JP6604500B2 - Medical implant and method for assembling medical implant - Google Patents

Description

  The present invention relates to a medical implant and a method for assembling a medical implant.

The hip joint is a joint at the base of the leg and is between the trunk and the leg. The hip joint plays a role of supporting weight when a person stands or walks. The hip joint is about 3 times the weight when walking, about 6 to 7 times the weight when standing, and a slightly lower position such as the floor. It is said that it takes 10 times as much weight as the body from the start.
In the hip joint, the spherical portion of the femur (the femoral head) is fitted into the concave portion (acetabulum) forming the spherical seat of the pelvis. The joint part, that is, the surface of the femoral head is covered with cartilage, and absorbs the weight and force applied to the above-mentioned hip joint, and facilitates the movement of the femoral head and the acetabulum.

An intramedullary nail is known as a jig for treating a fracture of a femur that forms a hip joint. The intramedullary nail is, for example, a rod member or a hollow tube member, and is inserted into the lumen from the proximal portion of the femur so as to penetrate the fractured femurs.
For example, Patent Document 1 discloses a proximal portion arranged on the femoral head side, a tapered portion that is continuous with the distal side of the proximal portion and has a smaller diameter toward the distal side, and a distal portion of the tapered portion. An intramedullary nail is disclosed that includes a distal portion connected to the distal side and a through-hole through which a fixing member inserted into the femoral head can pass. In the intramedullary nail described in Patent Document 1, one open end of the through hole opens on the surface including the boundary between the proximal portion and the tapered portion, and the other open end of the through hole opens on the surface of the proximal portion. ing. This configuration solves the problem that the entire intramedullary nail is limited in thickness because the tapered portion can be connected to the proximal portion that is formed thick due to the need to increase the mechanical strength. There is provided an intramedullary nail that is formed thin as a whole without reducing its strength.

On the other hand, typical diseases of the hip joint include hip osteoarthritis, rheumatoid arthritis and the like. For these diseases, hip replacement may be performed when hip pain is not alleviated even after conservative therapy, or when symptoms are considerably advanced. In addition, hip replacement may be performed at the time of fracture of the proximal femur due to falls or the like.
Hip replacement is an operation in which worn cartilage and damaged bone are removed and replaced with a metal or plastic hip joint.

The artificial hip joint includes a metal cup, a head ball, and a member called a stem, and a plastic liner serving as a substitute for cartilage is fitted inside the cup.
For example, Patent Document 2 has a bone tissue intrusion fixing portion in which a plurality of grooves are formed on the surface of a medical implant, and all or part of the bone tissue intrusion fixing portion is other than the bone tissue intrusion fixing portion. A configuration is disclosed that is raised so that it rises higher than the surface of the medical implant.
The medical implant described in Patent Document 1 has a bone tissue intrusion fixing portion in which a plurality of grooves are formed. Therefore, the medical implant has excellent adhesion and fixation with a bone, and all or part of the bone tissue intrusion fixing portion is raised. It has excellent strength.

JP 2011-206420 A JP 2007-296250 A

  In recent years, the number of hip replacements has been increasing, and with the increase of hip replacements, the number of patients who have fractures around the hip prosthesis and the proximal femur has been increasing rapidly. For example, approximately 4% of patients who have undergone hip replacement have been reported to cause periprosthetic fractures (Neumann et al., 2012).

However, in a hip joint to which an artificial hip joint has already been applied, the stem of the artificial hip joint is inserted into the lumen of the proximal part of the femur. Therefore, when a conventional intramedullary nail including the intramedullary nail described in Patent Document 1 is inserted into the lumen of the femur, the intramedullary nail on the proximal side of the femur is moved to the distal end of the substantially sharp stem. It hits the side edge and is not stable. In addition, since the intramedullary nail is manufactured according to the length dimension of the femur, the intramedullary nail at the distal part of the femur is the same as the length dimension in which the stem is inserted into the lumen of the femur. There is a risk of protruding from the distal femur of the lumen.
That is, it is difficult to insert a conventional intramedullary nail into the femoral lumen in a hip joint that has already been subjected to an artificial hip joint. Therefore, conventionally, conservative treatment (conservative therapy) has been performed by fixing the fracture portion around the artificial hip joint with a cast.

However, with conservative therapy using a cast, the treatment is prolonged, the fixed period of the cast applied to the entire leg takes several months, and the patient's distress is long and large. In addition, complications may occur due to prolonged treatment. In addition, rehabilitation after a fixed period of casts was also painful for the patient.
As described above, conventionally, there is no medical implant such as an intramedullary nail that can be applied to a bone that has already been subjected to an artificial hip joint, and there has been a problem that even if conservative therapy is performed, the patient suffers greatly. In the above description, the hip joint is exemplified as one of the joints. However, the above-described problem is a joint that can be replaced with an artificial joint, and may occur similarly in a joint such as a knee joint or an elbow joint.

The inventors have fixed a bone by inserting a medical implant having a function of grasping a distal end portion of a stem of an artificial joint into a bone lumen, and without causing pain to a patient, for a short period of time. Discovered that it would be possible to treat broken bones. In addition, the shape of the stem of the artificial joint is fully taken into account, and the structure that allows the distal end of the stem to be more stably grasped with simple components and various core members to be inserted into the bone lumen is found. The present invention has been completed.
The present invention has been made in order to solve the problem that there is no medical implant such as an intramedullary nail that can be applied to a bone having an artificial hip joint as described above. Provided is a medical implant that can be applied to a formed bone, and a method for assembling the medical implant.

The medical implant of the present invention is a medical implant to be inserted into a bone lumen provided with an artificial joint, the gripping portion gripping the distal end of the stem of the artificial joint in the lumen; A shaft portion coupled to the grip portion and disposed in the lumen from a distal end portion of the stem to a distal end portion of the bone , wherein the grip portion is distal to the stem. A plurality of thin rods which can be arranged with the stem extending direction and the axis line aligned on an outer peripheral side of the side end portion, and a distal end portion of the thin rod at a proximal end portion of the shaft portion; And a connecting portion into which the distal end of the stem can be inserted through the thin rod .

The medical implant of the present invention, the sectional shape of the front KiHosobo may be rectangular.

Further, the method for assembling the medical implant of the present invention is a method for assembling the medical implant, wherein the connecting portion is filled with the axial direction of the thin rods aligned with the extending direction of the shaft, Until the distal end of the stem is locked to the proximal end of the shaft via the thin rod, the distal end of the stem is moved from the proximal side of the plurality of thin rods. Advancing distally to connect the shaft portion to the grip portion, gripping a distal end portion of the stem of the artificial joint by the grip portion, and connecting the stem, the grip portion, and the shaft portion and wherein the Rukoto turn into one body.

In the medical implant of the present invention, the distal end portion of the stem of the artificial joint is stably gripped by the grip portion, and the grip portion is connected to the shaft portion. Therefore, the stem, gripping portion, and shaft portion of the artificial joint can be inserted into the bone lumen consistently and stably, and the shaft portion can be easily prevented from protruding from the lumen.
In the method for assembling the medical implant of the present invention, the distal end portion of the stem of the artificial joint can be gripped by the grip portion, and the distal end portion of the grip portion can be connected to the shaft portion.
Therefore, according to the present invention, there are provided a medical implant that can be applied to bone that has undergone artificial joint replacement, and a method for assembling the medical implant.

It is the schematic of the medical implant which is one Embodiment of this invention. It is a figure which shows the medical implant which is one Embodiment of this invention, and is sectional drawing seen by the arrow AA shown in FIG. It is the schematic for demonstrating the assembly method of the medical implant which is one Embodiment of this invention. It is the schematic for demonstrating the assembly method of the medical implant which is one Embodiment of this invention. It is the schematic of the medical implant which is one Embodiment of this invention penetrated by the lumen | bore of the femur. 2 is a graph showing theoretical values and actual measurement values of pin rigidity in Example 1; In Example 2, it is a graph which shows the measured value of the rigidity of a pin when the protrusion amount of the pin from a rod is 10 mm and 15 mm. It is a figure of the finite element model of the medical implant used in Example 3, Comprising: (a) is sectional drawing corresponding to the case where it sees from the front, (b) is the side surface corresponding to the case when it sees from the outside FIG. It is a figure of the finite element model used in Example 3, Comprising: (a) is a partial enlarged view, (b) is sectional drawing which shows the conditions which apply load. In each model obtained by the finite element analysis of Example 3, it is a figure which shows the stress distribution immediately after an implant, (a) is a partial enlarged view, (b) is the connection part of a stem and a medical implant. It is an enlarged view. In each model obtained by the finite element analysis of Example 3, it is a figure which shows stress distribution at the time of an implant after stable, Comprising: (a) is a partial enlarged view, (b) is a stem and a medical implant. It is an enlarged view of a connection part. In each model obtained by the finite element analysis of Example 3, it is a figure which shows the stress distribution at the time of applying a load of 600N, (a) is a partial enlarged view, (b) is a stem and medical use It is an enlarged view of the connection part of an implant. It is a figure which shows a mode that tension and compression are applied in the cross section of the finite element model corresponding to the case where it sees from the front of the medical implant used in Example 3. FIG. It is a figure which shows distribution of the load pressure of the part corresponded to the area | region Q of FIG. 13, Comprising: (a) is distribution immediately after an implant, (b) And (c) is distribution at the time of stable after an implant. It is a figure which shows the displacement distribution in the finite element model which displayed the displacement magnification | multiplying_factor 10 times, (a) is a figure corresponding to the case of front view, (b) is a figure corresponding to the case of side view. It is a graph which shows the displacement dependence of the resultant force when applying a load to the model of a medical implant.

  Hereinafter, a medical implant which is an embodiment of the present invention and a method for assembling the medical implant will be described with reference to the drawings. The drawings used in the following description are schematic, and the length, width, thickness ratio, and the like are not necessarily the same as actual ones, and can be changed as appropriate.

  FIG. 1 is a schematic view of a medical implant 1 which is an embodiment to which the present invention is applied (hereinafter referred to as this embodiment). FIG. 2 is a view showing the medical implant 1, and is a cross-sectional view taken along the line AA shown in FIG.

[Configuration of Medical Implant of this Embodiment]
The medical implant 1 is a medical implant that is inserted into a lumen S of a femur (bone) provided with an artificial hip joint (artificial joint) 10, and includes at least a gripping portion as shown in FIGS. 1 and 2. 2 and a shaft portion 4.

The artificial hip joint 10 includes a cup, a liner, a bone head ball having a shape that can be spherically fitted to an acetabulum in a pelvis (not shown), and a stem 12 that can be connected to the bone head ball via a neck portion 14. I have. In FIG. 1, the cup, liner, and head ball are omitted.
The acetabulum forms a spherical seat, and the cup, liner, and head ball are fitted in this order along the spherical surface inside the spherical seat. By this spherical fitting, the artificial hip joint 10 can be rotated with respect to the pelvis.

  The stem 12 is a part that is inserted into and fixed to the femoral lumen S in the artificial hip joint 10 (see FIG. 5), and is a member having a predetermined length. As shown in FIG. 1, a neck portion 14 is connected to the proximal end portion (ie, the upper end portion shown in FIG. 1) 12a of the stem 12 in a direction inclined from the extending direction of the stem 12 toward the pelvis. Has been. On the other hand, the width dimension of the distal end portion (ie, the lower end portion shown in FIG. 1) 12b of the stem 12 is made smaller toward the tip. By having such a shape, the stem 12 can be easily inserted into the lumen S of the femur from the distal end 12b.

  The material of the artificial hip joint 10 is not particularly limited, but a metal excellent in biocompatibility is preferable. Examples of such a metal include a titanium alloy (for example, Ti—Al—V alloy, Ti—Ni alloy), single titanium, stainless steel (SUS316, etc.).

The grip portion 2 is a portion that grips the distal end portion 12 b of the stem 12 with the lumen S of the femur.
The grip portion 2 of the present embodiment has a plurality of thin bars 6,. The thin rod 6 can be arranged so that the extending direction of the distal end portion 12b of the stem 12 (that is, the direction of the arrow D1 shown in FIGS. 1 and 2) and the axis J6 are aligned. As shown in FIG. 2, in the grip portion 2, a plurality of thin rods 6 are arranged along the outer peripheral surface of the distal end portion 12 b of the stem 12 in the state where the thin rods 6 are arranged as described above.

  The length dimension of the thin rod 6 is not particularly limited, and is appropriately set in consideration of the length dimension of the stem 12. The cross-sectional shape of the thin rod 6 is not particularly limited, and may be a circle, a rectangle, a triangle, a polygon, or the like illustrated in FIG. The cross-sectional shape of the thin rod 6 is preferably a rectangle, more preferably a square. Thereby, when the thin rod 6 is interposed between the stem 12 and the shaft portion 4 to be described later, the length of the side contacting the stem 12 and the shaft portion 4 becomes larger, and the stability of the thin rod 6 is increased. Will increase. The width dimension of the cross section of the thin rod 6 is not particularly limited, and is appropriately set in consideration of the outer diameter of the stem 12 and the inner diameter of the shaft portion 4.

  The material of the grip portion 2 and the thin rod 6 is not particularly limited, but a metal excellent in biocompatibility is preferable. Examples of such metals include titanium alloys (for example, Ti—Al—V alloys, Ti—Ni alloys), single titanium, stainless steel (SUS316, etc.), as well as suitable metals constituting the artificial hip joint 10. It is done.

The shaft portion 4 is a portion that can be connected to the grip portion 2 and is disposed in the lumen S from the distal end portion 12b of the stem 12 to the distal end portion (not shown) of the femur.
The shaft portion 4 of the present embodiment has a bar member 5 formed with a predetermined length dimension.
The length of the rod member 5 is not particularly limited, but is the length from the distal tip of the stem 12 inserted into the femoral lumen S to the distal end of the femoral lumen S. It is preferable that the length is equal to or smaller than the dimension and is substantially equal to the length dimension. The cross-sectional shape of the bar member 5 is not particularly limited, and may be a circle, a rectangle, a triangle, a polygon, or the like illustrated in FIG. However, the cross-sectional shape of the bar member 5 is preferably a circular shape. Thereby, the rod member 5 can be smoothly inserted into the lumen S of the femur having a substantially circular cross-sectional shape, and the wall surface is hardly damaged when contacting the wall surface of the lumen S. The width dimension of the cross section of the rod member 5 is not particularly limited, and is appropriately set in consideration of the width dimension of the cross section of the lumen S of the femur so as not to hinder the flow of cerebrospinal fluid or the like in the lumen S. ing.

As shown in FIG. 1, a concave portion (connecting portion) 8 that opens to the proximal end surface 5 c is formed in the proximal end portion 5 a of the bar member 5.
The depth dimension of the recess 8 is not particularly limited, but the distal portion from the center in the longitudinal direction of the distal end 12b of the stem 12 and the plurality of thin rods 6,. The depth is larger than the possible depth, and is set appropriately in consideration of the length of the stem 12 and the thin rod 6. The width of the opening of the recess 8 is such that the distal end portion 12b of the stem 12 and a plurality of thin rods 6,... It is set appropriately considering the dimensions.
The recess 8 can receive the distal end 6 b of the thin rod 6 and functions as a connecting portion into which the distal end 12 b of the stem 12 can be inserted via the thin rod 6.
The recess 8 may penetrate the bar member 5 and open to the distal end surface 5d of the bar member 5. That is, the rod member 5 may be a hollow cylindrical body.

[Assembly method of medical implant of this embodiment]
3 and 4 are cross-sectional views for explaining an assembling method of the medical implant 1 of this embodiment.
When assembling the medical implant 1, first, the stem 12 of the artificial hip joint 10 is once taken out from the femur.
Subsequently, the grip portion 2 is connected to the concave portion 8 that is a connection portion of the shaft portion 4. Specifically, as shown in FIG. 3, a plurality of thin rods 6,..., 6 are filled in the concave portion 8 of the proximal end portion 5 a of the rod member 5 so that the axial direction thereof matches the extending direction of the rod member 5. To do.
Subsequently, the distal end portion 12 b of the stem 12 is gripped by the grip portion 2. Specifically, the distal end 12b of the stem 12 is advanced distally from the proximal side of the plurality of thin rods 6,. As shown in FIG. 4, as the distal end 12b of the stem 12 advances, the plurality of thin rods 6,..., 6 are sequentially pushed forward from the center in the width direction of the recess 8 toward the outer periphery. It is done. The distal end 12b of the stem 12 is advanced distally until the distal end 12b of the stem 12 is locked to the side wall surface of the recess 8 via the thin rod 6. At this time, the thin rod 6 not interposed between the distal end 12 b of the stem 12 and the rod member 5 falls to the distal end of the recess 8, and the recess 8 is the distal end surface of the rod member 5. If it opens to 5d, it is taken out from the distal end face 5d.
Through the above operations, the medical implant 1 shown in FIG. 1 is assembled.

Next, the medical implant 1 shown in FIG. 1 is inserted from the distal end 4b of the shaft 4 into the proximal end of the lumen S of the femur and advanced toward the distal side.
FIG. 5 is a cross-sectional view of the medical implant 1 inserted through the lumen S of the femur B. By causing the medical implant 1 to advance toward the distal side, the medical implant 1 is inserted through the entire length of the lumen S as shown in FIG. When the femur B is fractured, the medical implant 1 can be advanced distally while connecting the lumen S between the femurs B1 and B2 that are cracked or broken or separated. That's fine.
Thereafter, the neck portion 14 of the stem 12 is connected to the head bone of the artificial hip joint 10 (not shown). Thereby, installation of the medical implant 1 in the lumen S of the femur B is completed.

[Operational Effects of Medical Implant and Medical Implant Assembly Method of the Present Embodiment]
According to the medical implant 1 of the present embodiment described above, the distal end portion 12b of the stem 12 of the hip prosthesis 10 is stabilized by the stem 12 and the grip portion 2 along the radial direction of the lumen S of the femur. And is gripped. That is, the thin rod 6 is interposed between the outer wall portion of the concave portion 8 of the rod member 5 and the distal end portion 12b of the stem 12 without any gap, and the distal end portion 12b of the stem 12 is locked. Since the posture of the thin rod 6 matches the shape of the outer peripheral surface of the distal end portion 12 b of the stem 12, the distal end portion 12 b of the stem 12 is stably gripped by the recess 8. Further, the posture of the thin rod 6 is movable in accordance with the shape of the outer peripheral surface of the distal end 12b of the stem 12. Therefore, the movement of the stem 12 and the artificial hip joint 10 is not hindered.
Further, the grip portion 2 and the shaft portion 4 can be connected to each other, and these are arranged in the lumen S from the distal end 12 b of the stem 12 to the distal end of the femur B. That is,
Therefore, the stem 12, the grip portion 2, and the shaft portion 4 of the artificial hip joint 10 can be inserted into the lumen S of the femur B consistently and stably, and the shaft portion 4 projects from the lumen S. Can also be easily prevented.

  Further, according to the method for assembling the medical implant 1 of the present embodiment described above, the distal end 12b of the stem 12 is stably gripped by the grip portion 2, and the grip portion 2 is connected to the shaft portion 4. Thus, the medical implant 1 can be assembled.

  According to the medical implant 1 and the assembly method of the medical implant 1 of the present embodiment, the medical implant 1 can be applied to the femur B that has been subjected to artificial joint replacement in advance and has the artificial hip joint 10. . And the recovery of the fractured femur B is effectively promoted, and the recovery period of the femur B is shortened.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific embodiments, and various modifications are possible within the scope of the gist of the present invention described in the claims. Deformation / change is possible.

[Modification of Medical Implant of this Embodiment]
For example, the artificial joint of the present embodiment is not limited to the artificial hip joint 10 as long as it has a portion corresponding to the stem 12 and the stem 12, and may be an artificial knee joint, an artificial elbow joint, or the like. It may be a medical implant that can be applied to a joint.
In addition, the grip portion 2 of the present embodiment is not limited to the configuration having the plurality of thin rods 6,... As long as it can be inserted into the recess 8, it may be a foam or resin having elasticity such as a net cloth or sponge.

  Next, the present invention will be described in detail by the following examples, but the present invention is not limited to these examples.

(Example 1)
A three-point bending test of the thin rod 6 was performed using a load tester and a sensor (distributor: Nidec Shinpo Corporation). As the thin bar 6, one pin made of titanium alloy having a cross-sectional shape of square, perfect circle, and equilateral triangle was prepared. The length of one side of the square was 0.7 mm, the radius of the perfect circle was 0.5 mm, and the length of one side of the regular triangle was 0.5 mm. The forced displacement to each pin was 10 mm.

  FIG. 6 shows the theoretical value of the rigidity of the pin having each cross-sectional shape and the actual measurement value obtained using the load tester and sensor. As can be seen from FIG. 6, there is a slight error between the theoretical value and the actually measured value, but the tendency of the actually measured value is in good agreement with the tendency of the theoretical value. Moreover, it turns out that rigidity is high in order of a cross-sectional shape in a square, a perfect circle, and a regular triangle. The reason why the height of the rigidity is in this order is considered that the square has a large area and the stress on the pin is most efficiently distributed by two pairs of sides parallel to each other. Moreover, in a perfect circle, the area is the second largest after a square. In the triangle, the area is relatively small and the apex angle is likely to be loaded, and it is considered that stress concentrates on the apex angle.

(Example 2)
A model of the medical implant 1 of this embodiment shown in FIG. 1 was prepared, and a four-point bending test was performed on this model using the same load tester and sensor as in Example 1. As the thin rod 6, 15 to 30 pins made of titanium alloy having the same cross-sectional shape as in Example 1 having a square shape, a perfect circle shape, and an equilateral triangle shape were used. As the shaft portion 4, a rod body having a recess opening in the end face was used. The interval between the fracture sites of the femur B was about 10 mm. Further, the rigidity was compared by setting the forced displacement to 5 mm and the protruding amount of the pin from the rod (dimension X shown in FIGS. 3 and 4) to 10 mm and 15 mm.

For each pin, the measured value of the rigidity is shown in FIG. 7 when the protrusion amount from the rod is 10 mm and when it is 15 mm.
As can be seen from FIG. 7, when the cross-sectional shape is a square and a perfect circle, the protruding amount is changed from 10 mm to 15 mm, so that the rigidity of the pin is lowered. On the other hand, when the cross-sectional shape is an equilateral triangle, the protrusion amount is changed from 10 mm to 15 mm, so that the rigidity of the pin is slightly increased.
In the above embodiment, since the rigidity of the grip portion 2 varies depending on the cross-sectional shape of the thin rod 6 and the amount of protrusion from the rod member 5, the amount of protrusion of the thin rod 6 from the rod member 5 is appropriate in consideration of the rigidity. It is preferable that it is set to.

(Example 3)
Next, the same finite element model as the medical implant 1 of this embodiment shown in FIG. 1 was constructed, and finite element analysis was performed. The number of elements in the finite element analysis was 20000. FIG. 8A shows a cross section of the finite element model corresponding to the case when viewed from the front of the medical implant 1. FIG. 8B shows a finite element model corresponding to the case when viewed from the outside of the medical implant 1. Moreover, as shown to Fig.9 (a), (b), the distal side edge part of the pin was restrained in directions other than the axial direction of a rod. Then, as shown in FIG. 11, a load of 600 N was appropriately applied to the position corresponding to the neck portion of the stem of the artificial hip joint from a direction inclined about 25 ° with respect to the longitudinal direction of the medical implant 1. Furthermore, the material constants and element types in the finite element analysis were set as shown in Table 1.

10 to 12 show the stress distribution of each model obtained by the finite element analysis. FIGS. 10A and 10B show stress distributions immediately after insertion into the femoral lumen (that is, immediately after the implant), and FIGS. 11A and 11B show the stress distribution through the femoral lumen. 12A and 12B are stress distributions when a load of 600 N is applied to the neck portion.
In addition, in FIG. 13, the figure for demonstrating a mode that tension and compression are added in the cross section of the finite element model corresponding to the case where it sees from the front of the medical implant 1 is shown. FIG. 14 (a) shows an enlarged view of the region Q shown in FIG. Similarly, FIGS. 14 (b) and 14 (c) show the distribution of the load pressure when the post-implantation stable state is viewed from the front and rear of the medical implant. The enlarged view of the area | region Q shown in FIG.
As shown in FIGS. 10 to 14, the stress concentrated on the distal end of the pin immediately after the implant is slightly dispersed in the longitudinal direction of the medical implant 1 at the time of stabilization after the implant. Yes. In addition, when a load of 600 N is applied to the neck portion, the stress is dispersed throughout the pin. From these results, it can be said that the medical implant 1 is stable in the longitudinal direction, and the load from the proximal end portion is not concentrated in one place but is distributed to the thin rod 6 and the entire gripping portion 2.

  FIGS. 15A and 15B are diagrams corresponding to the front and side views of the displacement distribution in the finite element model in which the displacement magnification is 10 times. As can be seen from FIGS. 15 (a) and 15 (b), if the medical implant 1 of the present embodiment is provided in the lumen when the fracture is performed at the approximate center in the longitudinal direction of the femur, the displacement is reduced. It spreads from the center to the proximal side, and it is thought that a large load is not applied to the femur.

(Consideration of Example 1 to Example 3)
From the results of Example 1 to Example 3 described above, first, when the thin rod 6 having a wide cross section is disposed at the distal end portion of the stem 12, the fixation of the stem 12 is stabilized and the rigidity is increased. Considered to be higher.
Table 2 shows the theoretical values of the cross-sectional secondary moment in each of the simple support beams whose cross-sectional shapes are square, perfect circle, and equilateral triangle. Table 3 shows measured values when both ends in the longitudinal direction of these simple support beams are supported and a load is applied to the center.

  As can be seen from Table 2 and Table 3 above, the tendency regarding the cross-sectional shape of the rigidity of each simple support beam is the same as the tendency regarding the cross-sectional shape of the rigidity of the pin. These results also support the above considerations.

In general, the yield stress of titanium alloys is reported to be 1250 MPa. As a result of the finite element analysis, a stress value of 1/10 is shown, so that it is assumed that the medical implant is not damaged.
For fractures of the femur B, it is generally reported that the rigidity of the four-point bending test when the medical implant 1 is installed is 60000 N / m. Since this value is also 1/10 or less of the analysis result, it is presumed that the medical implant 1 of this embodiment has a rigidity equal to or higher than that of a conventional intramedullary nail.

  FIG. 16 shows the displacement dependence of the resultant force when an actual model of the medical implant 1 is prepared and a load is applied to the model using a load tester (distributor: Instron).

  As described above, the rigidity of the grasping portion 2 and the stress distribution in the femur B and the medical implant 1 vary depending on the cross-sectional shape of the thin rod 6 and various conditions of the medical implant 1. Therefore, it is preferable that various design parameters of the medical implant are appropriately set in consideration of these analysis results and the like.

DESCRIPTION OF SYMBOLS 1 ... Medical implant 2 ... Gripping part 4 ... Shaft part 6 ... Thin rod 8 ... Recessed part (connection part)
10 ... Artificial hip joint (artificial joint)
12 ... Stem 12b ... Distal end B ... Femur (bone)
S ... Lumen

Claims (3)

A medical implant inserted into a bone lumen provided with an artificial joint,
A grasping portion for grasping a distal end portion of the stem of the artificial joint in the lumen;
A shaft connected to the grasping portion and disposed in the lumen from a distal end of the stem to a distal end of the bone;
Equipped with a,
The gripping portion has a plurality of thin bars that can be arranged on the outer peripheral side of the distal end portion of the stem with the stem extending direction and the axis line aligned.
A proximal end portion of the shaft portion is provided with a connecting portion capable of receiving the distal end portion of the thin rod and inserting the distal end portion of the stem through the thin rod . Medical implant. The medical implant according to claim 1 , wherein the thin rod has a rectangular cross-sectional shape. A method for assembling a medical implant according to claim 1 or claim 2,
The axial direction of the plurality of thin rods is filled in the connecting portion in accordance with the extending direction of the shaft portion,
Until the distal end of the stem is locked to the proximal end of the shaft via the thin rod, the distal end of the stem is moved from the proximal side of the plurality of thin rods. Advancing distally to connect the shaft to the gripping portion, and gripping the distal end of the stem of the artificial joint by the gripping portion;
That turn into integrally with the shaft portion and the stem and the grip portion,
How to assemble a medical implant.