Reports on contact stresses have not incorporated clear exclusion criteria to define the “normal” hip. 17- 19 These studies reported proof-of-concept and results of parametric studies, but simplifying assumptions and a lack of validation limited their ability to provide definitive measurements of the magnitude and distribution of contact stresses in normal hips. Contact stresses have been predicted using both the discrete element analysis (DEA) technique 15, 16 and the finite element (FE) method. ![]() To date, no experimental methods are available to assess hip contact stresses on a subject-specific basis.Ĭomputational methods provide the means to predict hip joint cartilage mechanics for individual subjects. 11- 14 These measurements only approximate the true cartilage stresses since one joint surface has been replaced with an implant. In vivo studies used instrumented prostheses to measure equivalent joint reaction forces. In vitro measurements of contact stress used pressure-sensitive film or piezo-resistive sensors, 8- 10 but quantifying contact stress on the entire articulating surface is difficult with these techniques, and only a limited range of stresses can be measured. 3- 7ĭespite the importance of cartilage contact stresses to joint health, disagreement remains regarding the normal magnitudes and distributions of contact stress in the healthy hip. 1, 2 While a number of factors contribute to the progression of OA, bony abnormalities such as dysplasia and femoroacetabular impingement (FAI) seem to accelerate the onset of the disease. Abnormal contact stresses are thought to be a primary cause of hip osteoarthritis (OA). J Orthop Res 30:1133–1139, 2012Ĭontact stresses in the human hip play an important role in maintaining joint health and pain-free ambulation. These results demonstrate the diversity and trends in cartilage contact stress in healthy hips during activities of daily living and provide a basis for future comparisons between normal and pathologic hips. These effects tended to persist across all simulated activities. Relatively small incongruencies between the femoral and acetabular cartilage had a large effect on the contact stresses. ![]() The magnitude and area of contact stress were consistent between activities, although inter-activity shifts in contact pattern were found as the direction of loading changed. The distribution of contact stress was highly non-uniform, and more variability occurred among subjects for a given activity than among activities for a single subject. ![]() Average contact area across all activities was 34% of the surface area of the acetabular cartilage. ![]() Peak stress ranged from 7.52 ± 2.11 MPa for heel-strike during walking (233% BW) to 8.66 ± 3.01 MPa for heel-strike during descending stairs (261% BW). Acetabular contact stress and area were determined for seven activities. Bone and cartilage surfaces were segmented from volumetric image data, and subject-specific finite element models were constructed and analyzed using a validated protocol. Computed tomography imaging with contrast was performed on one hip. Ten volunteers without history of hip pain or disease with normal lateral center-edge angle and acetabular index were selected. Our objectives were to determine cartilage contact stress during walking, stair climbing, and descending stairs in a well-defined group of normal volunteers and to assess variations in contact stress and area among subjects and across loading scenarios.
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