Simulated Automotive Side Impact on the Isolated Human Pelvis: Phase I: Development of a Containment Device Phase II: Analysis of Pubic Symphysis Motion and Overall Pelvic Compression

PHASE I - A containment fixture was designed and manufactured to stabilize and preload isolated human pelves within a DYNATUP™ Drop Tower during simulated automotive side impact. The fixture was utilized during thirteen parametric tests aimed at determining boundary conditions which simulate inertial properties of whole cadavers during impacts of the isolated human pelvis. The resulting pelvic injuries (i.e., fractures) ranged from no fracture to complex acetabular fracture. These injuries were sustained with drop masses of 14.2-25.2 kg and impact velocities of 4.1-6.4 m/s. Peak force, measured during impact, ranged from 2.0-8.2 kN.

PHASE II - Phrase II studies used nine additional human pelves to explored pelvis stiffness and pubis symphysis mobility under lateral impact to the greater trochanter. The containment device designed and tested in Phase I was utilized to stabilize and compressively preload the specimens during impact. Preload was appropriately determined from the mass of each cadaver at death. Boundary conditions simulating the inertial properties of a pelvis with associated body mass were developed (i.e., during Phase I) and modified slightly for these impacts. Each specimen was constrained at the lower lumbar spine and ischial tuberosities with 40 grit sand paper while the contralateral iliac wing was supported by an adjustable metal shelf covered with 3 mm of flexible rubber gasket material. The right femur was held prior to impact (with break away restraints) in 90° of flexion and neutral internal/external rotation and abduction/adduction. The average impact velocity was 4.52 ± 0.06 m/s with an impact mass of 25.2 kg. The mean peak force was 5.03 ± 1.92 kN with an average time to peak force of 0.59 ± 0.20 ms. The resulting pelvic injuries (i.e., fractures) ranged from no fracture to nondisplaced acetabular fracture. The global motion of each specimen was captured with two KODAK EKTAPRO digital imagers calibrated to measure displacement of the pubic symphysis in the AP plane and lateral compression of the pelvis and pubic symphysis in the frontal plane. Motion analysis was completed with a KODAK EKTAPRO Hi-Spec Motion Analyzer. The average lateral displacement (i.e., in the direction of the impact) of the pubic symphysis during impact was 31.1 ± 8.1 mm. The average AP displacement was 0.6 ± 6.8 mm anterior to the position prior to impact. The average final position of the pubic symphysis was 19.7 ± 9.4 mm lateral and 1.9 ± 5.7 mm anterior to the original position. The average lateral compression across the pubic symphysis joint was 1.3 ± 0.04 mm; however, this measurement was at the resolution of the video equipment and was not believed to be accurate. It does indicate that the pubic symphysis exhibits a stiff response during simulated automotive side impact at 4.5 m/s. The average pelvic compression during impact as measured between the anterior inferior iliac spines was 11.2 ± 6.1 mm (5.87 ± 3.03 % pelvic compression). A detailed understanding of overall pelvic stiffness and symphyseal mobility could provide useful insights to enhance automotive safety in side impact collisions and improve anthropomorphic test dummy design.