Biomechanical evaluation of a bipedicular spinal fixation system: a comparative stiffness test.

STUDY DESIGN: This biomechanical study using cadaver thoracic spines evaluated the initial stiffness of two different fixation constructs using a new spinal implant: the bipedicular spinal fixation device (BSF). OBJECTIVE: To compare the biomechanical stiffness of a new construct using BSF with a regular construct using pedicular and laminar hooks. SUMMARY OF BACKGROUND DATA: Disadvantages of thoracic posterior implants and developments in in situ rod contouring led to the creation of a new implant for spine deformity surgery that would provide immediate stiffness to preserve spine correction, allow efficient postoperative rehabilitation, and obtain a good fusion rate. METHODS: Two age-paired groups of six human thoracic spines each (T3-T12) were compared: a regular group whose construct was in accordance with the Cotrel-Dubousset technique and the BSF group. In both groups, the spines were tested intact and then after injury. An injury was induced by transections of interspinous and anterior longitudinal ligaments and anterior discectomies. A three-dimensional ultrasonic measurement device, the Zebris 3D Motion Analyzer, was used to record the motion of the T6 relative to the T8 vertebra under loads, and to determine the ranges of motion (ROMs) between intact spines and the spine construct. RESULTS: In flexion-extension, the regular construct showed a significantly greater mean of relative ROMs than the BSF construct for principal rotation (88% and 69% respectively, P = 0.015). However, no significant differences were demonstrated in any of the other motions. CONCLUSION: The BSF construct showed stiffness similar to that of the regular construct, encouraging clinical investigation.

Laboratory Reconstructions of Real World Frontal Crash Configurations using the Hybrid III and THOR Dummies and PMHS.

Load-limiting belt restraints have been present in French cars since 1995. An accident study showed the greater effectiveness in thorax injury prevention using a 4 kN load limiter belt with an airbag than using a 6 kN load limiter belt without airbag. The criteria for thoracic tolerance used in regulatory testing is the sternal deflection for all restraint types, belt and/or airbag restraint. This criterion does not assess the effectiveness of the restraint 4 kN load limiter belt with airbag observed in accidentology. To improve the understanding of thoracic tolerance, frontal sled crashes were performed using the Hybrid III and THOR dummies and PMHS. The sled configuration and the deceleration law correspond to those observed in the accident study. Restraint conditions evaluated are the 6 kN load-limiting belt and the 4 kN load-limiting belt with an airbag. Loads between the occupant and the sled environment were recorded. Various measurements (including thoracic deflections and head, thorax and pelvis accelerations and angular velocities on the dummies) characterize the dummy and PMHS behavior. PMHS anthropometry and injuries were noted. This study presents the test methodology and the results used to evaluate dummy ability to discriminate both restraint types and dummy measurement ability to be representative of thoracic injury risk for all restraint types. The injury results of the PMHS tests showed the same tendency as the accident study. Some of the criteria proposed in the literature did not show a better protection of the 4 kN load limiter belt with airbag restraint, in particular thoracic deflection maxima for both dummies. The four thoracic deflections measured on the THOR and Hybrid III dummies may allow more accurate analysis of the loading pattern and therefore of injury risk.

Abdominal response to high-speed seatbelt loading.

UNLABELLED: This study was conducted to address injury risk due to high-speed loading of the abdomen by a seatbelt during the pretension phase. Indeed, a better coupling of occupants to the structure of the vehicle in frontal impact can be achieved by a strong pretension of the lap belt. However, out of position considerations have to be taken into account in the development of pretension systems. In particular, when the lap belt is on the abdomen instead of the pelvis at the time of pretension, the penetration of the belt into the abdomen should not lead to injuries. Given the sensitivity of pyrotechnic pre-tensioners to the resistance that they encounter, it is important to have an understanding of the behaviors of both human and dummy abdomens in order to evaluate injury risk. These data are indispensable for the evaluation, with dummy tests, of the effects of pre-tensioners on occupants and for the estimation of the levels of injury risk. New experiments were necessary to obtain data on abdomenbehavior in the pretension range of velocity. Six fixed-back cadavers were tested in two configurations: the belt was placed just above the iliac crest and tensed either symmetrically or not from 11 m/s to 23 m/s. Belt forces and kinematics were measured. Autopsies were performed. Tests were duplicated on the THOR dummy. RESULTS: Load penetration characteristics and injury outcomes are provided and compared to other published data. A spring-damper equivalent model of the abdomen is provided in order to give a means by which to evaluate dummies. The stiffness is 12.9 kN/m and the damping is 765 Ns/m. Static stiffness for the THOR dummy is too high, while the viscous component is four times too low when compared to the tested cadavers.