Experimentally Dissociating the Acute Mechanisms of Endplate Fracture Lesions and Schmorl's Node Injuries Using a Porcine Cervical Spine Model.

Abstract

Study design: This is an in vitro biomechanical study.

Objective: This study evaluated the influence of localized trabecular bone strength deficits and loading rate as determinants of Schmorl's node and fracture lesion incidence. The failure load (ultimate compression tolerance [UCT]), loading stiffness, and failure morphology were assessed after acute compression loading and failure.

Summary of background data: The cartilaginous endplate is vulnerable to injuries such as Schmorl's nodes and fracture lesions. While both injuries are associated with acute compression traumas, the factors that distinguish their incidence are poorly understood.

Methods: Forty-eight porcine spinal units (domestic hog, 5-10 mo, ~110 kg) were assigned to one of eight experimental groups that differed by initial condition (control, sham, experimentally produced chemical fragility, and structural void) and loading rate (3 kN/s, 9kN/s). A servo-hydraulic materials testing system was used to perform acute compression testing until observed failure in the specimen. Post-loading dissection was performed to classify injury morphologies. Between group differences in UCT and loading stiffness were evaluated using a general linear model and injury distributions were evaluated using chi-squared statistics.

Results: Schmorl's nodes occurred exclusively in chemical fragility (63%) and structural void groups (37%) and were more prevalent with a 9 kN/s (75%) loading rate compared with 3 kN/s (25%). In contrast, fracture lesions occurred in all FSUs assigned to the control groups (100%) and the majority of those assigned to the sham groups (92%). No between-group differences were observed for UCT and loading stiffness.

Conclusion: Pre-existing strength deficits of the subchondral trabecular bone can alter endplate injury morphology, particularly when coupled with high loading rates, but the localized strength deficits that were associated with Schmorl's nodes did not appreciably influence measured joint properties.