Three-Dimensional Computed Tomography-Based Specimen-Specific Kinematic Model for Ex Vivo Assessment of Lumbar Neuroforaminal Space

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Abstract

Study Design.

Cadaveric study to accurately measure lumbar neuroforaminal area and height throughout the flexion-extension range of motion (ROM).

Objective.

Create a new computed tomography (CT)-based specimen-specific model technique to provide insight on the effects of kinematics on lumbar neuroforamen morphology during flexion-extension ROM.

Summary of Background Data.

Nerve root compression is a key factor in symptomatic progression of degenerative disc disease because these changes directly affect neuroforaminal area. Traditional techniques to evaluate the neuroforamen suffer from poor accuracy, have inherent limitations, and fail to provide data throughout the ROM.

Methods.

Six cadaveric specimens (L1-sacrum) were instrumented with radiopaque spheres and CT scanned. 3-Dimensional reconstructions were made of each vertebra and the sphere locations determined. During kinematic testing, the spheres were located in relation to optoelectronic targets attached to each vertebra. The result was a 3-dimensional representation of the specimen's CT reconstruction moving in response to experimental data. Bony contours of the L2–L3 and L4–L5 neuroforamen were digitized producing continuous neuroforaminal area and height data throughout the ROM.

Results.

Neuroforaminal area and height linearly increased in flexion and decreased in extension. There was significant correlation between flexion-extension motion and percent change in area (L2–L3: 3.1%/deg, R2 = 0.94, L4–L5: 2.5%/deg, R2 = 0.90) and neuroforaminal height (L2–L3: 2.1%/deg, R2 = 0.95, L4–L5: 1.6%/deg, R2 = 0.93). Regression analysis showed that the ratio between neuroforaminal height and area is at least 1:1.5 such that a 100% increase in height is associated with an area increase of more than 150%.

Conclusion.

This is the first study to measure lumbar neuroforaminal area and height throughout flexion-extension ROM. The CT-based specimen-specific model technique can accurately evaluate the effect of kinematics on morphological features of the spine. The demonstrated increase in neuroforaminal dimension in flexion is consistent with treatment modalities used in clinical therapies to relieve radicular symptoms.

Conclusion.

Level of Evidence: N/A

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