JPS628177B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an artificial humeral head for artificially replacing the humeral head.

The head of the humerus, which constitutes the human shoulder joint, is affected by various causes such as traumatic comminuted fractures, ischemic head necrosis, rheumatoid arthritis, bone tumors, and osteoarthritis, resulting in Impairment of joint function is frequently encountered in daily clinical practice. Artificial femoral heads are used for functional reconstruction of such dysfunctional shoulder joints.

By the way, general joint function reconstruction techniques include total joint replacement and partial joint replacement. Among these, total joint replacement surgery is widely applied clinically to hip joints and knee joints. On the other hand, partial joint replacement surgery includes artificial femoral head replacement surgery and humerus artificial head replacement surgery. It concerns the femoral head.

By the way, unlike in the case of total joint replacement, it is generally considered that an artificial femoral head should have a shape as close to that of a living body as possible. This is because, in total joint replacement surgery, the components inserted into each of the two elements that make up the joint, namely the proximal and distal ends, are:
It is sufficient that the points or surfaces where the components join each other function in the same way as the original joints, and it does not matter what shape each component takes. However, in partial joint replacement surgery, especially in shoulder arthroplasty head replacement to which the present invention relates, the two elements that make up the shoulder joint, namely the scapula and humerus, are left untouched. Since the original shape remains as it is, the artificial head that replaces the humeral head that no longer functions has a functional anatomical structure that follows the original shape of the humeral head before it no longer functions. The closer they are scientifically, the better the functional results will be after surgery. The present invention was achieved based on this recognition and as a result of efforts to understand the original functional and anatomical shape of the humerus.

To briefly explain the method, a positive contrast agent is applied to the head of the humerus, and then an X-ray is taken of the humerus to obtain a frontal image of the humerus and an axial image perpendicular to this. A diagram as shown in Figure 2 was drawn, the shapes of the femoral head, neck, and diaphysis were converted into numerical values, and the obtained numerical values were statistically processed. From this, we found that the artificial femoral head described below is optimal. These methods adopted by the present invention for measuring the humerus have succeeded in depicting articular cartilage that cannot be seen with plain X-rays, and are new methods that have not been seen before.

In the present invention, the femoral head of the artificial femoral head has a shape obtained by cutting a small part from an ellipsoidal sphere and partially extending a 3D shape that is symmetrical to the elliptical sphere downward, and has a major axis a and a minor axis b. , small part height
c ₁ , the height of the symmetrical three-dimensional shape c ₂ , a: 34 ~ 47 mm,
b: 32 to 46 mm, c ₁ : 12 to 20 mm, and c ₂ : 3 to 7 mm.

By the way, since the conventional artificial shoulder bone head has a regular spherical shape, the physiological anatomy is different from another element that makes up the shoulder joint, that is, the glenoid fossa of the scapula, which has an elliptical concave curved surface. sufficient scientific compatibility has not been achieved. However, the present invention
Because the femoral head exhibits an elliptical convex curved surface, it is extremely compatible with the glenoid fossa of the scapula, and the way the artificial femoral head and the articular surfaces of the scapula come together approaches the original physiological one. This enables smooth and efficient movement of the shoulder joint.

By the way, at first glance, the shoulder joint appears to be a multidirectional universal joint, but unlike the hip joint, it does not have a ball-and-socket mechanism, and in reality, the humeral head has an elliptical convex curved surface. Raising the upper arm through the glenoid fossa of the scapula, which has a concave curved surface of an elliptical sphere, sometimes makes a rotational movement like a rolling ball, and sometimes makes a sideways sliding movement or a rotational movement. During movement, it has been observed that the scapula and the scapula move in concert with a certain movement angle ratio, and the artificial femoral head must meet these biomechanical demands. In response to this need, the present invention overcomes the following disadvantages of conventional spherical artificial heads.

In other words, the articulating surfaces of the spherical artificial bone head and the scapula are not physiologically connected and do not have sufficient compatibility. have
A sufficient fulcrum for polycentric movement cannot be obtained, preventing smooth joint movement and leading to low efficiency in mechanical work. In other words, to raise the upper limb by the same angle, the conventional artificial femoral head requires more work, which is due to the underlying disease and the muscles around the shoulder joint that occur during the post-surgical rest period. This is disadvantageous for patients with muscle weakness. The present invention, which overcomes these disadvantages, can easily achieve a range of motion of the shoulder joint that exceeds that of conventional artificial head replacement techniques.

The present invention also has excellent features in the following points. That is, in the present invention, the angle α43° to 47°, preferably 45°, represents the functional anatomical inclination angle between the head and the diaphysis of the humerus. Furthermore, in the present invention, the ratio 82 in which the long axis a of the femoral head incision is divided by the central axis of the stem is 82.
~78%: 18-22% Preferably 80%: 20% is an important factor that determines the positional relationship between the femoral head of the artificial femoral head and the humeral shaft, and the present invention provides It satisfies these functional and anatomical requirements. Now, if we consider the case where these requirements are not met,
In such a shoulder joint, when the arm is at rest and the arm is hanging down, the compatibility between the artificial bone head and the scapula is poor, and unnecessary tension is transmitted to the various muscle groups around the shoulder joint. Regardless, the shoulder joint lacks calmness and rest, and furthermore, this causes poor initial retardation when starting shoulder joint movements. Conventional artificial femoral heads do not fully meet the requirements just described. However, unless these functional and anatomical requirements are met, sufficient functional recovery of the shoulder joint cannot be expected after surgery.

Next, regarding the neck, the dorsal fin A has its small hole to fasten the greater and lesser tuberosities of the humerus with wire and fix the artificial bone head to the humerus, and the pair of lateral fins B ₁ B ₂ and the lower fin C have the purpose of preventing the stem portion of the artificial head inserted into the medullary cavity of the humerus from making abnormal rotational movements within the medullary cavity, and the lateral fins B ₁ B ₂ The small holes are made to be used for fixation of bone fragments. In addition, the lower fin of the conventional artificial head has a triangular shape, which does not fit the cortex of the humeral neck and has a weak rotation prevention force, whereas the lower fin C of the present invention has a concave curve. , it has good conformity to the cervical bone cortex, and its strong anti-rotation force makes it difficult for the stem to loosen.

In addition, the stem inserted into the humeral shaft has an oval-shaped cross section, and the tip of the stem is determined to go beyond the narrowest part of the medullary canal of the humerus, and the major diameter of the cross section is 7 to 15 mm. Short diameter: 5~9mm, stem length: 10~
The length shall be 16mm.

In the present invention, the material is ceramics,
Any material commonly used for artificial bones, such as polycrystalline alumina ceramics, single crystal alumina ceramics, or apatite, can be used.

Conventional artificial femoral heads are made of metal, which inevitably suffers from a number of disadvantages that metal has. In other words, it is used to overcome the problems of corrosion ionization when metal materials are left in the body for a long period of time, problems with changes in the strength of the material, problems with damage caused by this, and problems with loosening caused by poor compatibility with the living body. These problems include the toxicity of the filling reinforcement and bone cement, the wear of the contralateral articular cartilage caused by the metal bone head, which has a hardness significantly different from that of living bone, and the resulting osteoarthritis.

On the other hand, ceramics do not undergo degeneration even if left in the body for a long period of time, and are not carcinogenic.
The mechanical strength remains unchanged, and the excellent compatibility with the living body prevents loosening, eliminating the need for harmful filler reinforcing agents.Furthermore, improvements in polishing technology have enabled the contralateral joint of the ceramic head to be easily loosened. It has excellent features not found in conventional materials, such as reduced wear on cartilage and resistance to osteoarthritis. Furthermore, unlike the hip and knee joints, the disadvantage of ceramics' physical properties, which is weak in bending, does not pose a problem in the shoulder joint, which is not a load-bearing joint. In proceeding with post-surgical rehabilitation for patients who suffer from these diseases and experience muscle weakness in various muscle groups,
It's a big advantage.

Example 1 Made of polycrystalline alumina ceramics, the long axis a of the femoral head is 38 mm, the short axis b is 36 mm, and the height c _is 15 mm.
c ₂ : 5mm, dorsal fin A height: 5mm, thickness: 3mm,
Length: 20mm, small hole diameter: 2mm, pair of horizontal fins
B ₁ B ₂ is height: 2.4mm, thickness: 3mm, small hole diameter:
1mm, length: 20mm, lower fin C is 5 points from the lower edge of the cut.
The thickness starts from the inside of mm and moves to the stem while drawing a concave curve, the thickness is 3 mm, the angle α is 45°, the ratio of the long axis a of the cut of the bone head divided by the central axis of the stem is 80%: 20%, and the stem Length f: 135mm,
Long diameter of stem d: 9mm, short diameter of stem e: 7mm,
The back surface of the femoral head is made into an artificial femoral head with a wavy shape.

Example 2 Made of polycrystalline alumina ceramics, the major axis a of the femoral head is 43 mm, the minor axis b is 42 mm, and the height c ₁ is 17 mm.
c ₂ : 5mm, dorsal fin A height: 5mm, thickness: 3mm,
Length: 20mm, small hole diameter: 2mm, pair of horizontal fins
B ₁ B ₂ is height: 4.5mm, thickness: 3mm, small hole diameter: 2
mm, length: 22mm, lower fin C is 5mm from the lower edge of the cut
Starting from the inside and moving to the stem while drawing a concave curve, the thickness is 3 mm, the angle α is 45°, the ratio of the long axis a of the cut of the bone head divided by the central axis of the stem is 80%:20%, and the stem Length f: 135mm,
Long diameter of stem d: 13mm, short diameter of stem e: 11mm,
The back surface of the femoral head is made into an artificial femoral head with a wavy shape.

We have performed shoulder arthroplasty using the artificial bone head of the present invention for patients who have suffered from chronic rheumatoid arthritis for many years and patients who have developed necrosis of the humeral head after trauma, resulting in painless and extremely easy-to-move shoulder arthroplasty. Obtained.

In the future, as the population ages, it is naturally expected that shoulder injuries due to falls and the like and chronic diseases such as rheumatism will become more prolonged, and the demand for the artificial femoral head according to the present invention is expected to increase even more.

[Brief explanation of the drawing]

Figure 1-A: Front view of the artificial bone head, Figure 1-
B: A side view of the artificial bone head, FIG. 1-C: A view of the artificial bone head seen from above, FIG. 2-A: A front view of an X-ray photograph, FIG. The area between each arrow is the object of measurement. The shaded area indicates articular cartilage. The x and y axes are the straight lines Zf and Zs obtained by connecting cartilage cuts, and the axes pass through the center of the diaphysis.

Claims (1)

[Claims] 1. In an artificial humeral head consisting of the femoral head, neck, and stem, the femoral head has a shape obtained by cutting out a small part from an elliptical sphere and partially extending a symmetrical three-dimensional shape downward at the cut end. , the neck has a dorsal fin A, a pair of lateral fins B ₁ and B ₂ , and a lower fin C, and the dorsal fin A has three small holes and has a convex curve,
A pair of side fins B ₁ and B ₂ each have two small holes and have a convex curve, the lower fin C has a concave curve, and the stem has an oval cross section. bone head.