Lumbar disc herniation auxiliary cutting device capable of preventing nerve injury

Abstract

The invention belongs to the technical field of medical apparatus and instruments, and discloses a lumbar disc herniation auxiliary cutting device capable of preventing nerve injury, the lumbar disc herniation auxiliary cutting device comprises a sleeve, the interior of the sleeve is movably connected with a limiting rod, the bottom end of the outer wall of the sleeve is fixedly connected with a drag hook, and the bottom end of the limiting rod is fixedly connected with a blade; through cooperation of a sleeve, a limiting rod, a clamping assembly, a spring and other structures, a blade is conveniently shrunk, then the risk of nerve injury is reduced, by pressing the limiting rod, the blade is driven to move to the outside of the sleeve, then the blade extends out, and when the limiting rod moves, a third inclined block is driven to abut against the inclined face of a first inclined block, so that nerve injury is avoided. After abutting of the third inclined block is relieved, the third inclined block can be reset under the action of the elastic force of the first elastic piece and abut against the bottom of the first inclined block, then the position of the limiting rod after moving is fixed, damage to peripheral nerves in the intervertebral disc area is avoided, and then the risk of damage to the nerves is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of medical devices, and in particular is a lumbar disc herniation auxiliary cutting device capable of preventing nerve damage. Background Art

[0002] The lumbar intervertebral disc is located between two vertebrae and is composed of a central nucleus pulposus, a surrounding annulus fibrosus, and upper and lower cartilage end plates. Under normal circumstances, the nucleus pulposus is tightly wrapped in the annulus fibrosus, but due to various reasons, such as long-term poor posture (sitting for a long time, bending over to lift heavy objects, etc.), trauma, aging leading to disc degeneration, etc., the annulus fibrosus may rupture. Once the annulus fibrosus ruptures, the nucleus pulposus will protrude from the rupture, which is a lumbar disc herniation. The protruding nucleus pulposus may compress the surrounding nerve tissue (such as nerve roots, cauda equina), causing a series of symptoms. Therefore, surgical resection is required.

[0003] During the existing lumbar disc herniation surgery, a nerve retractor is generally used to pull open the nerve roots around the cutting site, and then a long-handled sharp knife is used to remove the protruding disc. However, due to the narrow design of the retractor, the cutting field of the surgery is reduced. At the same time, in a complex spinal surgery environment, there are many important nerve structures around, such as the cauda equina and nerve roots, which may cause serious nerve damage if not handled with care. When the sharp knife O-shaped incision is placed in the area where the patient needs to be cut, it may cause damage to the surrounding nerves, leading to serious complications. Therefore, a lumbar disc herniation auxiliary cutting device that can prevent nerve damage is proposed to solve the problems raised in the background technology. Summary of the invention

[0004] In order to solve the problems raised in the above background technology, the present invention provides a lumbar disc herniation auxiliary cutting device that can prevent nerve damage, which has the advantage of facilitating the retraction of the blade, thereby reducing the risk of nerve damage.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: an auxiliary cutting device for lumbar disc herniation that can prevent nerve damage, comprising a sleeve, the interior of the sleeve is movably connected to a limit rod, the bottom end of the outer wall of the sleeve is fixedly connected to a hook, the bottom end of the limit rod is fixedly connected to a blade, a clamping assembly is arranged inside the sleeve, a round block is movably clamped in the middle of the limit rod, a spring is fixedly connected to the bottom of the round block, a fourth oblique block is movably clamped on one side of the limit rod close to the hook, and an expansion assembly is movably connected inside the hook; Among them, the clamping assembly includes a support block fixedly connected to the sleeve, the top of the support block is fixedly connected to a first inclined block, the middle of the support block is movably connected to a second inclined block, the interior of the limit rod is symmetrically and movably connected to two third inclined blocks, and the opposite ends of the two third inclined blocks are fixedly connected to a first spring sheet.

[0006] Preferably, the unfolding assembly comprises a limiting plate, and two inclined grooves are symmetrically provided in the middle of the limiting plate, and the two inclined grooves are oriented in opposite directions.

[0007] Preferably, a fifth inclined block is fixedly connected to one side of the limiting plate close to the fourth inclined block, the top of the fifth inclined block is inclined, the bottom of the fourth inclined block is inclined, and the inclined surfaces of the fourth inclined block and the fifth inclined block abut against each other.

[0008] Preferably, a second elastic sheet is fixedly connected to a side of the limiting plate away from the fifth inclined block, and the limiting plate is elastically connected to the draw hook via the second elastic sheet; Two square plates are symmetrically arranged inside the drag hook, and one side of the square plate penetrates the outer wall of the drag hook and extends to the outside of the drag hook.

[0009] Preferably, a round rod is fixedly connected to the bottom of the square plate, and the round rod is movably connected to the inside of the inclined groove. The inner wall of the hook is respectively provided with sliding grooves for limiting the limiting plate and the round rod.

[0010] Preferably, the top end of the limiting rod passes through the outer wall of the sleeve and extends to the outside of the sleeve, a gap is left between the top end of the limiting rod and the top of the sleeve, and the blade is initially retracted inside the sleeve.

[0011] Preferably, the surface of the pull hook is provided with anti-slip texture, the inner wall of the sleeve is provided with a limiting groove matching the round block, the round block is elastically connected to the sleeve through a spring, and the inner wall of the sleeve is provided with a square groove for limiting the fourth inclined block in the vertical direction.

[0012] Preferably, the top of the first inclined block is in the shape of an inclined surface, the upper and lower sides of the second inclined block are both in the shape of an inclined surface, and the bottom of the first inclined block is provided with a slot matched with the second inclined block.

[0013] Preferably, the opposite ends of the two third inclined blocks are both in the shape of inclined surfaces, the third inclined blocks penetrate the outer wall of the limiting rod and extend to the outside of the limiting rod, and the third inclined blocks abut against the inclined surface of the first inclined block in an initial state.

[0014] Preferably, the third inclined block is elastically connected to the limiting rod via a first elastic sheet, a gap is left between the first inclined block and the second inclined block, and a semi-arc groove matching with the supporting block is provided in the middle of the limiting rod.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention facilitates the retraction of the blade and reduces the risk of nerve damage by cooperating among structures such as the sleeve, the limit rod, the clamping assembly and the spring. The limit rod is pressed to drive the blade to move to the outside of the sleeve and extend the blade. The movement of the limit rod drives the third inclined block to abut the inclined surface of the first inclined block. When the third inclined block is released from the abutment, it will reset under the action of the elastic force of the first spring sheet and abut against the bottom of the first inclined block, thereby fixing the position of the limit rod after movement, thereby fixing the extended state of the blade and facilitating subsequent cutting operations. The blade is retracted into the sleeve in the initial state, so that when the sleeve is extended into the patient's intervertebral disc area, it will not cause damage to the peripheral nerves in the intervertebral disc area, thereby reducing the risk of nerve damage.

[0016] The present invention improves the pulling angle and range of the nerve root through the coordination between the structures such as the retractor, the fourth oblique block and the unfolding assembly, thereby providing a wider field of view for the operation. The fourth oblique block is driven downward by the limit rod, so that the fourth oblique block passes through the fifth oblique block and drives the limit plate to move toward the square plate. The two oblique grooves are in opposite directions, so that after the limit plate moves, the round rod can drive the two square plates to move in opposite directions along the trajectory of the oblique groove, thereby increasing the contact area between the retractor and the nerve root, thereby providing a larger pulling angle and range, and then being able to pull the nerve root to one side within a larger range, providing a wider field of view for the surgical operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the overall structure of the present invention; Figure 2 It is a schematic diagram of the front cross-section structure of the present invention; Figure 3 for Figure 2 Enlarged view of point A in the middle; Figure 4 for Figure 2 Enlarged view of point B in the middle; Figure 5 It is a schematic diagram of the position relationship among the limit rod, the clamping assembly, the round block and the fourth inclined block of the present invention; Figure 6 It is a partial schematic diagram of the cross section of the sleeve of the present invention; Figure 7 This is an exploded view of the unfolded components of the present invention.

[0018] In the figure: 1. sleeve; 2. limiting rod; 3. hook; 4. blade; 5. clamping assembly; 51. support block; 52. first inclined block; 53. second inclined block; 54. third inclined block; 55. first spring piece; 6. round block; 7. spring; 8. fourth inclined block; 9. unfolding assembly; 91. limiting plate; 92. inclined groove; 93. fifth inclined block; 94. second spring piece; 95. square plate; 96. round rod; 10. limiting groove. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] like Figures 1 to 7 As shown, the present invention provides a lumbar disc herniation auxiliary cutting device capable of preventing nerve damage, comprising a sleeve 1, a limiting rod 2 is movably connected inside the sleeve 1, a hook 3 is fixedly connected to the bottom end of the outer wall of the sleeve 1, a blade 4 is fixedly connected to the bottom end of the limiting rod 2, a clamping assembly 5 is arranged inside the sleeve 1, a round block 6 is movably clamped at the middle part of the limiting rod 2, a spring 7 is fixedly connected to the bottom of the round block 6, a fourth oblique block 8 is movably clamped at one side of the limiting rod 2 close to the hook 3, and an expansion assembly 9 is movably connected inside the hook 3; Among them, the clamping assembly 5 includes a support block 51 fixedly connected to the sleeve 1, the top of the support block 51 is fixedly connected to the first inclined block 52, the middle of the support block 51 is movably connected to the second inclined block 53, the inside of the limiting rod 2 is symmetrically and movably connected to two third inclined blocks 54, and the opposite ends of the two third inclined blocks 54 are fixedly connected to the first spring piece 55.

[0021] The above scheme is adopted: by pressing the limit rod 2, the blade 4 is driven to move to the outside of the sleeve 1, and then the blade 4 is extended. When the limit rod 2 moves, the third inclined block 54 is driven to abut against the inclined surface of the first inclined block 52. When the third inclined block 54 is released from the abutment, it will be reset under the action of the elastic force of the first spring piece 55, and abut against the bottom of the first inclined block 52, thereby fixing the position of the limit rod 2 after movement, thereby fixing the extended state of the blade 4, thereby facilitating subsequent cutting operations, and by retracting the blade 4 into the sleeve 1 in the initial state, when the sleeve 1 is extended into the patient's intervertebral disc area, it will not cause damage to the peripheral nerves in the intervertebral disc area, thereby reducing the risk of nerve damage.

[0022] like Figure 4 and Figure 7 As shown, the unfolding component 9 includes a limiting plate 91, and two inclined grooves 92 are symmetrically opened in the middle of the limiting plate 91, and the two inclined grooves 92 are in opposite directions. A fifth inclined block 93 is fixedly connected to the side of the limiting plate 91 close to the fourth inclined block 8, and the top end of the fifth inclined block 93 is inclined, and the bottom end of the fourth inclined block 8 is inclined, and the inclined surface of the fourth inclined block 8 and the inclined surface of the fifth inclined block 93 abut against each other.

[0023] The above scheme is adopted: the fourth inclined block 8 is driven downward by the limiting rod 2, so that the fourth inclined block 8 passes through the fifth inclined block 93, and drives the limiting plate 91 to move toward the square plate 95. The two inclined grooves 92 are in opposite directions, so that after the limiting plate 91 moves, the round rod 96 can drive the two square plates 95 to move in opposite directions along the trajectory of the inclined groove 92, thereby increasing the contact area between the retractor 3 and the nerve root, thereby providing a larger traction angle and range, and then being able to retract the nerve root to one side within a larger range, providing a wider field of view for surgical operations.

[0024] like Figure 7 As shown, a second spring piece 94 is fixedly connected to one side of the limit plate 91 away from the fifth inclined block 93, and the limit plate 91 is elastically connected to the hook 3 through the second spring piece 94. Two square plates 95 are symmetrically arranged inside the hook 3. One side of the square plate 95 passes through the outer wall of the hook 3 and extends to the outside of the hook 3. A round rod 96 is fixedly connected to the bottom of the square plate 95. The round rod 96 is movably connected to the inside of the inclined groove 92, and the inner wall of the hook 3 is respectively provided with sliding grooves for limiting the limit plate 91 and the round rod 96.

[0025] The above scheme is adopted: through the design of the second spring piece 94, its function is that when the limiting rod 2 drives the blade 4 to retract into the sleeve 1 again, at this time, the limiting rod 2 drives the fourth inclined block 8 to move upward, thereby releasing the contact with the fifth inclined block 93, and then the limiting plate 91 drives the fifth inclined block 93 to reset under the action of the elastic force of the second spring piece 94. When the limiting plate 91 is reset, the two square plates 95 are also retracted to the inside of the retractor 3 under the action of external force, so as to facilitate the device to be taken out from the patient's intervertebral disc and convenient for the next use; A sliding groove is provided on the inner wall of the hook 3 to limit the limit plate 91 and the round rod 96. Its function is that when the fourth inclined block 8 squeezes the fifth inclined block 93, the limit plate 91 can only make the fifth inclined block 93 drive the limit plate 91 to move horizontally in a straight line toward the second spring piece 94 under the action of the sliding groove. When the limit plate 91 moves, the round rod 96 will slide along the track of the inclined groove 92. At this time, the round rod 96 is horizontally limited by the sliding groove, so that the round rod 96 can only move along the track of the inclined groove 92, driving the two square plates 95 to move in opposite directions.

[0026] like Figure 2 As shown, the top end of the limiting rod 2 passes through the outer wall of the sleeve 1 and extends to the outside of the sleeve 1. A gap is left between the top end of the limiting rod 2 and the top of the sleeve 1. The blade 4 is initially retracted inside the sleeve 1. The surface of the hook 3 is provided with anti-slip textures. The inner wall of the sleeve 1 is provided with a limiting groove 10 that matches the round block 6. The round block 6 is elastically connected to the sleeve 1 through a spring 7. The inner wall of the sleeve 1 is provided with a square groove for limiting the fourth inclined block 8 in the vertical direction.

[0027] Adopt the above scheme: a square groove is opened through the inner wall of the sleeve 1, as shown in the following figure: Figure 6 Its function is that when the limit rod 2 rotates, the square groove will circumferentially limit the fourth inclined block 8, so that the fourth inclined block 8 remains stationary, thereby ensuring the normal operation of the device. Through the design of the limit groove 10, its function is that the limit groove 10 is used to circumferentially limit the round block 6, so that the round block 6 remains stationary when the limit rod 2 rotates, thereby preventing the limit rod 2 from driving the round block 6 to rotate, causing a large torque on the spring 7, and affecting the service life of the device.

[0028] like Figure 3 and Figure 5 As shown, the top of the first inclined block 52 is in the shape of an inclined surface, the upper and lower sides of the second inclined block 53 are both in the shape of an inclined surface, a slot matching the second inclined block 53 is provided at the bottom of the first inclined block 52, the opposite ends of the two third inclined blocks 54 are both in the shape of an inclined surface, the third inclined block 54 passes through the outer wall of the limiting rod 2 and extends to the outside of the limiting rod 2, the third inclined block 54 abuts against the inclined surface of the first inclined block 52 in the initial state, the third inclined block 54 is elastically connected to the limiting rod 2 through the first spring sheet 55, a gap is left between the first inclined block 52 and the second inclined block 53, and a semi-arc groove matching the support block 51 is provided in the middle of the limiting rod 2.

[0029] The above scheme is adopted: a semi-arc groove is opened in the middle of the limit rod 2, and its function is that when the limit rod 2 moves downward, the support block 51 will slide inside the semi-arc groove, thereby preventing the limit rod 2 from colliding with the clamping assembly 5 when moving, thereby ensuring the normal operation of the device.

[0030] The working principle and use process of the present invention are as follows: first, the blade 4 is initially retracted inside the sleeve 1, so that when the sleeve 1 is extended into the patient's intervertebral disc area, it will not cause damage to the peripheral nerves in the intervertebral disc area. When the sleeve 1 is extended into the patient's intervertebral disc protrusion site that needs to be cut, the nerve root that needs to be cut is pulled apart by the retractor 3. Then, the operator presses the top of the limit rod 2, so that the limit rod 2 drives the blade 4 to move downward, and then the blade 4 moves to the outside of the sleeve 1. When the limit rod 2 moves downward, it also drives the two The three inclined blocks 54 slide along the inclined surface of the first inclined block 52, and then the two third inclined blocks 54 are squeezed into the limiting rod 2 by the inclined surface of the first inclined block 52, until the third inclined block 54 is released from the abutment with the first inclined block 52, and then the third inclined block 54 is reset under the elastic force of the first spring sheet 55 and is inserted into the gap between the first inclined block 52 and the second inclined block 53. At the same time, the top of the third inclined block 54 abuts against the bottom of the first inclined block 52, thereby fixing the position of the limiting rod 2, so that the blade 4 always remains in the extended state; When the limiting rod 2 moves downward, it will also drive the fourth inclined block 8 to move together, so that the fourth inclined block 8 abuts against the inclined surface of the fifth inclined block 93, and then squeezes the fifth inclined block 93 to drive the limiting plate 91 to move in the direction of the second spring piece 94. When the limiting plate 91 moves, the inner groove of the retractor 3 limits the round rod 96 in the horizontal direction, so that the round rod 96 can only move along the trajectory of the inclined groove 92, driving the two square plates 95 to move in the opposite direction, and then the two square plates 95 move to the outside of the retractor 3, thereby expanding the cross-sectional area of ​​the retractor 3, and then increasing the contact area between the retractor 3 and the nerve root, providing a larger traction angle and range, so that the nerve root can be pulled to one side within a larger range, thereby providing a wider field of view for surgical operations. When it is necessary to cut the intervertebral disc, the operator rotates the limit rod 2, thereby driving the blade 4 to rotate, so as to smoothly cut the herniated area of ​​the intervertebral disc. When the cutting is completed, the blade 4 needs to be retracted into the inside of the limit rod 2. At this time, the operator presses the top of the limit rod 2 again, so that the limit rod 2 continues to move downward, and then drives the inclined surfaces of the two third inclined blocks 54 to abut against the inclined surfaces on the upper side of the second inclined block 53 through the limit rod 2, and slide along the inclined surfaces of the upper layer of the second inclined block 53 to the inclined surfaces of the lower layer. Then, when the limit rod 2 is pressed to the predetermined position, the operator releases the pressure on the limit rod 2, so that the round block 6 drives the limit rod 2 upward under the action of the elastic force of the spring 7. When the limiting rod 2 moves upward, the friction force between the third inclined block 54 and the second inclined block 53 drives the second inclined block 53 to move upward together, and the second inclined block 53 is stuck in the slot at the bottom of the first inclined block 52, so that the first inclined block 52 and the second inclined block 53 overlap each other. Subsequently, the limiting rod 2 drives the third inclined block 54 to continue to move upward under the action of the elastic force of the spring 7, so that the third inclined block 54 slides along the inclined surface of the lower layer of the second inclined block 53 to the inclined surface of the first inclined block 52, so that the third inclined block 54 is released from the clamping connection with the first inclined block 52, thereby releasing the fixation of the limiting rod 2, and then the blade 4 is retracted into the sleeve 1. Finally, the operator takes the device out of the patient's body and completes the operation.

[0031] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0032] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lumbar disc herniation auxiliary cutting device capable of preventing nerve damage, comprising a sleeve (1), characterized in that: The sleeve (1) is internally movably connected to a limit rod (2), the bottom end of the outer wall of the sleeve (1) is fixedly connected to a draw hook (3), the bottom end of the limit rod (2) is fixedly connected to a blade (4), a clamping assembly (5) is provided inside the sleeve (1), a round block (6) is movably clamped in the middle of the limit rod (2), a spring (7) is fixedly connected to the bottom of the round block (6), a fourth inclined block (8) is movably clamped on a side of the limit rod (2) close to the draw hook (3), and an expansion assembly (9) is movably connected inside the draw hook (3); The clamping assembly (5) comprises a support block (51) fixedly connected to the sleeve (1), a first inclined block (52) fixedly connected to the top of the support block (51), a second inclined block (53) movably connected to the middle of the support block (51), two third inclined blocks (54) symmetrically movably connected inside the limit rod (2), and first spring plates (55) fixedly connected to opposite ends of the two third inclined blocks (54).

2. The auxiliary cutting device for lumbar disc herniation capable of preventing nerve damage according to claim 1, characterized in that: The unfolding assembly (9) comprises a limiting plate (91), and two inclined grooves (92) are symmetrically provided in the middle of the limiting plate (91), and the two inclined grooves (92) are oriented in opposite directions.

3. The auxiliary cutting device for lumbar disc herniation capable of preventing nerve damage according to claim 2, characterized in that: A fifth inclined block (93) is fixedly connected to one side of the limiting plate (91) close to the fourth inclined block (8); the top end of the fifth inclined block (93) is in the shape of an inclined surface, the bottom end of the fourth inclined block (8) is in the shape of an inclined surface, and the inclined surface of the fourth inclined block (8) abuts against the inclined surface of the fifth inclined block (93).

4. The auxiliary cutting device for lumbar disc herniation capable of preventing nerve damage according to claim 2, characterized in that: A second elastic sheet (94) is fixedly connected to a side of the limiting plate (91) away from the fifth inclined block (93), and the limiting plate (91) is elastically connected to the draw hook (3) via the second elastic sheet (94); Two square plates (95) are symmetrically arranged inside the drag hook (3), and one side of the square plate (95) penetrates the outer wall of the drag hook (3) and extends to the outside of the drag hook (3).

5. The auxiliary cutting device for lumbar disc herniation capable of preventing nerve damage according to claim 4, characterized in that: A round rod (96) is fixedly connected to the bottom of the square plate (95), and the round rod (96) is movably connected to the inside of the inclined groove (92). The inner wall of the hook (3) is respectively provided with sliding grooves for limiting the limiting plate (91) and the round rod (96).

6. The auxiliary cutting device for lumbar disc herniation capable of preventing nerve damage according to claim 1, characterized in that: The top end of the limiting rod (2) penetrates the outer wall of the sleeve (1) and extends to the outside of the sleeve (1), a gap is left between the top end of the limiting rod (2) and the top of the sleeve (1), and the blade (4) is retracted inside the sleeve (1) in an initial state.

7. The auxiliary cutting device for lumbar disc herniation capable of preventing nerve damage according to claim 1, characterized in that: The surface of the draw hook (3) is provided with anti-slip textures, the inner wall of the sleeve (1) is provided with a limiting groove (10) matching with the round block (6), the round block (6) is elastically connected to the sleeve (1) via a spring (7), and the inner wall of the sleeve (1) is provided with a square groove for limiting the fourth inclined block (8) in the vertical direction.

8. The auxiliary cutting device for lumbar disc herniation capable of preventing nerve damage according to claim 1, characterized in that: The top of the first inclined block (52) is in the shape of an inclined surface, the upper and lower sides of the second inclined block (53) are both in the shape of inclined surfaces, and the bottom of the first inclined block (52) is provided with a slot adapted to the second inclined block (53).

9. The auxiliary cutting device for lumbar disc herniation capable of preventing nerve damage according to claim 1, characterized in that: The opposite ends of the two third inclined blocks (54) are both in the shape of inclined surfaces. The third inclined blocks (54) penetrate the outer wall of the limiting rod (2) and extend to the outside of the limiting rod (2). In the initial state, the third inclined blocks (54) abut against the inclined surface of the first inclined block (52).

10. The auxiliary cutting device for lumbar disc herniation capable of preventing nerve damage according to claim 1, characterized in that: The third inclined block (54) is elastically connected to the limiting rod (2) via a first spring sheet (55); a gap is left between the first inclined block (52) and the second inclined block (53); and a semi-arc groove matching the supporting block (51) is provided in the middle of the limiting rod (2).

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