BACKGROUND
This is a retrospective study to assess the prognostic factors influencing the postoperative motion dynamics and clinical outcome following cervical arthroplasty with a Bryan disc.

METHODS
Twenty-seven patients (30 levels) consecutively underwent cervical arthroplasty using a Bryan disc (Medtronic Sofamor Danek, Memphis, Tennessee). Motion dynamics and clinical outcome (visual analogue score (VAS) and neck disability index (NDI) score) were examined preoperatively and at 1 month, 1 year, and final follow-up (average: 25 months). The prognostic factors influencing clinical outcome and postoperative motion dynamics were assessed.

RESULTS
At last follow-up, mean VAS and NDI scores were significantly decreased from 8.33 ± 1.52 to 1.10 ± 0.99 (P = .001) and from 25.0 ± 15.9 to 9.2 ± 5.9 (P = .001), respectively. In a comparative study of pre- and postoperative motion changes at operated segments, mean segmental range of motion (ROM) increased from 6.96° ± 2.03° to 8.93° ± 3.53° (P = .014), and mean segmental angle decreased from 2.85° ± 3.27° to 1.21° ± 5.93° (P = .126). Mean global angle increased significantly from 14.54° ± 10.32° to 18.36° ± 11.10° (P = .003), and ROM increased non-

significantly from 40.25° ± 13.51° to 41.56° ± 12.53° (P = .654). At upper and lower segments, ROMs did not change significantly postoperatively. The heights of functional segment units showed no change postoperatively (3.51 ± 0.21 to 3.49 ± 0.22, P = .701). No significant relationships were found between VAS and NDI improvement and changes in ROMs or segmental angles at last follow-up. Statistically, the postoperative functional segment unit (FSU) ROM decreased as the age of the patients increased (Spearman r = 0.391, P = .048). The gender and preoperative segmental ROM did not influence FSU ROM.

CONCLUSIONS
Our results demonstrate that cervical arthroplasty with the Bryan disc for the treatment of cervical degenerative provides a good clinical outcome and preserves motion postoperatively. The age of the patients and the preoperative segmental ROM significantly affect the postoperative FSU ROM. These factors however do not relate to the clinical outcome. The relationship between long-term outcome and these variables should be verified by a larger cohort study.

Key Words: Motion dynamics, cervical arthroplasty, cervical degenerative disease. SAS Journal. Spring 2008;2:86–91. DOI: SASJ-2007-0117-RR

From Department of Neurosurgery, Kang Nam St. Mary’s Hospital, Catholic University, Seoul, Korea (Ryu, Heo, Park); Department of Biomedical Engineering, Inje University, Kimhae, Korea (S. Lee); Bioengineering Research Center, Sejong University, Korea (K. Lee)

The authors have no financial interest or other potential conflicts of interest to report in relation to the device used in this study.

This work was supported by grant No. R01-2005-000-10116-0 from the Basic Research Program of the Korea Science & Engineering Foundation and in part by Synthes Asia Pacific.

Address correspondence to Chun-Kun Park, MD, Department of Neurosurgery, Kang Nam St. Mary’s Hospital, 505 Banpo-Dong, Seocho-Ku, Seoul, 137-701, Korea

This manuscript was submitted on October 4, 2007, and accepted for publication March 24, 2008.