Analysis of in vivo kinematics of 3 different cervical devices: Bryan disc, ProDisc-C, and Prestige LP disc.

OBJECT: Cervical arthroplasty has emerged as a means of preventing adjacent segment disease by preserving motion, restoring sagittal balance, and mimicking natural spinal kinematics. The purpose of this retrospective in vivo study was to characterize the impact of arthroplasty on sagittal balance and segmental kinematics of the cervical spine. METHODS: Sixty patients receiving the Bryan disc, ProDisc-C, or Prestige LP disc were retrospectively analyzed. Only single-level arthroplasty cases were included in this study. Lateral dynamic radiographs of the cervical spine were evaluated using quantitative measurement analysis software to determine the kinematics at the index level both preoperatively and 1 year postoperatively. Collected parameters included range of motion (ROM), disc angles, shell angles, anterior and posterior disc heights (ADHs/PDHs), translation, and center of rotation (COR). Preoperative and postoperative data were compared using the Student t-test, with p < 0.05 indicating significance. RESULTS: The Bryan and Prestige LP discs preserved motion, whereas the ProDisc-C increased segmental ROM from extension to flexion. Following surgery, the Bryan disc exhibited significant shell angle kyphosis, while ProDisc-C and Prestige LP retained lordosis. Both ADHs and PDHs decreased following insertion of the Bryan disc. In contrast, the ProDisc-C increased the ADHs and PDHs by 80% and 52%, respectively, and the Prestige LP disc increased the ADHs and PDHs by 20%. Only the ProDisc-C demonstrated significant translation of 0.7 mm. The ProDisc-C shifted the COR x by 0.9 mm anteriorly, while the Prestige LP disc demonstrated a significant superior shift of 2.2 mm in COR y. CONCLUSIONS: All discs adequately maintained ROM at the surgical level. The greatest difference among the 3 devices was in the disc height and index angle measurements.

Effect of arthroplasty design on cervical spine kinematics: analysis of the Bryan Disc, ProDisc-C, and Synergy disc.

OBJECT: Cervical total disc replacement has emerged as a surgical option to preserve motion and potentially avoid adjacent-segment disease after anterior cervical discectomy and fusion. Recently, much attention has been directed at the ability of a given device to maintain and/or restore normal segmental alignment. Nonphysiological disc and segmental angulation could result in increased stresses transmitted to the facet joints and posterior elements, conflicting with the essence of arthroplasty and potentially leading to adjacent-segment disease. The goal of this study was to contrast device alignment and segmental kinematics provided by 3 different cervical disc prostheses. METHODS: Sixty patients were retrospectively analyzed and divided into 3 groups receiving the Bryan, ProDisc-C, or Synergy disc. Only single-level arthroplasty cases were included in the study. Lateral dynamic radiographs of the cervical spine were analyzed using quantitative motion analysis software (Medical Metrics, Inc.) to analyze the kinematics at the index level both preoperatively and postoperatively. Several parameters were noted, including range of motion, disc angles, shell angles, anterior and posterior disc heights, translation, and center of rotation. Preoperative and postoperative data were compared using the Student t-test with a significance level of p < 0.05. RESULTS: Postoperatively, all 3 disc groups maintained adequate range of motion at the implanted level. With respect to the shell angles, the Synergy disc demonstrated the least variability, maintaining 6 degrees lordotic configuration between the device endplates. In the Bryan disc group, significant shell kyphosis developed postoperatively (p < 0.0001). Both ProDisc-C and Synergy discs significantly increased anterior and posterior disc heights (p < 0.0001). The Bryan and Synergy discs maintained the natural center of rotation, whereas significant anterior shift occurred with ProDisc-C. CONCLUSIONS: The goal for motion preservation at the implanted level was achieved using all 3 devices. The Synergy disc was unique in its ability to alter device angulation by 6 degrees. The Bryan disc demonstrated device endplate kyphosis. Both the Synergy disc and ProDisc-C increased disc space height.

Surgical treatment of C2 fractures in the elderly: a multicenter retrospective analysis.

STUDY DESIGN: Multicenter retrospective analysis. OBJECTIVES: To review the results of surgical treatment during the last 6 years of C2 fractures in patients over the age of 70. SUMMARY OF BACKGROUND DATA: Little information exists about the clinical outcome of surgical treatment of elderly patients with C2 fractures, their ability to return to their previous environment, and their postoperative level of independence. METHODS: The medical records and radiographs of 29 patients who had undergone surgical treatment for C2 fractures were reviewed. The type of C2 fracture, neurologic examination at presentation, type of surgical treatment, perioperative morbidity and mortality, presence of osseous union, and stability of alignment were recorded. Long-term disposition was determined from office visits or by telephone interview. RESULTS: Twenty-four of 29 patients had type II dens fractures alone. The remaining 5 had associated C1 fractures. All patients were neurologically intact at presentation except for 2 patients with signs and symptoms of central cord syndrome. Perioperative complications occurred in 3 patients (10.3%). One patient died on postoperative day 6 from a myocardial infarction. Mean+/-SD radiographic follow-up was 9+/-3.2 months (range, 3 to 24). Of the 16 patients who underwent odontoid screw fixation, 6 (37.5%) had osseous union, and 9 (56.2%) were stable on radiographs. An additional patient who had odontoid screw initially required a posterior approach reoperation. Of the 13 posterior fusions, 4 (30.7%) had osseous unions and 9 (69.2%) were stable on flexion extension radiographs. Mean+/-SD clinical follow-up was 18+/-2.2 months (range, 3 to 72 mo). Twenty-five of 29 patients (86.2%) returned to their previous environment. Two patients died of unrelated etiology. CONCLUSIONS: C2 fractures in the elderly can be treated surgically with both anterior and posterior approaches with acceptable morbidity and mortality rates. The majority of patients can be mobilized early and return to their previous levels of independence.