The present application is based on, and claims priority from, J.P. Application No. 2008-115286, filed on Apr. 25, 2008, the disclosure of which is hereby incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to an ultrasonic horn and an ultrasonic hand piece, and in particular, relates to an ultrasonic horn and an ultrasonic hand piece suitable for cutting living bone tissue.
2. Description of the Related Art
In a conventional orthopedic operation of a spine or a cervical spine, a treatment including; (a) fixing a plurality of pedicle screws to centrums and (b) coupling the pedicle screws to a plate in order to fix the centrums together has been commonly used. In order to fix a pedicle screw to a centrum, a doctor normally cuts and removes the vertebral arch from the centrum, and then uses a drill to form a guide hole in the cancellous bone of the pedicle into which a pedicle screw is to be screwed. The guide hole typically has a diameter ranging between 3 and 4 mm and a length of about 13 mm.
The cancellous bone is exposed over a relatively large area in the part of the centrum where the vertebral arch is removed. The cancellous bone is connected to the interior of the centrum through a narrow area sandwiched between cortical bones. Since a radicle of a nerve is present adjacent to the narrow area and is very close to the cortical bone, breaking through the cortical bone with the drill may lead to damage on the surrounding nerves or vessels. Furthermore, if the pedicle screw is not fixed in an appropriate direction, then adjacent radicles may be compressed by the force that is exerted on the pedicle screw when the pedicle screw is coupled to the plate. Accordingly, it is necessary that the guide hole be formed such that the pedicle screw can be screwed straight toward the centrum through the region between the cortical bones.
Normally, when a guide hole is formed by means of a drill, a doctor manipulates the drill while checking the location at which the guide hole is formed by means of X-ray pictures. However, appropriately forming the guide hole relying on the X-ray pictures, which are two-dimensional images, requires a significantly high level of skill. Further, taking an X-ray picture requires suspension of the operation. Thus, it is desirable to form a guide hole without taking X-ray pictures in view of the need of rapid treatment and relieving the situation of the patient.
Under these circumstances and as a result of elaborate work, the present inventors found that the guide hole can be formed in the cancellous bone of the pedicle safely and easily by using an ultrasonic operative instrument (an ultrasonic hand piece). Irrespective of the lower cutting efficiency as compared to a drill, the ultrasonic operative instrument still offers easy cutting of the cancellous bone, in which the guide hole is formed, while it can not easily cut the cortical bone that is harder than the cancellous bone. This enables a doctor to clearly feel with his hand the difference between the cancellous bone and the cortical bone when an ultrasonic operative instrument reaches the cortical bone from the cancellous bone. Thus, a doctor can safely and easily form a guide hole without checking X-ray pictures by cutting a cancellous bone and by relying on his hand to feel the difference between cancellous and cortical bone.
A known ultrasonic operative instrument described above is disclosed in Japanese Patent Laid-Open No. 2005-152098.
An ultrasonic operative instrument includes an ultrasonic vibration mechanism for generating ultrasonic vibration and a horn that utilizes the vibration transmitted from the ultrasonic vibration mechanism in order to perform cutting at a distal end structure thereof. The distal end structure of the horn is generally formed in a straight tube having a constant outer diameter. However, a distal end structure having a constant outer diameter increases the side area of the horn that comes into contact with living tissue as cutting progresses and as the distal end structure is gradually inserted into the living tissue, such as a bone. An increase in the area of a horn that comes into contact with the living tissue produces higher friction between the horn and the living tissue, leading to a reduction in living tissue cutting efficiency and to generation of heat at the interface between the living tissue and the horn.
An object of the present invention is to provide an ultrasonic horn and an ultrasonic hand piece, as well as a treatment method using the same, that can prevent a reduction in cutting efficiency that may occur as cutting progresses.
To this end, an ultrasonic horn according to the present invention comprises a main body portion and a distal end structure formed at a distal end of the main body portion, the ultrasonic horn being adapted to be used to cut living tissue. The largest outer diameter of a portion of the ultrasonic horn is in the distal end structure, the portion being inserted into the living tissue when the living tissue is cut.
According to one embodiment of the present invention, an ultrasonic hand piece comprises: an ultrasonic vibration mechanism for generating ultrasonic vibration, an ultrasonic horn described above, the ultrasonic horn being coupled to the ultrasonic vibration mechanism, and an outer cylindrical portion covering the ultrasonic vibration mechanism and a part of the ultrasonic horn.
According to another embodiment of the present invention, a method for cutting living tissue to create a hole in the living tissue comprises inserting an ultrasonic horn into the living tissue, the ultrasonic horn including a main body portion and a distal end structure formed at a distal end of the main body portion, wherein a largest outer diameter of a portion of the ultrasonic horn is in the distal end structure, the portion being inserted into the living tissue when the living tissue is cut.
The present invention can provide an ultrasonic horn and an ultrasonic hand piece, as well as a treatment method using the same, that can prevent a reduction in cutting efficiency that may occur as cutting progresses.
The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.
Embodiments of the present invention will now be described with reference to the drawings.
First, an ultrasonic hand piece according to an embodiment of the present invention will be described with reference to
Referring to
Vibration transmitted from ultrasonic vibration mechanism 3 causes horn 2 to vibrate at a predetermined frequency in an axial direction thereof. Horn 2 cuts a desired portion of hard living tissue, such as a bone, at the distal end thereof that is in touch with the hard living tissue.
Outer cylindrical portion 1 is configured to cover horn 2 and ultrasonic vibration mechanism 3 that is coupled to the proximal end of horn 2. Ultrasonic vibration mechanism 3 includes flange 8, piezo elements 9, 10, electrodes 11, 12, front plate 13 and back plate 14. Piezo elements 9, 10, which are sandwiched between front plate 13 and back plate 14, generate vibration in the axial direction (in the traversing direction of
These elements are integrated by means of screws provided at the junction of the elements adjacent to each other.
The ultrasonic operative instrument utilizes ultrasonic vibration to crush, emulsify and suck in human living tissue in order to selectively remove the damaged portion. The distal end structure of horn 2 projecting from outer cylindrical portion 1 generates a large quantity of heat because it is the portion that comes into actual contact with the human portion to be cut and vibrates at a large amplitude (displacement). Consequently, joint 1b is provided on the outer periphery of outer cylindrical portion 1. Joint 1b is used to inject irrigation liquid in order to cool the distal end structure and to promote suction of removed objects.
Suction through-hole 15 is provided to extend through horn 2, front plate 13, piezo elements 9, 10, back plate 14 and outer cylindrical portion 1, which are configured as described above, along the central line of these elements. Crushed and emulsified living tissue is sucked in by an external suction pump via suction through-hole 15 and joint 1a shown in
Furthermore, vibration converting mechanism 17 is provided on horn 2. Vibration converting mechanism 17 is the same as that disclosed in JPA 2005-152098, the disclosure of which is hereby incorporated by reference herein in its entirety.
Groove portions 17a are engraved on horn 2 in parallel with each other at a predetermined interval. Each groove portion 17a is inclined on the side surface at predetermined angle α, which is set to be more than 0 degree and less than 90 degrees, with respect to central axis X-X of horn 2.
Groove portion 17a is formed in a rectangle having a width of 0.5 to 5 mm, a length of 3 to 30 mm and a depth of at least 0.5 mm.
It should be noted that the location of the groove portions serving as vibration converting mechanism 17 is not limited to the side surface of horn 2. The groove portions may be formed at a location between the distal end of horn 2 and the electrostrictive element of ultrasonic vibration mechanism 3, wherein the location includes the outer side surfaces of horn 2, ultrasonic vibration mechanism 3 and any members interposed between horn 2 and ultrasonic vibration mechanism 3.
The mechanism of vibration conversion performed by groove portions 17a can, at present, be explained as follows. As shown in
The above-described configuration enables a synthesized movement comprised of a high-speed pivotal movement and a high-speed reciprocating movement, and significantly improves not only the efficiency in cutting living tissue but also the sharpness in a cutting action, i.e., cutting quality. Thus, it is possible to cut a damaged site undisturbed without crushing adjacent living tissue.
In use, the distal-end tip of horn 2 is pressed against the site to be cut in order to crush and emulsify the living tissue in the site. The irrigation liquid injected via joint 1b cools horn 2 when it flows between cylindrical portion 1 and horn 2, and, after being discharged from cylindrical portion 1, is sucked out to the outside via suction through-hole 15 together with pieces of the living tissue cut into fragments.
An embodiment of the ultrasonic horn according to the present invention will now be described.
Horn 2 according to the present embodiment is 110 mm in total length; main body portion 2b is 2.5 mm in outer diameter; and suction through-hole 15 is 2.0 mm in diameter. Distal end portion 2a is 2.8 mm in diameter and 3.0 mm in length. However, these dimensions are mere examples of horn 2 and do not limit the horn according to the present invention.
Horn 2 according to the present embodiment shown in the left part of
On the other hand, in the case of horn 2′ having a constant outer diameter, as shown in the right part of
The distal edge of distal end structure 2a of horn 2 according to the present embodiment is chamfered. Thus, even if distal end structure 2a of horn 2 is moved away from the region between the cortical bones in the cutting process and distal end structure 2a comes into contact with the cortical bone, damage on the cortical bone can be avoided because of the dull distal edge of distal end structure 2a. Moreover, as described above, when distal end structure 2a of horn 2 reaches the cortical bone from the cancellous bone, a doctor can recognize this with his hand. Thus, the chamfered portion can be slid along the cortical bone in order to modify the cutting direction, as shown by an arrow in
A first variation of the horn shown in
According to the present embodiment, the area of the horn that is in contact with the living tissue (actual crushing area) is reduced, and accordingly, there is an improvement in the efficiency in cutting living tissue because distal end structure 2a has a larger diameter than the other portions. Therefore, a larger amount of bone fragments to be sucked out through suction through-hole 15 per unit time is discharged as compared to a conventional horn. In a normal condition, it is possible for the configuration having suction through-hole 15 with a constant diameter to successfully suck in bone fragments or the like, as shown in the right part of
In contrast, suction through-hole 15 of horn 2 shown in the left part of
Furthermore, because of the expanding and contracting movements of horn 2 during an operation, horn 2 is subjected to stress because of these movements. This stress may cause metal fatigue in horn 2, which may result in the failure of horn 2. In particular, distal end structure 2a of horn 2 tends to be more easily damaged because of the stress that occurs during the operation and additionally because of the pressing force that horn 2 exerts against the living tissue during cutting. However, horn 2 shown in the left part of
First diameter portion 15a preferably has a reduced length in order to prevent suction through-hole 15 from being clogged with the bone chips or the like. In the example shown in
Moreover, as shown in
Horn 2 shown in
With reference to
The present invention has been described in conjunction with the embodiments and the variations thereof. However, the present invention is not limited to the embodiments and the variations. Furthermore, the configurations according to the embodiments and variations may be combined together where possible. It also should be understood that various changes and modifications may be made without departing from the spirit or scope of the appended claims.
Number | Date | Country | Kind |
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JP2008-115286 | Apr 2008 | JP | national |