近半世紀以來全人工髖關節手術已廣泛應用骨關節相關疾病，並得到十分良好的手術成功率。目前全人工髖關節手術失敗原因大多是髖臼杯組件的相關問題所導致，其中以磨耗和鬆脫為主。近年來磨耗問題已被廣泛討論，但鬆脫的相關研究甚少。金屬髖臼杯植入人體髖臼窩後由於承受人體重量，會造成髖臼杯和骨盆間有微小位移量(micro-motion)，此初始的不穩定會降低氫氧基磷灰石(Hydroxyapatite)誘導骨質長入(bone-ingrowth)的能力，無法達到較佳之骨整合(osseous integration)效果。因此初期穩定度(initial stability)是影響手術長期成功率的重要指標。本研究利用臨床常使用的髖臼杯建立有限元素模型，並以實驗來驗證此模型的準確性，同時以人體步態負荷施力，探討髖臼杯組件尺寸以及螺絲鎖入數目、位置對固定髖臼杯的初期穩定度進行探討。
本研究結果顯示，發現偏心骨螺絲以及鎖入螺絲的力量是影響穩定度的重要因素之一。髖臼杯組件尺寸在不考慮磨耗問題之下，球頭或內襯尺寸減少以及髖臼杯厚度增加，可減少髖臼杯和骨盆間相對位移量的產生，其中又以增加髖臼杯厚度對穩定度的貢獻最大。而由螺絲數目、位置對穩定度之模擬結果可知，鎖入三根骨螺絲即可達到相當於固定四根或五根螺絲的穩定程度。另外人體步態動作中髖球頭合力大多指向髖臼窩後上(posterior-superior)方區域為主，由本研究模擬結果可知，如果以三根骨螺絲來作固定，建議臨床醫師在骨螺絲無偏心問題及手術技巧允許下，可將其中二根骨螺絲鎖在髖臼窩的後側區域，一根在前側區域，如此可以增加支持面積、縮短負荷力臂，減少相對位移量，達到較佳的穩定效果，同時也可以使骨整合的更好，提高手術長期的成功率。

Total hip arthroplasty has been popularized for almost half century and greatly improved life quality of patients with osteoarthrosis of the hip. The major failure modes of the cementless cup are polyethylene wear and cup loosening. Many studies have focused on the wearing, while studies of the loosing were relatively less. The unstable of cup would induce large micro-motion under dynamic loading. The large micro-motion would reduce bone ingrowth on the HA (Hydroxyapatite) coated cup surface and prohibit the osseous integration. The initial fixation is a vital factor for bone ingrowth and thus the long-term success of the implant. In this study, 3-D finite element models of the clinical available acetabular cups were established to investigate the initial stabilization under gait loadings with particular emphasize on the component dimensions and the screw numbers and screw locations. The finite element approach was also validated by the simplified experiment.
The results showed that the eccentric for screw insertion and the applied torque are important for the stability of cup. Ignoring the wearing effect, decreasing the dimension of the femoral head and the PE liner or increasing the cup thickness would reduce the micro-motion between the pelvis and cup. Among these, the cup thickness has the greatest impact. As for the numbers of screw, three screws are sufficient to reach the stability provided by four or five screws. With three screws, based on the simulation results, it is suggested that using two screws at the posterior region with one screw at the anterior region could provide better stability outcome since this arrangement would supply a large supporting area and less moment arm under gait loading. (The direction of the gait loading is orientated toward the posterior-superior direction.) With this study it is hoped to provide clinical guideline for better cup stability, which can enhance the osseous integration and improve the long-term success of the implant.

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