Measurement Performance of a Computer Assisted Vertebral Motion Analysis System.
BACKGROUND
Segmental instability of the lumbar spine is a significant cost within the US health care system; however current thresholds for indication of radiographic instability are not well defined.


OBJECTIVE
To determine the performance measurements of sagittal lumbar intervertebral measurements using computerassisted measurements of the lumbar spine using motion sequences from a video-fluoroscopic technique.


METHODS
Sensitivity, specificity, predictive values, prevalence, and test-retest reliability evaluation of digitized manual versus computer-assisted measurements of the lumbar spine.


METHODS
A total of 2239 intervertebral levels from 509 symptomatic patients, and 287 intervertebral levels from 73 asymptomatic participants were retrospectively evaluated.


METHODS
Specificity, sensitivity, negative predictive value (NPV), diagnostic accuracy, and prevalence between the two measurement techniques; Measurements of Coefficient of repeatability (CR), limits of agreement (LOA), intraclass correlation coefficient (ICC; type 3,1), and standard error of measurement for both measurement techniques.


METHODS
Asymptomatic individuals and symptomatic patients were all evaluated using both the Vertebral Motion Analysis (VMA) system and fluoroscopic flexion extension static radiographs (FE). The analysis was compared to known thresholds of 15% intervertebral translation (IVT, equivalent to 5.3mm assuming a 35mm vertebral body depth) and 25° intervertebral rotation (IVR).


RESULTS
The VMA measurements demonstrated greater specificity, % change in sensitivity, NPV, prevalence, and reliability compared with FE for radiographic evidence of instability. Specificity was 99.4% and 99.1% in the VMA compared to 98.3% and 98.2% in the FE for IVR and IVT, respectively. Sensitivity in this study was 41.2% and 44.6% greater in the VMA compared to the FE for IVR and IVT, respectively. NPV was 91% and 88% in the VMA compared to 62% and 66% in the FE for IVR and IVT, respectively. Prevalence was 12.3% and 11.9% for the VMA compared to 6.1% and 5.4% for the FE in IVR and IVT, respectively. Intra-observer IVR and IVT had a CR of 2.49 and 2.62, respectively. Inter-observer IVR and IVT had a CR of 1.99 and 2.81, respectively. Intra-subject (test/retest) CR were 2.49 and 3.11 for IVR and IVT, respectively.


CONCLUSIONS
The VMA system showed greater measurement performance in the detection of radiographic instability compared with FE radiographs.
Department of Neurosurgery, Greater Baltimore Medical Center, Baltimore, MD.
Reginald J
RJ
Davis
Southern Neurologic and Spinal Institute, Hattiesburg MS.
David C
DC
Lee
Department of Industrial and Systems Engineering, Auburn University, Auburn, AL.
Chip
C
Wade
Department of Neurosurgery, Drexel University College of Medicine, Pittsburgh, PA.
Boyle
B
Cheng
Flexion/Extension Radiographs; Lumbar Instability; Motion Analysis