Early clinical and biomechanical results following cervical arthroplasty.

OBJECT: Spinal arthroplasty may become the next gold standard for the treatment of degenerative cervical spine disease. This new modality must be studied rigorously to ensure in vivo efficacy and safety. The authors review the preliminary clinical experience and radiographic outcomes following insertion of the Bryan Cervical Disc Prosthesis (Medtronic Sofamor Danek, Memphis, TN). METHODS: This prospective cohort study included 26 patients undergoing single- or two-level implantation of the Bryan artificial cervical disc for treatment of cervical degenerative disc disease resulting in radiculopathy and/or myelopathy. Radiographic and clinical assessments were made preoperatively 1.5, 3 months, and at 6, 12, and up to 24 months postoperatively. The Neck Disability Index (NDI) and Short Form-36 (SF-36) questionnaires were used to assess pain and functional outcomes. Segmental sagittal rotation from C2-3 to C6-7 was measured using quantitative motion analysis software. A total of 30 Bryan discs were placed in 26 patients. A single-level procedure was performed in 22 patients and a two-level procedure in the other four. Follow-up duration ranged from 1.5 to 27 months, with a mean duration of 12.3 months. A statistically significant improvement in the mean NDI scores was seen between pre- and late postoperative follow-up evaluations. A trend toward improvement in the SF-36 physical component was also found. Motion was preserved in the treated spinal segments (mean range of motion 7.8 degrees ) for up to 24 months postsurgery. The relative contribution of each segment to overall spinal sagittal rotation differed depending on whether the disc was placed at C5-6 or C6-7. Overall cervical motion (C2-7) was moderately increased on late follow-up evaluations. CONCLUSIONS: The Bryan artificial cervical disc provided in vivo functional spinal motion at the treated level. Overall cervical spinal motion was not significantly altered. Sagittal rotation did not change significantly at any level after surgery.

Effects of a cervical disc prosthesis on segmental and cervical spine alignment.

OBJECT: Cervical arthroplasty offers the promise of maintaining motion of the functional spinal unit (FSU) after anterior cervical discectomy. The impact of cervical arthroplasty on sagittal alignment of the FSU needs to be addressed, together with its effect on overall sagittal balance of the cervical spine. METHODS: The authors prospectively reviewed radiographic and clinical outcomes in 14 patients who received the Bryan Cervical Disc prosthesis (Medtronic Sofamor Danek, Memphis, TN), for whom early (< 6 months) and late (6-24 months) follow-up data were available. Static and dynamic radiographs were measured by hand and computer to determine the angles formed by the endplates of the natural disc preoperatively, those formed by the shells of the implanted prosthesis, the angle of the FSU, and the C2-7 Cobb angle. The range of motion (ROM) was also determined radiographically, whereas clinical outcomes were assessed using the Neck Disability Index (NDI), and Short Form-36 (SF-36) questionnaires. The ROM was preserved following surgery, with a mean preoperative sagittal rotation angle of 8.96 degrees , which was not significantly different from the late postoperative value of 8.25 degrees . When compared with the preoperative disc space angle, the shell endplate angle in the neutral position became kyphotic in the early and late postoperative periods (mean change -3.8 degrees in the late follow-up period; p = 0.0035). The FSU angles also became significantly more kyphotic postoperatively, with a mean change of -6 degrees (p = 0.0006). The Cobb angles varied widely preoperatively and did not change significantly after surgery. There was no statistical correlation between the NDI and SF-36 outcomes and cervical kyphosis. CONCLUSIONS: Cervical arthroplasty preserves motion of the FSU. Both the endplate angle of the treated disc space and the angle of the FSU became kyphotic after insertion of the Bryan prosthesis. The overall sagittal balance of the cervical spine, however, was preserved.