Femoral Strains Resulting From Individual Muscles During Periods Of Single Support In Gait

Stress analysis of long bones is by no means a new field; it is believed that the earliest work dates back to Galileo in 1638 (Huiskes et al., 1981). Bone is a unique material in its ability of altering its mechanical properties when subjected to loads; According to Wolff's law, bones can adapt to the loads they experience, increasing in bone mass when subjected to a higher level of activity and alternatively decreasing in mass in periods of prolonged bed rest or a reduction in activity (Campoli et al., 2012). These loads then causes microstrain along the bone which promotes the remodelling process; excessive strains that are not within biological range can consequently damage the bone (Gefan 2003). This damage can causes resorption, where the bone is broken down faster than it is added, and implant loosening either due to the increase or decrease of bone mass (Duda et al., 2001).

In the field of orthopaedics there has always been an interest to understand stresses and strains in loaded bones; predominantly the femur as the femur is a large and strong weight bearing bone (Cristofolini et al., 2009). Other than external loads muscle activity and forces transmitted from muscles during gait can also alter the strain pattern. It is therefore important to understand effects of strain during movement as muscle loading plays a vital role in the processes of, fracture healing, bone modelling and remodelling, and in the primary stability of implants (Heller et al., 2001). There has been an extensive amount of knowledge and research that has been gathered in recent years in the field of pathological loading of the musculoskeletal system (Duda et al., 2001). Studies have shown that in order to produce reliable values of forces in the bone, muscle activity has to be clearly identified (Duda et al., 2001).

This study aims to analyse the single support phase during the gait cycle. Understanding muscle forces present during this period is of particular importance not only due to the increase in head load, but also when designing prosthesis for the elderly; as their gait cycle is slower, there is an increase in the stance phase period (McLeish et al., 1970) resulting in forces that are unlike those present in younger adults. Currently there is no general agreement on which muscles should be simulated across each phase of gait. A major contribution has been shown to result from the abductors, adductors and quadriceps. Analysis of current literature poses the question, what is the relevant role of individual muscles in the single legged stance and what muscles should be included in future modelling in order to accurately represent the physiological situation. As abductors play a major role producing forces in this stance and only one extensive study has simulated each individual gluteal muscle, this investigation also aims to study the effect of each individual gluteal muscle as well as measuring displacement of the head. Strain gauges will be bonded along the shaft of the femur and subjected to loads in three different configurations. 1. Joint reaction force 2. Joint reaction force + Individual gluteal muscles 3. Joint reaction force + glutei Strains will be measured for each configuration and comparisons will be made with older studies.

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