Lumbosacral stability of consolidated anteroposterior fusion after instrumentation removal determined by roentgen stereophotogrammetric analysis and direct surgical exploration.
METHODS
The intervertebral stability of bony consolidated anteroposterior lumbosacral spondylodesis is evaluated by roentgen stereophotogrammetric analysis and direct surgical exploration before and after removal of the internal fixator.


OBJECTIVE
To determine the remaining in vivo stability of spinal arthrodesis solely retained by a bony integrated carbon fiber cage.


BACKGROUND
Roentgen stereophotogrammetric analysis studies on posterolateral lumbar fusions demonstrate primary spinal stability after additional dorsal instrumentation, which is retained during bony fusion healing. Animal models show a persistent stabilizing effect of the fixator despite the presence of bony fusion. Although direct surgical inspection is the most reliable method to evaluate fused vertebrae, roentgen stereophotogrammetric analysis has also proven to be a highly accurate method to evaluate spinal stability.


METHODS
In 10 patients lumbosacral fusion was performed using carbon interbody implants and an internal fixator. Ten months after initial surgery (range 7-15 months) the internal fixation was removed to reduce local soft tissue impingement as soon as bony fusion was achieved. Fusion site exploration in the course of instrumentation removal was performed by applying distraction, compression, and torque to the grafted area under fluoroscopic control. Any motion indicated a pseudarthrosis. Lumbosacral stability was evaluated by serial roentgen stereophotogrammetric analysis after fusion and after instrumentation removal.


RESULTS
During instrumentation removal the mechanical stress test under fluoroscopic control did not indicate pseudarthrosis. After instrumentation removal, roentgen stereophotogrammetric analysis measurements revealed a nonsignificant increase in lumbosacral micromotions within the fused segment with 0.14, 0.31, and 0.44 mm in the transverse, vertical, and sagittal axes, respectively.


CONCLUSIONS
The internal fixator could be removed without endangering the stability of the fusion. Direct surgical exploration confirmed the adequacy of roentgen stereophotogrammetric analysis as a reliable in vivo method to evaluate lumbosacral stability after anteroposterior fusion.
Pape
Dietrich
D
Institute for Medical Biometrics, Epidemiology and Medical Informatics, University of Saarland, Homburg/Saar, Germany. Dr.D-Pape@t-online.de
Fritsch
Ekkehard
E
Kelm
Jens
J
Müller
Katja
K
Georg
Thomas
T
Kohn
Dieter
D
Adam
Frank
F
D000328:Adult; D004185:Disability Evaluation; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000706:statistics & numerical data; D007432:Intraoperative Period; D008161:Lumbosacral Region / Q000000981:diagnostic imaging / Q000601:surgery; D008297:Male; D010780:Photogrammetry; D019736:Prostheses and Implants; D019919:Prosthesis Implantation; D011859:Radiography; D012086:Reoperation / Q000009:adverse effects; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods / Q000706:statistics & numerical data; D013131:Spine / Q000000981:diagnostic imaging / Q000601:surgery*; D013168:Spondylolisthesis / Q000601:surgery*; D016896:Treatment Outcome