RU2810363C1 - Device for lower jaw prosthetics - Google Patents

Abstract

FIELD: medicine; maxillofacial surgery.

SUBSTANCE: device for lower jaw prosthetics includes a bone plate designed to be fixed on the body of the lower jaw, and a lower jaw prosthesis with the ability to move them relative to each other. The device contains an oblong body equipped with a slider, to which a prosthesis of the lower jaw is attached, and on one side of the elongated body a bone plate is attached via a rotary axis with the possibility of fixing the angle of rotation, and on the other side — a means for moving the slider along the oblong body, containing a screw for moving the slider, the end part of which is located on the side opposite to the bone plate, and has a mechanism for step-by-step movement of the slider. The mechanism for step-by-step movement of the slider contains an adapter with a multifaceted longitudinal hole and a transverse through hole in the wall, welded to the end of the screw located on the side opposite the bone plate, into which a multifaceted end protrusion of a removable drive with a spring-loaded retainer is inserted, containing a rod with a ring-shaped widening, placed inside a through transverse hole inside the body of the end polyhedral protrusion of the removable drive.

EFFECT: possibility to eliminate functional disorders and facial asymmetry is achieved by expanding the elements of the prosthesis without causing unwanted stress in the structure and without dislocating the fixing screws; lengthening in the body and jaw branches; preventing reverse twisting of prosthetic elements; gradual expansion of the prosthetic elements is as convenient and comfortable for the patient as possible with minimal surgical trauma.

3 cl, 42 dwg, 1 ex

Description

The invention relates to medicine, namely maxillofacial surgery, and can be used to eliminate extensive congenital and acquired defects of the lower jaw. The target group for this invention is pediatric patients.

It has been established that untimely elimination of defects and deformations of the bones of the facial skeleton, and in particular the lower jaw, leads to the development of secondary deformations that are difficult to treat. This, in turn, is accompanied by the formation of breathing, swallowing, chewing, and speech disorders.

All of the above has an extremely negative impact not only on the child’s health, but also significantly complicates his social adaptation.

With pronounced underdevelopment of the lower jaw, the presence of a defect in its branches and body, the root of the tongue, together with the complex of tissues of the floor of the oral cavity, shifts towards the posterior stack of the pharynx. As a result, the lumen of the upper respiratory tract narrows, which leads to the formation of respiratory disorders (obstructive breathing disorders), manifested in the form of obstructive apnea syndrome. With the congenital nature of the pathology of the lower jaw, such breathing disorders can occur immediately after the birth of the child.

Currently, in the medical community, the question of the method and extent of reconstructive operations for this group of patients has not been completely resolved. There are a large number of different methods for eliminating defects of the lower jaw (auto-, allotransplantation, the use of implants from various materials, compression-distraction osteosynthesis), however, they all have a number of disadvantages, some of them are not applicable in childhood.

The most common technique used to eliminate large defects of the lower jaw is bone grafting with an autograft on a vascular pedicle (1). The rib, iliac crest, and fibula can be used as a donor site. This type of surgery is widespread in adults, but has a number of significant disadvantages in pediatric patients. Removal of an autograft is an additional injury that aggravates and lengthens the recovery period; partial resorption of the graft always occurs, the volume of which cannot be accurately calculated. There is also a risk of graft rejection, and the transplanted bone does not grow, which requires repeated surgical interventions. In young children, such an operation is impossible due to the small size of the donor zone, its inadequate ossification, and the risk of damage to the growth zones at the site of graft collection.

An alternative technique that can be used to eliminate the defect of the lower jaw is the use of external compression-distraction devices (2). In this case, a compression-distraction device is applied to the jaw, between the legs of which an osteotomy of bone fragments is performed. Subsequently, the elements of the apparatus are expanded, during which the section of bone on which the compression-distraction apparatus is applied is lengthened. This technique is complex in execution, multi-stage (it requires sequential installation and removal of several compression-distraction devices to eliminate an extensive defect in the body and ramus of the lower jaw), allows eliminating the defect of the lower jaw only in one plane (it is impossible to restore the volume and shape of the lower jaw similar to its healthy half ). When using this technique, it is impossible to recreate the structures of the temporomandibular joint (articular head, articular fossa).

A device for mandibular prosthetics is known, including a bone plate for fixation on the body of the lower jaw, and a lower jaw prosthesis with the ability to move them relative to each other (3, 4). This device is essentially designed to correct a defect in the lower jaw. It has the ability to lengthen as the healthy half of the lower jaw grows. As noted above, the said device includes an individual bone plate for fixation on the body of the lower jaw with screws and a prosthesis of the lower jaw, in particular, a prosthesis of the lower jaw branch, including an articular head, with the possibility of moving two of these parts relative to each other, leading to increasing the total length of the device along the length of the body of the lower jaw.

The bone plate and the mandibular ramus prosthesis are connected to each other by a screw, when rotated, one part moves along the other (extends). At the same time, the total length of the device increases.

This technical solution was adopted as a prototype of the claimed invention, since it is the closest to it in terms of the totality of common essential features.

Let's take a closer look at the design features of this device.

Its important feature is that the bone plate is rigidly connected to the healthy part of the lower jaw on one side and to the prosthetic branch of the lower jaw, the end of which rests against the prosthetic glenoid fossa, on the other. In plan (in the axial plane), these two parts in the assembly, together with the lower jaw, have a shape resembling the shape of an isosceles triangle, the ends of the femurs of which are fixed in the articular fossae of the temporal bones. Over time, the healthy half of the lower jaw (one of the sides of the triangle) grows. At the same time, the previously established design remains unchanged, which is manifested in the formation and increase of facial asymmetry, bite deformation and the formation of various functional disorders (up to the development of obstructive apnea syndrome due to the posterior displacement of half of the lower jaw, and with it the complex of tissues of the floor of the oral cavity). To eliminate these emerging anatomical imbalances, it is necessary to lengthen the installed structure. By rotating the screw, the prosthetic branch of the lower jaw moves relative to the bone plate, which is accompanied by an increase in the length of the entire structure along the length of the body of the lower jaw.

However, the following disadvantages arise.

As noted above, the bone plate, the prosthesis of the mandibular ramus and the lower jaw itself in plan resemble an isosceles triangle, the ends of the femurs of which are rigidly connected to the articular fossae and the distance between them is constant. Since the bone plate is rigid and solid, the expansion of the device elements due to the impossibility of rotating the bone plate and the branch prosthesis relative to each other leads to the emergence of significant stress in the bone plate, which is rigidly connected to the body of the lower jaw. This may result in either a fracture of the structure or dislocation of the bone screws holding the bone plate in place.

The next drawback is the absence of a mechanism that prevents the screw from turning back, and with it the elements of the device, under the influence of chewing movements.

It should also be noted that the design described above does not have the necessary elements that would make it convenient and comfortable for the patient to carry out step-by-step extension of the prosthetic elements, similar to a compression-distraction device. This design provides for only one-stage extension of the structure during surgery. In this case, the strong stretching of the tissues that occurs when the structure is simultaneously extended over a significant distance (more than 5 mm) leads to the development of ischemic disorders in the soft tissues, which is accompanied by pain, and can also provoke exposure of the elements of the prosthesis.

Another disadvantage is the location of the screw head (into which a screwdriver is inserted to rotate it) in the projection of the chin area, which requires surgical access to the screw head in an aesthetically significant area.

The purpose of the invention is:

• creation of a device that allows eliminating functional disorders and facial asymmetry that arise as the healthy half of the lower jaw grows, due to the expansion of prosthetic elements without causing unwanted stress in the structure and without dislocating the fixing screws;

• development of a sliding device with a mechanism that prevents the reverse twisting of prosthetic elements under the influence of chewing movements;

• development of a technical solution that allows for gradual, rather than immediate, expansion of prosthetic elements as convenient and comfortable for the patient as possible with minimal surgical trauma;

• Creation of a device that allows surgical access to the prosthesis screw for its rotation in an aesthetically acceptable area;

• Expansion of the range of devices intended for carrying out operations of this type.

This goal is achieved by the fact that the device for prosthetics of the lower jaw includes a bone plate, which is fixed on the body of the lower jaw, and a lower jaw prosthesis with the ability to move them relative to each other, and, according to the invention, the device contains an elongated body equipped with a slider to which is attached prosthesis of the lower jaw, with a bone plate attached to the oblong body on one side by means of a rotating axis with the ability to fix the angle of rotation, and on the other side a means for moving the slider along the oblong body is attached.

This set of essential features characterizes the essence of the invention. It is necessary and sufficient for any implementation of the invention.

A device characterized by this set of features allows:

• eliminate functional disorders and facial asymmetry that arise as the healthy half of the lower jaw grows due to the expansion of prosthetic elements without causing unwanted stress in the structure and without dislocating the fixing screws;

• carry out, if necessary, lengthening not only in the body area, but also in the branch area;

• prevent reverse twisting of prosthetic elements;

• carry out gradual, rather than immediate, expansion of the prosthetic elements as convenient and comfortable for the patient as possible with minimal surgical trauma;

• perform surgical access to the screw of the prosthesis to rotate it and expand the elements of the prosthesis in an aesthetically acceptable area;

• Expansion of the range of devices intended for carrying out operations of this type.

In addition, the applicant considers it necessary to highlight the following developments and/or clarifications of the set of essential features related to special cases of implementation or use.

According to the applicant, it is preferable that the elongated body would be made with an elongated through groove with protrusions directed towards each other on the sides, inside of which a slider would be placed with the possibility of reciprocating movement, and the means for moving the slider along the elongated body would contain a screw for moving the slider , installed in a through hole of the slide equipped with a screw thread, the end part of which, on the side of the bone plate, is installed with the possibility of rotation in the through hole in a transverse plug rigidly connected to the elongated body on the side of the bone plate, and the end part of the screw located on the side of the bone plate, has an external widening at the end with the possibility of support on a transverse plug located on the side of the bone plate, and the end part of the screw, located on the side opposite to the bone plate, is installed with the possibility of rotation in a through hole in a transverse plug rigidly connected to the elongated body, located on the side opposite on the bone plate, and has a mechanism for step-by-step movement of the slider.

A significant advantage of this design is the ease of installation, ease of sliding of its elements, as well as comfort for patients and a good aesthetic result.

The mechanism for stepwise movement of the slider can have various designs.

In the simplest case, this mechanism may include a slot made in the screw head for the tip of a screwdriver, and the screwdriver itself, the tip of which is inserted into the slot for rotation, which is performed in stages, for example, each time at a certain angle, or, in other words, step by step, the step size is determined according to an individual distraction protocol drawn up by the attending physician.

This design is obvious and does not require special drawings for explanation.

Another mechanism for step-by-step movement of the slider may contain an adapter with a multifaceted longitudinal hole and a transverse through hole in the wall, welded directly to the end of the screw, located on the side opposite the bone plate, into which a multifaceted end protrusion of a removable drive is inserted with a spring-loaded retainer containing a rod with ring-shaped widening, placed inside the through transverse hole inside the protrusion of the removable drive, and the annular widening of the rod with one side is installed with the possibility of contact with the ledge made inside the through transverse hole of the protrusion of the removable drive, and with the other side - in the through hole of the plug welded to the protrusion, and inside In the cavity between the annular widening of the rod and the plug, a spring is installed to ensure that the annular widening of the rod is pressed against the ledge and, at the same time, when the annular widening of the rod comes into contact with the ledge, the end part of the rod protrudes above the surface of the ledge of the removable drive.

This design is obvious and does not require special drawings for explanation. It is stated in this application as a special case of implementation.

This design is characterized by ease of installation, postoperative care and can significantly facilitate the rehabilitation period for patients.

It is preferable that the multifaceted longitudinal hole of the adapter be made of a hexagonal shape, and the end polygonal shape of the removable drive protrusion inserted into it would also be made of a hexagonal shape.

The applicant considers it necessary to especially draw the examiner's attention to the following feature of this application.

Along with the device described above, there are other designs of the mechanism for step-by-step movement of the slider, which is used in this application.

The part of the claimed device related to the rotation of the oblong body relative to the bone plate is very important.

According to the applicant, it is advisable that for this purpose the bone plate would have a loop at the end, and the oblong body would have a pair of loops, in the gap between which a bone plate loop is installed, while the through holes of the loops would coincide to form a common through hole, and the rotary axis would be made in the form of a tubular axis, rigidly attached at one end to the outer side of the loop of the oblong body and having a length corresponding to the total length of the loop of the oblong body and the loop of the bone plate, moreover, the tubular axis has a longitudinal through hole with a screw thread on part of the length from the side of attachment to the outer side of the loop of the oblong body, and on the remaining part of the length, through longitudinal slots are made in its wall, and the thickness of the walls corresponding to the longitudinal slots gradually decreases towards the end of the tubular axis, forming the surface of a straight circular cone of the walls of the longitudinal through hole of the tubular axis corresponding to the slots, in this case, a tubular axis screw rod with a slotted head is screwed into the screw thread of the tubular axis, and the tubular axis screw rod and the screw head are connected by a transition part having a conical shape, forming the surface of a straight circular cone of the tubular axis screw transition part, located in the place in which the thickness of the walls of the tubular axis corresponding to the longitudinal slots gradually decreases towards the end of the tubular axis.

The advantage of this design is the ease of installation, the convenience of moving its elements apart, as well as comfort for patients and a good functional and aesthetic final result.

To summarize, we can note the following:

The developed device has the following advantages relative to known analogues:

• the ability to eliminate functional disorders and facial asymmetry that arise as the healthy half of the lower jaw grows due to the expansion of prosthetic elements without causing unwanted stress in the structure and without dislocating the fixing screws;

• the possibility of carrying out, if necessary, lengthening not only in the area of the body of the lower jaw, but also in the area of the branch of the lower jaw;

• prevention of reverse twisting of prosthetic elements;

• carrying out a gradual, rather than one-stage, extension of the prosthetic elements as convenient and comfortable for the patient as possible with minimal surgical trauma;

• performing surgical access to the screw of the prosthesis to rotate it and expand the elements of the prosthesis in an aesthetically acceptable area.

The advantages described above are achieved due to the design features of the proposed device.

The presence of a slider between the oblong body and the lower jaw prosthesis allows you to gradually move (move apart) the elements of the device relative to each other, which leads to the gradual elimination of facial asymmetry and normalization of the position of the lower jaw. The connection of the bone plate with the oblong body using a rotary axis with the possibility of fixing the angle of rotation prevents the occurrence of unwanted stresses when moving apart the elements of the device, and also prevents dislocation of the fixing screws (the latter are screwed through holes in the bone plate into the body of the lower jaw). The presence at the end of the slider moving screw, opposite to the bone plate, of a step-by-step mechanism for moving the slider allows you to gradually move apart the elements of the device without causing ischemic disorders in the surrounding soft tissues, and also prevents reverse unscrewing of the elements of the device under the influence of chewing movements. This in turn ensures the stability of the treatment results. The presence of a mechanism for step-by-step movement of the slider allows, with minimal trauma to the patient, almost painlessly, to move apart the elements of the device and, thereby, eliminate facial asymmetry. The presence of a removable drive on the opposite side of the bone plate allows the drive to be brought out through the skin in an aesthetically acceptable, inconspicuous (behind the ear) area of the face, which is important for the psychological comfort of the patient. The very possibility of detaching the drive to turn the screw eliminates the need for postoperative care at the site where the drive exits the skin, which also has a beneficial effect on the patient’s quality of life in the postoperative period.

In conclusion of this section of the description, it should be noted that in addition to the advantages noted above, the advantage of the present invention also lies in the fact that the device can be manufactured on technological equipment already used in the medical industry.

The device also allows you to expand the range of devices used for treatment.

The invention is illustrated by the drawing.

In fig. Figure 1 shows a device for lower jaw prosthetics installed on the lower jaw, side view, axonometry;

Note: The screws for attaching the bone plate to the mandible are not shown.

In fig. 2 - the same, view from the other side, axonometry;

In fig. 3 - the same, front view, axonometry;

In fig. Figure 4 shows a separate device for lower jaw prosthetics, top view, axonometry;

In fig. 5 shows a separate device for prosthetics of the lower jaw at the moment when the slider is in the closest position to the bone plate, side view from above, axonometry;

In fig. 6 - the same, when the slider is in the farthest position from the bone plate, side view from above, axonometry;

In fig. 7 shows an oblong body, end view from the side of the hinges, axonometry;

In fig. 8 - the same; end view without hinges, axonometry;

In fig. 9 - the same, side view, axonometry;

In fig. 10 shows a slider to which the lower jaw prosthesis is attached, view from the side of the slider, axonometry;

In fig. 11 - the same, view from the side to which the slider is not attached, axonometry;

In fig. 12 shows an oblong body, in the oblong groove of which a slider with a lower jaw prosthesis is installed, and the walls of the oblong body are made transparent, axonometry;

In fig. 13 - the same, in which a transverse plug from the side of the bone plate and a transverse plug from the side opposite to the bone plate are schematically shown, axonometry;

In fig. 14 shows the slider moving screw, top view;

In fig. 15 shows an oblong body, in the oblong groove of which, on the transverse plug on the side of the bone plate and the transverse plug on the side opposite to the bone plate, there is a screw installed, previously screwed into the slider, connected to the lower jaw prosthesis, and the walls of the oblong body are made transparent, view of the oblong body from the side of the loops of the oblong body, axonometry;

In fig. 16 - the same, view of the oblong body from the side opposite to the loops of the oblong body, axonometry;

In fig. 17 - the same, vertical section according to AA of Fig. 16;

In fig. 18 shows a cross section BB of FIG. 17;

In fig. 19 shows a transverse plug from the side opposite to the bone plate, a view from the side on which there are no protrusions with inclined walls, axonometry;

In fig. 20 shows a transverse plug from the side opposite to the bone plate, a view from the side on which there are protrusions with inclined walls, axonometry;

In fig. 21 shows a slider moving screw with a cylindrical extension made on the extension of the slider moving screw on the side opposite the bone plate with longitudinal grooves ending in an end cylindrical widening, and with a sleeve with a through longitudinal cavity put on the screw extension on the side opposite the bone plate and protrusions on one side, as well as a bushing spring placed on the screw extension, side view, axonometry;

Note: the longitudinal ring is not shown so as not to overload the figure.

In fig. Figure 22 shows the bushing from the side of the protrusions inside the through longitudinal cavity, axonometry,

In fig. 23 shows a separate view of the bushing mounted on the slider displacement screw, axonometry;

Note: the longitudinal ring is not shown so as not to overload the figure.

In fig. 24 - the same, vertical section B-B of Fig. 22 along the longitudinal axis of the slider moving screw;

Note: the longitudinal ring is not shown so as not to overload the figure.

In fig. 25 shows a means for controlling the movement of the slider with the bushing, at a time when a pair of oppositely located protrusions with inclined walls on the transverse plug on the side opposite to the bone plate are located inside a pair of oppositely located recesses with inclined walls at the end of the bushing, side view.

In fig. 26 - the same, at the moment when a pair of oppositely located protrusions with inclined walls on the transverse plug on the side opposite to the bone plate are located outside the pair of oppositely located recesses with inclined walls at the end of the sleeve, side view.

In fig. Figure 27 shows an adapter with a multifaceted longitudinal hole and a transverse through hole in the wall, intended for installing the end multifaceted protrusion of a removable drive with a spring-loaded lock into it, axonometry.

In fig. Figure 28 shows the end polyhedral protrusion of a removable drive with a spring-loaded lock, intended for installation in an adapter with a multifaceted longitudinal hole, axonometry.

In fig. 29 - the same, with the polyhedral-shaped end protrusion of the removable drive shown transparent, axonometry.

In fig. 30 shows a cross-section of the end polyhedral projection of the removable drive, passing through the spring-loaded retainer.

In fig. Figure 31 shows an adapter with a multifaceted longitudinal hole and a transverse through hole in the wall, into which the end multifaceted protrusion of a removable drive with a spring-loaded lock is inserted, axonometry.

In fig. 32 - the same, and the adapter with a multifaceted longitudinal hole and a transverse through hole in the wall, as well as the multifaceted end protrusion of a removable drive inserted into it with a spring-loaded lock, are shown transparent, axonometry.

In fig. 33 shows an on-bone plate and an oblong body with a slider and a means of moving the slide along the oblong plate, and the loops of the oblong body and the on-bone plate coincide with the formation of a common through hole, while the loops on the on-bone plate are shown as transparent, axonometry.

In fig. Figure 34 shows the bone plate, internal view, axonometry.

In fig. 35 shows a tubular axis, axonometry.

Note: The screw thread (item 74) is not shown to avoid overcrowding the figure.

In fig. 36 shows a tubular axis, longitudinal section.

Note: The screw thread (item 74) is not shown to avoid overcrowding the figure.

In fig. 37 shows an on-bone plate and an oblong body with a slider and a means for moving the slide along the oblong body, and the loops of the oblong body and the on-bone plate coincide with the formation of a common through hole, as well as a tubular axis, before its installation in a common through hole, while the loops of the on-bone plate are shown transparent, axonometry.

Note: The carvings are not shown to avoid overcrowding the figure.

In fig. 38 - the same, after installing the tubular axis into the common through hole, with all the loops of the oblong body and the bone plate shown transparent, axonometry.

Note: The carvings are not shown to avoid overcrowding the figure.

In fig. 39 shows a screw of a tubular axis, view from the slot side, axonometry.

Note: The screw thread (item 84) is not shown to avoid overcrowding the figure.

In fig. 40 shows a tubular axis screw, side view.

Note: The thread (item 84) is not shown to avoid overcrowding the figure.

In fig. 41 shows a longitudinal section of a screw of a tubular axis.

In fig. 42 shows a bone plate and an oblong body with a slider and a means of moving the slider along the oblong plate, and the loops of the oblong body and the bone plate coincide with the formation of a common through hole, as well as a tubular axis fixed in a common through hole, into the longitudinal through hole of which a tubular screw is screwed axles, partial breakout.

Note: the threads are not shown to avoid overcrowding the figure.

Device 1 for prosthetics of the lower jaw includes a bone plate 2 for connection with the body 3 of the lower jaw 4, and a prosthesis 5 of the lower jaw, with the ability to move them relative to each other, and the device contains an oblong body 6, equipped with a slider 7, to which the prosthesis 5 of the lower jaw is attached jaw, and to the oblong body 6, on one side, a bone plate 2 is attached via a rotary axis 8 with the ability to fix the angle of rotation, and on the other side, a means 9 for moving the slider along the oblong body is attached (Fig. 1 - Fig. 6).

This is the general design of the claimed device.

Let us now consider its individual components and parts.

The oblong body 6 is made with a longitudinal through groove 10 of a T-shape with protrusions 11 directed towards each other on the sides, inside of which there is a slider 7 with the possibility of reciprocating movement inside the longitudinal through groove 10, and a means 9 for moving the slider 7 along the oblong body 6 contains a screw 12 for moving the slider, installed in a through hole 14 of the slider 7 equipped with a screw thread 13, the end part 15 of which, located on the side of the bone plate, is installed with the possibility of rotation in the through hole 16 in a transverse plug 17 rigidly connected to the elongated body 6, located with sides of the bone plate 2, and the end part 15 of the screw, located on the side of the bone plate, has an external widening 18 at the end with the possibility of support on the transverse plug 17, located on the side of the bone plate 2, and the end part 19 of the screw, located on the side opposite to the bone plate , is installed with the possibility of rotation in the through hole 20 in a transverse plug 21 rigidly connected to the elongated body 6, located on the side opposite to the bone plate 2, and has a mechanism 22 for step-by-step movement of the slider, which is designed to fix the position of the screw during rotation, counting the turns of the screw with the purpose of determining by the attending physician a fixed amount of movement of the slider, and, consequently, the amount of distraction.

The applicant draws attention to the fact that the surface of the part of the screw 12 between its end parts 15 and 19 has a thread 23.

Let us consider separately the design of the mechanism 22 for step-by-step movement of the slider.

It contains, on the transverse plug 21, located on the side opposite to the bone plate, an annular protrusion 24 with a pair of oppositely located additional protrusions 25 with inclined walls 26, made on the end part of the screw 12, located on the side opposite to the bone plate 2, an elongated cylindrical part 27 with a smooth surface, a cylindrical widening 28 with longitudinal grooves 29, ending with an additional cylindrical widening 30, mounted on the end part 19 of the screw 12, located on the side opposite the bone plate 2, a sleeve 31 with a through longitudinal cavity 32 and protrusions 33 inward on one side , while the sleeve 31 covers the widening 28 of the cylindrical shape of the screw 12 with longitudinal grooves 29 so that the protrusions 33 of the bushing 31 are placed inside the longitudinal grooves 29 with the possibility of longitudinal movement, and the end part 34 without protrusions of the sleeve 31 covers the additional cylindrical widening 30 of the screw 12, Moreover, in the cavity 35 between the widening 28 of the cylindrical screw 12 with longitudinal grooves 29 and the end part 34 without protrusions of the sleeve 31, a spring 36 is placed, and the end 37 of the sleeve 31 abuts against the transverse plug 21, located on the side opposite to the bone plate, and at the end 37 sleeve 31 there is a pair of oppositely located recesses 38 with inclined walls 39, corresponding in size to additional protrusions 25 with inclined walls 26 on the annular protrusion 24 of the transverse plug 21, located on the side opposite the bone plate 2, while on the elongated cylindrical part 27 of the screw with a smooth surface, inside the annular protrusion 24 on the transverse plug 21, located on the side opposite the bone plate 2, with a stop directly into the transverse plug 21, a longitudinal ring 40 is attached, having a longitudinal length along the screw 12 equal to the height of the annular protrusion 24 without taking into account the height of a pair of oppositely located 25 additional projections with 26 inclined walls.

This longitudinal ring 40 is pressed onto the screw 12 when assembling the mechanism 22 for step-by-step movement of the slider, and is a supporting element during distraction. When the screw 12 rotates and the slider 7 moves backward, the longitudinal ring 40 receives force from soft tissues or bones that resist stretching.

The assembly of this part of the device with a means of moving the slide along the oblong body is carried out as follows:

• first of all, take the oblong body 6 and insert the slider 7 into its longitudinal through groove 10, to which the prosthesis 5 of the lower jaw is already attached;

• then take screw 12 and put spring 36 on it so that it rests against the additional cylindrical widening 30;

• put the sleeve 31 on the screw 12 so that it covers the spring 36 with the end part 34 without protrusions and at the same time the protrusions 33 of the sleeve 31 would be placed inside the longitudinal grooves 29 of the screw 12 with the possibility of longitudinal movement;

• put a longitudinal ring 40 on the elongated cylindrical part 27 of the screw with a smooth surface, secured by tension, thus fixing the sleeve 31 with the spring 36 on the screw 12 with the possibility of limited movement of the sleeve 31 with the spring 36 along the screw 12;

• take the transverse plug 21, located on the side opposite the bone plate, and attach it to the end of the oblong body 6, for example, by microwelding;

• take the transverse plug 17, located on the side of the bone plate, and attach it to the other end of the oblong body 6, for example, by microwelding;

• through the through hole 20 in the transverse plug 21, the end part 15 of the screw, located on the side of the bone plate, is inserted into the oblong body 6 in the direction of the slider 7;

• screw the screw thread 23 screw 12 into the screw thread 13 of the through hole 14 of the slider 7 through the holes and continue to do this until the end part 15 of the screw, located on the side of the bone plate, passes through the through hole 16 in the rigidly connected to the elongated body 6 transverse plug 17 from the side of the bone plate;

• create a widening 18 at the end of the end part 15 of the screw, located on the side of the bone plate. In the opinion of the applicant, it is preferable that the extension 18 be made in the form of a washer 41 connected to the end of the screw 12, for example, using microwelding.

The diameter of both end parts 15 and 19 of the screw 12 is slightly smaller than the diameter of the corresponding through holes 16 and 20 of the transverse plugs 17 and 21, and the screw 12 can rotate in the through holes, moving the slider 7.

The device operates as follows.

If you grab the protrusion 42 at the end of the screw 12 with a tool (for example, pliers) or your fingers, then when you turn the screw 12, the rotation through the longitudinal grooves 29 on the screw 12 and the protrusions 33 on the sleeve 31 is transmitted to the sleeve 31. The sleeve 31 rotates. It is important that the sleeve 31 is pressed against the transverse plug 21, located on the side opposite the bone plate, using a spring 36. When the sleeve 31 is rotated together with the screw 12, the inclined walls 39 of the recesses (grooves) 38 slide along the inclined walls 26 of additional protrusions 25 of the transverse plug 21. The protrusions 33 of the bushing 31 move along the axis of the screw 12 in the longitudinal grooves 29. In this case, the spring 36 is slightly compressed.

Thus, when the screw 12 rotates, the sleeve 31 also rotates. In this case, the transverse plug 21, located on the side opposite the bone plate 2, remains motionless, since it is welded to the oblong body 6. The inclined walls 39 of the recesses 38 of the sleeve run over the inclined walls 26 onto the fixed additional projections 25 of the fixed transverse plug 21, located on the side , opposite the bone plate 2. As a result, the sleeve 31 moves back to the height of the recesses (grooves) 38 and slides along additional protrusions 25 until it enters the next recesses (grooves) 38.

An alternative way to rotate the screw 12 is to use a removable drive 49 inserted into an adapter 44 with a multifaceted longitudinal hole 45. The rotation of the removable drive 49, and therefore the screw 12, is carried out using finger rotation or a special key or screwdriver (not indicated in the drawings).

The described mechanism 22 for step-by-step movement of the slider is needed for the following purposes:

• fixing the position of screw 12 during rotation;

• counting the number of screw turns 12;

• determining the amount of movement of the slider 7;

• determination by the surgeon at the clinical stage of the amount of distraction and creation of favorable conditions for gradual stretching of the tissues surrounding the prosthesis.

To ensure rotation of the screw 12 to the protrusion 42 at the end of the screw 12, located on the side opposite the bone plate, an adapter 44 with a multifaceted longitudinal hole 45 and a transverse through hole 46 in the wall 47, into which an end polyhedral protrusion is inserted, is microwelded along line 43 48 of a removable drive 49 with a spring-loaded latch 50 containing a rod 51 with a ring-shaped widening 52, placed inside a through transverse hole 53 inside the body 54 of the end polyhedral protrusion 48 of a removable drive 49, and the ring-shaped widening 52 of the rod 51 on one side is installed with the possibility of contact with the ledge 55 , made inside the through transverse hole 53 of the end polyhedral protrusion 48 of the removable drive 49, and the other side with the possibility of contact with the surface made with the through hole 56 for the rod 51 by a plug 57 welded to the end polyhedral protrusion 48, and inside the cavity 58 between the annular widening 52 of the rod 51 and a plug 57, a spring 59 is installed to ensure that the annular widening 52 of the rod 51 is pressed to the ledge 55 and, at the same time, when the annular widening 52 of the rod 51 comes into contact with the ledge 55, the end part 60 of the rod 51 protrudes above the surface 61 of the end polyhedral shaped protrusion 48 of the removable drive 49 .

For the convenience of explaining the design, the applicant notes that position 53 denotes the entire through transverse hole, position 58 denotes its part, that is, the cavity between the annular widening 52 of the rod 51 and the plug 57, in which the spring 59 is placed (installed).

In this case, the multifaceted longitudinal hole 45 of the adapter 44 is made of a hexagonal shape, and the end multifaceted protrusion 48 of the removable drive 49 inserted into it is also made of a hexagonal shape.

When assembling, first the rod 51 is inserted into the through hole 53 until the annular widening 52 stops in the ledge 55. Then, in the through transverse hole 53, a spring 59 is put on the rod 51. After this, a plug 57 is installed on the end part 62 of the rod 51 so that the end part 62 fits into the through hole 56 of the plug 57. The plug 57 is micro-welded to the end polyhedral protrusion 48 of the removable drive 49.

In the initial position, the end part 60 of the rod 51 protrudes above the surface 61 of the end polyhedral protrusion 48 of the removable drive 49 under the influence of the spring 59.

To connect, it is necessary to press the end part 60 of the rod 51 flush with the surface 61 of the end polyhedral protrusion 48 of the removable drive 49 with a finger or a screwdriver, compressing the spring under the influence of the spring 59. Then insert the end polyhedral protrusion 48 into the multifaceted longitudinal hole 45 of the adapter 44 so that after input, the end part 60 of the rod 51 would be opposite the transverse through hole 46 in the wall 47 of the adapter 44. In this case, the end part 60 of the rod 51 under the influence of the spring 59 will extend and fix the connection of the adapter 44 with the end polyhedral protrusion 48 of the removable drive 49.

To disconnect, you must first recess the end part 60 of the rod 51 flush with the surface 61 of the end polyhedral protrusion 48 of the removable drive 49, compressing the spring 59, for example, with a thin rod, the diameter of which is less than the diameter of the transverse through hole 46 in the wall 47, in particular, with the end of a screwdriver of the corresponding size. Then pull out the end polyhedral protrusion 48 of the removable drive 49 from the adapter 44.

Let us now consider the design of the rotary axis 8 with the possibility of fixing the angle of rotation in more detail.

As noted above, the oblong body 6 is connected to the bone plate 2 through a rotary axis 8 with the possibility of fixing the angle of rotation, and the bone plate 2 at the end has a loop 63 with a through hole 64, and the oblong body 6 has a pair of loops, namely, a loop 65 with a through hole 66 and a loop 67 with a through hole 68, in the gap 69 between which a loop 63 of the bone plate 2 is installed, while the through holes of the loops coincide with the formation of a common through hole 70, and the rotary axis 8 is made in the form of a tubular axis 71, rigidly connected to one end 72 to the outer side of the loop 65 of the oblong body 6 and having a longitudinal length corresponding to the total longitudinal length of the loop 65 of the oblong body 6 and the loop 63 of the bone plate 2, and the tubular axis 71 has a longitudinal through hole 73 with a screw thread 74 on part of the length from the side attachment to the outer side of the loop 65 of the oblong body 6, and on the remaining part of the length in its wall there are through longitudinal slots 75, and the thickness of the walls of the tubular axis 71 on the part of the length corresponding to the loop 63 of the bone plate 2 gradually decreases towards the end 76 of the tubular axis 71, forming the surface of a straight circular cone of the walls of the longitudinal through hole 73 of the tubular axis 71, corresponding to the through longitudinal slots 75, while the rod 77 of the screw 78 of the tubular axis is screwed into the screw thread 74 of the tubular axis 71 with a head 80 equipped with a slot 79, and the rod 77 of the screw 78 The tubular axle and the head 80 of the tubular axle screw 78 are connected by a transition part 81 having a conical shape, forming a straight circular cone surface of the transition part 81 of the tubular axle screw 78, located at a place in which the thickness of the walls of the tubular axle 71 corresponding to the longitudinal slots gradually decreases in direction towards the end 76 of the tubular axis 71.

When screwing the screw 78 into the screw thread 74, the transition part 81, which has a conical shape, rests from the inside against the tubular axis 71 at the location of the through longitudinal slots 75, where the thickness of the walls of the tubular axis for part of the length of the corresponding loop 63 of the bone plate 2 gradually decreases towards the end 76 of the tubular axis 71. Due to the presence of several through longitudinal slots on the tubular axis 71 with the formation of several strips 82, when screwing the screw 78 into the screw thread 74, the adapter part 81, which has a conical shape, rests from the inside against the tubular axis 71 at the location of the through longitudinal slots 75 and spreads the strips 82 apart. These strips 82 are tightly pressed against the surface of the through hole 64 of the loop 63 and keep the bone plate 2 from rotating. It is important to note that the tubular axis 71 is welded during assembly to the loop 63 of the bone plate 2 from the outside after combining the loops 63, 65, 67 and forming a common through hole 70, into which the tubular axis 71 is inserted, followed by microwelding.

Thus, during assembly, the tubular axle 71 is inserted from above into the common through hole 70 and microwelded around the perimeter of the end 72, and the screw 78 is inserted from below into the tubular axle 71 and screwed into this tubular axle. In this case, the transition part 81 of the screw, which has a conical shape, presses on the strips 82 of the tubular axis 71. As a result, the transition part 81 of the screw, which has a conical shape, expands (spreads apart) the strips 82 and they engage with the walls of the through hole 64 of the loop 63 of the bone plate 2 at with the help of friction, thus fixing the position of the bone plate 2 relative to the oblong body 6.

During surgery, the bone plate 2 is fixed with screws (not shown) through pre-selected holes 83 to the body 3 of the lower jaw 4. The articular head of the prosthesis 5 is installed in the articular fossa.

After a certain time, as the healthy half of the lower jaw grows and functional and cosmetic disorders occur, the need arises to extend the claimed device. To do this, the surgeon makes quick access to the junction of the bone plate 2 and the oblong body 6, unscrews the screw 78, the screw thread 84 of which on the rod 77 is unscrewed from the screw thread 74 of the tubular axis 71. As a result, the strips 82 of the tubular axis 71 are released and it becomes possible to rotate the bone plates 2 relative to the oblong body 6. This is necessary to compensate for angular changes. To unscrew the screw 78, the head 80 of the screw 78 has a slot 79 for a screwdriver used to turn the screw 78.

Thanks to the design described above, the likelihood of breakage of the bone plate during chewing due to the occurrence of unwanted stresses in it and/or dislocation of the bone screws fixing the plate is reduced.

A device for lower jaw prosthetics allows:

• eliminate functional disorders and facial asymmetry that arise as the healthy half of the lower jaw grows due to the expansion of prosthetic elements without causing unwanted stress in the structure and without dislocating the fixing screws;

• prevent reverse twisting of prosthetic elements;

• carry out gradual, rather than immediate, expansion of the prosthetic elements as convenient and comfortable for the patient as possible with minimal surgical trauma;

• perform surgical access to the screw of the prosthesis to rotate it and expand the elements of the prosthesis in an aesthetically acceptable area.

As a result of the use of the invention, the movement of the slider when extending the prosthesis fixed on the lower jaw occurs along a trajectory that mirrors the contour of the healthy half of the lower jaw (the choice of trajectory is made together with the attending physician at the stages of preoperative planning of the installed structure), which is an important advantage of the proposed invention.

The essence of the invention is illustrated by a clinical example.

Patient Ya., 7 years old, was admitted to the Department of Maxillofacial Surgery of the Children's City Clinical Hospital of St. Vladimir with a diagnosis of Goldenhar syndrome: underdevelopment of the upper jaw, defect of the lower jaw on the right, underdevelopment of the lower jaw on the left. Obstructive sleep apnea syndrome. It is known from the anamnesis that due to the presence of a dermoid cyst in the area of the right eye, the patient contacted an ophthalmologist with a request to remove the cyst. Due to the presence of severe underdevelopment and posterior displacement of the lower jaw, and the associated significant narrowing of the lumen of the upper respiratory tract at the level of the root of the tongue, the child was denied general anesthesia and was recommended to consult a maxillofacial surgeon in order to normalize the position and movements of the lower jaw.

Upon admission to the department, the patient’s parents complained of the child’s loud snoring during sleep, periodic interruptions of sleep, as well as difficulty chewing due to impaired closure of the dentition and facial asymmetry.

In the department of maxillofacial surgery, the patient was examined according to the general rules in surgery. During a clinical examination, facial asymmetry was determined due to a decrease in the volume of tissue in the parotid-masticatory and cheek areas on the right, and a shift in the midline of the chin to the right. The right corner of the mouth was located higher than the left. When examining the face in profile, the chin was sloping. When opening the mouth, there was a shift in the midline of the lower dentition to the right, pronounced crowding of the teeth and deformation of the dentition. On the right, closure of the molars was noted according to class II of Engle’s classification, on the left according to class I. There was no contact between the incisors in the anterior region. General blood and urine tests, a biochemical blood test were taken, an ECG and multislice computed tomography of the facial bones (MSCT) were performed. MSCT revealed the absence of the branch, head and distal edge of the body of the lower jaw on the right. The midline of the lower jaw was shifted to the right by 5 mm. It was decided that it was necessary to normalize the position of the lower jaw and eliminate the defect of the lower jaw on the right using an individual titanium prosthesis of the lower jaw with the ability to expand and a prosthetic fossa made of high molecular weight polyethylene. Based on computed tomography data, the CONMET LLC company produced a virtual model of the patient’s skull bones, planned the movement of the lower jaw to the correct anatomical position, modeled an individual titanium mandibular prosthesis with the ability to expand and an individual prosthesis of the articular fossa made of high-molecular polyethylene. After agreeing on the design with the attending physician, a solid-state model of the patient’s skull was made and individual designs were developed. Surgical intervention is planned on the model.

After the specified preoperative preparation, surgical intervention was performed under general anesthesia: after processing the surgical field under inhalation endotracheal anesthesia, an incision was made in the right submandibular region, the lower jaw on the right was skeletonized in layers, and the hypoplastic, deformed articular fossa of the temporal bone was skeletonized. In the area of the latter, an individual prosthesis of the glenoid fossa made of high molecular weight polyethylene was installed and fixed using 4 titanium screws with a diameter of 2 mm. An individual sliding titanium prosthesis of the lower jaw is installed on the lower jaw so that its bone plate fits tightly to the edge of the defect of the lower jaw, and the head is located in the prosthesis of the articular fossa. The bone plate is fixed to the lower jaw using 9 titanium screws with a diameter of 2 mm. At the same time, the protrusion of the lower jaw, as planned on the model, occurred. The wound is washed with an antiseptic and sutured with interrupted sutures in layers. Between the seams there is a flat drainage made of glove rubber. Hemostasis was achieved during the operation using an electrocoagulator. An aseptic sling-like dressing was applied.

The postoperative period proceeded smoothly, antibacterial, anti-inflammatory and physical therapy were carried out. The wound healed by primary intention, the drainage was removed on the 3rd day after surgery after the cessation of exudation, the sutures were removed on the 10th postoperative day. The patient was discharged home with improvement. The complaints described above have been completely eliminated.

After 3 years, at the age of 10 years, the patient turned to the St. Children's City Clinical Hospital. Vladimir again with complaints of increasing facial asymmetry, deformation of the dentition and disruption of the process of chewing food. During examination, a displacement of the chin of the lower jaw to the right relative to the midline of the face was determined. When examining the face in profile, the lower lip was located posterior to the upper lip, and the chin was slanted. In the oral cavity, combined deformation of the dentition increased; the midline of the lower dentition was shifted to the right by 4 mm. There was a narrowing of the upper and lower dentition. A multislice computed tomography scan of the bones of the facial skeleton was performed, which revealed that the previously installed structure did not change its linear parameters and its fixation was satisfactory. At the same time, the healthy half of the lower jaw lengthened in the area of the body and branches according to age. It was decided that it was necessary to expand the previously installed individual lower jaw prosthesis.

For this purpose, surgical intervention was performed under general anesthesia: under endotracheal inhalation anesthesia, after processing the surgical field, an incision was made along the scar in the submandibular region on the right. The posterior edge of the lower jaw prosthesis is skeletonized in layers. The plug was removed from the adapter connector welded to the prosthesis screw, and a removable drive was installed to carry out distraction of the prosthesis. The wound is washed with an antiseptic and sutured in layers with interrupted sutures around the removable drive. Hemotasis was carried out during the operation using an electrocoagulator. An aseptic dressing is applied. The postoperative period proceeded smoothly, antibacterial and anti-inflammatory therapy was carried out. The sutures were removed on the 10th day after surgery. The sutures were cleaned daily and the aseptic dressing around the removable drive was changed. Distraction of the lower jaw prosthesis began on the first day after surgery, 1 mm per day in 4 doses. The duration of the distraction period was 12 days. Thus, the prosthesis was lengthened by 12 mm. At the same time, the position of the lower jaw was normalized, the relationship of the dentition and the appearance of the child was improved.

After this, under inhalation mask anesthesia, the removable drive was removed from the prosthesis screw adapter, the wound was washed with an antiseptic, and a plug was installed in the hole of the adapter for the removable drive. The edges of the surgical wound are brought together using one interrupted suture. The postoperative period proceeded smoothly, the suture was removed on the 7th day after surgery. A control computed tomography (CT) scan of the facial skeleton was performed. According to CT data, the position of the installed prosthesis and fixing screws is satisfactory, the elements of the prosthesis are moved apart by 12 mm.

This observation illustrates the most typical example of a patient with a defect of the lower jaw, for the treatment of which the claimed invention can be used.

Thus, through the use of the proposed invention, the following is achieved:

• elimination of functional disorders and facial asymmetry that arise as the healthy half of the lower jaw grows, due to the gradual expansion of the prosthetic elements without causing unwanted stress in the structure and without dislocating the fixing screws;

• prevention of reverse twisting of prosthetic elements;

• minimizing surgical trauma during repeated surgery to expand the elements of the prosthesis;

• gradual, rather than immediate, expansion of the prosthesis elements as convenient and comfortable for the patient as possible; at the same time, the risk of developing ischemia and necrosis in the tissues surrounding the prosthesis is significantly minimized;

• the possibility of surgical access to the prosthesis screw in an aesthetically acceptable area.

In addition to the above embodiments of the invention, numerous other modifications are possible.

All of them are covered by the following claims.

Sources of information taken into account:

1. Verbo E.V., Karayan A.S., Nerobeev A.I., Drobot G.V.; Central Research Institute of Dentistry. A method of forming a graft to close defects of the lower jaw. Patent No. 2133590 RF, IPC A61B 17/24. No. 97120617/14; Application 12/22/1997; Publ. 07/27/1999.

2. Method for simultaneous elimination of underdevelopment of the branch and body of the lower jaw: Pat. 2289342 Ross. Federation: MPK51 A61B 17/56 / Komelyagin D.Yu., Roginsky V.V., Dubin S.A., Sedykh A.A., Khaspekov D.V.; applicant and patent holder ZAO Moscow Center for Pediatric Maxillofacial Surgery. - No. 2005123721/14; application 07/26/2005; publ. 12/20/2006, Bulletin. No. 35. 2 p.

3. Prospect LLC "LOGIX Medical Systems" st. Inzhenernaya, 20, Novosibirsk, Russia, 630090, 09.30.2021, 12:39.

4. Information on the Internet: ED jaw 421054. https://docs.yandex.ru/docs/view?url=ya- mail%3A%2F%2F177047760351058313%2F1.3&name=Oncological ED jaw 421054).pdf&ui ... (prototype ).

Claims (5)

1. A device for lower jaw prosthetics, including a bone plate designed to be fixed on the body of the lower jaw, and a lower jaw prosthesis with the ability to move them relative to each other, characterized in that the device contains an elongated body equipped with a slider to which the lower jaw prosthesis is attached jaw, and to the oblong body, on one side, a bone plate is attached by means of a rotary axis with the possibility of fixing the angle of rotation, and on the other side, a means for moving the slider along the oblong body is attached, and the means for moving the slider along the oblong body contains a screw for moving the slider, the end part of which is located with side opposite to the bone plate, and has a mechanism for step-by-step movement of the slider, while the mechanism for step-by-step movement of the slider contains an adapter with a multifaceted longitudinal hole and a transverse through hole in the wall, into which the end a multifaceted protrusion of a removable drive with a spring-loaded retainer containing a rod with a ring-shaped widening placed inside a through transverse hole inside the body of the end polyhedral protrusion of a removable drive. 2. The device according to claim 1, characterized in that the elongated body is made with a longitudinal through groove with protrusions directed towards each other on the sides, inside of which a slider is placed with the possibility of reciprocating movement, the slider moving screw is installed in a through hole of the slider equipped with a screw thread , the end part of which, on the side of the bone plate, is installed with the possibility of rotation in a through hole in a transverse plug rigidly connected to the elongated body on the side of the bone plate, and the end part of the screw, located on the side of the bone plate, has an external widening at the end with the possibility of support on a transverse plug located on the side of the bone plate, and the end part of the screw, located on the side opposite to the bone plate, is installed with the possibility of rotation in a through hole in a transverse plug rigidly connected to the elongated body, located on the side opposite to the bone plate. 3. The device according to claim 2, characterized in that the ring-shaped widening of the rod on one side is installed with the possibility of contact with a ledge made inside the through transverse hole of the end polyhedral shaped protrusion of the removable drive, and with the other side with the possibility of contact with the surface made with a through hole for the rod a plug welded to the end polyhedral protrusion, wherein a spring is installed inside the cavity between the annular widening of the rod and the plug to ensure that the annular widening of the rod is pressed against the ledge, and the end part of the rod is made to protrude above the surface of the end polyhedral protrusion of the removable drive upon contact of the annular widening rod with a ledge. 4. The device according to claim 3, characterized in that the multifaceted longitudinal hole of the adapter is made of a hexagonal shape, and the multifaceted end protrusion of the removable drive inserted into it is also made of a hexagonal shape. 5. The device according to claim 1, characterized in that the bone plate has a loop at the end, and the oblong body has a pair of loops, in the gap between which a bone plate loop is installed, and the through holes of the loops coincide to form a common through hole, and the rotary axis made in the form of a tubular axis, rigidly attached at one end to the outer side of the loop of the oblong body and having a longitudinal length corresponding to the total longitudinal length of the loop of the oblong body and the loop of the bone plate, and the tubular axis has a longitudinal through hole with a screw thread on part of the length from the attachment side to the outer side of the loop of the oblong body, and on the remaining part of the length, through longitudinal slots are made in its wall, and the thickness of the walls of the tubular axis on the part of the length corresponding to the longitudinal slots gradually decreases towards the end of the tubular axis, forming the surface of a straight circular cone of the walls of the longitudinal through holes of the tubular axis corresponding to the longitudinal through slots, wherein a tubular axis screw rod with a head equipped with a slot is screwed into the screw thread of the tubular axis, and the tubular axis screw rod and the screw head are connected by a transition part having a conical shape, forming the surface of a straight circular cone of the screw transition part tubular axis, located in a place where the thickness of the walls of the tubular axis corresponding to the longitudinal slots gradually decreases towards the end of the tubular axis.