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Purpose To develop a finite element analysis of the eye and orbit that can be subjected to virtual shaking forces. Methods LS-DYNA computer software was used to design a finite element model of the human infant eye, including orbit, fat, sclera, retina, vitreous, and muscles. The orbit was modeled as a rigid solid; the sclera and retina as elastic shells; the vitreous as viscoelastic solid or Newtonian fluid; and fat as elastic or viscoelastic solid. Muscles were modeled as spring-damper systems. Orbit-fat, fat-sclera, sclera-retina, and vitreous nodes-retina interfaces were defined with the use of the tied surface-surface function in LS-DYNA. The model was subjected to angular acceleration pulses obtained from shaking tests of a biofidelic doll (Aprica 2.5 kg dummy). Parametric studies were conducted to evaluate the effect of varying the material properties of vitreous/fat on maximum stress and stress distribution. Results With the vitreous modeled as a Newtonian fluid, the repeated acceleration-deceleration oscillatory motion characteristic of abusive head trauma (AHT) causes cumulative increases in the forces experienced at the vitreoretinal interface. Under these vitreous conditions, retinal stress maximums occur at the posterior pole and peripheral retina, where AHT retinal hemorrhage is most often found. Conclusions Our model offers an improvement on dummy and animal models in allowing analysis of the effect of shaking on ocular tissues. It can be used under certain material conditions to demonstrate progressive "stacking" of intraocular stresses in locations corresponding to typical AHT injury patterns, allowing a better understanding of the mechanisms of retinal hemorrhage patterns.

A new lower leg/ankle/foot system has been designed and fabricated to assess the potential for lower limb injuries to small females in the automotive crash environment. The new lower extremity can be retrofitted at present to the distal femur of the 5th percentile female Hybrid III dummy. Future plans are for integration of this design into the 5th percentile female THOR dummy now under development. The anthropometry of the lower leg and foot is based mainly on data developed by Robbins for the 5th percentile female, while the biomechanical response requirements are based upon scaling of 50th percentile male THOR-Lx responses. The design consists of the knee, tibia, ankle joints, foot, a representation of the Achilles tendon, and associated flesh/skins. The new lower extremity, known as THOR-FLx, is designed to be biofidelic under dynamic axial loading of the tibia, static and dynamic dorsiflexion, static plantarflexion and inversion/eversion. Instrumentation includes accelerometers, load cells, and rotary potentiometers to capture relevant kinematic and dynamic information from the foot and tibia. This paper will describe the performance requirements for THOR-FLx, the methodology used in its' development, results of component tests, and the biofidelity tests conducted on the full assembly.

A new lower extremity has been developed to be used with Thor, the National Highway Traffic Safety Administration (NHTSA) Advanced Frontal Dummy. The new lower extremity, known as Thor-Lx, consists of the femur, tibia, ankle joints, foot, a representation of the Achilles' tendon and the associated flesh/skins. It has been designed to improve biomechanical response under axial loading of the femur during knee impacts, axial loading of the tibia, static and dynamic dorsiflexion, static plantarflexion and inversion/eversion. Instrumentation includes a standard Hybrid III femur load cell, accelerometers, load cells, and rotary potentiometers to capture relevant kinematic and dynamic information from the foot and tibia. The design also allows the Thor-Lx to be attached to the Hybrid III, either at the hip, or at the knee. This paper will describe the performance requirements for Thor-Lx developed by NHTSA, the modeling studies undertaken to define primary design parameters, results of component and assembly tests, and the final design that evolved. Some results from recent testing of the lower leg, ankle and foot assembly will also be presented.