an alternative to decompression and arthrodesis in patients with refractory disc disease in the cervical spine.
Inclusion criteria include symptomatic disc disease at
Biomaterials and biomechanics
The goals of cervical TDR are to reproduce the normal motion of the cervical spine and to retain the normal biomechanical properties of the intervertebral disc. Because it is not possible to reproduce the exact biomechanical properties of native interverterbral disc, existing biomaterials represent a compromise of material strength and function. Materials that are commonly used in design include metals and polymers. Metals provide the necessary strength, ductility, and toughness needed for load
Cervical total disc replacement implant types
Over the past 40 years, there have been several designs for cervical disc prosthesis. Current systems for TDR in the cervical spine use different materials and geometric configurations. Metal-on-metal prostheses include the Bristol Disc, the Cummins design, and the Prestige Disc (Medtronic Sofamor Danek, Memphis, Tennessee), and the Cervicore (SpineCore, Stryker Spine, Allendale, New Jersey) system. Another commonly used design uses metal end plates with a “plastic” center. Prostheses using a
Summary
Cervical TDR is an attractive alternate to arthrodesis for management of disc degeneration and herniation in the cervical spine. Theoretic advantages of TDR include preservation of normal motion and biomechanics in the cervical spine and reduction of adjacent-segment degeneration. Other potential advantages include faster return to normal activity and elimination of the need for bone graft and associated donor site morbidity.
This article introduces the rationale and various implant types
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