This investigation presents a new approach in the measurement of the mechanical properties of the ligament substance from tensile testing of a bone-ligament-bone complex. Such basic information should be one of the necessary prerequisites in the evaluation of ligament repair as well as reconstruction by autogenous tissue grafts or artificial ligament implants. The use of a video system permits the determination of tensile strains of the mid-medial collateral ligaments from the canine, swine, and rabbit without mechanically interfering with the ligament deformation during testing. This methodology further eliminates the difficulties of measuring the initial length of the entire medial collateral ligament, as its insertions to bones are ambiguous and cover a large area. It was found that the strain of the ligament substance is consistently and considerably less than specific deformation of the bone-ligament-bone complex. These data suggest that the ligament-bone structure stretches nonuniformly with the highest deformation occurring near or at the ligament insertion sites to bone. Other interesting findings include the variation of tensile strains along the ligament substance for all animal species studied.

The finite element method (FEM) , an advanced method of computer simulation, is used to examine biomechanieal studies of hydrocephalus. Biot's theory of consolidation, whieh describes the mechanical behavior of a porous medium containing viscous fluid, is applied to represent the coupled behavior of tissue and fluid in the hydrocephalic brain . A computer simulation of the hydrocephalic process is carried out by FEM to evaluate the mathematical model. A two-dimensional finite element model is constructed using a horizontal computed tomographie (CT) slice of the brain. Specifying the material properties of the brain parenchyma , the loading characteristics, and the boundary conditions, the change of interstitial pressure, intracerebral stress distribution , and ventricular configuration are computed and graphieally represented. The result s of the computer simulation are compared with the findings of CT and magnetie resonance imaging of hydrocephalic patients. The progress of periventrieular cerebrospinal fluid edema and ventrieular enlargement is weIl represented by the mathematical model. The model demonstrated that stress concentration in the brain tissue and increased parenchymal hydraulie conductivity play an important roIe in the generation of periventricular cerebrospinal fluid edema. (Neurosurgery 21: 898-904 , 1987)

The finite element method (FEM), an advanced method of computer simulation, is used to examine biomechanical studies of hydrocephalus. Biot's theory of consolidation, which describes the mechanical behavior of a porous medium containing viscous fluid, is applied to represent the coupled behavior of tissue and fluid in the hydrocephalic brain. A computer simulation of the hydrocephalic process is carried out by FEM to evaluate the mathematical model. A two-dimensional finite element model is constructed using a horizontal computed tomographic (CT) slice of the brain. Specifying the material properties of the brain parenchyma, the loading characteristics, and the boundary conditions, the change of interstitial pressure, intracerebral stress distribution, and ventricular configuration are computed and graphically represented. The results of the computer simulation are compared with the findings of CT and magnetic resonance imaging of hydrocephalic patients. The progress of periventricular cerebrospinal fluid edema and ventricular enlargement is well represented by the mathematical model. The model demonstrated that stress concentration in the brain tissue and increased parenchymal hydraulic conductivity play an important role in the generation of periventricular cerebrospinal fluid edema.