JP2001190579A - Interbody spacer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an interbody spacer capable of reducing the possibility of the destruction of base bed vertebra caused by the interbody spacer, made of titanium and having a screw structure, and preventing the movement and dropping of the spacer to the spinal cord side after its insertion. SOLUTION: This interbody spacer 1 is made of ceramic and provided with a screw on its outer peripheral surface of a shaft part, and the screw is a tapered screw 2. As the spacer 1 is made of ceramic, it is free from the problem on the destruction of base bed vertebra, and as the tapered screw structure different from a parallel screw, is applied, the excess screwing-in and movement to the back side between vertebral bodies Z, Z, and the dropping to the spinal cord side can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intervertebral body spacer used in the medical field of surgery, neurosurgery, or orthopedic surgery, and more particularly, to a cervical, thoracic, or lumbar intervertebral disc which has been resected due to osteoporosis. In some cases, the present invention relates to an intervertebral body spacer (hereinafter, also simply referred to as a spacer) which is inserted between and complements the upper and lower vertebral bodies.

[0002]

2. Description of the Related Art As this kind of intervertebral body spacer, the technique described in Japanese Patent Application Laid-Open No. H8-10275 is known. This is a screw structure in which a screw is provided on the outer peripheral surface of a columnar body, and the same publication exemplifies a titanium (titanium alloy) or ceramic material.

[0003] These intervertebral body spacers are used to remove the intervertebral disc and then to adjust the distance between the upper and lower vertebral bodies (intervertebral height) using an adjusting device.
Is adjusted to an appropriate value, and while maintaining the spacing, a prepared hole is formed in the end face of the vertebral body using a reamer or the like, and the screw is inserted after being screwed up.

[0004]

However, among the above-mentioned conventional intervertebral body spacers made of titanium, the hardness thereof is too high compared with the cervical vertebrae (bone), so that after being filled, the mother vertebrae is destroyed. Occurred, and there were problems such as gaps between the vertebral bodies. It is considered that the titanium-made product does not have a direct healing force with the bone, and thus bites into the bone due to its hardness difference. Titanium products are not toxic, but have been reported to diffuse into body tissues, suggesting a possible carcinogen. Further, there is a problem that it is difficult to determine bone fusion by X-ray, and it is difficult to evaluate postoperative progress because images are disturbed even by MRI.

On the other hand, among the above-mentioned conventional intervertebral body spacers, those made of ceramic do not have the disadvantages of those made of titanium described above, and have a biocompatibility or a fusion force with new bone (compared to those made of titanium). (Bonding property) is extremely high, and thus it can be said that the material is preferable as a spacer. However, in this type of conventional spacer replacement surgery, for example, when inserting the screw between the vertebral bodies from the front side to the back side, when the spacer is inserted or after insertion, it moves to the back side. There was a danger of slipping into the spinal cord. In order to avoid such a danger, it is conceivable that a screw hole is formed and screwed so as not to penetrate in tapping after drilling the pilot hole. However, since the screw hole formed in such a mother bed is provided between the upper and lower vertebral bodies after removing the intervertebral disc, the screw groove is a part of an arc and escapes to the dorsal side depending on the screwing force. There is a risk. On the other hand, if the screw is screwed with a small torque, a sufficient fixing force cannot be obtained.

The present invention has been made in view of these problems, and has no problems such as destruction of the vertebrae of the mother bed as in the case of the intervertebral body spacer having a screw structure made of titanium as described above. It is an object of the present invention to provide an intervertebral body spacer which can prevent a problem such as a risk of moving to the side of the spinal cord and dropping to the side of the spinal cord.

[0007]

To achieve the above object, the present invention according to claim 1 is an intervertebral body spacer inserted between vertebral bodies, wherein a thread is provided on the outer peripheral surface of a shaft. In a ceramic device, the screw is a tapered screw.

Since the intervertebral body spacer is made of ceramic, there is no problem such as destruction of the vertebrae of the mother bed, and the intervertebral body spacer has a tapered screw structure different from a conventional ordinary screw (parallel screw). It is possible to prevent the screw from being excessively screwed into the dorsal side in between, and even after screwing (insertion), the risk of moving to the dorsal side and falling out to the spinal cord side can be reduced.
In addition, due to the tapered screw structure, a strong fixing force is exerted in the radial direction of the screw when the screw is screwed firmly, and early bone fusion is expected.

In the above means, the taper of the taper screw ((maximum screw diameter−minimum screw diameter) / total length of the screw portion) is
It is good to be 1/20 to 1/4. This taper is 1 /
If it is smaller than 20, it is too close to the parallel screw, and the intervertebral body spacer is likely to fall back during or after its insertion. On the other hand, if the taper is larger than 1/4, there is a risk of causing excessive physiological forehead.

[0010] A large-diameter end (end face) of the tapered screw is provided with a three-dimensional or polygonal concave part or a convex part such as a polygonal knob for screwing, that is, for screwing. Is preferred. The tapered screw is preferably provided over the entire shaft portion (over the entire length), but may be provided partially or largely.

In any of the above means (intervertebral body spacer), the thread of the tapered screw is substantially triangular,
Preferably, the angle of the thread is 70 degrees or more. This is because ceramics can be easily manufactured and the strength can be increased. In any of the above means (intervertebral body spacer), the thread of the tapered screw may be substantially trapezoidal, and the angle of the thread may be 70 degrees or more.

The ceramic is preferably a hydroxyapatite, tricalcium phosphate, or a calcium phosphate-based ceramic containing a composite material of these materials as a main component, but may be an alumina ceramic or a zirconia ceramic. The material is not limited as long as it is a material.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an interbody spacer according to the present invention will be described in detail with reference to FIGS. FIG. 1 is a front view of a spacer 1 of the present example, and FIG. 2 is an end view showing an end portion (end surface) 3 on the large diameter side. And the screw (outer) diameter D1 of the end portion 5 on the small diameter side is 9 m.
m, the screw (outer) diameter D2 of the end portion 3 on the large diameter side forms a tapered screw 2 having a diameter of 10 mm. Here, the screw (outer) diameter D1 of the end portion 5 on the small diameter side is set to be slightly larger than the gap after removing the intervertebral disc between the end faces of the upper and lower vertebral bodies to be supplemented. And its total length (length along the axis)
Is set smaller than the front and rear thickness of the vertebral body, inserted between the vertebral bodies, and when the large-diameter end 3 substantially coincides with the front edge of the end face of the vertebral body, the small-diameter end (tip face) 5) is a short length that does not touch the spinal nerve.

The taper of the taper screw 2 ((D2-D
1) / the total length of the screw portion) is exaggerated, but is 1/11 in the present embodiment. The thread of the tapered screw 2 is triangular, the thread angle θ is 90 degrees, the pitch of the threads is 2.5 mm, and the radii of the peaks and valleys are 0.5 mm. An oval (oval) recess 7 is formed at the center of the large diameter end 3 of the screw for a spiral screw. The spacer 1 of the present embodiment is a ceramic sintered body containing hydroxyapatite as a main component, and is formed by press-molding a raw material powder and then firing.

Next, with reference to FIG. 3 and FIG. 4, how to use the spacer 1 of the present embodiment configured as described above, cervical spondylopathy exhibiting a spinal cord condition in which the spinal cord is compressed and a root condition in which the nerve root is compressed. In contrast, a case in which the cervical spine is fixed in the front will be described. In using the spacer 1 of the present embodiment, the upper and lower vertebral bodies Z,
The intervertebral disc between Zs is removed, and the prolapsed herniated disc, ligaments, and osteophytes that are causing nerve compression are removed. Then, although not shown, the upper and lower vertebral bodies Z, Z are fixed by a vertebral body fixing and intervertebral foramen, and the interval (intervertebral height) is adjusted to an appropriate value.

Under this condition, a pilot hole is made from the front with a medical cutting tool (drill or reamer) (not shown) having an outer diameter of 6.5 mm, and a taper corresponding to the taper screw 2 of the spacer 1 is formed in the pilot hole. A tap having a cutting edge such that an internal thread is formed is formed to form a tapered tapered screw hole N. However, the screw hole N is formed such that when the spacer 1 is screwed in, the large-diameter end 3 of the spacer 1 substantially matches the opening end of the entrance of the screw hole N. In addition, since the intervertebral disc between the vertebral bodies Z and Z is removed, the screw hole N formed in this manner has a shape in which cortical bone on the surface of the end surface of the upper and lower vertebral bodies Z and Z is slightly cut. It becomes an arc-shaped thread groove when viewed from the front (see FIG. 3B). In this operation, the spacer 1 is generally supplemented symmetrically to the left and right in order to secure a balance. Therefore, as shown in FIG. 3B, screw holes N are formed at two places on the left and right.

The spacer 1 of the present embodiment has the small-diameter end 5 facing the screw hole N formed between the vertebral bodies Z and Z, and the surgical operation is performed on the concave portion 7 of the large-diameter end 3. Fit the tip of a dedicated screwdriver for rotation. Then, the spacer 1 is screwed into the screw hole N and rotated (forward) while rotating.
And inserted. Then, as shown in FIG. 4, when a predetermined screwing state is achieved by the action of the taper screw of the spacer 1, further screwing (screw-in) is restricted, and excessive screwing is prevented. In this embodiment, the large diameter side end 3 is set to stop at a position substantially coincident with the opening end of the entrance of the screw hole N. However, the spacer 1 can be screwed (inserted) even after screwing (insertion) due to the taper screw action. It is prevented from moving to the dorsal side or coming off to the spinal cord side.

In addition, since the spacer 1 has a tapered screw structure, when it is screwed firmly, a large fixing force is exerted in the radial direction of the screw, and a stable fixing force is maintained. Early bone fusion is expected without the need for long-term extracorporeal fixation. Thus, after the operation, the cause of the compression of the spinal cord is eliminated, and at the same time, the height of the intervertebral space can be restored by acting as a spacer, and the intervertebral foramen through which the nerve root passes can be reproduced. Further, since the spacer 1 is made of ceramic, there is no problem such as destruction of the vertebrae of the mother bed unlike the spacer made of titanium.

Further, in this embodiment, the thread angle θ of the thread is 9
Since the angle is 0 degrees, the angle is larger than that of a normal triangular screw of 60 degrees, so that it is easy to mold as a ceramic member and hardly causes a decrease in strength. It is also effective in preventing bites into bones.

In the above embodiment, the thread is triangular and the thread angle is 9
Although the angle is 0 degree, the thread is not shown, but may be trapezoidal. Regardless of the shape of the thread, the thread angle is preferably 70 degrees or more.

In the above description, the vertebral body of the cervical vertebrae is interpolated. However, the vertebral body of the present invention can be applied to any vertebral body such as a cervical vertebra, a thoracic vertebra, and a lumbar vertebra. At this time, the length and diameter of the spacer and the taper may be set according to the size of the end face of the vertebral body and the thickness of the intervertebral disc. The present invention is not limited to the above-described embodiment, and can be embodied by appropriately changing the design without departing from the gist thereof.

[0022]

As is apparent from the above description, according to the spacer of the present invention, since it is made of ceramic, there is no problem such as destruction of the vertebrae of the mother bed, and the conventional spacer (parallel screw) can be used. With a different tapered screw structure, when inserted from the front, it is possible to prevent excessive screwing into the back side, and even after screwing, the risk of moving to the back side and falling out to the spinal cord side can be reduced. Moreover, due to the tapered screw structure, a strong fixing force is exerted in the radial direction by strongly screwing, and early bone fusion is expected.

[Brief description of the drawings]

FIG. 1 is a front view of an embodiment of an interbody spacer of the present invention.

FIG. 2 is a left end view showing a large-diameter end (end face) of the spacer of FIG. 1;

FIG. 3A is a side sectional view schematically illustrating a state in which a pilot hole is made between vertebral bodies and a screw is made, and B is a front view thereof.

FIG. 4 is a side sectional view in which a spacer is inserted into a screw hole between vertebral bodies in FIG. 3;

[Explanation of symbols]

 1 Intervertebral body spacer 2 Taper screw θ Thread angle Z Upper and lower vertebral body

Claims (4)

[Claims] 1. An intervertebral body spacer which is inserted between vertebral bodies and which is made of ceramics having a screw on an outer peripheral surface of a shaft portion, wherein the screw is a tapered screw. Spacer. 2. The taper of the taper screw, wherein the taper is 1/20 to
2. The interbody spacer of claim 1, wherein said spacer is in the range of 1/4. 3. The intervertebral body spacer according to claim 1, wherein the thread of the tapered screw is substantially triangular, and the angle of the thread is 70 degrees or more. 4. The intervertebral body spacer according to claim 1, wherein the thread of the tapered screw is substantially trapezoidal, and the angle of the thread is 70 degrees or more.