Hip joint forces : hip joint forces of 40 to 60 year old normal and total hip replacement subjects during walking and stair, ramp and camber negotiation
To design and test hip joint prosthesis it is essential to know the magnitude and character of forces that may be applied to them in-vivo. For this thesis the hip joint forces of 40 to 60 year old subjects (five male and six female normal subjects and five male hip replacement) were studied. To allow the calculation of hip joint forces data from three-dimensional motion analysis and force plates were applied to a model of the lower limb. The model included the hip, knee and talocrural joints with 3 hip, 8 knee and 8 ankle joint forces, 4 knee ligaments and 47 muscle elements. A double linear optimisation technique (first minimising the maximum muscle stress then minimising the sum of the forces in the force bearing structures) was applied to solve the redundancy problem of force distribution in the muscles. Walking and stair, ramp and camber negotiation were characterised. Ground reaction forces, joint angles, intersegmental forces and moments, joint and ligament forces and muscle forces are presented. Muscle forces predictions were in general agreement with those in the literature, although the model was not capable of correctly distributing forces in the vasti or in the ankle only muscles as patella and talocalcaneonavicular joint equilibria were not included. In general, hip replacement subjects demonstrated lower hip joint forces than normal subjects. The range of maximum resultant hip joint forces for all activities was 3.04 to 11.85 for male normal subjects, 4.18 to 11.50 for female normal subjects, 3.73 to 6.81 and 2.21 to 8.77 for male hip replacement subjects for their natural and replaced sides respectively. The results presented define in three dimensions the hip joint forces in both pelvic and femoral axes systems and thus characterise the probable in-vivo requirements of hip joint prostheses during performance of the activities studied.