86S Proceedings of the NASS 28th Annual Meeting / The Spine Journal 13 (2013) 1S–168S

OUTCOME MEASURES: radiographic study only.

METHODS: From 2009-2011, patients who underwent elective primary

posterior spinal fusion for the diagnosis of spondylolisthesis at a large ter-

tiary referral spine center had their plain films assessed for the degree of

spondylolisthesis and were designated ‘‘dynamic’’ or ‘‘static,’’ as defined

by historical measures. Axial and sagittal T2 MRIs were evaluated for as-

sociated facet fluid (FF), facet cysts (FC), interspinous fluid (ISF) and facet

hypertrophy (FH). These finding were then statistically evaluated for asso-

ciations between dynamic and static spondylolisthesis on flexion/extension

radiographs and characteristic MRI findings.

RESULTS: Ninety patients were included in the study with 114 levels ex-

amined for spondylolisthesis. Patients with greater than 3 mm of instability

on flexion/extension films were more likely to have facet fluid (p50.018)

and interspinous fluid (p!0.001). Of the patients who had a greater than 3

mm of instability, 39.5% did not demonstrate spondylolisthesis on the sag-

ittal MRI reconstruction. If interspinous fluid was present on MRI, there

was a positive predictive value (PPV) of 69.0% that there would be greater

than 3 mm instability on flexion/extension films. Absence of facet fluid on

MRI had a PPV of 75.6% for instability less than 3 mm on flexion/exten-

sion films. In the presence of interspinous fluid on MRI, the likelihood ra-

tio (LR) of finding more than 3 mm of instability on flexion/extension films

was 3.68. The presence of facet fluid on the MRI had a LR of 1.43 for in-

stability. A total of 36.8% of all spondylolisthesis reduced when supine on

MRI. The presence of FF and/or ISF is associated with instability greater

than 3 mm in flexion/extension radiographs.

CONCLUSIONS: The differentiation between static versus dynamic spon-

dylolisthesis has been neglected in the literature. The findings presented

here may be significant in stratifying future study population to determine

the benefits of certain surgical strategies. Namely, sub-stratification of pa-

tients to static and dynamic spondylolisthesis should be performed to re-

solve the necessity of non-instrumented fusion, instrumented fusion,

interbody fusion, and other multitudes of surgical techniques currently used

to treat degenerative lumbar spondylolisthesis.

FDA DEVICE/DRUG STATUS: This abstract does not discuss or include

any applicable devices or drugs.

http://dx.doi.org/10.1016/j.spinee.2013.07.235

168. Moved to Value Abstract Awards Session

http://dx.doi.org/10.1016/j.spinee.2013.07.236

169. Diagnostic Misclassification of Lumbar Instability and Post-

Fusion Pseudoarthrosis from Standard Bending Radiographs

Boyle C. Cheng, PhD1, Chip Wade, PhD2, Edward R. Prostko, MD3;1Mars, PA, US; 2Auburn University, Austin, TX, US; 3Pittsburgh, PA, US

BACKGROUND CONTEXT: Segmental instability of the lumbar spine

has been suggested to be a major cause of low back pain and a primary

indication for spinal fusion. Similarly, patients presenting with a pseu-

doarthrosis have also been indicated for revision surgery. Both conditions

are generally clinically diagnosed via measurements of intervertebral mo-

tion taken from standard bending radiographs (SBR). With regard to the

detection of lumbar instability using intervertebral rotation, published

thresholds of instability that are widely used in clinical practice include

the AMA Guide to the Evaluation of Permanent Impairment 5th Edition,

as well as the InterQual guidelines for determining the criteria by which

fusion surgeries are approved for coverage (InterQual). As for the detec-

tion of pseudoarthrosis, intervertebral rotation of over 5� in a functional

spinal unit is a widely-accepted threshold according to the FDA.

PURPOSE: To assess the rate of diagnostic misclassification errors (false

positives and false negatives) in the detection of lumbar instability and

post-fusion pseudoarthrosis when diagnosed using measurements of

Refer to onsite Annual Meeting presentations and postmeeting proceedings for po

reporting disclosures and FDA device/drug

intervertebral motion taken from standard bending radiographs and com-

pared against published thresholds.

STUDY DESIGN/SETTING: All 202 subjects were consented in the pro-

spective investigation. The research was designed to compare studies in-

volving SBR to that using the Vertebral Motion Analysis (VMA, Ortho

Kinematics, Inc). Patients subjected to either X-ray film or fluoroscopic

still images were used to capture SBR patient studies while cine fluoros-

copy was used to capture VMA data.

PATIENT SAMPLE: Patients having both SBR and VMA studies where

included in the final analysis (47 asymptomatic and 45 symptomatic). 26

post-fusion patients were analyzed based on matched SBR and VMA at

the fused level.

OUTCOME MEASURES: False positives were identified when the SBR

measurement for an asymptomatic volunteer was above the disease thresh-

old but the VMA measurements were below. False negatives were identi-

fied when the SBR measurement for a patient (either preop or postop) was

below the disease threshold but the VMA measurement was above. The

VMA measurement was used to identify true negatives and true positives

according to this method because: (1) VMA measurements have demon-

strated higher accuracy and repeatable than SBR measurements (FDA)

and (2) the device-assisted bending that is part of the VMA testing process

is known to avoid over- and under-bending during imaging

METHODS: The VMA measurements for assessing intervertebral motion

was characterized by the use of: (1) a handling device that assists patients

through a standard arc of lumbar bending in both an upright and recumbent

posture (70� flexion/extension arcs; 60� left/right bending arcs); (2) video

fluoroscopy imaging of the lumbar spine during bending (capturing images

at 8 frames per second); and (3) image processing software capable of au-

tomatic frame-to-frame registration and tracking of vertebral bodies across

the sequence of video-fluoroscopic images to derive measurements of in-

tervertebral rotation and translation. The SBR were assessed from volun-

tary bending by the patient.

RESULTS: Statistical significance was found in identifying false positives

and false negatives for each of the three measurement criteria, AMA, In-

terQual and FDA, in flexion/extension bending. False positive identifica-

tions were 8.1%, 9.2%, and 7.4% respectively; while false negatives

were 3.0%, 4.9%, and 11.8% respectively.

CONCLUSIONS: The current standard of care for detecting lumbar insta-

bility using SBR results in both false positive and false negative type di-

agnostic misclassification errors. For instability assessments, rates of

false positive type errors were uniformly higher than false negative errors,

suggesting that the use of the VMA would result in a net reduction in de-

finitive diagnoses for instability based on intervertebral rotation. Reducing

diagnostic misclassification errors would also be expected to improve the

efficacy rates of surgeries indicated for these conditions.

FDA DEVICE/DRUG STATUS: This abstract does not discuss or include

any applicable devices or drugs.

http://dx.doi.org/10.1016/j.spinee.2013.07.237

170. Correlation Between Cervical Spinal Stenosis and the

Morphology of Congenital Lumbar Stenosis

Nicholas T. Spina III1, Jesse L. Even, MD2, Joon Y. Lee, MD3; 1Pittsburgh,

PA, US; 2Arlington Orthopedic Associates, Arlington, TX, US; 3University

of Pittsburgh Medical Center, Pittsburgh, PA, US

BACKGROUND CONTEXT: Neurogenic claudication from lumbar spi-

nal stenosis can be either due to degenerative pathology or congenitally

narrowed spinal canal. Recent cadaveric studies have linked existence of

congenital lumbar stenosis with cervical spinal stenosis. Dagi et al. defined

this clinical picture as tandem stenosis noting an incidence of 5%-25% in

individuals. It has been our experience that sagittal MRI morphology of

congenitally narrowed lumbar spine can differ between individuals with

3 characteristic presentations. The morphological categories include: (1)

‘‘Rapidly tapering’’ stenosis in which the canal begins to gradually narrow

ssible referenced figures and tables. Authors are responsible for accurately

status at time of abstract submission.