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Biomedical subjects

E B MacMahon

Publications and source records attributed to E B MacMahon.

3 recordsLinked to original sources

Knee surgery assistance: patient model construction, motion simulation, and biomechanical visualization.

We present a new system that integrates computer graphics, physics-based modeling, and interactive visualization to assist knee study and surgical operation. First, we discuss generating patient-specific three-dimensional (3-D) knee models from patient's magnetic resonant images (MRIs). The 3-D model is obtained by deforming a reference model to match the MRI dataset. Second, we present simulating knee motion that visualizes patient-specific motion data on the patient-specific knee model. Third, we introduce visualizing biomechanical information on a patient-specific model. The focus is on visualizing contact area, contact forces, and menisci deformation. Traditional methods have difficulty in visualizing knee contact area without using invasive methods. The approach presented here provides an alternative of visualizing the knee contact area and forces without any risk to the patient. Finally, a virtual surgery can be performed. The constructed 3-D knee model is the basis of motion simulation, biomechanical visualization, and virtual surgery. Knee motion simulation determines the knee rotation angles as well as knee contact points. These parameters are used to solve the biomechanical model. Our results integrate 3-D construction, motion simulation, and biomechanical visualization into one system. Overall, the methodologies here are useful elements for future virtual medical systems where all the components of visualization, automated model generation, and surgery simulation come together.

Biomechanical Phenomena↗

Physiologic bowing in children: an analysis of the pendulum mechanism.

Prompted by common observations, we investigated why physiologic bowing occurs in infants and what purpose is served by its characteristic varus to valgus to neutral movement of the mechanical axis of the knee which we term "pendulum-like swing" in the frontal plane. Anthropomorphic data were readily available on age-related increase in weight, femoral and tibial lengths, and changes in lower extremity to allow construction of an "average" leg representing "normal" limb alignment of a growing infant male aged 1-8 years. This enabled us to calculate the bending moments on five anatomic levels of the limb about the knee; more important, during some growth periods the bending moments are minimal and may be used to diagnose pathologies of the lower limb. This form of analysis may prove useful in pathologies in which mechanisms serve to "mask" problems diagnosed on the basis of knee angle alone. When the child begins to stand, the pendulum mechanism is needed to equalize physeal growth about the knee.

Biomechanical Phenomena↗

Forces and moments on the human leg in the frontal plane during static bipedal stance.

An experimental apparatus was assembled that permitted measurement of the vertical and lateral ground reaction forces as the hip is abducted, resulting in foot separations ranging from 0.25 to 71 cm, with the knee in 0 degree flexion. Twelve healthy volunteers (8 men and 4 women) were tested. The hip joint was located by means of center of rotation measurements on each subject's legs, and the location of the knee joint was determined using anatomical measurements. It was observed that the mediolateral force was nonzero and directed toward the body midline, even when the subject's feet were placed together. With the feet placed at shoulder width, the population mean mediolateral force was 3% of body weight. It was determined that simplifying assumptions based upon either "zero lateral force," or "zero hip moment," produced errors, when compared with our measured values, over various ranges of foot separation, with the zero hip moment assumption providing accuracy over a broader range. The inclination of the tibial plateau, with respect to the long axis of the tibia, that would produce minimal mediolateral shear at the knee is presented. Research and clinical applications of our results and techniques are discussed.

Adult↗