THREE-DIMENSIONAL GUIDE FOR WIRE FOR FORMING PEDICLE SCREW INSERTION HOLE AND METHOD OF PRODUCING THE SAME

Abstract

A three-dimensional guide for a wire for forming a pedicle screw insertion hole is produced based on a CT image of a spine, and includes a contact surface section that comes in surface contact with a morphological surface of a bone at an insertion site, and a guide block section that is provided upright from the contact surface section. The guide block section has a guide hole that restricts the insertion direction of the wire. The guide hole has an inner diameter slightly larger than the outer diameter of the wire. The guide hole has a length of 15 to 30 mm to restrict the insertion position and the insertion direction of the wire.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of International Patent Application No. PCT/JP2011/067955, having an international filing date of Aug. 5, 2011, which designated the United States, the entirety of which is incorporated herein by reference. Japanese Patent Application No. 2010-181119 filed on Aug. 12, 2010 is also incorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to a three-dimensional guide for a wire for forming a pedicle screw insertion hole that may suitably be used to insert a pedicle screw used for spinal surgery into an anatomically appropriate site, and a method of producing the same.

Spinal bones allow a motion or movement in an arbitrary direction while surrounding and protecting a number of veins, arteries, nerves, and the like.

An adult human spine is made up of more than twenty distinct bones that are joined through a posterior intervertebral joint and a cartilage plate (intervertebral disc) that are positioned between adjacent vertebrae.

The spinal bones are anatomically classified into cervical vertebrae, thoracic vertebrae, lumbar vertebrae, and sacral vertebrae.

The cervical vertebrae, the thoracic vertebrae, the lumbar vertebrae, and the sacral vertebrae form a specific curvature referred to as a cervical lordosis, a thoracic kyphosis, a lumbar flexure, and a sacral kyphosis.

A pedicle screw may be used during spinal surgery in order to achieve a therapeutic effect by securing the spine.

However, since the configuration of the spine significantly differs among individuals, and the spine may be deformed to a large extent in patients who suffer from scoliosis or the like, a severe complication may occur when inserting a pedicle screw. For example, quadriplegia due to spinal injury and death due to vertebral artery injury have been reported.

A CT cutout technique that develops a life-sized CT image, draws the insertion position and the insertion angle of a pedicle screw directly on the CT film, and cuts the CT film along the insertion line and the posterior margin of the lamina has been proposed in The journal of the Japan Spine Research Society 19(1), 2008, p. 31 (author: Hiroshi Miyamoto).

The CT cutout technique can accurately obtain the insertion position, but does not reliably ensure the stability of the insertion direction.

SUMMARY

The invention may provide to a three-dimensional guide for a wire that is used to form an insertion hole for inserting a pedicle screw at an anatomically appropriate position, and a method of producing the same.

According to one aspect of the invention, there is provided a three-dimensional guide for a wire for forming a pedicle screw insertion hole that is produced based on a CT image of a spine, the three-dimensional guide including a contact surface section that comes in surface contact with a morphological surface of a bone at an insertion site, and a guide block section that is provided upright from the contact surface section, the guide block section having a guide hole for restricting an insertion direction of the wire.

It is necessary to form a pedicle screw insertion hole having an anatomically appropriate depth in the pedicle of vertebral arch in an anatomically appropriate direction when inserting a pedicle screw into the pedicle of vertebral arch.

In this case, a K-wire is inserted into the pedicle of vertebral arch, and a preliminary hole is formed in the pedicle of vertebral arch along the K-wire inserted into the pedicle of vertebral arch using a hollow drill.

The drill is then removed while allowing the K-wire to remain, and a thread is formed in the inner circumference surface of the preliminary hole along the K-wire using a hollow tap.

One aspect of the invention provides a three-dimensional guide that contributes to stabilization of the insertion position and the insertion direction of the K-wire.

Since the vertebral arch has processes such as a transverse process, a spinous process, and a articular process, it is preferable that the contact surface section include a morphological surface section that corresponds to the morphological surface of the bone at the insertion site, and a process contact section that comes in contact with the process of the vertebral arch so that the position of the three-dimensional guide is stabilized during surgery. It is preferable that the guide hole have a length of about 15 to about 30 mm from the viewpoint of insertion stability.

If the length of the guide hole is less than 15 mm, the insertion direction may become unstable. If the length of the guide hole exceeds 30 mm, the height of the guide block increases although the insertion direction becomes stable.

The three-dimensional guide may be produced by a method that includes capturing a CT image of a spine, extracting a pedicle screw insertion site based on the CT image, designing the shape of a block that has a contact surface section that corresponds to the morphological surface of the bone at the extracted insertion site, producing a mold based on the designed shape, and molding the three-dimensional guide in the mold.

Since the three-dimensional guide according to one aspect of the invention includes the contact surface section that comes in surface contact with the morphological surface of a bone, and the guide hole that three-dimensionally guides the insertion direction of the wire, a pedicle screw can be safely inserted into an appropriate site (part) of a spine in a stable manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a bone model of cervical vertebrae, and an example of a three-dimensional guide that is produced to come in surface contact with the morphological surface of the bone.

FIGS. 2A and 2B illustrate an example in which a three-dimensional guide according to one embodiment of the invention is brought into contact with cervical vertebrae to position a guide hole, wherein FIG. 2A illustrates a state before the three-dimensional guide is brought into contact with cervical vertebrae, and FIG. 2B illustrates an example in which a guide hole 13 is positioned by fitting a process contact section 14 to a process 2 of the bone.

FIGS. 3A and 3B are side views illustrating cervical vertebrae, and illustrate an example in which the insertion direction of a K-wire is determined using a guide hole 13 so that a vertebral artery 3 is not damaged, wherein FIG. 3A illustrates a state before the three-dimensional guide is brought into contact with cervical vertebrae, and FIG. 3B illustrates a state after the three-dimensional guide has been brought into contact with cervical vertebrae.

FIGS. 4A to 4C are cross-sectional views illustrating the positional relationship between a pedicle of vertebral arch and a three-dimensional guide, wherein FIG. 4A illustrates a state before the three-dimensional guide is brought into contact with the pedicle of vertebral arch, FIG. 4B illustrates a state in which a process contact surface 14a of the three-dimensional guide that is in the shape of a recess is brought into contact with a process 2 of the bone, and FIG. 4C is a bottom view illustrating the three-dimensional guide.

FIGS. 5A and 5B are front views illustrating a state in which a three-dimensional guide is brought into contact with a pedicle of vertebral arch, wherein FIG. 5A is a partial cross-sectional view illustrating a state before the three-dimensional guide is brought into contact with a pedicle of vertebral arch, and FIG. 5B is a partial cross-sectional view illustrating a state after the three-dimensional guide has been brought into contact with the pedicle of vertebral arch.

FIGS. 6A to 6C illustrate a state in which a K-wire is inserted along a guide hole formed in a three-dimensional guide, wherein FIG. 6A illustrates a state before the K-wire is inserted, FIG. 6B illustrates a state after the K-wire has been inserted, and FIG. 6C illustrates a state in which the three-dimensional guide is removed from the K-wire.

FIGS. 7A to 7C illustrate an example in which a pedicle is drilled into a pedicle of vertebral arch along a K-wire using a hollow drill, wherein FIG. 7A illustrates a state in which the K-wire is inserted into a hollow section of a drill, FIG. 7B illustrates a state during drilling, and FIG. 7C illustrates a state after a preliminary hole P₁ has been formed.

FIGS. 8A to 8C illustrate an example in which the inner circumference surface of a preliminary hole is tapped along a K-wire using a hollow tap, wherein FIG. 8A illustrates a state in which the K-wire is inserted into the tap, FIG. 8B illustrates a state during tapping, and FIG. 8C illustrates a state after a pedicle screw insertion threaded hole has been formed.

FIGS. 9A to 9C illustrate an example in which a pedicle screw is inserted into an insertion threaded hole formed in a pedicle of vertebral arch using a dedicated driver, wherein FIG. 9A illustrates a state before the pedicle screw is inserted, FIG. 9B illustrates a state after the pedicle screw has been inserted, and FIG. 9C illustrates a state after the driver has been removed.

FIG. 10 illustrates an example in which a plurality of pedicle screws are connected using a rod.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A three-dimensional guide according to one embodiment of the invention may be applied to an arbitrary part of a spine. An example in which the three-dimensional guide is applied to cervical vertebrae is described below.

The configuration (morphology) of the bones in the operative site is captured as a CT image, and a bone model A (see FIG. 1) is formed using plaster or the like.

Since a spine has a complex configuration in which vertebral arches are joined through an intervertebral disc, an anatomically appropriate insertion direction and insertion depth of a pedicle screw are determined using the bone model A and the CT image.

A spinal bone (vertebral arch) 1 has processes 2 (e.g., transverse process, spinous process, and articular process), and the surface of each bone has a complex and irregular configuration.

As illustrated in FIGS. 3A to 4B, a vertebral artery 3 passes through the spinal bone 1.

When the insertion site and the insertion direction have been anatomically determined taking account of the above situation, the shape of a plurality of (three in FIG. 1) three-dimensional guides 10, 10A, and 10B is determined based on the CT image.

When determining the shape of the three-dimensional guides 10, 10A, and 10B, it is necessary to set the size of contact surface sections 11, 11A, and 11B that come in surface contact with the bone along the irregular configuration of the bone at the insertion site, and the shape and the size of guide block sections 12, 12A, and 12B.

The following description focuses on the three-dimensional guide 10, and description of the three-dimensional guides 10A and 10B is omitted (corresponding reference signs are used for the three-dimensional guides 10A and 10B in the drawings).

The contact surface section 11 may have a process contact section 14 that comes in contact with the process (spinous process) 2 of the vertebral arch so that the three-dimensional guide 10 can be positioned by merely bringing the three-dimensional guide 10 into contact with the vertebral arch.

According to this configuration, the three-dimensional guide 10 is necessarily accurately positioned, and is not shifted due to the shape of the contact surface section (may be referred to as “morphological surface section”) 11 that is formed by a gradual irregular curved surface that corresponds to the morphological surface (morphology) of the bone at the insertion site, and the shape of the process contact section 14 that is formed by a steep slope, by merely placing the three-dimensional guide 10 in the vicinity of the insertion site.

Since it is necessary to pull out the three-dimensional guide 10 after inserting a K-wire in order to form an insertion hole for inserting the pedicle screw, the contact surface section 11 and the process contact section 14 are designed so that an undercut section is not formed.

In one embodiment of the invention, the process contact section 14 has a process contact surface 14a that is in the shape of a recess that corresponds to the shape of the spinous process 2 (see FIGS. 4A to 4C, 5A, 5B, and 6A). Note that the configuration is not limited thereto as long as the three-dimensional guide 10 can be effectively positioned.

A guide hole 13 is formed in the guide block section 12 to restrict the insertion direction of a K-wire 20 while guiding the K-wire 20.

After the shape of the three-dimensional guide 10 has been determined, a mold that has the determined shape is produced.

A resin or the like is injected into the mold to produce a three-dimensional guide having a given shape.

The insertion position and the insertion direction of the K-wire can be accurately determined by placing the three-dimensional guide 10 thus produced at the insertion site of the spine.

A method of forming a pedicle screw insertion hole using the three-dimensional guide 10 is described below.

FIGS. 2A and 2B are rear views illustrating cervical vertebrae, and FIGS. 3A and 3B are side views illustrating cervical vertebrae.

FIGS. 4A to 4C are cross-sectional views illustrating a pedicle of vertebral arch, and FIGS. 5A and 5B are enlarged views illustrating the spinous process 2.

As illustrated in FIGS. 2A, 3A, 4A, and 5A, the three-dimensional guide 10 that is produced based on the CT image includes the process contact section 14 in which the process contact surface 14a that is in the shape of a recess that corresponds to the shape of the spinous process 2 is formed, the contact surface section 11 that comes in contact with the morphological surface of the bone in an area from the spinous process 2 to the insertion site of a pedicle screw 50, and the guide block section 12 in which the guide hole 13 is formed.

Note that the contact surface section 11 comes in approximately surface contact with the morphological surface of the bone. The entire contact surface section 11 need not necessarily come in contact with the bone.

When the three-dimensional guide 10 is placed on the morphological surface of the bone that corresponds to the operative site, the process contact surface 14a that is in the shape of a recess is fitted to the spinous process 2 of the bone, and the contact surface section 11 is fitted to the irregular morphological surface of the bone in an area from the spinous process 2 to the guide hole 13, so that the three-dimensional guide 10 is positioned. Therefore, the insertion direction of the K-wire 20 is accurately determined by the direction of the guide hole 13 (see FIG. 6A).

The K-wire has a diameter of 1 to 2 mm, and the guide hole 13 has an inner diameter slightly larger than the outer diameter of the K-wire. It is desirable that the guide hole 13 have a length of 15 mm or more.

The stability of the insertion direction is improved as the length of the guide hole 13 increases. The length of the guide hole 13 is preferably 30 mm or less from the viewpoint of insertion operability and producibility of the guide block section 12.

Since the K-wire 20 is inserted along the guide hole 13 of the three-dimensional guide 10, the artery 3 and the like are not damaged.

When the K-wire 20 has been inserted into the pedicle of vertebral arch (see FIG. 6B), the three-dimensional guide 10 is removed from the K-wire 20 (see FIG. 6C).

A hollow drill 30 is inserted into the pedicle of vertebral arch along the K-wire 20 while rotating the drill 30 (see FIGS. 7A and 7B) to form a preliminary hole P₁ (see FIG. 7C).

A tap 40 (tapping drill) is inserted into the pedicle along the K-wire 20 and the preliminary hole P₁ while rotating the tap 40 (see FIGS. 8A and 8B) to form a pedicle screw insertion hole P₂ having a thread groove (see FIG. 8C).

An external thread section 50a of the pedicle screw 50 is screwed into the insertion hole P₂ using a dedicated driver 60 (see FIGS. 9A and 9B), and the driver 60 is removed after the external thread section 50a has been screwed into the insertion hole P₂.

The angle of a head 50b of the pedicle screw 50 thus inserted is adjusted, and a plurality of pedicle screws 50 are connected using a rod 70 (see FIG. 10) to secure the bone 1.

The outer diameter of the external thread section 50a of the pedicle screw 50 is normally 3.5 to 4 mm.

The three-dimensional guide 10 may be used in many institutions in which spinal surgery is performed.

Although only some embodiments of the present invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within scope of this invention.

Claims

1. A three-dimensional guide for a wire for forming a pedicle screw insertion hole that is produced based on a CT image of a spine, the three-dimensional guide comprising:

a contact surface section that comes in surface contact with a morphological surface of a bone at an insertion site; and

a guide block section that is provided upright from the contact surface section,

the guide block section having a guide hole for the wire, and

the guide hole having an inner diameter slightly larger than an outer diameter of the wire, and having a length of 15 to 30 mm to restrict an insertion position and an insertion direction of the wire.

2. The three-dimensional guide as defined in claim 1,

the contact surface section including a morphological surface section that is formed by a gradual irregular curved surface that corresponds to the morphological surface of the bone at the insertion site, and a process contact section that is formed by a steep slope and comes in contact with a process of a vertebral arch.

3. A method of producing a three-dimensional guide for a wire for forming a pedicle screw insertion hole, the method comprising:

extracting a pedicle screw insertion site based on a CT image of a spine;

producing a mold based on the extracted pedicle screw insertion site; and

molding the three-dimensional guide in the mold, the three-dimensional guide including a contact surface section that comes in surface contact with a morphological surface of a bone at the insertion site, and a guide block section that has a guide hole for restricting an insertion position and an insertion direction of the wire.

4. The method as defined in claim 3,

the molding of the three-dimensional guide including molding the contact surface section in the mold so that the contact surface section includes a morphological surface section that is formed by a gradual irregular curved surface that corresponds to the morphological surface of the bone at the insertion site, and a process contact section that is formed by a steep slope and comes in contact with a process of a vertebral arch.