Femoral stem and artificial hip joint system

Abstract

This femoral stem (1) of an artificial hip joint includes a main body (11) to be inserted into a medullary cavity (101) of a femur (100), and a neck section (12) to which a stem head is attached. A recess (14) in which the tip (21) of a stem inserter (2) is stored is provided in the shoulder section (13) of the main body (11). The recess (14) includes a spherical surface section (15) in contact with the tip (21) of the stem inserter (2), and a key groove (16) extending from the spherical surface section (15) to the inner side and regulating the turning of the stem inserter (2).

Description

Technical Field

[0001] The present invention relates to a femoral stem of an artificial hip joint and an artificial hip joint system including the femoral stem and a stem inserter for inserting the femoral stem into the femur.

Background Art

[0002] Conventionally, in order to restore the function of the hip joint whose function has deteriorated due to a disease or an accident, etc., an artificial hip joint replacement surgery for replacing the hip joint with an artificial one has been performed.

[0003] Here, in the artificial hip joint replacement surgery, among the members constituting the artificial hip joint, an artificial femoral stem is inserted into the medullary cavity of the human femur. In order to improve the insertability, in Patent Document 1, a configuration is disclosed in which the inclination in the inner and outer direction of the stem inserter at the time of insertion can be adjusted.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the femoral stem and the artificial hip joint system disclosed in Patent Document 1 have a problem that the contact area between the femoral stem and the stem inserter becomes small because the inner wall portion and the rear wall portion of the concave portion formed in the shoulder portion of the femoral stem have flat regions in order to make the rotation angle of the stem inserter adjustable.

[0006] Therefore, an object of the present invention is to provide a femoral stem and an artificial hip joint system capable of increasing the contact area between the femoral stem and the stem inserter while making the rotation angle of the stem inserter adjustable. [Means for solving the problem]

[0007] A first aspect of the present invention is a femoral stem for an artificial hip joint, The main body is inserted into the medullary cavity of the femur, It has a neck portion to which the stem head is attached, The shoulder portion of the main body has a recess formed therein, in which the tip of the stem inserter is housed. The recess has a spherical portion that contacts the tip of the stem inserter, and a keyway that extends inward from the spherical portion and restricts the rotation of the stem inserter.

[0008] According to the above configuration, the rotation angle of the femoral stem can be adjusted using the keyway, and by providing a spherical portion that contacts the tip of the stem inserter, the contact area between the femoral stem and the stem inserter can be increased, thereby improving the durability of the stem inserter and the ease of inserting the femoral stem.

[0009] The first embodiment preferably further comprises the following configuration:

[0010] (1) The spherical portion is in contact with the tip of the stem inserter with an arcuate surface.

[0011] (2) The keyway extends inward from the inner tip of the spherical portion.

[0012] (3) The length of the keyway in the inward and outward directions is shorter than the diameter of the spherical portion.

[0013] (4) The width of the keyway is shorter than the diameter of the spherical portion.

[0014] According to the above configuration (1), the contact area between the spherical portion and the tip of the stem inserter can be easily increased by bringing the spherical portion and the tip of the stem inserter into contact with each other using an arcuate surface.

[0015] According to the above structure (2), since the key groove extends inward from the inner tip of the spherical surface portion, the recess can be positioned outside the shoulder portion and the recess can be arranged on the central axis of the femoral stem.

[0016] According to the above structure (3), the retention of the stem inserter by the spherical surface portion can be improved.

[0017] According to the above structure (4), the rotation of the stem inserter by the key groove can be easily restricted.

[0018] A second aspect of the present invention is an artificial hip joint system, comprising: the femoral stem of the first aspect, and a stem inserter for inserting the femoral stem into the medullary cavity of the femur. The stem inserter includes a spherical tip portion that contacts the spherical surface portion and a key portion that engages with the key groove.

[0019] According to the above structure, it is possible to provide an artificial hip joint system that can improve the durability of the stem inserter and the insertability of the femoral stem while adjusting the rotation angle of the femoral stem.

[0020] The second aspect preferably further includes the following structure.

[0021] (1) The key portion is formed so as to protrude outward from the tip portion.

[0022] (2) The tip of the key portion has an arc shape in a side view.

[0023] (3) The tip portion of the stem inserter is adapted to contact the spherical surface portion with an arc surface.

[0024] According to the above structure (1), the key portion of the stem inserter can be easily engaged with the key groove of the recess of the femoral stem.

[0025] According to the above structure (2), the inclination in the inner and outer directions of the stem inserter can be easily adjusted.

[0026] According to the above structure (3), by making the spherical surface part and the tip part of the stem inserter contact with each other on an arc surface, the contact area between the spherical surface part and the tip part can be easily increased.

Advantages of the Invention

[0027] In short, according to the present invention, it is possible to provide a femoral stem and an artificial hip joint system that can increase the contact area between the femoral stem and the stem inserter while enabling adjustment of the rotation angle of the stem inserter.

Brief Description of the Drawings

[0028] [Figure 1] It is a schematic view seen from the front side of the artificial hip joint system according to an embodiment of the present invention. [Figure 2] It is a partially enlarged view of FIG. 1. [Figure 3] It is a schematic view of FIG. 1 seen from the III direction. [Figure 4] It is a partially enlarged view of FIG. 3. [Figure 5] It is a perspective view of the shoulder. [Figure 6] It is a top view of the shoulder. [Figure 7] It is a side view of the shoulder. [Figure 8] It is a partial perspective view of the stem inserter. [Figure 9] It is a partial side view of the stem inserter. [Figure 10] It is an X arrow view of the stem inserter in FIG. 9. [Figure 11] It is a perspective view showing engagement of the stem inserter with the femoral stem. [Figure 12] It is a perspective view showing adjustment of the inclination in the inner and outer directions of the stem inserter after engaging the stem inserter with the femoral stem. [Modes for carrying out the invention]

[0029] Figure 1 is a schematic diagram of the artificial hip joint system 10 according to an embodiment of the present invention, viewed from the front, and Figure 2 is a partially enlarged view of Figure 1. Furthermore, Figure 3 is a schematic diagram of Figure 1 viewed from direction III (outside), and Figure 4 is a partially enlarged view of Figure 3. In this document, Figures 1 to 4 show the artificial hip joint system 10 applied to the left leg, but the artificial hip joint system 10 of the present invention can also be applied to the right leg.

[0030] For the sake of explanation, when the artificial hip joint system 10 is attached to a human body, the side closer to the head of the human body compared to a comparison object will be referred to as the proximal side, and the side further from the head of the human body compared to the comparison object will be referred to as the distal side. Also, when the artificial hip joint system 10 is attached to a human body, the side closer to the midline of the human body compared to a comparison object will be referred to as the medial side, and the side further from the midline of the human body compared to the comparison object will be referred to as the lateral side. Furthermore, when the artificial hip joint system 10 is attached to a human body, the direction the human body's face is facing will be referred to as the anterior side, and the direction the human body's back is facing will be referred to as the posterior side.

[0031] As shown in Figures 1 to 4, the artificial hip joint system 10 comprises a femoral stem 1 and a stem inserter 2 for inserting the femoral stem 1 into the medullary cavity 101 of the femur 100.

[0032] The femoral stem 1 has a main body portion 11 that is inserted into the medullary cavity 101 of the femur 100, and a neck portion 12 that is attached to the acetabulum via a stem head and acetabular component. The femoral stem 1 has a curved, roughly rod-like shape, and the length of the femoral stem 1 from the shoulder portion to the distal end on the central axis of the stem is, for example, 90 to 200 mm.

[0033] The base material of the femoral stem 1 is made of titanium alloy, pure titanium, cobalt-chromium alloy, stainless steel, etc., and the surface that comes into contact with the medullary cavity 101 is coated with pure titanium, titanium alloy, hydroxyapatite, calcium hydrogen phosphate, etc.

[0034] In a frontal view, the proximal portion 11a of the main body 11 has an inner surface that is longer than the outer surface. The distal portion 11b of the main body 11 has an outer surface that is approximately equal to the inner surface. Here, the central axis S1 of the femoral stem 1 is defined in a frontal view by the angle bisector of the angle between the inner and outer surfaces of the distal portion 11b.

[0035] The proximal portion 11a has shoulder portions 13 on its proximal end and outer side. Figure 5 is a perspective view of the shoulder portion 13, Figure 6 is a top view of the shoulder portion 13, and Figure 7 is a side view of the shoulder portion 13. As shown in Figures 5 to 7, the shoulder portion 13 has a recess 14 formed therein that accommodates the tip portion 21 of the stem inserter 2.

[0036] The recess 14 has a spherical portion 15 that contacts the tip 21 of the stem inserter 2, and a keyway 16 that extends inward from the inner tip of the spherical portion 15 and restricts the rotation of the stem inserter 2. A portion of the recess 14 is positioned on the stem central axis S1.

[0037] The recess 14 has a screw hole 14a at its distal end. The screw hole 14a allows for screw fixation with a screw portion located at the tip of a stem extractor when the femoral stem 1 is to be removed for any reason after it has been inserted into the medullary cavity 101.

[0038] The keyway 16 has an arc shape when viewed from the side, and the length L1 in the inner-outer direction and the width W1 (length in the front-rear direction) of the keyway 16 are shorter than the diameter R1 of the spherical portion 15.

[0039] The width W1 of the keyway 16 is approximately 1.0 mm to 6.0 mm, preferably approximately 2.0 mm to 5.0 mm.

[0040] The effective depth D1 of the keyway 16 (the distance from the center O1 of the tip portion 21 to the bottom surface of the keyway 16) is approximately 5.0 mm to 10.0 mm, preferably approximately 5.5 mm to 8.5 mm, when the radius of the tip portion 21 is 4.5 mm.

[0041] The effective depth D2 of the keyway 16 (distance from the spherical portion 15 to the bottom surface of the keyway 16) is approximately 0.5 mm to 5.5 mm, preferably approximately 1.0 mm to 4.0 mm, when the radius of the tip portion 21 is 4.5 mm.

[0042] Figure 8 is a partial perspective view of the stem inserter 2, Figure 9 is a partial side view of the stem inserter 2, and Figure 10 is a view of the stem inserter 2 in Figure 9 from the direction of arrow X. Figure 11 is a perspective view showing the engagement of the stem inserter 2 with the femoral stem 1, and Figure 12 is a perspective view showing the adjustment of the inward and outward inclination of the stem inserter 2 after it has been engaged with the femoral stem 1. As shown in Figures 8 to 12, the stem inserter 2 comprises a spherical tip portion 21 that contacts the spherical portion 15 and a key portion 22 that engages with the keyway 16. At least a portion of the tip portion 21 is housed in the spherical portion 15 and has a shape corresponding to the spherical portion 15. At least a portion of the key portion 22 is housed in the keyway 16 and has a shape corresponding to the keyway 16. The tip portion 21 and the key portion 22 are integrally molded and made of a material such as stainless steel that can withstand sterilization processes for surgical instruments, such as high-pressure steam sterilization.

[0043] The key portion 22 is formed to protrude outward from the tip portion 21 inward. The key portion 22 extends over substantially the entire vertical length of the tip portion 21, and the vertical length 22L of the key portion 22 is slightly shorter than the vertical length of the tip portion 21. More specifically, the lower end 22D of the key portion 22 is located above the lower end of the tip portion 21.

[0044] The key portion 22 has a roughly rectangular shape when viewed from above, and its tip has an arc shape when viewed from the side. The upper end 22U of the tip of the key portion 22 is located inward compared to the lower end 22D of the tip.

[0045] In particular, as shown in Figures 11 and 12, the tip portion 21 of the stem inserter 2 is in contact with the spherical portion 15 at an arcuate surface 15a. The arcuate surface 15a is the upper edge surface of the spherical portion 15 and has a roughly C-shape because its inner side is cut out by the keyway 16.

[0046] Therefore, when the tip portion 21 and key portion 22 of the stem inserter 2 are housed in the recess 14, the stem inserter 2 can be tilted in the directions of arrows A1 and A2 around the tip center O1. As a result, when inserting the femoral stem 1 into the femur, the stem inserter 2 can be freely tilted in the directions of arrows A1 and A2 around the tip center O1, making it possible to insert the femoral stem 1 from various angles. Here, the tilt angle θ of the stem inserter 2 is the angle between the rotation axis O2 of the stem inserter 2 and the reference line S2. The reference line S2 is a line that passes through the tip center O1 and is parallel to the stem central axis S1.

[0047] If we define the inclination angle θ of the stem inserter as positive for angles outside the reference line S2 and negative for angles inside the reference line S2, then in this embodiment, the inclination angle θ of the stem inserter 2 will be in the range of a maximum of +49 degrees to -66 degrees.

[0048] Furthermore, even if the insertion angle changes while inserting the femoral stem 1, the insertion angle can be controlled by tilting the stem inserter 2, allowing the femoral stem 1 to be inserted while maintaining control of the insertion angle.

[0049] Furthermore, since the key portion 22 engages with the keyway 16, when the stem inserter 2 is rotated around the inserter's rotation axis in the directions of arrows B1 and B2, the rotation of the key portion 22 relative to the keyway 16 is restricted. Therefore, the femoral stem 1 can be rotated in the directions of arrows b1 and b2. As a result, the femoral stem 1 can be inserted while adjusting the rotation angle of the femoral stem 1. Note that the key portion 22 contacts the keyway 16 when the stem inserter 2 is rotated, but the key portion 22 is shaped so that it does not contact the bottom surface of the keyway 16.

[0050] The artificial hip joint system 10 with the above configuration can provide the following effects.

[0051] (1) By providing a keyway 16 in the recess 14 of the femoral stem 1, the rotation angle of the femoral stem 1 can be adjusted using the keyway 16. By providing a spherical portion 15 that contacts the tip 21 of the stem inserter 2, the contact area between the femoral stem 1 and the stem inserter 2 can be increased, thereby improving the durability of the stem inserter 2 and the ease of inserting the femoral stem 1.

[0052] (2) The spherical portion 15 of the femoral stem 1 is in contact with the tip portion 21 of the stem inserter 2 at the arcuate surface 15a, so the contact area between the spherical portion 15 and the tip portion 21 can be easily increased.

[0053] (3) Since the keyway 16 extends inward from the inner tip of the spherical portion 15, the recess 14 can be positioned on the stem central axis S1. As a result, the force applied when inserting the femoral stem 1 can be more easily applied to the femoral stem 1.

[0054] (4) Since the keyway 16 is formed only at the inner tip of the spherical portion 15, a portion of the recess 14 is located on the stem central axis S1. As a result, the force applied when inserting the femoral stem 1 can be easily applied to the femoral stem 1.

[0055] (5) Since the length of the keyway 16 in the inward and outward directions is shorter than the diameter of the spherical portion 15, the retention of the stem inserter 2 by the spherical portion 15 can be improved.

[0056] (6) Since the width of the keyway 16 is shorter than the diameter of the spherical portion 15, the rotation of the stem inserter 2 can be easily restricted by the keyway 16.

[0057] (7) The artificial hip joint system 10 comprises a femoral stem 1 and a stem inserter 2 for inserting the femoral stem 1 into the medullary cavity 101 of the femur 100. The stem inserter 2 has a spherical tip portion 21 that contacts the spherical portion 15 of the femoral stem 1 and a key portion 22 that engages with the keyway 16 of the femoral stem 1. This allows for adjustment of the rotation angle of the femoral stem 1 while improving the durability of the stem inserter 2.

[0058] (8) The key portion 22 of the stem inserter 2 is formed to protrude outward from the tip, so that the key portion 22 of the stem inserter 2 can be easily engaged with the key groove 16 of the recess 14 of the femoral stem 1.

[0059] (9) The tip of the key portion 22 has an arc shape when viewed from the side, so that the inclination of the stem inserter 2 in the inward and outward directions can be easily adjusted.

[0060] (10) Since the key portion 22 engages with the keyway 16, when the stem inserter 2 is rotated in the directions of arrows B1 and B2 around the inserter rotation axis, the rotation of the key portion 22 relative to the keyway 16 is restricted. Therefore, the femoral stem 1 can be rotated in the directions of arrows b1 and b2. As a result, the femoral stem 1 can be inserted while adjusting the rotation angle of the femoral stem 1.

[0061] (11) The tip portion 21 of the stem inserter 2 is in contact with the spherical portion 15 of the femoral stem 1 at an arcuate surface 15a, so the contact area between the spherical portion 15 and the tip portion 21 can be easily increased.

[0062] (12) Since the keyway 16 has an arc shape when viewed from the side, the inclination angle of the stem inserter 2 can be increased.

[0063] (13) The width W1 (length in the front-to-back direction) of the keyway 16 is specified to be within a predetermined range of approximately 1.0 mm to 6.0 mm, thereby improving the durability of the key portion 22 of the stem inserter 2 and the main body portion 11 of the femoral stem 1. However, if the width W1 of the keyway 16 is too small, the key portion 22 of the stem inserter 2 will become thinner, raising concerns about a decrease in the durability of the key portion 22. Also, if the width W1 of the keyway 16 is too large, the cutout of the keyway 16 will become larger, raising concerns about a decrease in the durability of the main body portion 11.

[0064] (14) The effective depth D1 of the keyway 16 (distance from the center O1 of the tip portion 21 to the bottom surface of the keyway 16) is specified to be approximately 5.0 mm to 10.0 mm when the radius of the tip portion 21 is 4.5 mm, thereby ensuring the rotational capability of the femoral stem 1 by the stem inserter 2 and improving the durability of the main body portion 11 of the femoral stem 1. However, if the effective depth D1 of the keyway 16 is too shallow, there is a concern that it will be difficult to rotate the femoral stem 1 by the stem inserter 2. Also, if the effective depth D1 of the keyway 16 is too deep, the carving of the keyway 16 will be larger, which may reduce the durability of the main body portion 11.

[0065] (15) The effective depth D2 of the keyway 16 (distance from the spherical portion 15 to the bottom surface of the keyway 16) is specified to be approximately 0.5 mm to 5.5 mm when the radius of the tip portion 21 is 4.5 mm, thereby ensuring the rotational ability of the femoral stem 1 by the stem inserter 2 and improving the durability of the main body portion 11. However, if the effective depth D2 of the keyway 16 is too shallow, there is a concern that it will be difficult to rotate the femoral stem 1 by the stem inserter 2. Also, if the effective depth D2 of the keyway 16 is too deep, the carving of the keyway 16 will become larger, which may reduce the durability of the main body portion 11.

[0066] (16) The recess 14 of the femoral stem 1 has a screw hole 14a at its distal end. Therefore, the femoral stem 1 can be removed from the medullary cavity 101 of the femur 100 using a stem extractor having a screw portion at its tip.

[0067] (17) The key portion 22 is shaped so that it does not come into contact with the bottom surface of the keyway 16. Therefore, when inserting the femoral stem 1 by striking the stem inserter 2 with another tool (hammer), etc., it is possible to reduce the load on the key portion 22.

[0068] In the above embodiment, one keyway 16 is formed extending inward from the inner tip of the spherical portion 15, but multiple keyways may be formed. In that case as well, it is preferable that all of the multiple keyways extend inward from the inner edge of the spherical portion 15 in order to bring the recess 14 closer to the stem central axis S1.

[0069] Various modifications and alterations can be made without departing from the spirit and scope of the invention as described in the claims. [Industrial applicability]

[0070] The present invention provides a femoral stem 1 and an artificial hip joint system 10 that allows for adjustment of the rotation angle of the stem inserter 2 while increasing the contact area between the femoral stem 1 and the stem inserter 2, thus having great industrial value. [Explanation of Symbols]

[0071] 1. Femoral stem 11 Main body 12 Neck 11a Proximal part 11b Distal part 13 Shoulder 14 recess 15 Spherical part 16 keyways 2 Stem Inserter 21 Tip section 22 Key section 10. Artificial hip joint systems 100 Femur S1 Stem central axis S2 reference line O1 Center of tip O2 rotation axis

Claims

1. This is a femoral stem for an artificial hip joint. The main body is inserted into the medullary cavity of the femur, It has a neck portion to which the stem head is attached, The shoulder portion of the main body has a recess formed therein, in which the tip of the stem inserter is housed. The femoral stem has a recess having a spherical portion that contacts the tip of the stem inserter, and a keyway that extends inward from the spherical portion and restricts the rotation of the stem inserter.

2. The femoral stem according to claim 1, wherein the spherical portion is configured to contact the tip of the stem inserter with an arcuate surface.

3. The femoral stem according to claim 1, wherein the keyway extends inward from the inner tip of the spherical portion.

4. The femoral stem according to claim 1, wherein the length of the keyway in the inward and outward directions is shorter than the diameter of the spherical portion.

5. The femoral stem according to claim 1, wherein the width of the keyway is shorter than the diameter of the spherical portion.

6. The femoral stem according to claim 1, The device comprises a stem inserter for inserting the aforementioned femoral stem into the medullary cavity of the femur, The artificial hip joint system comprises a stem inserter having a spherical tip that contacts the spherical portion and a key portion that engages with the keyway.

7. The artificial hip joint system according to claim 6, wherein the key portion is formed to protrude outward from the tip portion.

8. The artificial hip joint system according to claim 6, wherein the front end of the key portion has an arc shape when viewed from the side.

9. The artificial hip joint system according to claim 6, wherein the tip of the stem inserter is configured to contact the spherical portion with an arcuate surface.

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