Radiostereometric analysis of postoperative motion after application of dynesys dynamic posterior stabilization system for treatment of degenerative spondylolisthesis.
METHODS
Prospective case series


OBJECTIVE
This was designed to precisely measure motion after posterior dynamic stabilization using Dynesys instrumentation.


BACKGROUND
The Dynesys posterior dynamic stabilization system, which stabilizes the spinal segment while potentially decreasing the risk of adjacent segment disease, is undergoing evaluation by the US Food and Drug Administration for treatment of degenerative spondylolisthesis without fusion. Evaluation of adjacent segment disease requires precise characterization of motion on the surgical level. Unfortunately, routine clinical radiographic techniques are imprecise and unreliable for full characterization of spinal segment motion. Radiostereometric analysis, which is very precise and reliable for in vivo measurement of motion, was used to examine spinal segment motion after dynamic stabilization with Dynesys.


METHODS
Six patients (age 59+/-7 y) underwent posterior decompression followed by posterior stabilization using Dynesys instrumentation (4 one-level, 2 two-levels). Three to 5 tantalum beads were placed in each vertebral body. Postoperative biplanar radiographs were obtained in flexion, extension, right, and left lateral bending, and 3-dimensional reconstruction was performed using radiostereometric analysis at 3, 6, 12, and 24 months postoperatively. The translations and rotations of the superior vertebral body were measured relative to the inferior vertebral body.


RESULTS
Over the 24-month follow-up period, mean flexion, extension, left, and right lateral bending of the motion segments were noted to be 1.0 degrees, 2.4 degrees, 0.6 degrees, and 0.6 degrees or less, respectively. There were no statistically significant changes in the degree of motion. During follow-up, no significant changes in neutral position of the device were noted in any of the 3 planes, and minimal translation was noted in the postoperative period.


CONCLUSIONS
The Dynesys dynamic instrumentation system seems to stabilize degenerative spondylolisthesis. As expected in the degenerative lumbar spine, the segmental motion of the implanted level in this study was limited and considerably less than normal spinal motion.
Fayyazi
Amir H
AH
Penn State College of Medicine, Center for Advanced Healthcare, PA, USA. amirfayyazi@yahoo.com
Ordway
Nathaniel R
NR
Park
Soo-An
SA
Fredrickson
Bruce E
BE
Yonemura
Kenneth
K
Yuan
Hansen A
HA
D000368:Aged; D019299:Decompression, Surgical / Q000379:methods; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011859:Radiography; D016059:Range of Motion, Articular; D020127:Recovery of Function; D013123:Spinal Fusion / Q000379:methods; D013168:Spondylolisthesis / Q000000981:diagnostic imaging / Q000601:surgery*; D016896:Treatment Outcome