JP4518403B2 - Artificial hip joint - Google Patents

Description

  The present invention relates to an artificial hip joint that is replaced with a hip joint.

  When a hip joint suffers from rheumatism, osteoarthritis, trauma, etc., replacement with an artificial hip joint is performed. This artificial hip joint consists of a shell cup that is a hemispherical concave body inserted into the glenoid fossa of the pelvis and a spherical head formed at the tip of the stem that is inserted into the medullary cavity of the femur. It fits into the shell cup and allows omnidirectional behavior. The movement of the hip joint is complicated with back and forth bending, right and left rotation, and varus / valgus, but it is desired that the range of motion is wide in all of them. However, in the case where the spherical head is fitted to the concave cup, the stem hits the cup at a certain angle in any movement, and the range of motion is limited.

If the range of motion is limited, it will interfere with daily life, and if it is forced to move, there is a risk of dislocation. For this reason, as in Patent Document 1 below, the boundary (neck) between the bone head and the stem is made narrower so that the range of motion can be expanded. However, since such a structure causes a decrease in the strength of the neck, it is necessary to determine the degree of narrowness and shape in balance with the expansion of the movable range. The conventional narrow structure is simply a narrow neck of a cylindrical body, and has not been fully examined in relation to strength and range of motion.
JP-A-7-299087

  The present invention does not reduce the neck diameter, but provides a notch with a small decrease in strength, and sets the degree and shape of the notch as small as possible to suppress the decrease in strength, but the range of motion is omnidirectional. It is made not to narrow down.

Under the above-described problems, the present invention provides a concave body in which a spherical head is formed through a neck at the upper portion of a stem inserted into a femur, and the head is inserted into a glenoid glenoid of the pelvis. in hip fitted rotatably to the shell cup, a neck section, the front - a front cut-away surface extending inwardly, rearwardly - into which cut out a cylinder with a rear notch surface extending outwardly In addition, the angle of the notch is such that the angle between the vertical line dropped from the center of the neck to the front notch surface and the front-rear direction line is 35 to 42 °, The artificial hip joint is characterized in that the angle is 19 to 27 ° .

  According to the first aspect of the present invention, it is possible to avoid the required range of motion required for the hip joint from being narrowed compared to the conventional neck simply reduced in diameter, and to reduce the size of the excision and suppress the decrease in strength. It is done.

  Hereinafter, the best mode for carrying out the present invention will be described. FIG. 1 is a partially sectional side view showing an artificial hip joint, FIG. 2 is a partially sectional side view of each element, and FIG. 3 is a side view of a state where the hip joint is replaced. 1 and the pelvis side member 2, and the femoral side member 1 includes a stem 4 inserted into the femur 3 and a bone head 5 attached to the upper end of the stem 4. On the other hand, the pelvic side member 2 includes a shell cup 7 that is inserted into the glenoid cavity 6 of the pelvis and a shell liner 8 that is housed in the shell cup 7.

  The femoral side member 1 including the stem 4 and the head 5 is made of a medical metal such as chromium molybdenum alloy, titanium alloy or ceramics or ceramics, and the stem 4 is connected to the proximal end of the medullary cavity of the femur 3. Insert until the flange 9 formed in the middle hits the bone end surface. In this case, the stem 4 has an elliptical cross section that is long to the left and right so that the fixation in the medullary cavity is strengthened, and has a large contact area. And along the medullary cavity. In addition, there is a type in which a bone or bone formed by forming a mesh or a porous surface is inserted into the surface to enhance the fixing force.

  The upper end side of the flange 9 is formed in a narrow neck 10, and the head 5 is attached to the upper end of the neck 10. In this case, the axis of the neck 10 is inclined at an angle α with respect to the axis of the stem 4 (this is called the neck angle). In addition, in this example, the head 10 is attached to the neck 10 by forming a tapered insertion portion 10 a at the tip of the neck 10, and this insertion portion 10 a is inserted into the tapered insertion hole 5 a formed in the bone head 5. Stopped by driving or press-fitting. The insertion portion 10a and the head 5 may be attached by screwing or screwing.

  By adopting the above configuration, the center plane of the stem 4 (the plane passing through the center of the stem 4 in parallel with the bending direction) can be freely twisted with respect to the bone head 5, and the surgeon can The torsion angle is determined according to the bone condition. The artificial hip joint according to the present invention is designed so that the torsion angle is forward-twisted about 20 ° forward and is most effective when loaded at this angle.

  The shell cup 7 that is the pelvic side member 2 is a concave body having a hemispherical shape, and is also made of a medical metal such as a chromium molybdenum alloy, a titanium alloy, or ceramics or ceramics, and is loaded into the glenoid 6 of the pelvis. (At this time, the glenoid 5 is shaped with a cup reamer or the like so as to match the shape of the shell cup 7). Since the shell cup 7 also needs to be fixed in the glenoid 5, in this example, several holes 11 are made in the shell and screwed into the glenoid 6 through the screw 12 from the inside. In addition, although the number and arrangement | positioning of the hole 11 are not specifically limited, A number is 5-10 pieces and arrangement | positioning is preferable to arrange | position equally or unequally in the middle of a center and a diameter. Further, the fixing method is not limited to the above method, and in order to strengthen the fixing, a mesh or a porous material may be formed on the surface as described above.

  A shell liner 8 is provided in the shell cup 7. The shell liner 8 is also a hemispherical concave body similar to the shell cup 7, and is made of a medical resin such as ultrahigh molecular weight polyethylene that has a good compatibility with metals and ceramics, and is fitted into the shell cup 7. It is. The shell liner 8 also needs to be fixed to the shell cup 7. In this example, the flange 8b in which a hole or notch 8a is formed on the end surface of the shell liner 8 is formed, and an extension of the hole or notch 8a is formed. The shell cup 7 is provided with a screw hole 7a, and the screw 13 is screwed into the screw hole 7a from the hole or notch 8a to be stopped. However, this is also an example, and the same is not limited thereto. By the way, the above is a set in which the shell cup 7 and the shell liner 8 are set, but there is also a case in which only the shell liner 8 is configured.

  A spherical hole 14 is formed in the center of the shell liner 8 so as to open to the end face, and the bone head 5 is fitted therein. The depth of the spherical hole 14 is set to be the same as or slightly larger than the radius of the bone head 5. When the femoral member 1 and the pelvis side member 2 are loaded into the femur 3 and the glenoid 6 respectively, and then the head 5 is inserted into the spherical hole 14, the spherical hole 14 has a volume slightly larger than that of the bone head 5. It is supported so that it can rotate. It should be noted that the neck 10 side of the bone head 5 is left so that the spherical portion can be seen from the end face of the shell cup 8 to some extent, and spherical contact is achieved when the bone head 5 rotates through the spherical hole 14.

  When the above artificial hip joint functions as a hip joint, the movement of the head 5 with respect to the shell liner 8 extends in all directions by leg back-and-forth bending, inversion and inversion, and inward and outward rotation. For this reason, when the rotation angle exceeds a certain angle, the neck 10 interferes with the shell liner 8 (or the shell cup 7) and cannot be rotated any further. If this angle is small, the daily life is hindered. Sometimes. Therefore, the neck 10 is made thinner and the range of motion is expanded. However, if the neck 10 is made thinner, the strength is lowered and there is a risk of breakage as described above. In the present invention, the diameter, that is, the neck 10 is effectively removed, and the range of motion can be expanded while suppressing the strength reduction.

  Even in the present invention, the front and rear surfaces of the neck 10 of the cylindrical body are partially cut out to make the diameter narrower, but differ in that the direction and depth of the cutout surface are taken into consideration. FIG. 4 is a cross-sectional view of the neck 10 showing the notch for the right hip joint when bent 100 ° according to the present invention (125 ° when the neck angle is (A), 130 ° when (B) is ( C) is set to 135 °), and the neck 10 portion is formed by cutting the oblique front and back surfaces of a cylinder (circular in section) with a front notch surface 15 and a rear notch surface 16.

According to the present invention, the front notch surface 15 in a certain cross section is a line extending in the front-inner direction, and the rear notch surface 16 is a line extending in the rear-outer direction. However, it is a feature that the remaining areas (remaining ratios) cut out in the respective directions and these lines are set to specific ranges. Now, it is assumed that the direction and the remaining rate are expressed by angles β and γ from the front and rear lines of the perpendicular lines L ₁ and L ₂ drawn from the center O to the front notch surface 15 and the rear notch surface 16 and a radius ratio R.

  According to this, when a neck with a notch from a cylinder with a radius of 6 mm is adopted, when the neck angle is 125 °, β≈35.0 ° in the inner direction, R≈74.3%, and γ≈ The outer direction is 26.5 °, and R≈49.2%. For 130 °, β≈37.5 ° in the inner direction and R≈64.9%, γ≈24.0 ° in the outer direction, and R≈55.9%. Further, in the case of 135 °, β≈39.5 ° in the inner direction and R≈55.2%, γ≈22.0 ° in the outer direction, and R≈62.9%. In addition, in the case of 140 °, β≈41.5 ° in the inner direction and R≈44.6%, γ≈19.5 ° in the outer direction, and R≈67.6%. FIG. 5 is a cross-sectional view of the neck 10 showing a notch situation when the cervical body angle is 130 ° and bent 100 °. In this case, the front notch surface 15 is a notch surface that enables a forward bending angle of 100 °, and the rear notch surface 16 is a notch surface that enables backward bending / external rotation that can be taken in daily life.

  Of course, it is easy to think that some errors are allowed in these values. In that sense, it is assumed that the allowable error is about ± 5% for both the direction and the afterimage ratio. Yes. As can be understood from the above, the front notch surface 15 is suitable for an angle of about 35 to 42 ° in the front-inside direction, and the rear notch surface 16 is about 19 to 27 ° in the rear-outside direction. The angle is appropriate. Further, the remaining ratio is in a range of about 44 to 75% when the front cut surface 15 is used, and about 49 to 68% when the rear cut surface 16 is used.

  Examining the movement of the hip joints in daily life, it was found that the movement of bending forward, which is a squatting action, requires the largest bending angle. Further, it has been found that the angle of the movement of bending backward and outward due to backward bending is required to be larger than that of the conventional product. On the other hand, it has also been found that a large angle is not required for the movement caused by the backward bending other than the backward-outward direction. In the present invention, the front notch surface 15 and the rear notch surface 16 described above are set on the basis of such facts, so that the excision area can be made as small as possible while securing the necessary movable range, and the strength is reduced. Was able to be suppressed.

  Now, a notch is made with a cervical angle of 130 °, a sphere with a bone head of 22.225 mm in diameter, and a cylinder with a neck of 6 mm in radius, with an angle β of the front notch of 37.5 ° and an angle γ of the rear notch of 24 °. The maximum forward bending angle was compared using the product (shown in FIG. 5) as the product of the invention and the product with the neck radius of 6 mm (without the notch) as the conventional product.

Invention Maximum bending angle (°) Conventional product Maximum bending angle (°)
Residuality (mm) L1 = 3.9 100.1 | Neck radius 6 87.1
L2 = 3.36 │ Neck radius 5 95.1
│ Neck radius 4.36 100.1
│

  It can be seen from this that, in the case of the invention product, the maximum front bending angle of 100.1 ° could be secured by setting the remaining amount inside the front of the neck to 3.9. In order to secure the angle, the neck radius must be 4.36 mm (the circle of the alternate long and short dash line in FIG. 5). However, in the invention, the cutouts are outside the cutout line extending at an angle β in the forward-inward direction and outside the cutout line extending at the angle γ in the backward-outward direction, and does not cover both cutout lines. Inside, a full circle with a radius of 6 mm remains, and the cross-sectional area of the invention is about 36% larger than the area of the circle with a neck radius of 4.36 mm. Therefore, it can be seen that the product of the invention is much higher in strength.

It is a partial cross section side view which shows the assembly state of the artificial hip joint which concerns on this invention. It is a partial cross section side view for every element of the artificial hip joint which concerns on this invention. It is a side view of the state which replaced the artificial hip joint which concerns on this invention with the hip joint. It is sectional drawing of the neck concerning this invention. It is sectional drawing of the neck concerning this invention.

DESCRIPTION OF SYMBOLS 1 Femoral member 2 Pelvic side member 3 Femur 4 Stem 5 Head 5a Insertion hole 6 Glenoid 7 Shell cup 7a Screw hole 8 Shell liner 8a Notch or hole 8b Flange 9 Flange 10 Neck 10a Insertion part 11 Hole 12 Screw 13 Screw 14 Spherical hole 15 Front notch 16 Back notch

Claims (1)

In a hip prosthesis, a spherical head is formed through the neck at the top of the stem inserted into the femur, and the head is pivotally fitted to a concave shell cup inserted into the glenoid fossa . The cross section is made by notching a cylinder with a front notch surface extending in the forward-inward direction and a rear notch surface extending in the rear-outward direction, and the angle of the notch is lowered from the center of the neck to the front notch surface. An artificial hip joint characterized in that the angle between the vertical line and the front-rear direction line is 35 to 42 °, and the angle between the vertical line dropped from the center of the neck to the rear notch and the front-rear direction line is 19 to 27 ° .