| 摘要: | 全髖關節置換手術(THR)是髖關節炎最常見的治療方式，儘管此類的有柄式植入物(stemmed)無論在外型、材質、或表面塗布上已有相當成熟的發展，但對於應力遮蔽、植體鬆動及骨溶解等問題依然無法解決。因此，為解決有柄式植入物在手術過程中需切除整顆球頭、鋸除全部股骨頸及掏空骨髓腔等步驟，便衍生出無柄式植入物(non-stemmed)的設計，以求保留髖關節大部分的骨質。而現已發行的無柄式植入物僅由中心柱或骨釘與股骨頸固定，臨床上常發生中心柱斷裂，或罩杯晃動滑脫而未能達到治療目的。
為解決目前無柄式植入物遭遇的問題，本研究由術前規劃開始，重建骨頭模型，取得中心軸及股骨頸外部曲面資料等參數進行植入物設計，並以電腦數值模擬與生物力學測試的方式，研究不同植入物於股骨上的力學傳遞差異性，並參考分析結果，配合臨床醫師提供意見，進行植入物的設計修改。後續考量到臨床上可能遇到的問題，再以電腦數值模擬對骨釘斷裂情況及手術切除誤差進行探討。此外，為了簡單化及標準化手術流程，提高手術的精確性，設計專用之切除及組裝手術器械，規劃其手術流程，並使用3D列印技術製作出樣本以模擬過程，驗證客製化無柄式植入物設計的可行性。
客製化的植入物由於外型與股骨頸貼近，因此在植入物、骨釘、骨頭上的應力，均比現有的無柄式植入物有更好的表現，以生物力學測試的結果看來，客製化的外型確實可降低鬆動的發生，在骨釘斷裂與手術切除誤差的情況下，依然能緊密地固定在股骨頸上。但無柄式相較有柄式植入物的設計，其穩定度還是比較低，因此在選擇置換手術系統時，必須在手術便利性與結構穩定性之間取捨。對於只有關節磨損、退化性或類風濕性關節炎及年輕的病患，無柄式植入物是較好的選擇，但如果患有骨質疏鬆、股骨頸缺血性壞死或骨折的病患，還是以全髖關節置換手術為佳。
;Total hip replacement (THR) is the most common treatment modality in hip osteoarthritis. Despite improvements in shape, material, and coating for hip stem, both stress shielding and aseptic loosening have been the major drawbacks of stemmed hip arthroplasty. Some non-stemmed systems were developed to avoid rasping off the intramedullary canal and evacuating the bone marrow due to stem insertion. At present, the non-stemmed design resulted in cup loosening and central bar fracturing in clinically because it was insufficient in the restriction.
In this study, many cup systems with minimal removal of the healthy neck were investigated to evaluate their biomechanical effects on the proximal femur and implants. The finite-element models of one intact, stemmed, resurfacing, cylinder, parallel, cross and nail femora were developed. The resurfacing and cylinder were selected as the representative of the ready-made implants. The parallel, cross and nail systems were selected as the representative of the custom-made implants. The stress distribution and interface micromotion were selected as the comparison indices. The biomechanical experiment were using cylinder, parallel and cross models to compare stability on the cup design and two screw constructions. The finite element analysis results showed that both stress distribution of all non-stemmed femora are consistently more similar to the intact femur than the stemmed one. Around the proximal femur, the stem definitely induces the stress-shielding phenomenon. The custom-made system with the anatomy-shaped cup can make intimate contact with the neck cortex and reduce the bone-cup micromotion and the implant stress. Comparatively, the reamed femoral head provides weaker support to the resurfacing cup causing higher interfacial micromotion. All the screws of the non-stemmed systems were highly stressed to serve as the potential for the failure of plastic yielding or fatigue cracking. The biomechanical experiment results showed that the stiffness of the custom-made cup and assisted screw with the cortical bone were better than the contrapositions.
In conclusion, the reserved femoral neck could act as the load-transferring medium from the acetabular cup, femoral neck to the diaphysial bone, thus depressing the stress-shielding effect below the neck region. If the hip-cup construct can be definitely stabilized, the non-stemmed design could be an alternative of hip arthroplasty for the younger or the specific patients with the disease limited only to the femoral head. |
