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Shvoong Home>Science>Primary Hip Stem Stability: The Effect of Bone Pathology on Micromotion Summary

Primary Hip Stem Stability: The Effect of Bone Pathology on Micromotion

Article Summary   by:fadzlina     Original Authors: A.K. Mohammed Rafiq; K. Nazri
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The effect of bone quality on the success of hip arthroplasty remains a topic of debate. Skeletal disease such as osteoporosis cause a significant loss of cancellous bone stock and structural deterioration of bone tissue. The reduced bone quality affects the decision made by surgeons in terms of selection of suitable hip stem as osteoporosis increases the likelihood of fracture and instability. It has been suggested that patients with poor bone stock would be better served having cemented hip stems to ensure strong primary fixation. However, there are reports that also cementless stems are reliable for patients suffering osteoporosis. A finite element model in conjunction with a novel methodology for predicting hip stem stability was experimentally validated in a previous study. In this study the methodology was applied to two CT datasets from osteoarthritic patients about to undergo hip replacement. Based on DEXA scans of the two patients, the Young Adult T-score showed in one case marked osteoporosis in all regions of the femur. 3D models were constructed from these two CT datasets and the material properties were assigned based on the grey-scale values on an element-by-element basis.
A third femur model was created as ‘non-pathological’ control using the Visible Human Project (VHP) CT dataset. During the analyses, all interfacial contacts on surfaces with micromotion larger than a threshold limit for bone ingrowth of 50 mikro meter were removed, and the iteration continues until either a stable-state condition is achieved or instability occurred. The results showed that the stems fixed in the control and osteoarthritic bones were stable. For the osteoporotic bone, the stem was found to be unstable due to a progressive reduction in surface area feasible for bone ingrowth. The results showed that bone quality affects the stability and therefore the potential success of hip stems.
Published: April 23, 2007   
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