Comparison of Artificial Disc Implants in Cervical Disc Arthroplasty

Will measure flexion/extension, lateral bending, rotation, protraction/retraction in degrees. The outcome will reflect any improvement in physiological neck range of motion be patients undergoing this procedure.

Will administer surveys on neck disability index, work status, pain intensity worksheet, treatment satisfaction form, and the SF-12 v2 Health Survey. The 12-item Short Form Survey version 2 (SF-12 v2) is a general health questionnaire that reports two summary scores - a mental component score (MCS-12) and a physical component score (PCS-12). The scores are reported as Z-scores (difference compared to the population average, measured in standard deviations) with the US population average PCS-12 and MCS-12 being both 50 points. Scores range from 0 to 100, with higher scores indicating better physical and mental health functioning. Overall, these assessments will help to gauge overall quality of life, pain, and patient satisfaction with their treatment.

Will take place as part of standard care for this operation. A gait assessment will be performed according to Nurick's Classification. Nurick's classification is graded from 0-5 or normal, with a number grade denoting some neurological deficit. 0 is least severe, with the patient showing root signs and symptoms with no evidence of spinal cord involvement. Grade 5 is most severe, described as chair bound or bedridden.

The foraminal compression test is a physical examination technique which reduces the opening of the foramen which may demonstrate if there is pressure upon the exiting spinal nerve. The test is done to detect spinal nerve root involvement, a herniated disc, bulging disc, or foraminal stenosis. The scoring is binary, either negative or positive, to test for any pain the patient experiences during the exam.

Will take place as part of standard care for this operation. Anterior and Posterior Disc Height will be measured from neutral lateral radiographs. Anterior (Posterior) Disc Height is defined as the distance between the anterior-inferior (posterior-inferior) corner of the superior vertebra, and the corresponding corner of the inferior vertebra. This distance is measured perpendicular to the superior endplate of the inferior vertebra and will be reported in units of millimeters. Average Disc Height is calculated as the simple average of the Anterior and Posterior Disc Heights.

Disc Angle is the angle formed between the endplates of adjacent vertebrae. Disc Angle will be measured on neutral lateral radiographs to assess local segmental lordosis and will be reported in degrees.

Global range of motion will be measured on lateral flexion-extension views to evaluate global range of motion. Global C2-C6 range of motion will be calculated by subtracting the C2-C6 angle in flexion from the C2-C6 angle in extension. Global range of motion will be measured between the inferior endplate of C2 and the inferior endplate of C6. C2-C6 Angle will be measured in units of degrees.

Translational Motion will be calculated from flexion-extension radiographs. Translational Motion is defined as displacement of the posterior-inferior corner of the superior vertebra in a direction defined parallel to the superior endplate of the inferior vertebra. Translational Motion will be reported in units of millimeters and as a percent of the AP dimension of the superior endplate of the inferior vertebra.

Device Subsidence will assess significant cranial-caudal movement of the implant and will be graded in accordance with the following definitions:

• None: No evidence of cranial or caudal subsidence of the implant > 3 mm.

• Cranial: Presence of cranial movement of the device > 3 mm relative to the initial position of the implant at PostOp.
• Caudal: Presence of caudal movement of the device > 3 mm relative to the initial position of the implant at PostOp.

Subsidence will be evaluated relative to the first available post-operative visit. A threshold of >3 mm of implant motion will be used to define significance. Subsidence will be assessed in the cranial and caudal directions perpendicular to the vertebral endplates and based on the degree of penetration of the implant into the bony margins of the vertebral body.

Kellgren-Lawrence ALDD at the adjacent levels will be graded in accordance with the following definitions adapted from Kellgren and Lawrence:

• None: No degenerative changes.

• Doubtful: Minimal osteophytosis only.
• Minimal: Definite osteophytosis with some sclerosis of anterior part of vertebral plates.
• Moderate: Marked osteophytosis and sclerosis of vertebral plates with slight narrowing of disk space.
• Severe: Large osteophytes, marked sclerosis of vertebral plates, and marked narrowing of disk space.

The assessment of Kellgren-Lawrence Osteoarthritis Grade will be graded by the reviewers based on an assessment from X-ray of three component factors: disc space narrowing (assessed relative to an nearby normal disc), osteophyte formation and endplate sclerosis.

Intervertebral Angle is used to define the endplate angle of the superior vertebra relative to the inferior vertebra. The difference in the angles measured is equivalent to a change in the Disc Angle. Intervertebral Angles will be measured in the sagittal plane from flexion and extension images separately and in the coronal plane from left and right bending images separately. All values will be reported in degrees. Intervertebral Angle will be calculated from lateral flexion-extension radiographs. Intervertebral Angle, also known as rotation, is defined as the change in angle between the adjacent endplates of the motion segment. Intervertebral Angle will be reported in units of degrees.