Facet Joint and Disc Kinematics During Simulated Rear Crashes With Active Injury Prevention Systems

Abstract

Experimental and computational biomechanical analyses of simulated rear crashes. The objectives were to determine cervical facet joint and disc kinematics and ligament strains during simulated rear crashes with the Whiplash Protection System (WHIPS) and active head restraint (AHR) and to compare these data with those obtained with no head restraint (NHR). Previous biomechanical studies document abnormal cervical facet kinematics and potentially injurious ligament strains during simulated rear crashes with no injury prevention system. A human model of the neck, consisting of a neck specimen mounted to the torso of BioRID II and carrying a surrogate head and stabilized with muscle force replication, was subjected to simulated rear crashes in a WHIPS seat (n = 6, 12.0 g, ΔV 11.4 km/h) or AHR seat and subsequently with NHR (n = 6: 11.0 g, ΔV 10.2 km/h with AHR; 11.5 g, ΔV 10.7 km/h with NHR). Lower cervical spine facet and disc motions and ligament strains during the crashes were computed and average peak values statistically compared (P < 0.05) between WHIPS, AHR, and NHR. Average peak facet and disc translations and ligament strains could not be statistically differentiated between WHIPS and AHR or between AHR and NHR. WHIPS significantly reduced peak capsular ligament strain and peak disc separation at C6/C7 as compared with NHR. Facet compression at C6/C7 reached 2.9 mm with WHIPS, 1.9 mm with AHR, and 3.2 mm with NHR. WHIPS and AHR generally reduced peak disc separation and anterior longitudinal ligament strain as compared with NHR. WHIPS and AHR limited capsular strain below the subfailure threshold but did not protect against potential facet joint compression injuries, which may occur during or after contact of the head with the head restraint.