Cervical disc arthroplasty for less-mobile discs

OBJECTIVE The published clinical trials of cervical disc arthroplasty (CDA) have unanimously demonstrated the success of preservation of motion (average 7 degrees-9 degrees) at the index level for up to 10 years postoperatively. The inclusion criteria in these trials usually required patients to have evident mobility at the level to be treated (>= 2 degrees on lateral flexion-extension radiographs) prior to the surgery. Although the mean range of motion (ROM) remained similar after CDA, it was unclear in these trials if patients with less preoperative ROM would have different outcomes than patients with more ROM. METHODS A series of consecutive patients who underwent CDA at the level of C5-6 were followed up and retrospectively reviewed. The indications for surgery were medically refractory cervical radiculopathy, myelopathy, or both, caused by cervical disc herniation or spondylosis. All patients were assigned to 1 of 2 groups: a less-mobile group, which consisted of those patients who had an ROM of <= 5 degrees at C5-6 preoperatively, or a more-mobile group, which consisted of patients whose ROM at C5-6 was >5 degrees preoperatively. Clinical outcomes, including visual analog scale, Neck Disability Index, and Japanese Orthopaedic Association Scale scores, were evaluated at each time point. Radiological outcomes were also assessed. RESULTS A total of 60 patients who had follow-up for more than 2 years were analyzed. There were 27 patients in the less-mobile group (mean preoperative ROM 3.0 degrees) and 33 in the more-mobile group (mean ROM 11.7 degrees). The 2 groups were similar in demographics, including age, sex, diabetes, and cigarette smoking. Both groups had significant improvements in clinical outcomes, with no significant differences between the 2 groups. However, the radiological evaluations demonstrated remarkable differences. The less-mobile group had a greater increase in Delta ROM than the more-mobile group (DROM 5.5 degrees vs 0.1 degrees, p = 0.001), though the less-mobile group still had less segmental mobility (ROM 8.5 degrees vs 11.7 degrees, p = 0.04). The rates of complications were similar in both groups. CONCLUSIONS Preoperative segmental mobility did not alter the clinical outcomes of CDA. The preoperatively lessmobile (ROM = 5 degrees) discs had similar clinical improvements and greater increase of segmental mobility (Delta ROM), but remained less mobile, than the preoperatively more-mobile (ROM > 5 degrees) discs at 2 years postoperatively.