JPS63158053A - Formation of artificial joint - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for making biomaterials, especially artificial bones, to be implanted in a living body. The present invention relates to a method for creating a devised artificial joint.

(Prior art) Various human joints are deformed due to various causes (trauma).
It may be destroyed. If joint destruction becomes significant, daily life will be severely restricted due to pain and joint dysfunction.

The most effective treatment currently used to improve this condition and allow patients to return to normal social life is artificial joint replacement.

Furthermore, in the field of dentistry, many people have had their teeth removed due to cavities, alveolar pyorrhea, etc., and they have had to experience inconvenience, especially when it comes to eating habits. A treatment method that has recently been widely used to recover from these conditions is an implant method using an artificial tooth root.

Among the characteristics required for artificial bones, artificial joints, artificial tooth roots, etc., an important issue is the method of fixation to the bone. That is, compared to the case of an artificial organ which is the same implant material, an artificial bone or the like needs to function as a part of the bone, and therefore receives a very large load.

For example, during normal walking, it is said that a maximum load of 4 to 8 times the body weight is applied to the hip joints, and a load of 2 to 4 times the body weight is applied to the knee joints. Furthermore, these loads are repeatedly applied over a long period of time in an extremely chemically harsh environment in vivo.

Conventionally, methods for fixing the above-mentioned artificial bone to bone in the living body include a method of mixing a so-called polymethyl methacrylate polymer powder called bone cement with a monomer liquid and polymerizing and hardening it. , a method of thermally spraying ceramics such as alumina and hydroxide apatite, which have excellent bone affinity, or a method of making the surface porous by sintering wires or beads on the bone contact surface and allowing bone to grow therein. There is.

(Problems to be Solved by the Invention) The above conventional method has various problems as described below.

In other words, with the bone cement method, the heat generated by the polymerization reaction causes necrosis of surrounding tissues and the toxicity of residual monomers, which causes loosening called loosening during long-term use. There was a problem.

In addition to the essential problems of the conventional technology (fixation method), there is also the problem of individual insertion differences in joint shapes.

In other words, in order to accommodate this individual input difference, conventional artificial joints are manufactured in a wide variety of shapes, and several types of artificial joints that are potentially compatible are prepared based on X-ray fluoroscopic images. During replacement surgery, a suitable method is selected, and the artificial joint is inserted into the bone in the living body and fixed with cement, etc., while sometimes changing or modifying the resection range of the natural bone.

However, it is extremely difficult to completely resolve individual differences in joint shape using such a method. It is not easy to prepare a large number of artificial joints with different shapes in advance (in reality, we have to choose from about 20 types of artificial joints, so we have to accept some differences in individual parts and perform replacement surgery. The reality was that they were not able to obtain the desired results.

The problems of the prior art described above are solved as follows.

(1) The suitability of the sliding surface of the artificial joint deteriorates from the preset sliding condition, causing distortion at the interface between the artificial joint and natural bone, resulting in pain and abnormalities on the sliding surface of the artificial joint. Phenomena such as wear and tear occur that reduce the lifespan of the artificial joint.

(2) In addition, abnormal wear increases frictional force, which applies a large force to the interface between the artificial joint and the bone, causing loosening.

(3) The gap between the artificial joint and the natural bone becomes large, and a large amount of bone cement is required, which increases the necrotic area of the surrounding tissues and drastically reduces the effectiveness of joint replacement surgery.

SUMMARY OF THE INVENTION An object of the present invention is to provide a technique for manufacturing an artificial joint that can solve the above-mentioned problems and is well adapted to the shape and damage condition of each individual joint to be subjected to joint replacement surgery.

(Means for Solving the Problems) In order to achieve the above-mentioned purpose, the present invention provides a creation method having the following points as a gist: namely, preparing a small number of general wax models based on the basic shape, and Based on X-ray fluoroscopic images of the joints of patients, the general wax model is modified to determine the difference from the normal model, and a precision wax model that fits each piece obtained in this way is created, and this precision wax model is As a means to solve this problem, we propose a method for creating an artificial joint, which is characterized by precision casting using the method.

(Function) As a result of conducting research on a method for creating an artificial joint that closely matches the shape and damage state of each individual joint that is the target of joint replacement surgery, the inventors first determined the basic shape of the artificial joint. I learned that it is important to decide.

The basic shape was designed through investigation and consideration of the shape of a normal joint, the artificial joint that will remain after joint replacement surgery, and the shape of the remaining bone (natural bone) that will be connected to it.

The first feature of the configuration of the present invention is to prepare a wax model that is prefabricated with respect to the basic shape of the artificial joint, leaving some precision machining allowance by an automated processing machine. This wax model may be produced by pressurized injection into a mold using the usual method, but if economic efficiency is more important, it is better to cast it by pouring it into a plaster mold or the like. Note that, in order to reduce the time required for precision machining, it is in accordance with the spirit of the present invention to prepare several basic shapes. Of course, since the basic shape and the shape of the wax model prepared in advance have free-form surfaces, it is not possible to instruct an automated processing machine, so the free-form surface data is stored in a computer with a huge storage capacity. It is preferable to memorize and use it. In addition, when precision casting the wax model, there is a necessary molten metal injection port for the mold, a riser part to compensate for solidification shrinkage, and a molten metal injection flow that replaces the gas in the mold, Provide gas vent holes as necessary to prevent defects from remaining in the cast product.

In this way, two types of free-form surface data are stored in the computer: 1) the basic shape, and 2) the shape of the wax model prepared in advance.

Next, the shape of each individual joint to be subjected to joint replacement surgery is collected as data from front and side X-ray fluoroscopic images, as well as the degree of damage to the joint. Such an X-ray fluoroscopic image is displayed on a cathode ray tube at a magnification of 1.00±0.01 by strictly adjusting the distances between the X-ray source and the subject, and between the subject and the image conversion device for the transmitted X-ray image.
The images are projected to double the size and recorded using an industrial image recording device. At this time, the angle of the subject with respect to the X-ray optical system is also extremely important, and the angle is controlled to ±1°.

The recorded image is reproduced on a cathode ray tube of an image analysis device, and on the cathode ray tube, an orthopedic surgeon who is planning to perform a joint replacement writes an appropriate shape of the artificial joint on two fluoroscopic images, front and side. X-ray CT exchanged by computer
Using the device, it is in principle possible to determine the shape of an artificial joint for a patient. However, some patients have diseased joints, and in this case, it is difficult to obtain an artificial joint with an ideal shape using the shape determining method described above. In order to overcome these difficulties in shape design, the present inventors devised a method that involves comparison with an ideal concrete shape. That is, the written data is transferred to a computer, smoothed, and compared with two cross-sectional images corresponding to the basic shape of the artificial joint to determine the basic shape.
It is compared with 10 representative values to determine the artificial joint representative value of the patient undergoing joint replacement surgery.

The theory for determining the artificial joint representative values is that the basic shape is determined based on the shape of a normally functioning joint, so proportional allocation based on the ratio between the representative values of the basic shape is sufficient. The shape of the joint surface with the remaining (natural) bone after surgery for a patient undergoing artificial joint replacement is determined by the person scheduled to undergo the procedure by observing the wear and tear of the patient's joints on an X-ray fluoroscopic image on a cathode ray tube. However, judging from the actual situation of the treatment, the shape does not need to be a free-form surface, and a combination of flat surfaces is sufficient.

Based on the shape of the artificial joint of the patient undergoing joint replacement surgery determined in this way, the difference between the shape of the wax model, which was manufactured in advance with a precision machining allowance, and the artificial joint is automatically processed. It is calculated in a computer as data for precision machining and output to automated processing machines. In addition,
The calculation of the difference in shape may be determined by fixing the relative location of the two shapes and using it as a reference line, or by performing calculations within a computer to minimize the processing time by an automated processing machine. .

In this way, wax models of two artificial joints can be manufactured by precision processing the two wax models that have been manufactured in advance. Here, one of the two wax models is a wax model used for precision casting, and the other is a wax model for the practitioner or the person being treated.

Furthermore, as mentioned above, the shape of the interface with the remaining (natural) bone is determined by the orthopedic surgeon on a cathode ray tube, so it is easy to issue instructions for cutting the joint bone during joint replacement surgery from a computer. be.

Note that the wax model for precision casting takes into account the shrinkage of the precision cast metal, the shrinkage of the mold machine, and the dimensional changes caused by the final molding of the cast product.

Of course, the features of the present invention largely depend on the latest computer-based design technology and image processing technology as described above, but wax model molding technology is also an important component. Ordinary casting wax has a low melting point of approximately 70°C, making machining extremely difficult, but the present inventors have developed a product with a melting point of approximately 95°C, which has superior moldability and processability compared to resin products such as acrylic. ℃ processing wax is used.

(Example) Three examples regarding an artificial knee joint to which the method of the present invention is applied will be described below.

As shown in FIG. 1, in the knee joint, a femur 1 and a tibia 2 are in contact with each other across cartilage, allowing movement.

Generally, when using a metal casting for this knee joint,
The coefficient of friction becomes significantly larger than that between living bones.

Therefore, a structure is generally adopted in which high-density polyethylene 3 is placed on the femur' bone joint surface on the tibia side, and this is backed up with a metal molded product (support 4). In this way, the coefficient of friction can be kept 3 to 10 times that between living bones and considerably smaller than that between metals.

In this case, the artificial joint on the tibial side may be divided into two parts, with the upper part made of high-density polyethylene and the lower part made of metal casting. Since the tibial artificial joint has a simpler shape than the femoral artificial joint, the femoral artificial joint will be described below.

The femoral prosthesis was constructed mainly of free-form surfaces, and was manufactured by injecting a machinable wax model having the following representative dimensions into a mold. In addition, here a, ~ a3 (crane) is the maximum of the artificial joint,
C3~c3 (mm) is the maximum depth, h, ~h3
(u) is the maximum height.

■a+=77, c+=63. ht=65.
b+=33■azW? 2. cz□60+h
z=59. bz=31■az□67, Cz=5
8. hi=54. bz=29 Also, b, -b3(t
m) is the maximum depth of the artificial joint to be joined with the residual volume. On the other hand, the basic design values of the artificial femur are as follows.

■a+'=74. c+'=60. h+'=62.
b,'=37■az'69+ cz'=57+hz'
=56. bz'=35■azi=64. ci'=5
5+hi'=51. bi'=32 On the premise that joint replacement surgery will be performed, three cadaveric bones were used as virtual patients, and frontal and lateral XwA fluoroscopic images of the knee joint were examined. It was determined that the first virtual patient had significant joint damage and therefore required extensive resection of the femur.
If expressed as a+'=74.5. c+'=60-7+h+'=6
2.4. It was found that b+'=33.6, and as a casting wax model (ml) a+'=75.2+ C+'=61.3. tl+'J
3.0. A product with t,'=33.8 was manufactured from the wax model of
The V alloy was cast in a vacuum electron beam melting and casting furnace. In this case, the alloy injection temperature was 1920°C and the injection rate was 2.
It was 5 kg/sec. The casting mold has a 0.12 mm thick tungsten metal layer on the contact surface with the Ti alloy.
A stabilized zirconia layer of 1.5 mm is placed behind it, and a high alumina layer of 1.8 mm is further placed behind it.The precision cast product is made by precision cutting the runner in accordance with the usual method, sandblasting, pickling, and coloring. After checking and XwA fluoroscopy to confirm that there were no internal or surface defects, the joint was subjected to joint replacement surgery.

Next, since the damage to the joint was minor in the second virtual patient, it was determined that representative dimensions that were approximately equal to the basic design dimensions were appropriate, and a wax model with the following dimensions was created using automated machining using the wax model in ■. An artificial femur made of Ti-6%Ai4%V alloy was manufactured under the same casting conditions as in the previous example. The finishing processing conditions of the automated processing machine are: tool depth of cut 0.2 mm, cutting speed 80 mm/sec.
And so.

a z'=68.8 Cz'=57.2 h zp=5
5.8 b z"35.1a z'; 69.4 Cz'
・57.7 h z'□56.3 b z'□35.3
(mm) Furthermore, the third hypothetical patient is a woman whose femur is abnormally small, but with little damage.A wax model with the following representative dimensions was created from the wax model in ■, and was the same as that for the first patient. The artificial joint was manufactured under conditions such as casting. In addition, the representative dimensions of the artificial joint that have been finished and quality inspected after casting are on average 0 with respect to the desirable dimensions indicated by the subscript P.
．． 071 mm, with a standard deviation of 0.032 mm, which is significantly smaller than the maximum error of 1.0 to 2.5 n+m that would be expected when inserting an artificial joint using conventional technology, making the artificial femur more suitable for the patient. Joint replacement surgery using this method has become possible.

a :1p=60. C3p=51. h3'=
47. b 2'=27a 3'=60.5
C: l'=51.3 h3'=47.3
b: +”27.5 DI) The implantation status and activity of the artificial joints in these virtual patients were significantly better than those of the conventional method. For casting, it was possible to cast a single wax model with a runner, or to cast a tree in which many wax models were connected to a single runner.

(Effects of the Invention) As can be seen from the above explanation and the results of the examples, the following effects can be expected according to the production method of the present invention.

+11 Artificial joints that fit well with the patient's joints can be manufactured.

(2) Therefore, the range of motion after joint replacement surgery is expanded compared to conventional methods.

(3) Furthermore, it is possible to extend the life of the artificial joint and avoid reoperation.

[Brief explanation of the drawing]

FIG. 1 is a side view of the knee joint in an upright state, and FIG. 2 is a side view of the knee joint in a bent state. 1...Femur 2...Tibia 3...High-density polyethylene 4...Metal support

Claims (1)

[Claims] 1. A small number of general wax models are prepared based on the basic shape, and the general wax models are modified by determining the difference from the normal model based on the X-ray fluoroscopic image of the joint of the patient being treated, and thus obtained. A method for creating an artificial joint, characterized by creating a precision wax model suitable for each piece, and precision casting the artificial joint using this precision wax model.