CN111035430A - Visual real-time bone trepan that goes of backbone scope scale - Google Patents

Abstract

The real-time boning trepan with visualized backbone endoscope scales comprises a protective sleeve, a saw body, a backbone endoscope and a boning amount calculating device; the protective sleeve comprises a hollow tube body, one end of the hollow tube body is arranged in the form of an inclined plane, the other end of the hollow tube body is provided with a first handle, the first handle is provided with a first through hole communicated with the hollow tube body, the saw body comprises a hollow saw body main body part, one end of the hollow saw body main body part is provided with saw teeth, the other end of the hollow saw body main body part is provided with a second handle, the second handle is provided with a second through hole communicated with the hollow saw body main body part, wherein the hollow saw body main body part is arranged in the hollow tube body through the first through hole, and the spinal endoscope is arranged in the hollow saw body main body part through the second through hole; and the bone removal amount calculation means calculates one or more of a bone removal area, a bone removal depth, and a bone removal volume.

Description

Visual real-time bone trepan that goes of backbone scope scale

Technical Field

The invention relates to the technical field of medical treatment, in particular to a real-time boning trepan with visualized backbone endoscope scales.

Background

Lumbar disc herniation and lumbar spinal stenosis are the major causes of back pain in many patients and these conditions can be alleviated by conservative treatments such as bed rest, taking anti-inflammatory drugs, receiving physical therapy or injecting steroids. However, these basic treatments are not effective for some patients, and patients still suffer from great pain due to back pain, are unable to perform daily activities normally, and may even develop chronic low back pain. Surgical treatment is another option for treating the diseases, and spinal endoscopy is a minimally invasive surgery, and has the characteristics of small wound, quick recovery, visual safety, relatively low cost and the like, so that in recent years, the spinal endoscopy is gradually paid attention and popularized in China. The target site of operation is usually located in the vertebral canal and surrounded by hard bony structures, so that bone removal to establish a working channel or decompression becomes the primary premise of spinal endoscopic surgery. The existing bone removal tools under a spinal endoscope are a power abrasive drill, an ultrasonic osteotome, a traditional bone drill, a blind trepan and an under-lens trepan. However, the traditional bone drill and blind trepan cannot be observed in real time, so that nerve roots and dural sac are easily injured, and a beginner is difficult to master; the power grinding drill and the ultrasonic osteotome are very expensive and have limited popularity; in comparison, the under-mirror trepan is low in price, and meanwhile, the safety and the effectiveness are outstanding.

However, the handle of the existing under-mirror trephine is not favorable for holding force of a palm, and has the problems that the bone removal depth and the bone removal amount cannot be accurately measured. Therefore, it is necessary to provide a real-time bone-removing trepan with visualized backbone endoscope scales to solve the above problems.

Disclosure of Invention

According to one aspect of the invention, a real-time boning trepan with visualized backbone endoscope scales is provided, which comprises a protective sleeve, a saw body, a backbone endoscope and a boning amount calculating device; the protective sleeve comprises a hollow tube body, one end of the hollow tube body is arranged in the form of an inclined plane, the other end of the hollow tube body is provided with a first handle, the first handle is provided with a first through hole communicated with the hollow tube body, the saw body comprises a hollow saw body main body part, one end of the hollow saw body main body part is provided with saw teeth, the other end of the hollow saw body main body part is provided with a second handle, the second handle is provided with a second through hole communicated with the hollow saw body main body part, wherein the hollow saw body main body part is arranged in the hollow tube body through the first through hole, and the spinal endoscope is arranged in the hollow saw body main body part through the second through hole; and the bone removal amount calculation means calculates one or more of a bone removal area, a bone removal depth, and a bone removal volume.

The real-time bone-removing trepan for spinal endoscope scale visualization has the advantages of simple structure, high efficiency and safety in operation, can observe the bone-removing depth of the trepan in real time by naked eyes under the condition of not increasing a perspective device and radiation, provides objective data support, and avoids excessively deep damage to nerves and operation disorientation on the dorsal side.

Further features of the invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

Drawings

Fig. 1 is a schematic diagram of the overall configuration of a spinal endoscope scale visualization real-time bone removal trepan according to an embodiment of the invention.

FIG. 2 is a schematic view of a protective casing according to an embodiment of the invention.

Fig. 3 is a schematic structural diagram of a saw body according to an embodiment of the invention.

Fig. 4 is an enlarged structural view of a saw tooth according to an embodiment of the present invention.

Fig. 5 is a schematic structural diagram of a saw body according to an embodiment of the invention.

Fig. 6 is an enlarged schematic view of the invention at B of fig. 5.

Fig. 7 is a schematic diagram of calculating an osteotomy area and a bone removal amount according to an embodiment of the present invention.

In the figure: 1. protecting the sleeve; 2. a saw body; 3. an inclined surface; 4. a first handle; 5. a first through hole; 6. saw teeth; 7. a second handle; 8. a second through hole; 9. annular depth scales; 10. scale of area of longitudinal axis; 11. increasing the friction of the pores.

Detailed Description

The invention provides a scale-visualized real-time bone-removing trepan for a spinal endoscope, which has the advantages of simple structure, high efficiency and safety in operation.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings, but it should be understood that the following embodiments are only exemplary and are not intended to limit the present invention to these embodiments. Further, the size, material, shape, relative arrangement thereof, and the like of the constituent elements described in the embodiments may be appropriately changed according to the configuration, various conditions, and the like of the apparatus to which the present invention is applied. Therefore, the sizes, materials, shapes, relative arrangements thereof, and the like of the constituent elements described in the embodiments are not intended to limit the scope of the present invention to the following embodiments

Integral arrangement

First, referring to fig. 1, the overall configuration of a real-time deboning trepan for endoscopic scale visualization of the spine according to the present invention will be described.

The real-time bone-removing trepan with the visualized backbone endoscope scale comprises a protective sleeve 1, a saw body 2, a backbone endoscope and a bone-removing amount calculating device. Wherein protective sleeve 1 and saw body 2 are all set to hollow structure, and protective sleeve 1 is established in the outside of saw body 2 by the cover, plays the effect of carrying out the protection to saw body 2 to the sawtooth of saw body 2 is used for cutting the human bone of treating to get rid of, in order to reach the mesh of boning. In addition, a spinal endoscope is provided within the saw body 2 to view the bone to be removed, and a bone removal amount calculating means is used to calculate and monitor the bone area and bone volume removed, providing early warning and assistance for the bone removal operation.

Hereinafter, the respective components of the real-time bone-removing trepan for endoscopic scale visualization of the spine according to the present invention will be described in detail with reference to the accompanying drawings.

Protective sleeve

With reference to fig. 2, a protective sleeve 1 according to the invention is described. As shown in fig. 2, the protective sleeve 1 according to the present invention comprises a hollow tube body having one end provided in the form of an inclined surface and the other end provided with a handle provided with a through hole communicating with the hollow tube body.

The hollow tube body is, for example, a hollow cylindrical body, and the inner diameter of the hollow cylindrical body is, for example, 8mm, and the outer diameter is, for example, 10 mm. The length of the hollow tube body may be, for example, 20cm, 30cm or other suitable length, and may be configured in a telescopic configuration to suit different use environments or different types of trephines. The shape of the cross section of the hollow tubular body is not limited to a cylindrical shape, and may be, for example, a rectangular shape, a trapezoidal shape, a rhombic shape, or an irregular shape. But in order to facilitate the fixing of the protective sleeve in place it is preferred to provide the hollow tubular body as a hollow cylinder.

In addition, the side wall of the hollow tube body can be provided with structures such as lightening holes and lightening grooves, so as to lighten the whole weight of the protective sleeve 1. The hollow tube body may be formed using stainless steel, titanium alloy, or a combination thereof.

One end of the hollow tube according to the invention is provided in the form of an inclined surface 3 for abutment against a bone surface, such as a patient's articular process, a vertebral plate or the like. The inclined surface 3 may take various forms, for example, the inclined surface 3 may be projected in a straight line, a quadratic curve or other curved form in a projection direction parallel to the inclined surface 3. In the case of being projected as a straight line, this corresponds to cutting the hollow tube in a direction at an angle to the axis of the hollow tube. The angle may be, for example, 20 degrees, 30 degrees, 45 degrees or other angles, in which case a sharp tip of the inclined surface is formed. In the case of being projected as a curved line, for example, the tip of the inclined surface may be made an arc of a certain length instead of a point. In this way, the safety of the protective sleeve 1 can be increased.

The other end of the hollow tube body according to the invention is provided with a handle. The handle is fixedly connected with the hollow tube body, and the hollow tube body is rotated through the handle so as to enable the inclined surface 3 to abut against the articular process bone surface. The handle may be, for example, a T-handle, a hemispherical handle, or other shaped handle. The handle is provided with a through hole to be communicated with the cavity of the hollow pipe body. In particular, the through-hole may be arranged in the direction of the cavity of the hollow tube body. Alternatively, the hollow tube may be inserted into a through hole in the handle.

The hollow of the hollow tube and the through hole provided in the handle as a whole serve to accommodate a saw body to be described later. That is, the saw body is provided inside the protective sleeve 1 through the hollow of the hollow tube body and the through hole provided in the handle to protect the saw body.

Saw body

With reference to fig. 3, a saw body 2 according to the invention is described.

The saw body 2 according to the invention comprises a hollow saw body part, which is provided with saw teeth at one end and a handle at the other end, which handle is provided with a through hole communicating with the hollow saw body part.

The saw body portion may be provided in a hollow cylindrical shape, similar to the hollow pipe body. In this case, the inner diameter of the hollow cylindrical body is, for example, 6mm, and the outer diameter is, for example, 8mm to fit the inner diameter of the hollow tube body. In the case where the saw body main part and/or the hollow tubular body are provided with a cross section of, for example, a rectangular, trapezoidal, rhombic or irregular shape, the saw body main part should be provided so as to be rotatable within the hollow tubular body.

One end of the hollow saw body main body part is provided with sawteeth so as to realize the excision of the bone surface. As shown in fig. 4, which shows an example of the saw body 6 according to an embodiment of the present invention. The illustrated saw teeth 6 are composed of, for example, 10 teeth, and 10 teeth are circumferentially provided at one end of the saw body portion, each tooth having a height set to, for example, 1mm, and a distance of adjacent teeth set to, for example, 1.5 mm. In operation, the serrations 6 abut the facet to effect resection of the facet.

The other end of the hollow saw body main body part is provided with a handle which is fixedly connected with the saw body main body part. The handle may be, for example, a T-handle, a hemispherical handle, or other shaped handle. The handle is provided with a through hole to be communicated with the hollow cavity of the hollow saw body main body. In particular, the through hole may be arranged along the cavity direction of the hollow saw body. Alternatively, a hollow saw body may be inserted into a through hole in the handle.

Preferably, the saw body 2 includes a handle that is configured as a hemispherical handle 7 to increase the contact area with the operator's palm during operation to facilitate the cutting operation of the saw body 2. According to one embodiment, the handle 7 is provided with friction increasing holes 11, and the friction increasing holes 11 are provided through the handle 7. Thus, not only the friction force between the handle 7 and the hand can be increased, but also the weight of the handle 7 can be reduced.

Spinal endoscope

The spinal endoscope according to the present invention may employ existing or developing or later-invented spinal endoscopes. For example, the spinal endoscope according to the present invention may be a JOIMAX spinal endoscope system, a SPINENDOS spinal endoscope system, a STORZ spinal surgical endoscope, or other endoscope.

The spinal endoscope reaches the position of a bone surface or a focus through a channel established by a cavity of the saw body 2, under the condition that a light source of the spinal endoscope system provides illumination, an image of the articular process bone surface area is displayed on a display by a camera shooting and imaging system, the actions of tools entering the body of a patient are monitored, and the doctor directly performs bone cutting operation under the condition of direct vision.

Bone removal amount calculation device

The bone removing trepan according to the present invention is further provided with a bone removal amount calculating means. Specifically, referring to fig. 5 and 6, the inner side wall of the hollow saw body part according to the present invention is provided with annular depth scales 9 and longitudinal axis area scales 10, the annular depth scales 9 and the longitudinal axis area scales 10 are vertically and alternately distributed, and the annular depth scales 9 are used for marking and the longitudinal axis area scales 10 are used for marking and calculating the bone removal volume, thereby providing accurate bone removal amount.

Specifically, for example, the scale unit of the annular depth scale 9 may be set to 5mm, and the angle between the adjacent vertical scale lines of the longitudinal axis area scale 10 in the horizontal direction with respect to the axis of the hollow saw body main portion may be set to 45 °, and when measuring a bone of a human body, the area of the removed bone is calculated from the size of the annular depth scale 9 and the size of the bone on the longitudinal axis area scale 10.

Hereinafter, a calculation method of the bone loss amount is described with reference to fig. 7. In fig. 7, the circle shown is the field of view of the endoscope and a-H are the vertical axis area scales. In this example, the resolution of the vertical axis area scale is set to 45 degrees. Hereinafter, some examples of the bone-cut amount calculation result are given.

a. When the osteotomy line is determined to be CED, the osteotomy area is:

b. when the connecting line of the osteotomy is ACEDB, namely a semicircle, the osteotomy area is as follows:

c. when the osteotomy line is determined to be FACEDBH, the cutting area is:

d. when the osteotomy area is determined to be ACEDBHGFA, i.e. the whole circle:

area ═ pi r²；

In the above equations a, b, c and d, r is referred to as the radius of the inner diameter of the hollow cylindrical cavity of the saw body 2.

According to the bone cutting area calculation formula, the area of the cut bone can be calculated, and the problem that too little bone is cut to achieve an effective treatment effect or too much bone is cut to influence nerves and the direction of the deviated dorsal side bone saw is lost is avoided.

And multiplying the calculated bone cutting area by the bone cutting depth shown by the annular depth scale to obtain the bone cutting volume.

According to another embodiment, the circumferential depth scale of the osteotomy amount calculating device may be provided on the outer surface of the saw body main portion, a portion of the scale on the outer surface of the saw body main portion being blocked by the protection sleeve 1 due to the saw body 2 being provided within the cavity of the protection sleeve 1. In this case, the difference between the scale reading at the start of the operation and the scale reading at the end of the operation may be used as the bone cutting depth. While the longitudinal axial area scale may still be provided on the inner surface of the body portion of the saw.

According to a further embodiment, the saw body 2 may be connected with the protection sleeve 1 by means of a threaded connection. Since the distance that the saw body 2 advances by one rotation of the screw thread is the pitch of the screw thread, the depth of the osteotomy can be determined according to the number of rotations. Also, the accuracy can be adjusted by the pitch of the thread employed. That is, when the pitch of the thread is small, the depth of each feeding can be more accurately controlled, thereby more accurately controlling the bone mass.

Further, although in the above embodiment, the resolution of the vertical axis area scale is set to 45 degrees, the resolution of the vertical axis area scale is not limited thereto, and may be, for example, 30 degrees, 10 degrees, 1 degree, 0.5 degrees, or other degrees. It will be appreciated that as the resolution of the longitudinal axis and annular depth scale is increased, the accuracy of bone loss control is improved.

Although the above measures or calculates the amount of bone removed by means of a physical scale. But the amount of bone loss can also be read and calculated electronically. For example, a preliminary scene may be captured within the field of view of a spinal endoscope and the osteotomy area automatically calculated by the computing device. In addition, the bone removal amount calculating device also reads and stores the initial value of the annular depth scale, automatically calculates the bone removal volume according to the change of the annular depth scale along with the operation, and displays information such as the bone removal area, the bone removal depth and the bone removal volume on the display to assist the operation of a doctor.

Generally, the area of bone removal cannot be too large. Excessive bone removal area can affect the stability of the spinal structure. In addition, the depth of bone removal cannot be too deep (for example, except for preoperative imaging measurement, when the laminectomy depth exceeds 10mm, fluoroscopy positioning is needed, and when the articular process on the resected part of the lumbar vertebra side approach endoscope exceeds 15mm, fluoroscopy positioning is needed), the epidural sac and nerve or the deviated dorsal side sawn bone are easy to be damaged by too deep bone removal.

Therefore, the bone removal trepan or the bone removal amount calculation apparatus according to the present invention may further include an alarm apparatus. The alarm device gives an alarm when one or more of the bone cutting depth, the bone cutting area or the bone cutting volume exceeds a threshold value, or directly turns off an endoscope system, thereby ensuring the safety of the operation.

As an example, different thresholds, e.g., a first threshold, a second threshold, and a third threshold, may be set for the bone cutting depth, the bone cutting area, or the bone cutting volume, respectively.

In one embodiment, the system alerts or turns off the endoscopic system when one of the bone cut depth, bone cut area, and bone cut volume reaches a threshold. In another embodiment, the physician's threshold amount of operation may be increased by alerting when one of the bone cut depth, bone cut area and bone cut volume reaches a threshold value and by directly shutting down the system when two or more of the threshold values are reached. For example, the depth of the cut is a more sensitive parameter than the area of the cut, in which case the system is turned off directly when the depth of the cut reaches a threshold, and an alarm is raised when the depth of the cut does not reach the threshold and the area of the cut reaches the threshold, but the physician is still allowed to proceed further.

That is, in the trephine according to the present invention, parameters of the osteotomy are prioritized or differently weighted to monitor changes in certain parameters preferentially or intensively. For example, the alarm parameter may be set to the sum of the osteotomy depth, the osteotomy area and the osteotomy volume, and different weights may be set for each parameter, e.g., the weight of the osteotomy depth is set to 0.5, the weight of the osteotomy area is set to 0.3 and the weight of the osteotomy volume is set to 0.2. By combining with the visual scale, the safety can be further improved.

Further, although one or more of the bone cutting depth, the bone cutting area, and the bone cutting volume are used as parameters for the alarm, other parameters may be used for setting the alarm.

Hereinafter, a case where the present invention is applied to a lumbar endoscope will be described. When removing the bone, at first carry out the preoperative preparation, the patient bends the hip and bends knee and lies in the operation table on one side to the ilium waist bolster of good health side can make the operation side intervertebral foramen slightly open, then the fixed band should be placed between operation side buttock and greater trochanter, simultaneously chest hug pillow, good health side shoulder joint, knee joint outside bolster prevent the crush injury, vital signs such as conventional real-time supervision blood pressure, rhythm of the heart, heart electrograph, oxyhemoglobin saturation in addition.

And after the steps are finished, needle feeding points are carried out, firstly, standard lateral positions are adjusted under C-arm perspective, the lower incisal track of the bilateral vertebral pedicle of the superior vertebral body, the superior articular process of the bilateral superior vertebral body and the rear edge of the inferior vertebral body are respectively overlapped into an image, the lumbar vertebra segment of the operation is positioned under perspective, and the puncture point and the puncture direction are marked.

Then, a conventional disinfection drape (the disinfection range is 15-20cm away from the incision) is adopted, and then 0.7% of a matched local anesthetic and 60ml of a lidocaine solution are selected for standby application, wherein the lidocaine solution is prepared from 20ml of 2% lidocaine and 40ml of physiological saline, and the specific application methods of the lidocaine solution are subcutaneous 5ml, superficial fascia 10ml, deep fascia 10ml, superior articular process 10ml and intervertebral foramen 10 ml.

Then, the needle is inserted along the set puncture direction until the upper joint is protruded and stops after bone feeling is resisted, a guide wire and a blade are placed into the needle to cut the skin for 7mm, the guide wire is fixed by one hand, the 1-4-stage expansion tube is placed into the other hand step by step (the needle stops after the bone feeling is resisted), the inclined surface 3 of the protection sleeve 1 is sleeved into the expansion tube, wherein the lumbar spine endoscope puncture step is mature in the prior art and is not repeated again.

When bone removal is specifically carried out: the handle 4 on the protective sleeve 1 is held by hand, and is rotated and pushed forcefully until the inclined surface 3 props against the surface of the upper articular apophysis, and then the C arm is positioned in a perspective way; and pulling out the expansion sleeve, and penetrating the sawteeth 6 at the bottom end of the saw body 2 into the hollow pipe body in the protective sleeve 1 through the through holes 5 of the handle 4. The spinal endoscope penetrates into the hollow saw body part of the saw body 2 through the through hole 8 of the handle 7.

Then connecting a spinal endoscope operation system, and removing upper articular process soft tissues by using a radio frequency electric knife head under the conditions of continuous saline flushing and direct vision of the spinal endoscope to fully expose the bone surface. The spinal endoscope is held by the left hand, the second handle 7 is held by the right hand, the inclined surface 3 is tightly attached to the joint apophysis surface under the direct vision of the spinal endoscope, and the area of the resected bone surface is calculated according to the scale of the longitudinal axis area of the inner side surface of the saw body 2 (see the embodiment 2 for details). The right hand continuously exerts downward force clockwise, the spinal endoscope is visible in real time, and the bone blocks are immediately stopped when the bone blocks are observed to rotate along with the saw body 2. Note that the annular depth scale indicates that the depth should not exceed the pre-operative measurement range or the normal default, otherwise the orientation or fluoroscopy should be re-adjusted to confirm the serration 2 position in order to prevent overly deep nerve damage and disorientation of the dorsal aspect of the saw. This procedure may be repeated as necessary for a range of spinal decompression.

Although the present invention has been described above with reference to a spinal endoscope, it should be understood that the present invention is not limited thereto. For example, the present invention can also be applied to a thoracic endoscopic surgical resection of the articular facet (lateral approach), a lumbar posterior endoscopic surgical resection of the vertebral plate, a thoracic posterior endoscopic surgical resection of the vertebral plate, a cervical posterior endoscopic surgical resection of the vertebral plate, and the like.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims (10)

1. The utility model provides a visual real-time bone trepan that goes of backbone scope scale which characterized in that: comprises a protective sleeve (1), a saw body (2), a spinal endoscope and a bone removal amount calculating device;

the protective sleeve (1) comprises a hollow pipe body, one end of the hollow pipe body is arranged in a form of an inclined surface (3), the other end of the hollow pipe body is provided with a first handle (4), the first handle (4) is provided with a first through hole (5) communicated with the hollow pipe body,

the saw body (2) comprises a hollow saw body main part, one end of the hollow saw body main part is provided with sawteeth (6), the other end of the hollow saw body main part is provided with a second handle (7), the second handle (7) is provided with a second through hole (8) communicated with the hollow saw body main part,

wherein the hollow saw body part is arranged within the hollow tube via the first through hole (5) and the spinal endoscope is arranged within the hollow saw body part via the second through hole (8); and is

The bone removal amount calculation means calculates one or more of a bone removal area, a bone removal depth, and a bone removal volume.

2. The real-time bone-removing trepan with endoscopic spinal scale visualization according to claim 1, wherein the bone-removing amount calculating means is configured by an annular depth scale (9) and a longitudinal axis area scale (10) provided on the inner side surface in the body portion of the saw body (2), and the annular depth scale (9) and the longitudinal axis area scale (10) are vertically staggered with each other.

3. The endoscopic spinal scale visualized real-time bone-removing trepan according to claim 1, wherein said bone-removing amount calculating means is configured by an annular depth scale provided on the inner side surface inside the saw body main body portion of the saw body (2) and a longitudinal axis area scale provided on the outer side surface inside the saw body main body portion, and the annular depth scale and the longitudinal axis area scale are vertically staggered with each other.

4. The endospinal endoscopic scale visualized real-time bone-cutting trephine according to claim 2, wherein said protection sleeve (1) and saw body (2) are connected by screw thread, said longitudinal axis area scale is changed by rotation of saw body (2) relative to protection sleeve (1).

5. The real-time bone removal trephine for endoscopic spinal scale visualization of claim 1, further comprising an alarm device that alarms when one or more of bone removal area, bone removal depth and bone removal volume exceeds a respective threshold.

6. The endovertebral scale visualized real-time bone-removing trepan according to claim 5, wherein the bone-removing area, the bone-removing depth and the bone-removing volume are set with different priorities and the alarm device issues different levels of alarm according to the priorities.

7. The real-time bone-removing trephine according to claim 5, wherein the alarm means issues an alarm using a combination of the bone-removing area, the bone-removing depth and the bone-removing volume, and the bone-removing area, the bone-removing depth and the bone-removing volume are given different weights.

8. The real-time bone-removing trephine according to any one of claims 1-7, wherein the calculation result of the bone-removing amount calculating means and/or the alarm is displayed on a display.

9. The endoscopic spinal scale visualization real-time bone removal trephine of claim 1, wherein: the first handle (4) is a T-shaped handle, and the second handle (7) is a hemispherical handle.

10. The endoscopic spinal scale visualization real-time bone removal trephine of claim 9, wherein: the second handle (7) is hemispherical and is provided with a friction increasing hole (11).

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