人工大腿骨頭置換術における異径プロテーゼボールヘッドの有限要素解析

[Finite element analysis of different diameter prosthesis ball head in artificial femoral head replacement].

• Xue-Bin Wang
• Qing-Jiang Panf
• Xiao Yu

抄録

目的:

プロテーゼボールヘッドの適切なサイズを選択するために、異なる直径のプロテーゼボールヘッドを使用した場合の股関節の生体力学的変化を3次元有限要素解析により検討した。

OBJECTIVE: In order to select the proper size of prosthesis ball head, the biomechanical changes of hip joint using different diameter prosthesis ball head was studied by three-dimensional finite element analysis.

方法:

人工大腿骨頭の薄層CTデータと関連パラメータを用いて、人工大腿骨頭置換後の人工大腿骨頭のボール径を変えた場合の股関節の有限要素モデルを構築した(M0:術前モデル;M1:ボールヘッド径=元の大腿骨頭径;M2:ボールヘッド径=元の大腿骨頭径+1mm;M3:ボールヘッド径=元の大腿骨頭径-1mm;M4:ボールヘッド径=元の大腿骨頭径-2mm)。関節力と関連筋荷重を負荷し、ゆっくりと歩行したときの片足の起立状態を模擬して、寛骨臼周辺の骨・軟骨の応力分布と変化を解析しました。

METHODS: The thin-layer CT data and related parameters of artificial femoral head prosthesis were used to establish the finite element model of hip joint after artificial femoral head replacement with different ball diameter of prosthesis(M0:preoperative model;M1:ball head diameter=original femoral head diameter;M2:ball head diameter=original femoral head diameter+1 mm;M3:Ball head diameter= Original femoral head diameter -1 mm;M4:ball head diameter =original femoral head diameter -2 mm). Loading the joint forces and related muscle loads were loaded, and the stress distribution and change of bone and cartilage around acetabulum were analyzed by simulating the standing state of one foot when walking slowly.

結果:

(1) M1～M4では、骨盤内の応力濃度が異なっていた。M3の骨盤内のフォン・ミーゼス応力のピーク値は44.8MPaで、13.4%の増分で施術前に最も近い値であった。M3の骨盤の変位は、手術後の4群の中で最も小さく、1.40mmの増分であった。次いでM1がピーク値47.3MPa、増分19.7％、骨盤の変位1.59mmであった。(2)寛骨臼部では、M3のフォン・ミーゼス応力のピーク値は23.3MPaで術前に最も近く、約6.3％の増分であり、次いでM1のピーク値は24.0MPaで約8.1％の増分であった。(3)寛骨臼軟骨上では、M1とM3の応力分布は術前と同様であり、M3のフォン・ミーゼス応力のピーク値は18.5MPaで術前に最も近い値を示し、次いでM1が22.5MPaであった。(4) M1〜M4は人工大腿骨頭の外側上部象限に応力集中の程度は異なるが，その下では応力遮蔽を示し，その中でもM3のフォン・ミーゼス応力分布は他のモデルに比べて均一であり，そのピーク値(70.8MPa)は各グループで最も低く，M1(80.7MPa)に続いた．

RESULTS: (1) In M1 to M4, the stress concentration in pelvis was different. The peak value of Von Mises stress in the pelvis of M3 was 44.8 MPa, which was the closest to that before operation, with an increment of 13.4%. The displacement of the pelvis of M3 was the smallest in the four groups after operation, with an increment of 1.40 mm. The next was M1, with a peak value of 47.3 MPa, with an increment of 19.7%, and a pelvic displacement of 1.59 mm. (2) In acetabulum area, the peak value of Von Mises stress in M3 was 23.3 MPa, which was the closest to that before operation, with an increment of about 6.3%, followed by M1, with a peak value of 24.0 MPa and an increment of about 8.1%. (3) On the acetabulum cartilage, the stress distribution of M1 and M3 was similar to that before operation, and the peak value of Von Mises stress of M3 was 18.5 MPa, which was the closest to that before operation, followed by M1, which was 22.5 MPa. (4) M1 to M4 showed different degree of stress concentration in the outer upper quadrant of the artificial femoral head, but showed stress shielding under it;among them, the von Mises stress distribution of M3 was more uniform than that of other models, and its peak value (70.8 MPa) was the lowest in each group, followed by M1 (80.7 MPa).

結論:

大腿骨頭置換術を行う際には、置換前の股関節の自然な力学的特性に最も近いものを得て、サイズの違いによる合併症のリスクを軽減するために、直径1mm以下のプロテーゼボールヘッドと、元の大腿骨頭と同じ直径のプロテーゼボールヘッドを先に使用することが提案されています。

CONCLUSION: When femoral head replacement is performed, it is suggested that the prosthesis ball head with the diameter less than 1 mm and the prosthesis ball head with the same diameter as the original femoral head should be used first, so as to obtain the closest natural mechanical characteristics of the hip joint before the replacement and reduce the risk of complications caused by size differences.