711 - The Effect of Abnormal Disc Mechanics on Activities of Daily Living...

Oral Posters: Cervical

Presented by: M.F. Gornet - View Audio/Video Presentation (Members Only)

Author(s):

M.F. Gornet(1), J.A. Hipp(2), A.G. Copay(3), F.W. Schranck(3)

(1) The Orthopedic Center of St. Louis, St Louis, MO, United States
(2) Medical Metrics, Inc., Houston, TX, United States
(3) SPIRITT Research, St Louis, MO, United States

Abstract

Introduction: New objective intervertebral motion (IVM) metrics have been shown to be associated with MRI abnormalities and disc degeneration, but it is not clear if the presence of an IVM abnormality may affect patient symptoms and the different activities of daily living. Objective IVM metrics may help to resolve conflicting evidence about the effect of degenerative changes on patient complaints.

Methods: Intervertebral motion was retrospectively calculated from prospectively obtained preoperative flexion-extension radiographs for 131 patients that had been enrolled at a single-site into a single-level lumbar disc arthroplasty IDE study. The IVM was measured using previously validated and FDA cleared computer-assisted methods (QMA®, Medical Metrics). The change in disc height (CDH) between flexion and extension was measured at the anterior- and posterior-most aspects of the disc space at the treatment level. The CDH was normalized to the amount of intervertebral rotation to control for patient effort, and that ratio was reported as the number of standard deviations from the average CDH measured at the radiographically normal levels in 161 asymptomatic volunteers. This metric is referred to as the Disc Integrity Index (DII). A DII >2 is above the 95% confidence interval for normal spines and was used to classify discs as normal versus abnormal. Statistics were used to identify associations between abnormal DII, and the prospectively collected preoperative ODI scores as well as the responses to the ten individual sections of the ODI. The DII was only calculated when there was at least 5 degrees of rotation (to assure that the disc had been sufficiently stressed to obtain a valid measurement).

Results: Of the 61 discs that had sufficient rotation, 16% had an abnormally high anterior DII (> 2). No patients had an abnormal posterior DII. The ODI score was significantly higher (P=0.012) when the anterior-DII was > 2. Table 1 presents the significance level from ordered logistic regression tests of the effect of an abnormally high anterior DII on different activities assessed under the ODI. The anterior-DII was also observed to increase with increasingly severe facet degeneration and to increase with increasingly severe disc degeneration (Pfirrmann grading).

Conclusion: The results suggest that abnormally high motion measured at the anterior disc space is a simple objective metric that can help to diagnose lumbar spine abnormalities that can affect multiple aspects of a patient's life. Abnormalities in this metric may help to explain difficulties with walking, running, travel, sex and lifting in particular. The optimum treatment for patients with an abnormal DII remains to be determined.

High DII association with ODI questions