Effects of a cervical disc prosthesis on maintaining sagittal alignment of the functional spinal unit and overall sagittal balance of the cervical spine

Abstract

The object of this study is to review the early clinical results and radiographic outcomes following insertion of the Bryan Cervical Disc Prosthesis (Medtronic Sofamor Danek, Memphis, TN), together with its effect on maintaining sagittal alignment of the functional spinal unit (FSU) and overall sagittal balance of the cervical spine for the treatment of single-level or two-level symptomatic disc disease. Forty-seven patients with symptomatic single or two-level cervical disc disease who received the Bryan Cervical Artificial Disc were reviewed prospectively. A total of 55 Bryan disc were placed in 47 patients. A single-level procedure was performed in 39 patients and a two-level procedure in the other eight. Radiographic and clinical assessments were made preoperatively and at 1.5, 3, 6, 9, 12, and 18 and up to 33 months postoperatively. Mean follow-up duration was 24 months, ranging from 13 to 33 months. Periods were categorized as early follow up (1.5-3 months) and late follow up (6-33 months). The visual analogue scale (VAS), neck disability index(NDI), Odom's criteria were used to assess pain and clinical outcomes. Static and dynamic radiographs were measured by hand and computer to determine the range of motion (ROM), the angle of the functional segmental unit (FSU), and the overall cervical alignment (C2-7 Cobb angle). With all of these data, we evaluated the change of the preoperative lordosis (or kyphosis) of the FSU and Overall sagittal balance of the cervical spine during the follow-up period. There was a statistically significant improvement in the VAS score from 7.0 +/- 2.6 to 2.0 +/- 1.5 (paired-t test, P = 0.000), and in the NDI from 21.5 +/- 5.5 to 4.5 +/- 3.9 (paired-t test P = 0.000). All of the patients were satisfied with the surgical results by Odom's criteria. The postoperative ROM of the implanted level was preserved without significant difference from preoperative ROM of the operated level. Only 36% of patients with a preoperative lordotic sagittal orientation of the FSU were able to maintain lordosis following surgery. However, the overall sagittal alignment of the cervical spine was preserved in 86% of cases at the final follow up. Interestingly, preoperatively kyphotic FSU resulted in lordotic FSU in 13% of patients during the late follow-up, and preoperatively kyphotic overall cervical alignment resulted in lordosis in 33% of the patients postoperatively. Clinical results are encouraging, with significant improvement seen in the Bryan Cervical Artificial disc. The Bryan disc preserves motion of the FSU. Although the preoperative lordosis (or kyphosis) of the FSU could not always be maintained during the follow-up period, the overall sagittal balance of the cervical spine was usually preserved.

Footprint mismatch in total cervical disc arthroplasty

“…Those reports investigated small number of cases and were largely cadaver studies or based on plain radiographs [3,4]. CT evaluation of bony structures is more accurate, and determination of lumbar endplate dimensions showed a large discrepancy to those of lumbar arthroplasty devices [20]. In the present trial, a surprisingly small percentage of endplates matched the endplate of the largest available disc prosthesis.…”

“…It has already been reported that ideal footprint dimensions not only result in a significant reduction in subsidence, but also improve biomechanical loads [20]. Although subsidence of cervical disc devices , this kind of complication may increase with the imminent approval and widespread use of these devices.…”

“…Subsidence can result in loss of motion at the implanted disc and potentially increases stress at the adjacent levels due to loss of sagittal balance [19]. Kim [20] stated that 64 % of patients with preoperative lordotic sagittal orientation of the functional spinal unit were not able to maintain lordosis following total disc replacement. Link [16] suggested using a rectangular footprint size in cervical arthroplasty in order to cover as much as possible of the cervical endplate, because bending forces are much stronger in the lateral aspect of cervical vertebrae than in thoracic or lumbar vertebrae.…”

The demands of professional opera singing on cranio-cervical posture

“…Collectively these findings suggest that the degree of lordotic curvature is a postural variable of the cervical spine which functions independently from the other angular measures that describe cranio-cervical posture. It is common practice to evaluate cervical lordosis as a clinical outcome measure following surgical intervention [8]. However, our results indicate that change in cervical lordosis is not significant and therefore it would be inappropriate to use this as a baseline measure for the changes likely to impact on the cervical spine, at least in opera singers.…”

Sagittal alignment and kinematics at instrumented and adjacent levels after total disc replacement in the cervical spine

“…Some studies reported that sagittal alignment in the cervical spine could be altered after TDR implantation [25][26][27][28]. This adverse effect was particularly noted after implantation of Bryan TM disc [26,28].…”