【０００１】
【発明の属する技術分野】
本発明は加齢、事故、病気などで損傷した股関節を人工股関節に置換した場合に、人工股関節の潤滑性を向上させることで摩擦係数を低下させ、摩耗や摩擦発熱を抑制して、寿命の延長と快適性の向上を同時に実現させることのできる実用性の高い人工股関節に関するものである。
【０００２】
【従来の技術】
長寿命化によって関節疾患を患う人の数は増加の一途であり、人工関節全置換術は国内だけでも年間に約１０万例、世界的には１００万例以上に及びそのうち８０％が人工股関節の置換手術である。
世界的なバイオ技術開発競争の中で再生医療技術関連の研究に集中され、関節内の軟骨組織も実験室的には再生可能になりつつあるが、再生された軟骨の強度は弱く、最も重要な軟骨の表面組織については再生できる目処さえたっていない。
【０００３】
一方、すでに臨床実績のある人工関節については改善によって性能を飛躍的に高めることができれば、安価で信頼性の高いインプラントとして、すべてが再生医療に取って代わられることは将来的にもないと考えられる。現在の人工関節は主として軟骨部にポリエチレン等の超高分子材料を用い金属やセラミックスと組み合わせたものが多い。ところが人工関節全置換術の８割を占める股関節においては、微細なポリエチレン摩耗粉が発生し人工関節を緩める原因となることが明らかにされて以来、ポリエチレン分子のクロスリンク化、骨頭側材料の変更や大きさの検討など、様々な対策が施されつつ現在に至っているが、未だその機能、性能とも生体関節にははるかに及ばない。ポリエチレンを使用せず金属やセラミックスなど、硬質材同士を組み合わせて人工関節を作る先進的試みもあるが、米国においては全セラミックス関節を臨床応用した結果、僅か１年程度でトラブルが続出して訴訟問題に発展する深刻な問題となっている。
【０００４】
そのため現在主流のポリエチレン製軟骨を採用した人工関節が工学的にも安定なため、今後もポリエチレン製軟骨に代わる新素材が開発されない限り、使われ続けるものと考えられる。一般にポリエチレン製軟骨の摩耗を抑制するには素材の耐摩耗性を上げる努力のほかに、設計工学的なアプロ−チも重要である。関節は機械でいえば軸受に相当するので、軸受の潤滑状態を改善できれば人工関節使用時の快適性と長寿命化が同時に得られ、高齢社会に必要な福祉医療技術の一つになる。
【０００５】
従来の市販の人工股関節で代表的なモデルは、図６に示すように、球面骨頭１表面と、凹球面受座２内面間にポリエチレン等の弾性高分子材料で所定厚の凹球面に形成した人工臼蓋（以下弾性臼蓋カップと称する）３を介設し、球面骨頭１表面と弾性臼蓋カップ３内面の回動摺動域面をすべて真球面状に加工して球面軸受を構成し、球面骨頭部１下方のステム４を大腿骨に、凹球面受座２を骨盤側にそれぞれ挿入固定したものである。このため、歩行により負荷を受けると、ほとんどの変形は凹球面受座２側の弾性臼蓋カップ３に生じてその摩耗に至り前述の問題が惹起していた。
【０００６】
体内より抜去された凹球面受座２内の弾性臼蓋カップ３を観察すると、接触圧の違いに応じた摩耗形態の相違が明瞭に認められる。凹真球面加工した弾性臼蓋カップ３に金属あるいはセラミックスなどで作った球面骨頭部１を挿入して負荷を加えた際の接触圧力を求める一般式は未だ報告がない。しかしながら図７の圧力分布曲線ＣＬに示すように力のベクトルが真球面１Ｆと交わる点Ｐで接触圧力ＰＣが最大で、そこから両側に離れるに従い接触圧力が減少することは容易に想像できる。弾性臼蓋カップ３と球面骨頭部１との隙間に関節液があったとしても、球面同士の弾性臼蓋カップ３内面と球面骨頭部１表面が接触する以前に関節液のほとんどは接触圧力の低い周囲にスクイズアウトして、その状態で歩行による相対的な滑り運動を行えば潤滑上は益々極めて厳しい環境となって摩耗や摩擦熱の問題が生じる。
【０００７】
【発明が解決しようとする課題】
本発明の解決しようとする課題は、人工股関節に歩行による負荷を加えた際、球面骨頭部１と弾性臼蓋カップ３の接触圧力が局部的に増大することを抑制して、接触面間に関節液を保持することで潤滑液として有効に利用することにある。
【０００８】
【課題を解決するための手段】
本発明は上記課題を解決するものでありその特徴とするところは、上端に球面骨頭部を有するステムを大腿骨に嵌入固定し、内面に弾性臼蓋カップを配設した凹球面受座を骨盤側に固定し、該球面骨頭部を凹球面受座内の弾性臼蓋カップを介して回動自在に挿入受持せしめてなる人工股関節において、球面骨頭表面と凹球面受座内の弾性臼蓋カップの内面との回動摺動域の全表面を真球面形状にした際、歩行に伴う球面骨頭部の回動中に球面骨頭の真球面が弾性臼蓋カップとの接触で生じる最大接触圧力軌跡部分とその周囲に沿った部分の真球表面帯を真球表面よりバンド状に球心側に僅かに低い球状表面に加工したことを特徴とする人工股関節にある。
【０００９】
【発明の実施の形態】
即ち本発明の人工股関節は、図７に示すように球面骨頭１表面と凹球面受座２内の弾性臼蓋カップ３の内面との回動摺動域の全表面を真球面形状１Ｆにした際に、球面骨頭１の真球面が弾性臼蓋カップ３との接触で生じる最大接触圧力ＰＣ軌跡部分Ｐとその周囲に沿った部分の真球表面帯１ＦＺを、図１に示す前記バンド状部分３０の形成によって低減させ、且つ該バンド状部分３０の周辺の接触圧力分布を、図１の接触圧力分布曲線ＣＬ２のようにバンド状部分３０内部の接触圧力と同程度もしくは高くなるようにするものである。
これにより歩行に伴う回動中、すべり運動とともに該バンド状部分３０の内部に関節液をトラップしてバンド状部３０外に関節液を逃げ難くして、関節液つまり潤滑液の流れを円滑に維持して、該球面骨頭部２０と凹球面弾性臼蓋カップ１０との挿入受持部における弾性臼蓋カップ１０の、低摩擦化、低摩耗化を有利に実現させて、発熱防止、破損防止、緩み（ルーズニング）防止等を長期に渡って安定維持させるのである。
【００１０】
このように球面骨頭２０側に該バンド状部分３０を形成するだけで、歩行中の接触圧力状態と潤滑条件を同時に改善できる可能性に着目した点は、独創的であり新規なものである。この点に着目した研究および発明は、国内外を問わずこれまでにない。接触圧力分布が変わると潤滑状態が変わるため摩擦係数の変わることは、金属板上をポリエチレンで擦る基礎的実験ですでに明らかにしている。設計工学の基本原理を機構学より優先させて人工股関節に応用したことに本発明の新規性と優位性がある。
【００１１】
而して、本発明における球面骨頭２０に成形する該バンド状部分３０の非球状表面は、球面骨頭の真球面部との境を滑らかな低面変化部に加工し、これに連続してバンド状部分３０の長手方向に、及び又はそれに直交する方向に凸状に形成した単一曲率半径球状（球心は球面骨頭の真球面部の球心と同一でも非同一でも良い）又は曲率半径の異なる複数の球面部分及び又は湾曲面等で複合合成した非球面とするか、又は曲率半径を連続的に斬増又は斬減変化した非球面とする。
また、球面骨頭２０や凹球面受座５０の材質は、金属又はセラミックス等を用い、弾性臼蓋カップ１０は、クッション性、耐摩耗性、低摩擦性、耐圧性等の機能を有する前述したポリエチレン等の弾性高分子材料を用いるが、前記機能の他に通液性、捕液性を有する公知の弾性高分子材料でもよい。
【００１２】
【発明の実施例】
本発明の１実施例を図１〜図５に示す。
図１〜図５において、人工股関節の球面骨頭部２０は、金属製で曲率半径：１３ｍｍの真球面４０を骨頭２０の回転方向に加工して、弾性臼蓋カップ１０との間に荷重を加えない状態では最大でも０．０１ｍｍのバンド状隙間を作ったことを図４は隙間を強調して描いている。図５は回動方向に直交する方向の臼蓋カップ１０と加工骨頭２０の間の無負荷時での隙間の変化する様子を強調して描いている。凹球面受座５０は、厚み：３ｍｍの金属製で曲率半径：２３ｍｍの凹真球内面を形成し、弾性臼蓋カップ１０は、厚み：１０ｍｍのポリエチレン製で曲率半径：１３ｍｍの真凹球内面を形成したものである。
【００１３】
図２、図３は、本実施例の人工股関節における要部即ち、弾性臼蓋カップ１０を介して該球面骨頭部２０を回動自在に挿入受持した部分の拡大図である。図では球面骨頭２０表面のバンド状部分３０をイメ−ジしやすいように、弾性臼蓋カップ１０を半透明にして、バンド状部分３０が弾性臼蓋カップ１０の中央部にある状態を描いている。実際の人工股関節は図６のように傾いた状態で取付けられるため、必ずしも弾性臼蓋カップ１０の中央部にバンド状部分３０が位置するとは限らないが、弾性臼蓋カップ１０は内面が凹真球面であるため、バンド状部分３０がどの位置にあっても幾何学的には同じである。
球面骨頭部２０が凹球面受座５０内に設置した弾性臼蓋カップ１０と接触する回動摺動域の全表面が真球面４０の状態から、球面骨頭部２０において、歩行により球面骨頭部２０と弾性臼蓋カップ１０の間で荷重の最も大きくなる領域とその周囲をその球表面４０より球心側に最大０．０１ｍｍ低くした前記該バンド状部分３０を形成する。
これにより、図１に併記した圧力分布曲線ＣＬ２に示す如く、歩行による局部荷重を低減させる一方で低減されたバンド状部分３０の近傍周囲の接触面圧を上昇させる結果となる。このことが関節液を閉じ込めて潤滑性を上げる作用をする。
【００１４】
図３は、弾性臼蓋カップ１０の下側から見た図である。図２、図３ではバンド状部分３０の加工状態を分り易くするように極端に描いているが、本例では、図４、図５に示す複合球面形状にしてある。
つまり、歩行による球面骨頭部２０の回転方向１００に沿って形成するバンド状部分３０の球面形状は、図４に示す如く、球面骨頭部２０のすべり方向１００に沿って真球表面４０より球心側に最大０．０１ｍｍ低くする。球表面が真球面４０より球心側に低くなったことで無負荷状態では骨頭２０と凹球面受座５０内に配設した弾性臼蓋カップ１０との間のバンド状加工部分３０には関節液が保持されやすくなる。またバンド状部分３０の前端部３０ｆをすべり方向１００にそって弾性臼蓋カップ１０の外部まで延長することで、球面骨頭部２０の回動とともに関節液は導入されやすくなる。荷重の増加にしたがい弾性臼蓋カップ１０は弾性変形して僅かな隙間はさらに小さくなろうとするが内部にトラップされた関節液が圧力を発生することで球面骨頭部２０と弾性臼蓋カップ１０が直接接触して摩耗することを防ぐ。バンド状加工部３０の後端部３０ｂは真球面へと滑らかに変化することで関節液が負荷域より流出することを防ぐ。
【００１５】
また図５に示す如く、滑り方向１００と直交する方向１１１の球面形状は真球面４０より最も低くしたバンド状部分３０の中央部から滑らかに変化させて再び真球面４０に接続することで、負荷が小さいときには球面骨頭部２０と弾性臼蓋カップ１０の間に関節液を保持する隙間を作ると同時、負荷が大きくなればバンド状加工部３０側方の接触圧力が高くなることで関節液の側方漏れを防ぐ役割をする。
これにより図１の圧力分布曲線ＣＬ２に示す如く、球面骨頭部２０が歩行に伴う回動中、すべり運動とともに該バンド状部分３０内の接触圧力を低減し、且つ該バンド状部分３０の周辺の接触圧力をバンド状部分３０内部の接触圧力と同程度もしくは高くなるように接触圧力分布を形成させて、該バンド状部分３０内にトラップした関節液を、バンド状部分から逃げ難くして、関節液を潤滑液として有効に機能させようとするのである。
【００１６】
【発明の効果】
以上の説明で明らかなように、本発明の人工股関節は、球面骨頭部と弾性臼蓋カップとの回動摺動域の全表面を真球面にした際に生じる接触部中央での最大接触圧力帯を前記バンド状部分によって低減し、且つ該バンド状部分の前端部を除く周辺の接触圧力をバンド状部分内の接触圧力と同程度か、もしくは高くなるように接触圧力分布を形成することにより、歩行に伴う回動中、すべり運動とともに該バンド状部内にトラップした関節液に圧力を発生させることで球面骨頭部と弾性臼蓋カップとの局部的過大な直接接触部分を無くし、バンド状部分外には関節液を逃げ難くして、関節液つまり潤滑液の流れを円滑に維持して、該球面骨頭部と凹球面受座内の弾性臼蓋カップとの挿入受持部における低摩擦化、低摩耗化を有利に実現させて、発熱防止、破損防止、緩み（ルーズニング）防止等を長期に渡って安定維持させるのである。
【図面の簡単な説明】
【図１】本発明における球面骨頭と加工骨頭をそれぞれ凹球面受座内の弾性臼蓋カップに挿入して負荷を与えた場合の圧力分布を示す説明図である。
【図２】本発明の１実施例で人工股関節要部である該球面骨頭部２０が弾性臼蓋カップ１０に挿入された状態でバンド状部分３０の後端部３０ｂが見える位置から弾性臼蓋カップ１０を半透明にして立体的に示した説明図である。
【図３】図２に示す該球面骨頭部２０の前端部３０ｆが弾性臼蓋カップ１０の外にあることが弾性臼蓋カップ１０を半透明にして立体的に示した説明図である。
【図４】球面骨頭部２０に形成したバンド状部３０の中央部を、その滑り方向１００に沿って切断して見た湾曲形状を示す断面図である。
【図５】球面骨頭部２０に形成したバンド状部分３０を、その滑り方向１００と直交する方向１１１に切断して見た湾曲形状を示す断面図である。
【図６】従来の人工股関節を立体的に示す説明図である。
【図７】従来の球面骨頭と加工骨頭をそれぞれ凹球面受座内の弾性臼蓋カップに挿入して負荷を与えた場合の圧力分布を示す説明図である。
【符号の説明】
１０：弾性臼蓋カップ
２０：該球面骨頭部
３０：真球面より僅かに低いバンド状部分
４０：球面
５０：凹球面受座
１００：球面骨頭部２０の負荷時の回転方向
３０ｆ：バンド状部分３０の負荷時のすべり方向１００の前端部
３０ｂ：バンド状部分３０の負荷時のすべり方向１００の後端部
１１１：滑り方向１００と直交する方向[0001]
TECHNICAL FIELD OF THE INVENTION
When the hip joint damaged by aging, accident, illness, etc. is replaced with an artificial hip joint, the present invention reduces the friction coefficient by improving lubrication of the artificial hip joint, suppresses abrasion and frictional heat generation, and reduces the life. The present invention relates to a highly practical artificial hip joint capable of simultaneously realizing extension and improved comfort.
[0002]
[Prior art]
The number of people suffering from joint diseases is steadily increasing due to prolonged life, and total joint replacement is about 100,000 cases annually in Japan alone, more than 1 million cases worldwide, and 80% of them are hip joint prostheses. This is a replacement surgery.
Concentration on regenerative medicine technology-related research in the global biotechnology development competition, cartilage tissue in joints is becoming reproducible in the laboratory, but the strength of regenerated cartilage is weak and the most important There is no indication that the cartilage surface tissue can be regenerated.
[0003]
On the other hand, if the performance of artificial joints that have already been clinically improved can be dramatically improved by improvement, it is unlikely that all of them will be replaced by regenerative medicine as inexpensive and reliable implants. Can be At present, many artificial joints mainly use ultra-high molecular materials such as polyethylene for the cartilage and combine them with metals and ceramics. However, in the hip joint, which accounts for 80% of total hip arthroplasty, fine polyethylene abrasion powder was generated, which was found to cause loosening of the artificial joint. Although various measures such as examination of the size and size have been taken, it is still the present, but its functions and performance are still far below those of living joints. Although there are advanced attempts to create artificial joints by combining hard materials such as metals and ceramics without using polyethylene, in the United States, after applying all ceramic joints clinically, troubles continued in just one year, and lawsuits continued The problem has evolved into a serious problem.
[0004]
As a result, artificial joints employing polyethylene cartilage, which is currently mainstream, are technically stable, and will continue to be used unless a new material replacing polyethylene cartilage is developed in the future. In general, in order to suppress the wear of polyethylene cartilage, in addition to efforts to increase the wear resistance of the material, a design engineering approach is also important. Since a joint is equivalent to a bearing in terms of a machine, if the lubrication state of the bearing can be improved, comfort and a longer life when using the artificial joint can be obtained at the same time, and this is one of the welfare medical technologies required for an aging society.
[0005]
As shown in FIG. 6, a typical model of a conventional commercially available artificial hip joint has a concave spherical surface of a predetermined thickness made of an elastic polymer material such as polyethylene between the surface of the spherical head 1 and the inner surface of the concave spherical seat 2. An artificial acetabular lid (hereinafter referred to as an elastic acetabular cup) 3 is interposed, and the entire surface of the spherical head 1 and the inner surface of the elastic acetabular cup 3 are slid to form a spherical surface. The stem 4 below the spherical bone head 1 is fixed to the femur, and the concave spherical seat 2 is fixed to the pelvis side. For this reason, when a load is applied by walking, most of the deformation occurs in the elastic acetabular cup 3 on the concave spherical seat 2 side, leading to the abrasion thereof, thus causing the above-described problem.
[0006]
Observation of the elastic acetabular cup 3 inside the concave spherical seat 2 removed from the body clearly shows a difference in the form of wear according to the difference in the contact pressure. There has not yet been reported a general formula for determining the contact pressure when a load is applied by inserting the spherical bone head 1 made of metal or ceramics into the elastic acetabular cup 3 having a concave true spherical surface. However, as shown in the pressure distribution curve CL of FIG. 7, it can be easily imagined that the contact pressure PC is maximum at the point P where the force vector intersects the true spherical surface 1F, and the contact pressure decreases as the distance from both ends increases. Even if there is synovial fluid in the gap between the elastic acetabular cup 3 and the spherical bone head 1, most of the synovial fluid has a contact pressure before the inner surface of the elastic acetabular cup 3 and the surface of the spherical bone head 1 contact each other. If squeezing out to low surroundings and performing relative sliding motion by walking in that state, the lubrication environment becomes more and more severe, causing problems of wear and frictional heat.
[0007]
[Problems to be solved by the invention]
The problem to be solved by the present invention is to suppress a local increase in the contact pressure between the spherical bone head 1 and the elastic acetabular cup 3 when a load due to walking is applied to the artificial hip joint, and to reduce the contact pressure between the contact surfaces. The purpose of the present invention is to effectively use the lubricating fluid by retaining the synovial fluid.
[0008]
[Means for Solving the Problems]
The present invention solves the above-mentioned problems, and the feature thereof is that a stem having a spherical head at the upper end is fitted into and fixed to the femur, and a concave spherical seat in which an elastic acetabular cup is disposed on the inner surface is provided. Side, and the spherical bone head is rotatably inserted and received through an elastic acetabular cup in a concave spherical seat, and the elastic acetabular surface in the spherical spherical head surface and the concave spherical seat is provided. The maximum contact pressure that occurs when the spherical surface of the spherical head is in contact with the elastic acetabular cup during rotation of the spherical head during walking when the entire surface of the sliding sliding area with the inner surface of the cup is made spherical. The artificial hip joint is characterized in that the trajectory portion and the portion of the true sphere surface zone along the periphery thereof are processed into a spherical surface slightly lower to the center of the sphere in a band shape than the sphere surface.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
That is, in the artificial hip joint of the present invention, as shown in FIG. 7, the entire surface of the rotational sliding area between the surface of the spherical head 1 and the inner surface of the elastic acetabular cup 3 in the concave spherical seat 2 has a true spherical shape 1F. In this case, the maximum contact pressure PC locus portion P generated when the spherical surface of the spherical head 1 comes into contact with the elastic acetabular cup 3 and the true spherical surface zone 1FZ along the periphery thereof are shown in FIG. The contact pressure distribution around the band-shaped portion 30 is reduced by forming the band-shaped portion 30, and the contact pressure distribution around the band-shaped portion 30 is made equal to or higher than the contact pressure inside the band-shaped portion 30 as shown by a contact pressure distribution curve CL2 in FIG. It is.
Thus, during the rotation accompanying walking, the joint fluid is trapped inside the band-shaped portion 30 together with the sliding motion, so that it is difficult for the joint fluid to escape outside the band-shaped portion 30, and the flow of the joint fluid, that is, the lubricating fluid, is smoothly performed. By maintaining and maintaining the spherical bone head 20 and the concave spherical elastic acetabular cup 10 in the insertion receiving portion, the elastic acetabular cup 10 is advantageously reduced in friction and wear, thereby preventing heat generation and breakage. Thus, loosening prevention can be stably maintained over a long period of time.
[0010]
The point of focusing on the possibility that the contact pressure state during walking and the lubrication condition can be simultaneously improved only by forming the band-shaped portion 30 on the spherical head 20 side is original and novel. There has been no research or invention focusing on this point, both in Japan and overseas. It has already been clarified that the friction coefficient changes because the lubrication condition changes when the contact pressure distribution changes, in a basic experiment in which a metal plate is rubbed with polyethylene. The novelty and superiority of the present invention reside in that the basic principle of design engineering is applied to an artificial hip joint prior to mechanics.
[0011]
Thus, the non-spherical surface of the band-shaped portion 30 formed on the spherical head 20 in the present invention is processed into a smooth low surface change portion at the boundary between the spherical head and the true spherical portion, and the band is continuously formed. Of a single radius of curvature spherical (the spherical center may be the same as or not the same as the spherical center of the true spherical portion of the spherical head) or a radius of curvature formed in a convex shape in the longitudinal direction of the spherical portion 30 and / or in a direction perpendicular thereto. The aspherical surface is a composite aspherical surface composed of a plurality of different spherical portions and / or curved surfaces, or an aspherical surface with a continuously increased or decreased radius of curvature.
The material of the spherical head 20 and the concave spherical seat 50 is metal or ceramics, and the elastic acetabular cup 10 is made of the above-described polyethylene having functions such as cushioning, abrasion resistance, low friction, and pressure resistance. A known elastic polymer material having liquid permeability and liquid-trapping properties in addition to the above functions may be used.
[0012]
DESCRIPTION OF THE PREFERRED EMBODIMENTS
One embodiment of the present invention is shown in FIGS.
In FIG. 1 to FIG. 5, the spherical head 20 of the artificial hip joint is formed by processing a true spherical surface 40 made of metal and having a radius of curvature: 13 mm in the rotation direction of the head 20 and applying a load to the elastic acetabular cup 10. FIG. 4 highlights that a band-shaped gap of at most 0.01 mm was formed without the gap. FIG. 5 highlights the manner in which the gap between the acetabular cup 10 and the machined head 20 in a direction perpendicular to the rotation direction changes when there is no load. The concave spherical seat 50 is made of metal having a thickness of 3 mm and forms a concave true sphere inner surface having a radius of curvature of 23 mm. The elastic acetabular cup 10 is made of polyethylene having a thickness of 10 mm and a true concave inner surface having a radius of curvature of 13 mm. Is formed.
[0013]
2 and 3 are enlarged views of a main part of the artificial hip joint of the present embodiment, that is, a part in which the spherical bone head 20 is rotatably inserted and received via the elastic acetabular cup 10. FIG. In the figure, the elastic acetabular cup 10 is made translucent so that the band-shaped part 30 on the surface of the spherical head 20 can be easily imaged, and the band-shaped part 30 is drawn at the center of the elastic acetabular cup 10. I have. Since the actual artificial hip joint is mounted in an inclined state as shown in FIG. 6, the band-shaped portion 30 is not always located at the center of the elastic acetabular cup 10, but the elastic acetabular cup 10 has a concave inner surface. Since it is a spherical surface, it is geometrically the same no matter where the band-shaped portion 30 is located.
From the state where the entire surface of the rotation sliding area where the spherical bone head 20 comes into contact with the elastic acetabular cup 10 installed in the concave spherical seat 50 is a true spherical surface 40, the spherical bone head 20 is walked on the spherical bone head 20. The band-shaped portion 30 is formed between the elastic cup cap 10 and the region where the load becomes the largest and the periphery thereof is lowered by a maximum of 0.01 mm from the spherical surface 40 to the spherical center side.
As a result, as shown in the pressure distribution curve CL2 also shown in FIG. 1, the local load due to walking is reduced, while the reduced contact surface pressure around the band-shaped portion 30 is increased. This acts to confine the synovial fluid and increase lubricity.
[0014]
FIG. 3 is a view as seen from below the elastic acetabular cup 10. 2 and 3, the band 30 is extremely drawn to make it easier to understand the processing state, but in this example, the band-shaped portion 30 has a complex spherical shape as shown in FIGS.
That is, as shown in FIG. 4, the spherical shape of the band-shaped portion 30 formed along the rotation direction 100 of the spherical bone head 20 due to walking is more spherical than the true spherical surface 40 along the sliding direction 100 of the spherical bone head 20. Lower by up to 0.01 mm on the side. Since the sphere surface is lower on the spherical center side than the true spherical surface 40, the band-shaped processed portion 30 between the head 20 and the elastic acetabular cup 10 disposed in the concave spherical seat 50 in the unloaded state has a joint. The liquid is easily retained. Further, by extending the front end portion 30f of the band-shaped portion 30 to the outside of the elastic acetabular cup 10 along the sliding direction 100, the synovial fluid is easily introduced together with the rotation of the spherical bone head 20. As the load is increased, the elastic acetabular cup 10 is elastically deformed, and the slight gap tends to be further reduced. However, the joint fluid trapped inside generates pressure, so that the spherical bone head 20 and the elastic acetabular cup 10 are deformed. Prevents abrasion from direct contact. The rear end portion 30b of the band-shaped processing portion 30 smoothly changes to a true spherical surface, thereby preventing the synovial fluid from flowing out of the load area.
[0015]
As shown in FIG. 5, the spherical shape in the direction 111 perpendicular to the sliding direction 100 is smoothly changed from the center of the band-shaped portion 30 lower than the true spherical surface 40 and connected to the true spherical surface 40 again. When is small, the gap between the spherical bone head 20 and the elastic acetabular cup 10 is formed to hold the synovial fluid, and at the same time, when the load increases, the contact pressure on the side of the band-shaped processing part 30 increases, so that the Serves to prevent side leakage.
Thereby, as shown by the pressure distribution curve CL2 in FIG. 1, the contact pressure in the band-shaped portion 30 is reduced together with the sliding motion during the rotation of the spherical bone head 20 during walking, and the periphery of the band-shaped portion 30 is reduced. The contact pressure distribution is formed such that the contact pressure is equal to or higher than the contact pressure inside the band-shaped portion 30, so that the synovial fluid trapped in the band-shaped portion 30 is hard to escape from the band-shaped portion, and The liquid is intended to function effectively as a lubricating liquid.
[0016]
【The invention's effect】
As is clear from the above description, the artificial hip joint of the present invention has a maximum contact pressure at the center of the contact portion which is generated when the entire surface of the rotational sliding area between the spherical head and the elastic acetabular cup is made a true spherical surface. By reducing the band by the band-like portion, and forming a contact pressure distribution such that the peripheral contact pressure except for the front end of the band-like portion is equal to or higher than the contact pressure in the band-like portion. During rotation associated with walking, pressure is generated in the synovial fluid trapped in the band together with the sliding motion, thereby eliminating local excessive direct contact between the spherical head and the elastic acetabular cup, and the band It is difficult to escape the synovial fluid to the outside, and the flow of the synovial fluid, that is, the lubricating fluid is maintained smoothly, and the friction between the spherical bone head and the resilient acetabular cup in the concave spherical seat is reduced. , To realize low wear, Heat prevention, damage prevention, loosening (loosening) prevention is of letting a long period stably maintained.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a pressure distribution when a load is applied by inserting a spherical head and a processed head in an elastic acetabular cup in a concave spherical seat in the present invention.
FIG. 2 shows an elastic acetabular from a position where a rear end portion 30b of a band-shaped portion 30 can be seen in a state where the spherical bone head 20 which is a main part of the artificial hip joint is inserted into the elastic acetabular cup 10 in one embodiment of the present invention. It is explanatory drawing which made cup 10 translucent and three-dimensionally shown.
3 is an explanatory view showing the elastic acetabular cup 10 translucently and three-dimensionally showing that the front end 30f of the spherical bone head 20 shown in FIG. 2 is outside the elastic acetabular cup 10. FIG.
FIG. 4 is a cross-sectional view showing a curved shape of a central portion of a band-shaped portion 30 formed in a spherical bone head 20 when cut along a sliding direction 100 thereof.
FIG. 5 is a cross-sectional view showing a curved shape of the band-shaped portion 30 formed on the spherical bone head 20 when cut in a direction 111 orthogonal to the sliding direction 100 thereof.
FIG. 6 is an explanatory diagram three-dimensionally showing a conventional artificial hip joint.
FIG. 7 is an explanatory view showing a pressure distribution when a load is applied by inserting a conventional spherical head and a processed head into respective elastic acetabular cups in a concave spherical seat.
[Explanation of symbols]
10: Elastic acetabular cup 20: Spherical bone head 30: Band-shaped portion slightly lower than true spherical surface 40: Spherical surface 50: Concave spherical seat 100: Rotation direction 30f of spherical spherical head 20 when loaded: Band-shaped portion 30 Front end 30b of the sliding direction 100 under load: rear end 111 of the sliding direction 100 of the band-shaped portion 30 under load: a direction orthogonal to the sliding direction 100
