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A two-dimensional, dynamic bioengineering model of the lower limbs was developed in order to estimate muscle and joint forces present during running at 4.5 m s-1. Data were collected from four subjects using a force platform and cine film. Individual X-rays and anthropometric data from the lower limbs were utilized to produce accurate bone models of the subjects' legs. Electromyographic verification of the model was undertaken while a runner was undergoing treadmill running at 4.5 m s-1. Results indicate that peak muscle forces of 22 times subject body weight (22 BW) could be present in the quadriceps muscle group and 7 BW in the gastrocnemius. The anterior shin muscles were found to be active for the first 9% of stance phase only, and compressive loads of 33 BW were found in the knee joint. The relationship between these high forces in the lower limbs and running related injuries is discussed.

A number of total hip components explanted at revision with bearing surfaces in either cobalt-chromium-molybdenum alloy or titanium-6% aluminium-4% vanadium alloy were examined and compared to contemporaneously manufactured but unused items; particular attention was paid to the bearing surfaces which were examined visually, by low-power microscopy, scanning electron microscopy (SEM), confocal microscopy, white light interferometry, laser profilometry and conventional stylus profilometry. The cobalt alloy heads maintained their surface finish well over periods up to 12 years. The titanium implants became badly damaged over much shorter periods although even badly scratched heads continued to meet the current standards for titanium alloy heads. Analysis showed that the damage to the titanium alloy heads was not a random but a well-defined process of scarring of a consistent size created by abrasion with small particles of bone. These damaged heads had the potential to wear the matching UHMWPE components rapidly creating large amounts of polymer debris. The finding that measurement of these damaged heads is within current standards raises concerns as to whether current standards incorporate fully the requirements for clinical performance.

Various methods for the evaluation of the critical J-integral Jfc based on the standard ASTM E813-89 are analyzed by conducting investigations on a ductile medical grade ultra high molecular weight polyethylene (UHMW-PE) at room temperature. Differences in Jfc reaching almost 50% were recorded between the methods investigated. The controversy surrounding the construction of the crack blunting line is discussed in terms of the stretch zone width together with the size requirements of ASTM E813-89. The findings of this investigation suggest that an R-curve construction based on mid-thickness crack growth and ultimate tensile strength (UTS) combined with a blunting line of slope m = 2 and modified exclusion lines provides consistent and conservative Jfc values. Using this technique, a near plane strain value, smaller than previously published data, of 66.5 kJ/m2 was obtained at 23°C.

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