JP2005278876A - Artificial hip joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the movability of an artificial hip joint, particularly a complex movable area, prevent postoperative dislocation from occurring, and reduce activity limitations in Japanese style daily living. <P>SOLUTION: In this artificial hip joint 1 in which one end of a stem 2 is inserted into a medullary cavity of a femur, and the other end is provided with a stem neck 3, a head 4 having a spherical slide surface 6 is fitted to the stem neck 3, and the head 4 is turnably accepted in a recessed part provided to an acetabular cup 5 engaged and fixed with a hip bone acetabulum. An angle formed by the center axis of the stem neck and the center axis of the stem is within the range of 40° to 25°. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an artificial hip joint that replaces a hip joint portion of a human body.

  The hip joint of the human body is rotatably received in the acetabular cap in which the femoral head forms a recess, and the joint capsule, which is a fibrous soft tissue, surrounds the acetabular cap and the femoral head. The joint capsule is attached to the marginal part of the acetabular cap and the head and neck of the femur, and a number of muscles that move the lower limbs are formed around it, thereby obtaining the mobility and support of the hip joint.

  Due to various bone and joint diseases, when the acetabular acetabulum composing the hip joint and the articular cartilage of the femoral head wear out over time, and the surface of the bone tissue composing the joint is subsequently deformed, pain occurs in the hip joint. At the same time, hip joint dysfunction appears, such as a decrease in the range of motion of the hip joint.

 When disease progresses so high that it cannot be resolved by conservative treatment, artificial hip joint replacement is performed as a surgical final treatment, and the joint of the living body can be replaced with the artificial joint to obtain pain relief and mobility.

  The hip prosthesis used for this hip replacement usually has a stem neck at the other end of the stem into which one end is inserted into the femoral bone marrow cavity, and a head having a spherical sliding surface is fitted to the stem neck. In this structure, the head is rotatably received in the spherical concave portion provided in the acetabular cup engaged and fixed to the acetabular cap (Patent Document 1). There are two types of fixation to bone: bone cement and cementless without this.

In a conventional artificial hip joint, the angle formed by the central axis of the stem neck and the central axis of the stem is at least 45 °.
JP-A-11-206794

  By the way, dislocation hardly occurs in the human hip joint. On the other hand, many post-surgical dislocations have been reported in hip replacement, and post-operative dislocation is one of the major complications along with loosening and infection of artificial joints. 5%.

 This is because the range of motion of the artificial hip joint is smaller than that of a normal hip joint. The range of motion of a normal hip joint is 125 ° for flexion, 15 ° for extension, 45 ° for external rotation, 20 ° for internal rotation, 45 ° for external rotation, and 45 ° for internal rotation, but the artificial hip joint has an oscillation angle of 120 °. Is placed on the pelvis and femur under the condition of the outer opening angle of the cup 45 °, the front angle 20 °, and the stem front angle 0 °, the calculated bending angle is 110 °, which is smaller than normal. Only the range of motion can be obtained.

 Since the basic range of motion such as flexion extension, internal rotation external rotation, and adduction abduction becomes small in this way, when a patient with normal range of motion undergoes hip replacement, Depending on the installation conditions, the range of motion may be reduced before surgery. For this reason, operation restriction is unavoidable, and after the operation, people often live with a fear of dislocation. In fact, more than 80% of postoperative dislocations occur in the hyperinternal rotation after hyperflexion.

 In addition, Japanese people are characterized by Japanese-style daily life movements centered on the sitting position, such as sitting, but in such movements, the adduction / inward rotation in the bent position and the abduction / inward movement in the extended position are particularly important. It is necessary to secure a sufficient range of motion such as turning. However, it cannot be said that the conventional artificial hip joint has sufficient performance with respect to mobility.

  In view of these problems of the prior art, the present invention aims to improve the mobility of the hip prosthesis, particularly the combined range of motion, to prevent postoperative dislocation, and to reduce restrictions on Japanese-style daily activities. is there.

  In order to solve such a problem, the artificial hip joint of the present invention is a head provided with a stem neck at the other end of the stem into which one end is inserted into the femoral bone marrow cavity and having a spherical sliding surface on the stem neck. An artificial hip joint that is pivotably received in a recess provided in a acetabular cup that is fixedly engaged with the acetabular acetabular cap, wherein the stem neck has a central axis and a stem center. The angle formed with the shaft is in the range of 25 ° to 40 °.

  If this angle is larger than 40 °, the composite movable range is small. On the other hand, if the angle is smaller than 25 °, the neck is too close to the cup, and the limitation of the inward motion becomes large.

  According to the artificial hip joint stem of the present invention, when the artificial hip joint is subjected to internal / external rotation that rotates around the femoral axis, the range of movement of the stem neck is reduced, and as a result, the range of motion is improved. Can do. The range of movement of the internal and external rotations is a very important angle in preventing dislocation, and dislocation can be prevented by combining the artificial hip joint stem of the present invention with an ordinary cup.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an artificial hip joint according to this embodiment. In the figure, reference numeral 1 denotes an artificial hip joint, 2 denotes a stem, 3 denotes a stem neck, 4 denotes a head, and 5 denotes a acetabular cup (sectional view).

  One end of the stem 2 is inserted into the femoral bone marrow cavity, and the other end, that is, an end located outside the femoral bone marrow cavity and facing the acetabular cap. A stem neck 3 is provided. A head 4 having a spherical sliding surface 6 is fitted to the stem neck 3. And this head 4 is rotatably received by the acetabular cup 5 installed in an acetabular acetabulum.

  The stem portion 2 is a portion that is embedded and fixed in the bone marrow cavity of the femur, and includes a base portion and a distal end portion of the stem neck 3. In order to approximate the shape of the stem outer periphery and the bone marrow cavity, the stem 2 base is thicker than the stem neck 3 and the tip, and the shape is shaped to match the shape of the bone marrow cavity to be implanted. Has been. Further, since the distal end portion of the stem 2 is inserted to the inner part of the bone marrow cavity, it has a tapered shape.

  On the other hand, the stem neck 3 is a member for connecting the head 4 and the stem 2 and has a substantially cylindrical shape. The stem neck 3 is preferably formed continuously and integrally with the stem 2.

  Note that the acetabular cup 5 is usually fixed to the acetabular cap side through a thin metal shell (not shown) that is directly and firmly fixed to the acetabular cap, but directly without using the shell. It may be fixed to the acetabular cap. The head 4 may be formed integrally with the stem 2 and the stem neck 3.

The material of the head 4 is, for example, a material that is not harmful to the living body and desirably a dense ceramic or metal having biocompatibility. For example, alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), silica (SiO ₂ ) and titania (TiO ₂ ) can be mentioned, and these ceramics may contain auxiliary agents such as Ti, Mg, Zr, Hf, and Y as appropriate. Examples of the metal include stainless steel (for example, SUS316, SUS316L), cobalt-chromium alloy, cobalt-chromium-nickel alloy, titanium, titanium alloy (for example, Ti-6% Al-4% V, Ti-49 to 51%). A metal having excellent corrosion resistance such as Ni) can be used.

  The constituent materials of the stem 2 and the stem neck 3 are stainless steel (for example, SUS316, SUS316L), cobalt-chromium alloy, cobalt-chromium-nickel alloy, titanium, titanium alloy (for example, Ti-6% Al-4%). Examples thereof include metals and alloys having excellent corrosion resistance such as V). Among them, shape memory alloys (Ti-49 to 51% Ni) are preferably used. Since this shape memory alloy has excellent followability to repeated loads, resilience, and fatigue characteristics, stability and durability are improved during long-term embedding.

Further, for the time being with the stem 2 or the bone of the acetabular cup 5, a material having excellent affinity with the bone may be coated, and a calcium phosphate compound generally known as such a material is suitable. in, for example tricalcium _{TCP (Ca 3 (PO 4)} 2), tetracalcium phosphate _{(Ca 4 (PO 4) 2} O), octacalcium phosphate _{(Ca 8 H 2 (PO 4} ) 6 · 5H 2 O), calcium monohydrogen phosphate (CaHPO ₄ ), calcium dihydrogen phosphate (Ca (H ₂ PO ₄ ) · H ₂ O), hydroxyapatite HAP (Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ ), zirconia (ZrO ₂ ) can be used.

  The constituent material of the acetabular cup 5 is a polymer material having excellent wear resistance, such as the ceramic material or ultra-high molecular weight polyethylene.

  In the present invention, it is important that an angle α formed by the central axis of the stem neck 3 and the central axis of the stem 2 in the artificial hip joint 1 is 25 ° to 40 °, preferably 30 ° to 35 °. In the present invention, the angle α formed by these central axes is not an obtuse angle but an acute angle.

  As mentioned above, Japanese people are characterized by Japanese-style daily life movements centered on the sitting position, such as sitting, but in such movements, especially in the adduction / inward rotation in the bending position and in the extension position, Although it is necessary to sufficiently secure a composite movable range such as rolling and internal rotation, the configuration of the artificial hip joint 1 can improve the composite movable range.

  That is, for example, the installation conditions of the acetabular cup 5 were 45 ° outward opening angle and 20 ° opening angle, and the installation conditions of the stem 2 were 0 ° twisting angle and 7 ° valgus angle. Further, in a general setting where the oscillation angle, which is an important parameter in the movable range, is 120 °, the outer diameter of the acetabular cup 5 is 50 mm, and the ball is 28 mm, the maximum internal rotation angle is 50 ° or more and the maximum internal rotation angle is 30. It is possible to secure a large range of motion, both above °.

  Thereby, it becomes possible to prevent the occurrence of post-operative dislocation and to reduce the restriction in the Japanese-style daily life operation.

  If this angle is larger than 40 °, the composite movable range is small. On the other hand, if the angle is smaller than 25 °, the neck is too close to the cup, and the limitation of the inward motion becomes large.

  Next, a method for installing the artificial hip joint 1 will be described.

  The hip joint is a joint made up of a ball-like part and a socket-like part into which the ball enters. The ball part of the hip joint is called the femoral head, and the femoral head is fitted into the acetabulum (socket), synovial fluid It works in a state covered with a liquid called. One of the treatment methods when the bone surface or cartilage is damaged in this hip joint and arthritis is performed, and total hip replacement is sometimes performed. Replace with 1.

  In preparation for setting the artificial hip joint 1, the cartilage and bone surface damaged by using a special reamer are removed from the acetabulum while the patient's foot is moved well and the femoral head is dislocated from the acetabulum. The acetabular cup 5 is placed on the hip bone thus shaped by means such as bone cement.

  On the other hand, on the side of the femur, first remove the damaged femoral head using a special electric saw, remove a portion of the cancellous bone from the medullary cavity of the femoral bone, clean the medullary cavity according to the shape of the stem 2 Mold the inner wall.

  The stem 2 is inserted into this medullary cavity. To fix the stem 2, use bone cement or push the implant firmly into the medullary canal. When bone cement is used, the cement is first injected into the medullary cavity, and then the stem 2 is inserted into the medullary cavity. If bone cement is not used, insert it directly into the medullary canal.

  There are a type in which the stem 2 and the head 4 are integrated and a separate type as described above. In the case of different types, the head 4 is usually fitted and attached to the stem neck 3 after the stem 2 is inserted.

  When all the members of the hip prosthesis 1 are in a predetermined position, the head 4 that is a part of the femur is firmly pushed into the acetabular cup 5 fixed to the hipbone, so that the hip prosthesis 1 functions in the best condition. Thus, the ligament surrounding the artificial hip joint 1 is adjusted as necessary.

  In this way, the artificial hip joint 1 is installed.

    In the artificial hip joint 1 shown in FIG. 1, it is assumed that the angles α formed by the central axes are 25 ° to 45 ° (5 ° intervals), respectively, and as shown in FIG. The range of motion was added using 3D CAD.

(Maximum internal rotation angle)
The installation conditions of the acetabular cup 5 were an outward opening angle of 45 ° and a forward opening angle of 20 °, and the installation conditions of the stem 2 were a forward twist angle of 0 ° and a valgus angle of 7 °. The oscillation angle, which is an important parameter in the movable range, was 120 °, the cup outer diameter was 50 mm, and the ball was 28 mm.

  As a result, paying attention to the maximum internal rotation angle at a bend of 60 °, an internal rotation angle of 56 ° when the angle α formed by the central axis is 45 °, 60 ° at 40 °, 66 ° at 35 °, 70 ° at 30 °, It was 78 ° at 25 ° and 91 ° at 20 °.

  This tendency is the same even when the bending angle is changed, and it has been clarified that the degree of freedom of internal rotation at the bending position has a property inversely proportional to the angle α.

  As mentioned above, it has been suggested that the degree of freedom of rotation of the lower limbs is important for daily movements in the Japanese style, including complicated movements and individual differences in movement, as well as the setting of cups and stems in hip replacement. When considering the difficulty, it is desirable to increase the degree of freedom of internal rotation as much as possible. As a result, the occurrence of dislocation after hip replacement can be suppressed.

(Maximum adduction angle)
On the other hand, when the maximum adduction angle is calculated under the same conditions, the addendum angle is 52 ° when the angle α formed by the central axis is 45 °, 47 ° when 40 °, 42 ° when 35 °, 37 ° when 25 °, and 25 °. Is 32 °, and 20 ° is 27 °. Since the addendum angle is required to be about 20 ° in the normal range of motion of the hip joint, the angle α needs to be 20 °, but in order to appropriately design the distance between the important joint center and the femoral axis in an artificial hip joint Requires an angle α of 25 ° or more. In addition, in consideration of variations in the movement of the human body, it is also important to give a constant inversion angle. Therefore, the angle α is preferably 30 ° to 35 °.

  As mentioned above, although embodiment of this invention was illustrated, it cannot be overemphasized that this invention can be set as arbitrary forms, unless it is limited to the said embodiment and does not deviate from the objective of invention.

It is a partially broken front view of the artificial hip joint of this invention embodiment. It is explanatory drawing which shows the action | operation of the artificial hip joint of FIG.

Explanation of symbols

1 .. Hip prosthesis,
2. Stem,
3. Stem neck,
4. Head,
5 .. Acetabular cup,
6. Spherical sliding surface,
α ... An angle formed by the central axis,

Claims (2)

A stem neck is provided at the other end of the stem into which one end is inserted into the femoral bone marrow cavity, and a head having a spherical sliding surface is fitted to the stem neck, and the head is engaged with the acetabular cap. An artificial hip joint that is rotatably received in a recessed portion provided in a fixed acetabular cup, and an angle between a central axis of the stem neck and a central axis of the stem is in a range of 25 ° to 40 °. An artificial hip joint characterized by that. The artificial hip joint according to claim 1, wherein an angle formed by a central axis of the stem neck and a central axis of the stem is in a range of 30 ° to 35 °.

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