Cervical Arthroplasty: A Clinical Update

Abstract

large percentage of the world population and can significantly alter a patient’s quality of life. The presentation can vary but it generally consists of axial neck pain, radiculopathy, or myelopathy depending on the degree and location of the pathology. The incidence of cervical radiculopathy has been shown to peak between 50 and 54 years of age, with the average annual incidence rate per 100,000 patients being 83.2.1 Cervical myelopathy has a lower incidence rate, with an estimated hospital admission rate of 4.04/100,000 people in the United States.2 Cervical spondylosis and cervical disc disease with associated central or foraminal stenosis (Figure 1) have commonly been treated with anterior cervical discectomy and fusion (ACDF). This procedure allows for direct decompression of the disc space and thecal sac and combined direct and indirect decompression of the neural foramina. Cervical disc arthroplasty (CDA) seeks to mitigate many of the pitfalls of the ACDF procedure such as decreased cervical range of motion and development of adjacent segment degeneration (ASD). There have been many types of cervical disc prostheses with varying degrees of freedom, and they are generally categorized as constrained, unconstrained, and semiconstrained designs. Unconstrained designs allow the device to move independently and along all 3 rotational and translational axes. This device type allows for greater range of motion but also increases the force applied to the associated facet joints and ligaments that are required to stabilize that motion. Semiconstrained devices have some limitation in their degrees of freedom of movement but still have motion in both the translational and rotational planes. Constrained devices typically have a center of rotation but only allow movement in the 3 rotational axes, and these devices typically involve a ball and socket joint-type articulation rather than a mobile core, which is seen in unconstrained and semiconstrained designs. Due to the more immobile nature of semiconstrained and constrained devices, device placement must be more precise, midline, and centered. Constrained devices tend to also apply more force to the adjacent endplates with less translational force transferred to the soft tissues and facets.3,4 All of the designs aim to imitate a more physiologic stress distribution and range of motion.5 By maintaining normal biomechanical function and range of motion at the index level, CDAs may distribute physiologic loads more evenly among motion segments in the cervical spine and reduce the risk of degeneration within the adjacent disc and facet joints. Arthrodesis of the cervical spine has been found to limit the patient’s range of motion in the sagittal plane up to 0.66 ± 0.58 degrees at the index level.6,7 In contrast,