Rod reducer

Abstract

To provide a rod reducer that is facilitated in screwing a set screw into a female screw of a head of a pedicle screw.SOLUTION: A rod reducer 1 includes: a connector 4 for being joined to an extender to be fitted to a pedicle screw; a hollow reduction shaft 6 penetrating the connector 4; and a central shaft 7 disposed inside of the reduction shaft 6. A first grip 5 is rotatably held to the connector 4. A male screw 64 to threadably engage a female screw 51 of the first grip 5 is formed in the reduction shaft 6. A terminal part 71 of the central shaft 7 is an interface to which a set screw for fixing a spinal rod is fitted. A second grip 9 is installed to a base end part 72. A spring 8 for biasing the central shaft 7 in a direction oriented to the terminal part 71 from the base end part 72 is installed between the central shaft 7 and the reduction shaft 6.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a rod reducer used in spinal fixation surgery.

Background Art

[0002] In one technique of spinal fixation surgery, pedicle screws are screwed into continuously aligned pedicles, and these pedicle screws are connected to each other by a spinal rod. The pedicle screw includes an anchor formed with a male screw and a head that rotatably holds the anchor. The head is provided with a channel that transects the head in a direction orthogonal to the axial direction of the anchor, and a spinal rod is inserted into this channel. The spinal rod inserted into the channel is fixed to the head by a set screw.

[0003] More specifically, the head of the pedicle screw includes a pair of opposing walls facing each other with a channel for inserting the spinal rod therebetween, and female screws that engage with set screws for fixing the spinal rod are formed on the inner surfaces of these opposing walls.

[0004] The spinal rod is generally made of metal and is bent in advance or during the operation so as to follow the ideal (physiological) curvature of the spine. Reduction is performed by pushing the spinal rod into the channel of the head of the pedicle screw while receiving a reaction force. For this reduction, an instrument called a rod reducer may be used.

[0005] For example, Patent Document 1 discloses a rod reducer 100 as shown in FIG. 16. This rod reducer 100 is coupled to a cylindrical extender 200 that is attached to a pedicle screw 300 as shown in FIG. 18.

[0006] Specifically, as shown in FIG. 17, the rod reducer 100 includes a connector 110 for coupling with the extender 200 and a hollow reduction shaft 130 passing through the connector 110. The reduction shaft 130 presses the end of the spinal rod 400 (see FIG. 18) at the tip of the portion inserted into the extender 200.

[0007] A first grip 120 is rotatably held by the connector 110. A female thread 121 is formed on the first grip 120. On the other hand, a male thread 131 that engages with the female thread of the first grip 120 is formed on the reduction shaft 130. Therefore, when the first grip 120 is rotated, the reduction shaft 130 moves axially (advances toward the pedicle screw 300 or retreats away from the pedicle screw 300).

[0008] A central shaft 140 is disposed within the reduction shaft 130 so as to be axially slidable. The central shaft 140 includes a distal end portion 141 that projects from the reduction shaft 130 in the forward direction of the reduction shaft 130 and a proximal end portion 142 that projects from the reduction shaft 130 in the backward direction of the reduction shaft 130.

[0009] The distal end portion 141 is an interface to which a set screw (not shown) for fixing the spinal rod is attached. A second grip 150 is provided on the proximal end portion 142.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] When using the rod reducer 100 shown in FIG. 16, first attach a set screw to the end portion 141 of the central shaft 140. Then, while inserting the reduction shaft 130 into the extender 200, couple the rod reducer 100 to the extender 200 and rotate the first grip 120 to advance the reduction shaft 130. As a result, the reduction shaft 130 presses the spinal rod 400 and the spinal rod 400 is inserted into the channel 320 of the head 310 of the pedicle screw 300. Thereafter, advance the central shaft 140 until the set screw abuts against the head 310, and by rotating the second grip 150, the set screw is screwed into the female screw of the head 310.

[0012] However, in the rod reducer 100 shown in FIG. 16, in order to screw the set screw into the female screw of the head 310 of the pedicle screw 300, it is necessary to rotate the second grip 150 while pushing the central shaft 140 toward the end portion 141.

[0013] Therefore, an object of the present invention is to provide a rod reducer that can easily screw a set screw into the female screw of the head of a pedicle screw.

Means for Solving the Problems

[0014] In order to solve the above problems, the present invention provides a rod reducer comprising: a connector for coupling with an extender attached to a pedicle screw; a first grip having a female thread rotatably held by the connector; a hollow reduction shaft passing through the connector, having a male thread formed thereon that engages with the female thread of the first grip, and pressing a spinal rod at a distal end that is the tip of a portion inserted into the extender; a central shaft disposed within the reduction shaft so as to be axially slidable, having an interface at a distal end projecting from the reduction shaft in the forward direction of the reduction shaft where a set screw for fixing the spinal rod is mounted, and a second grip provided at a proximal end projecting from the reduction shaft in the backward direction of the reduction shaft; and a spring provided between the central shaft and the reduction shaft for biasing the central shaft in a direction from the proximal end toward the distal end.

[0015] According to the above configuration, since the central shaft is biased by the spring in a direction from the proximal end toward the distal end, the set screw mounted at the distal end of the central shaft is pressed against the female thread of the pedicle screw by the biasing force of the spring. Therefore, the set screw can be screwed into the female thread of the pedicle screw simply by rotating the second grip. Thus, the set screw can be easily screwed into the female thread of the head of the pedicle screw.

[0016] The reduction shaft includes a pair of pressing pieces that abut against the spinal rod and face each other with the central shaft therebetween, and a tubular portion interposed between the pair of pressing pieces and the male screw. A notch may be formed on the outer peripheral surface of the tubular portion to extend in the axial direction of the reduction shaft a space located on the same circumference as the pair of pressing pieces. According to this configuration, when the extender engages with the head of the pedicle screw and the rod reducer is coupled to the extender, a relatively large gap is formed between the outer peripheral surface of the tubular portion of the rod reducer and the inner peripheral surface of the extender. Therefore, when the pedicle screw has a tab, interference between the reduction shaft and the tab is avoided. Accordingly, the rod reducer can be used with both pedicle screws without tabs and pedicle screws with tabs.

Effect of the Invention

[0017] According to the present invention, there is provided a rod reducer that can easily screw a set screw into the female screw of the head of a pedicle screw.

Brief Description of the Drawings

[0018]

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Mode for Carrying Out the Invention

[0019] FIG. 1 shows a usage state of a rod reducer 1 according to an embodiment of the present invention. The rod reducer 1 is coupled to an extender 3 attached to a pedicle screw 2. Therefore, below, first, the pedicle screw 2 and the extender 3 will be described, and then the rod reducer 1 will be described.

[0020] (Pedicle screw) The pedicle screw 2 screwed into the pedicle may be the tabbed pedicle screw 2A shown in Fig. 2(a) or the tabless pedicle screw 2B shown in Fig. 2(b).

[0021] The tabless pedicle screw 2B includes an anchor 21 formed with a male thread and a substantially cylindrical head 22 that rotatably holds the anchor 21. A channel 25 that traverses the head 22 in a direction orthogonal to the axial direction of the anchor 21 is provided in the head 22. A spinal rod 10 (see Fig. 1) is inserted into the channel 25.

[0022] More specifically, the head 22 includes a disk portion 23 penetrated by the anchor 21 and a pair of opposing walls 24 that rise from the disk portion 23 and oppose each other with the channel 25 therebetween. Female threads 26 that engage with set screws for fixing the spinal rod 10 are formed on the inner surfaces of the opposing walls 24.

[0023] Furthermore, engaging grooves 27 for engaging with the extender 3 are respectively provided on the outer surfaces of both opposing walls 24. Each engaging groove 27 opens radially outward of the substantially cylindrical head 22 and extends in the circumferential direction of the head 22.

[0024] The difference between the tabbed pedicle screw 2A and the tabless pedicle screw 2B is only that the tabbed pedicle screw 2A has a pair of tabs 28. In the tabbed pedicle screw 2A, a pair of tabs 28 are respectively provided on a pair of opposing walls 24 so as to extend the channel 25 for inserting the spinal rod. Also, in the tabbed pedicle screw 2A, female threads 26 are formed not only on the inner surfaces of the opposing walls 24 but also at the base portions of the inner surfaces of the tabs 28.

[0025] (Extender) In this embodiment, the extender 3 engages with the head 22 of the pedicle screw 2. Specifically, as shown in FIGS. 3 and 4, the extender 3 includes an outer sleeve 31, and a pair of inner arms 36 and an actuator 38 disposed within the outer sleeve 31.

[0026] The outer sleeve 31 includes a cylindrical base 32 and a pair of arm portions 33 that project from the base 32 along the axial direction of the outer sleeve 31. The arm portions 33 face each other, and the cross-sectional shape of each arm portion 33 is arcuate. At the base end of the base 32 on the side opposite the arm portion 33, a pair of slots 32a (only one slot 32a is shown in FIGS. 3 and 4) for coupling with the rod reducer 1 are provided.

[0027] A slit 34 is formed between the arm portions 33. This slit 34 is continuous with a channel 25 provided in the head 22 for inserting a spinal rod when the extender 3 is attached to the pedicle screw 2. That is, the channel 25 and the slit 34 define the movable range of the spinal rod 10.

[0028] In the range from the tip of each arm portion 33 to about 1 / 4 of the total length of the arm portion, the width of each arm portion 33 becomes narrower. At the tip of each arm portion 33, a ridge 35 for engaging with an engagement groove 27 provided in the head 22 of the pedicle screw 2 is provided.

[0029] Each inner arm 36 extends from a base end 36a to a terminal end 36b with a substantially constant arcuate cross-sectional shape. In other words, both inner arms 36 have a shape such that a pipe that abuts against the inner surface of the arm portion 33 of the outer sleeve 31 is cut with the same width as the slit 34.

[0030] Each inner arm 36 is held by the outer sleeve 31 so as to be slidable in the axial direction of the outer sleeve 31 along the inner surface of the corresponding arm portion 33. Specifically, a pair of protrusions 36c are provided on the outer surface of each inner arm 36, and a pair of slots 33a for guiding the protrusions 36c are provided on each arm portion 33 of the outer sleeve 31.

[0031] The actuator 38 is for moving both inner arms 36 upon receiving a rotational operation, and is attached to the base portion 32 of the outer sleeve 31. The actuator 38 is a cylindrical body, and the end of the actuator 38 on the inner arm 36 side engages with the proximal ends 36a of both inner arms 36 on the actuator 38 side.

[0032] Also, a female thread is formed on the inner peripheral surface of the base portion 32 of the outer sleeve 31, while a male thread that screws into the female thread is formed on the outer peripheral surface of the actuator 38. Therefore, when the actuator 38 receives a rotational operation, both inner arms 36 move in the axial direction of the outer sleeve 31 together with the actuator 38.

[0033] A notch 37 that opens in the direction from the proximal end 36a toward the distal end 36b is formed at the distal end 36b of each inner arm 36 on the side opposite to the actuator 38, and the distal end 36b has a substantially U-shaped configuration. The ridge 35 of the outer sleeve 31 described above is located within the notch 37.

[0034] As shown in FIG. 10, when the inner arm 36 advances with the ridge 35 of the outer sleeve 31 engaged with the engagement groove 27 provided in the opposing wall 24 of the head 22 of the pedicle screw 2, the support surface located at the bottom of the U-shaped configuration of the distal end 36b of the inner arm 36 abuts against the end surface of the opposing wall 24, whereby the extender 3 is fixed to the head 22.

[0035] (Rod reducer) As shown in FIGS. 5 to 7, the rod reducer 1 includes a connector 4 for coupling with the extender 3, a hollow reduction shaft 6 passing through the connector 4, and a central shaft 7 disposed within the reduction shaft 6 so as to be axially slidable.

[0036] The connector 4 includes a cylindrical main body 41 into which the base end portion of the extender 3 (specifically, the base end portion of the base 32 of the outer sleeve 31) is inserted, and a pair of swing pieces 42 swingably attached to the main body. Each swing piece 42 has a hook engageable with the slot 32a of the outer sleeve 31, and swings between a normal position (the position shown in FIGS. 5 and 6) where the hook engages with the slot 32a and a disengaged position where the engagement between the hook and the slot 32a is released. Although not shown, a spring for maintaining the swing piece 42 in the normal position is disposed between the swing piece 42 and the main body 41.

[0037] A first grip 5 is rotatably held by the connector 4. The first grip 5 is held within the main body 41 of the connector 4, and approximately half of it protrudes from the main body 41 in the direction opposite to the extender 3. The first grip 5 is cylindrical, and an internal thread 51 is formed on the inner peripheral surface of the first grip 5.

[0038] The reduction shaft 6 presses the spinal rod 10 at the end which is the tip of the portion inserted into the extender 3. That is, the reduction shaft 6 advances so as to approach the pedicle screw 2 or retreats so as to move away from the pedicle screw 2. The central shaft 7 includes a distal end portion 71 protruding from the reduction shaft 6 in the advancing direction of the reduction shaft 6 and a proximal end portion 72 protruding from the reduction shaft 6 in the retreating direction of the reduction shaft 6.

[0039] More specifically, the reduction shaft 6 includes a pair of pressing pieces 61 that abut against the spinal rod 10, a first tubular portion 62 adjacent to the pressing piece 61, and a second tubular portion 63 located on the side opposite to the pressing piece 61 with the first tubular portion 62 interposed therebetween. In other words, the first tubular portion 62 is interposed between the pressing piece 61 and the second tubular portion 63. As shown in FIGS. 8 and 9(b), the pair of pressing pieces 61 face each other with the end portion 71 of the central shaft 7 therebetween.

[0040] As shown in FIG. 6, an external thread 64 that engages with the internal thread 51 of the first grip 5 is formed on the outer peripheral surface of the second tubular portion 63. Therefore, when the first grip 5 is rotated, the reduction shaft 6 moves in the axial direction. Although the description of the specific structure is omitted, the rotation of the reduction shaft 6 is prevented by the engagement between the reduction shaft 6 and the main body 41 of the connector 4.

[0041] In the present embodiment, the cross-sectional shapes of the outer peripheral surfaces of the first tubular portion 62 and the second tubular portion 63 are non-circular. More specifically, as shown in FIGS. 6, 9(a), and 9(b), a notch 62a that extends in the axial direction of the reduction shaft 6 and forms an arc-shaped space 61a located on the same circumference as the pressing piece 61 is formed on the outer peripheral surface of the first tubular portion 62. In other words, the outer peripheral surface of the first tubular portion 62 has a pair of large-diameter surfaces that are continuous with the outer surface of the pressing piece 61 and a pair of small-diameter surfaces that are smaller in diameter than the large-diameter surfaces. The small-diameter surface constitutes the bottom surface of the notch 62a.

[0042] Similarly, as shown in FIG. 6, a notch 63a that further extends in the axial direction of the reduction shaft 6 and forms a space 61a located on the same circumference as the pressing piece 61 is formed on the outer peripheral surface of the second tubular portion 63. In the present embodiment, both notches 63a form flat surfaces parallel to each other. In other words, the cross-sectional shape of the outer peripheral surface of the second tubular portion 63 is substantially oblong and long in the facing direction of the pressing pieces 61.

[0043] The above-described distal end portion 71 of the central shaft 7 is an interface to which the set screw 11 (see FIG. 10) for fixing the spinal rod is attached. A second grip 9 is provided at the above-described proximal end portion 72 of the central shaft 7. When the second grip 9 is rotated, the set screw 11 attached to the distal end portion 71 rotates together with the central shaft 7.

[0044] Furthermore, in the present embodiment, as shown in FIGS. 6 and 7, a spring 8 is provided between the central shaft 7 and the reduction shaft 6. The spring 8 biases the central shaft 7 in the direction from the proximal end portion 72 toward the distal end portion 71.

[0045] More specifically, as shown in FIGS. 7 and 8, the inner diameter of the second tubular portion 63 of the reduction shaft 6 and the inner diameter of a predetermined range on the second tubular portion 63 side of the first tubular portion 62 are set to be substantially equal to the diameter of the central shaft 7, but the inner diameter of a predetermined range on the pressing piece 61 side of the first tubular portion 62 is set to be larger than the diameter of the central shaft 7. That is, a stepped surface 62b is formed on the inner peripheral surface of the first tubular portion 62.

[0046] On the other hand, an enlarged diameter portion 73 facing the stepped surface 62b is provided on the central shaft 7. The spring 8 is a compression coil spring and is inserted through the central shaft 7. One end of the spring 8 abuts on the enlarged diameter portion 73 via a ring 81, and the other end abuts on the stepped surface 62b via a ring 82. The central shaft 7 is inserted into the reduction shaft 6 before the second grip 9 is attached, and then the second grip 9 is fixed to the proximal end portion 72 of the central shaft 7.

[0047] Next, with reference to FIGS. 10 and 11, a method of using the rod reducer 1 will be described. In FIGS. 10 and 11, the pedicle screw 2 is the tabbed pedicle screw 2A, but as described above, the pedicle screw 2 may be the non-tabbed pedicle screw 2B.

[0048] First, attach the set screw 11 to the end portion 71 of the central shaft 7. Next, insert the reduction shaft 6 into the extender 3 attached to the pedicle screw 2 and engage the hook of the swing piece 42 of the connector 4 with the slot 32a of the outer sleeve 31 of the extender 3, thereby coupling the rod reducer 1 to the extender 3. In this state, rotate the first grip 5 to advance the reduction shaft 6. As a result, the reduction shaft 6 presses the spinal rod 10 and the spinal rod 10 is inserted into the channel 25 of the head 22 of the pedicle screw 2.

[0049] At this time, in this embodiment, since the central shaft 7 is biased in the direction from the base end portion 72 toward the end portion 71 by the spring 8, the set screw 11 attached to the end portion 71 of the central shaft 7 is pressed against the female screw 26 of the pedicle screw 2 by the biasing force of the spring 8. Moreover, even when the reduction shaft 6 advances, the central shaft 7 is maintained at the position where the set screw 11 is pressed against the female screw 26, so that the spring 8 is compressed as the reduction shaft 6 advances.

[0050] Thereafter, by rotating the second grip 9, as shown in FIG. 11, the set screw 11 is screwed into the female screw 26. As described above, since the set screw 11 is pressed against the female screw 26 by the biasing force of the spring 8, the set screw 11 can be easily screwed into the female screw 26 of the head 22 of the pedicle screw 2 simply by rotating the second grip 9. Therefore, the set screw 11 can be easily screwed into the female screw 26 of the head 22 of the pedicle screw 2.

[0051] Moreover, in the present embodiment, since the notch 62a is formed in the first tubular portion 62 of the reduction shaft 6, when the rod reducer 1 is coupled to the extender 3, a relatively large gap is formed between the outer peripheral surface of the first tubular portion 62 of the rod reducer 1 and the inner peripheral surface of the extender 3 (more precisely, the inner peripheral surface of the inner arm 36) as shown in FIG. 12. For this reason, when the pedicle screw 2 is the tabbed pedicle screw 2A, interference between the reduction shaft 6 and the tab 28 is avoided. Therefore, the rod reducer 1 can be used for both the non-tabbed pedicle screw 2B and the tabbed pedicle screw 2A.

[0052] (Modification example) The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present invention.

[0053] For example, when the pedicle screw 2 is the non-tabbed pedicle screw 2B, the notch 62a may not be formed in the first tubular portion 62 of the reduction shaft 6, and the cross-sectional shape of the outer peripheral surface of the first tubular portion 62 may be circular.

[0054] Also, in the above embodiment, the extender 3 is engaged with the head 22 of the pedicle screw 2 (the tabbed pedicle screw 2A or the non-tabbed pedicle screw 2B). However, when the engagement groove 29 is formed at the tip of the tab 28 as in the case of the tabbed pedicle screw 2C shown in FIG. 13, the extender 3A that engages with the tip of the tab 28 as shown in FIGS. 14 and 15 may be employed, and the rod reducer 1 may be coupled to this extender 3A.

[0055] Specifically, the extender 3A includes a cylindrical main body 12 and a pair of swing pieces 14 swingably attached to the main body 12. At the base end of the main body 12, a pair of slots 12a for coupling with the rod reducer 1 are provided. At the distal end of the main body 12, a pair of openings 12b are formed at positions facing each other. Hereinafter, for convenience of explanation, the base end side of the main body 12 is referred to as the upper side, and the distal end side is referred to as the lower side. A portion 13 adjacent to the opening 12b above the opening 12b in the main body 12 abuts against the tip surface of the tab 28 of the pedicle screw 2C with a tab.

[0056] Each swing piece 14 has a hook located in the corresponding opening 12b. The hook is engageable with the engagement groove 29 of the pedicle screw 2C with a tab. Each swing piece 14 is attached to the main body 12 via a swing shaft 15 and is biased by a spring 16 to a position where the hook engages with the engagement groove 29.

[0057] Furthermore, a lock member 17 is attached to the main body 12 above the swing piece 14. The lock member 17 is rotatable in the circumferential direction of the main body 12 between a lock position that prohibits the swing of the swing piece 14 and an unlock position that allows the swing of the swing piece 14. The lock member 17 is provided with a spring 18 and a ball 19 that constitute a plunger. When the ball 19 fits into a recess formed in the main body 12, the lock member 17 is fixed to the lock position or the unlock position. In the lock position, a part of the lock member 17 enters between the operation portion 14a of the swing piece 14 and the main body 12, thereby prohibiting the swing of the swing piece 14.

[0058] With the extender 3A having such a structure, the extender 3A can be attached to the pedicle screw 2C with a tab simply by pressing the extender 3A against the tip of the tab 28 of the pedicle screw 2C with a tab (that is, with one touch).

Description of Reference Numerals

[0059] 1 Rod reducer 10 Vertebral rod 11 Stop screw 2 Pedicle screw 3, 3A Extender 4 Connector 5 First grip 51 Female thread 6 Reduction shaft 61 Pressing piece 61a Space 62, 63 Tubular part 62a Notch 64 Male thread 7 Central shaft 71 End part 72 Base end part 8 Spring 9 Second grip

Claims

1. A connector for coupling with an extender attached to a pedicle screw, A first grip having a female thread formed thereon, which is rotatably held by the connector, A hollow reduction shaft that passes through the connector, has a male thread formed thereon that engages with the female thread of the first grip, and presses a spinal rod at a distal end that is the tip of a portion inserted into the extender, A central shaft disposed within the reduction shaft so as to be axially slidable, having an interface at a distal end that projects in the forward direction of the reduction shaft from the reduction shaft and to which a set screw for fixing the spinal rod is attached, and a second grip provided at a proximal end that projects in the backward direction of the reduction shaft from the reduction shaft, A spring provided between the outer peripheral surface of the central shaft and the inner peripheral surface of the reduction shaft, which biases the central shaft in a direction from the proximal end to the distal end, A rod reducer comprising the above.

2. A connector for coupling with an extender attached to a pedicle screw, A first grip having a female thread formed thereon, which is rotatably held by the connector, A hollow reduction shaft that passes through the connector, has a male thread formed thereon that engages with the female thread of the first grip, and presses a spinal rod at a distal end that is the tip of a portion inserted into the extender, A central shaft disposed within the reduction shaft so as to be axially slidable, having an interface at a distal end that projects in the forward direction of the reduction shaft from the reduction shaft and to which a set screw for fixing the spinal rod is attached, and a second grip provided at a proximal end that projects in the backward direction of the reduction shaft from the reduction shaft, A spring provided between the central shaft and the reduction shaft, which biases the central shaft in a direction from the proximal end to the distal end, and comprising the above, The reduction shaft includes a pair of pressing pieces that contact the spinal rod and face each other with the central shaft interposed therebetween, and a tubular portion interposed between the pair of pressing pieces and the male thread. A rod reducer, wherein a notch extending in the axial direction of the reduction shaft is formed on the outer peripheral surface of the tubular portion, the notch defining a space located on the same circumference as the pair of pressing pieces.

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