No abstract

Purposeful stiffness modulation in fracture fixation is critical to facilitate uneventful fracture healing. Converting near cortical holes to slots allowed selective axial stiffness adjustment without sacrificing fixation stability under cyclic loading. With further refinement, this simple modification of standard implant application may allow the surgeon to decrease the modulus mismatch between plating constructs and bone to decrease the risk of fixation failure.

The material properties of the anterior cruciate ligament (ACL) in female rats with normal estrous cycles were compared to those regulated by oral contraceptive steroids. Forty female Sprague-Dawley rats were divided into two groups: an experimental group received daily ethinylestradiol and levonorgestrel in a dosing model designed to simulate a typical oral contraception regime in humans, while a control group received daily oral placebo. After eight cycles, six rats from each group underwent daily phlebotomy to measure serum estradiol and progesterone levels over the course of a single 5-day estrous cycle. Significant differences between groups were found for the area under the curve of blood progesterone levels versus time over the length of the estrous cycle (P=0.02). After 12 cycles, the rats were euthanized and one femur-ACL-tibia complex from each animal was dynamically loaded to failure. The ACLs from the rats in the experimental group had significantly decreased average and tangent stiffness, (P=0.002 and 0.0001, respectively), and significantly increased elongation (P=0.002) and total energy absorbed (P=0.03), or greater toughness than controls. In rats, it appears that the administration of reproductive hormones designed to simulate typical oral contraception in humans alters the mechanical properties of the rat ACL.

Redesigning the center console using less stiff materials and allowing some lateral translation of the seat could aid in reducing pelvic injuries in side impact collisions.