Kit for spinal fixation

Abstract

To provide an extender to be used for both of a pedicle screw without a tab and also a pedicle screw with a tab.SOLUTION: An extender includes an outer sleeve 4 and a pair of inner arms 5. The outer sleeve 4 includes a pair of arm parts 42, and an engagement ridge 43 with a pedicle screw 2 is arranged at the tip of each one of the respective arm parts 42. Each one of the inner arms 5 is held by the outer sleeve 4 so as to be slidable in an axial direction of the outer sleeve 4 along the inner side surface of the corresponding arm part 42. A thickness T of a part overlapped with the inner side surface of the corresponding arm part 42 in each one of the inner arms 5 is 1.5 times or less of a height H of the ridge 43 in a radial direction of the outer sleeve 4.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to an extender used in spinal fixation surgery and a spinal fixation kit including the extender.

Background Art

[0002] In one technique of spinal fixation surgery, pedicle screws are screwed into continuously aligned pedicles, and the 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 crosses 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] When the pedicle screws are connected to each other by a spinal rod, the orientation and position of the pedicle screws are adjusted to adjust the intervertebral space and the curvature of the spine. To adjust the orientation and position of the pedicle screw, an extender attached to the head of the pedicle screw to extend the length of the head may be used.

[0004] For example, Patent Document 1 discloses an extender 100 as shown in FIG. 9(a). This extender 100 includes an outer sleeve 110 and a pair of inner arms 120 disposed within the outer sleeve 110.

[0005] More specifically, the outer sleeve 110 includes a cylindrical base portion 111 and a pair of arm portions 112 protruding from the base portion 111. A slit 115 is formed between the arm portions 112. As shown in FIG. 9(b), this slit 115 is continuous with a channel 142 for inserting a spinal rod provided on the head 141 of the pedicle screw 140 when the extender 100 is attached to the pedicle screw 140. That is, the channel 142 and the slit 115 define the movable range of the spinal rod. At the tip of each arm portion 112, a ridge 113 for engagement with the head 141 of the pedicle screw 140 is provided.

[0006] Each inner arm 120 is held by the outer sleeve 110 so as to be slidable in the axial direction of the outer sleeve 110 along the inner surface of the corresponding arm portion 112. An actuator 130 for moving the inner arm 120 is attached to the base portion 111 of the outer sleeve 110.

[0007] The actuator 130 includes a nut disposed within the base portion 111 of the outer sleeve 110 and engaging the inner arm 120. A male thread is formed on the outer peripheral surface of the nut, while a female thread that mates with the male thread is formed on the inner peripheral surface of the base portion 111 of the outer sleeve 110. Therefore, when the actuator 130 receives a rotational operation, the inner arm 120 moves in the axial direction of the outer sleeve 110 together with the actuator 130.

[0008] A notch that opens along the axial direction of the outer sleeve 110 is formed at the end of each inner arm 120, and the end is substantially U-shaped. The ridge 113 of the outer sleeve 110 described above is located within the notch.

[0009] As shown in Fig. 9(b), when the inner arm 120 advances with the ridge 113 of the outer sleeve 110 engaged with the engagement groove 143 provided on the head 141 of the pedicle screw 140, the support surface located at the bottom of the above-described U-shape at the end of the inner arm 120 abuts against the end face of the head 141, whereby the extender 100 is fixed to the head 141.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] By the way, some pedicle screws have a pair of tabs provided on the head so as to extend the channel for inserting the spinal rod. For such a pedicle screw with tabs, the extender 100 shown in Fig. 9(a) cannot be used.

[0012] Therefore, an object of the present invention is to provide an extender that can be used for both tabless pedicle screws and pedicle screws with tabs, and a spinal fixation kit including the extender.

Means for Solving the Problems

[0013] To solve the above problems, the present invention provides an extender attached to a pedicle screw, comprising a cylindrical base and a pair of arm portions protruding from the base, and an outer sleeve provided with ridges for engagement with the pedicle screw at the tips of the respective arm portions; a pair of inner arms held by the outer sleeve so as to be slidable in the axial direction of the outer sleeve along the inner surfaces of the pair of arm portions; and an actuator attached to the base of the outer sleeve for moving the pair of inner arms upon receiving a rotational operation. The thickness of the portion of each of the pair of inner arms that overlaps with the inner surface of the corresponding arm portion is 1.5 times or less the height of the ridge in the radial direction of the outer sleeve.

[0014] According to the above configuration, since the thickness of the inner arm is set to be thin, when the pedicle screw has a pair of tabs, those tabs are disposed inside the inner arm. Therefore, the extender can be used for both a tabless pedicle screw and a pedicle screw with tabs.

[0015] For example, a female screw may be formed on the inner peripheral surface of the base of the outer sleeve, the actuator may be a cylindrical body having a male screw formed on its outer peripheral surface that is screwed with the female screw, a connecting groove extending in the circumferential direction of the outer sleeve may be formed on the outer surface of the proximal end on the actuator side of each of the pair of inner arms, and a connecting protrusion engaging with the connecting groove may be provided on the inner peripheral surface of the end on the pair of inner arm side of the actuator. A female screw may be formed on the inner peripheral surface of the base of the outer sleeve, the actuator may be a cylindrical body having a male screw formed on its outer peripheral surface that is screwed with the female screw, a connecting groove extending in the circumferential direction of the outer sleeve may be formed on the outer surface of the proximal end on the actuator side of each of the pair of inner arms, and a connecting protrusion engaging with the connecting groove may be provided on the inner peripheral surface of the end on the pair of inner arm side of the actuator.

[0016] In each of the pair of inner arms, a predetermined range including the proximal end is bent radially outward of the outer sleeve, and the inner arm may be disposed within the outer sleeve with the bend of the predetermined range corrected. According to this configuration, since the proximal end of the inner arm is pressed against the inner peripheral surface of the actuator, it is possible to make it difficult for the connecting protrusion to come off from the connecting groove.

[0017] The present invention also provides a spinal fixation kit including the above-described extender, an anchor, a head, and a pedicle screw including a pair of tabs, wherein when the extender is attached to the pedicle screw, the pair of tabs are disposed inside the pair of inner arms.

Advantages of the Invention

[0018] According to the present invention, an extender that can be used for both a tabless pedicle screw and a pedicle screw with tabs is provided.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0020] FIG. 1 shows the usage state of a spinal fixation kit 1 including an extender 3 according to an embodiment of the present invention. In FIG. 1, the kit 1 includes three pedicle screws 2, three extenders 3, and one spinal rod 10. However, the number of sets of the pedicle screws 2 and the extenders 3 included in the kit 1 can be appropriately changed, and it may be one, two, or four or more. Also, the kit 1 may include a plurality of spinal rods 10.

[0021] In FIG. 1, three pedicle screws 2 are screwed into the pedicles arranged continuously side by side, and three extenders 3 are respectively attached to those pedicle screws 2. The pedicle screws 2 are connected by a spinal rod 10.

[0022] The pedicle screw 2 includes a pedicle screw 2A with tabs shown in FIG. 2(a) and a pedicle screw 2B without tabs shown in FIG. 2(b). However, all of the pedicle screws 2 may be pedicle screws 2A with tabs, or all of the pedicle screws 2 may be pedicle screws 2B without tabs.

[0023] 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. The head 22 is provided with a channel 25 that traverses the head 22 in a direction orthogonal to the axial direction of the anchor 21. A spinal rod 10 is inserted into the channel 25.

[0024] More specifically, the head 22 includes a disk portion 23 that is penetrated by the anchor 21 and a pair of opposing walls 24 that rise from the disk portion 23 and face 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.

[0025] Furthermore, engaging grooves 27 for engagement 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.

[0026] 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 the 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 on the inner surfaces of the tabs 28.

[0027] As shown in FIGS. 3 and 4, the extender 3 includes an outer sleeve 4, and a pair of inner arms 5 and an actuator 6 disposed within the outer sleeve 4.

[0028] The outer sleeve 4 includes a cylindrical base portion 41 and a pair of arm portions 42 that project along the axial direction of the outer sleeve 4 from the base portion 41. The arm portions 42 face each other, and the cross-sectional shape of each arm portion 42 is arcuate.

[0029] A slit 44 is formed between the arm portions 42. As shown in FIGS. 5(a) and 5(b), this slit 44 is continuous with a channel 25 for inserting a spinal rod provided in the head 22 when the extender 3 is attached to the pedicle screw 2. That is, the channel 25 and the slit 44 define the movable range of the spinal rod 10.

[0030] As shown in FIG. 4, in the range from the tip of each arm portion 42 to about 1 / 4 of the total length of the arm portion, the width of each arm portion 42 becomes narrower. At the tip of each arm portion 42, a ridge 43 for engagement with an engagement groove 27 provided in the head 22 of the pedicle screw 2 is provided.

[0031] Each inner arm 5 extends from the proximal end 5a to the distal end 5b with a substantially constant arc-shaped cross-sectional shape. In other words, both inner arms 5 have a shape such that a pipe that abuts against the inner surface of the arm portion 42 of the outer sleeve 4 is cut with the same width as the slit 44.

[0032] Each inner arm 5 is held by the outer sleeve 4 so as to be slidable in the axial direction of the outer sleeve 4 along the inner surface of the corresponding arm portion 42. In the present embodiment, a pair of slots 46 extending in the axial direction of the outer sleeve 4 are provided in each arm portion 42 of the outer sleeve 4. The pair of slots 46 are arranged in the axial direction of the outer sleeve 4.

[0033] On the other hand, a pair of protrusions 53 that are respectively fitted into the pair of slots 46 are provided on the outer surface of each inner arm 5. By being guided by the slots 46, the inner arm 5 is slidable in the axial direction of the outer sleeve 4.

[0034] Further, while the protrusion 53 has an enlarged portion at its tip, the slot 46 has a widened portion at its proximal end (the end on the base 41 side) through which the enlarged portion of the protrusion 53 can be inserted, and the width of the portion of the slot 46 other than the proximal end is set narrower than the enlarged portion of the protrusion 53. Therefore, by engaging the enlarged portion of the protrusion 53 with the portion of the slot 46 other than the proximal end, the inner arm 5 is held by the corresponding arm portion 42.

[0035] The actuator 6 is for moving both inner arms 5 upon receiving a rotational operation, and is attached to the base 41 of the outer sleeve 4. The actuator 6 is a cylindrical body, and the end of the actuator 6 on the inner arm 5 side engages with the proximal ends 5a of both inner arms 5 on the actuator 6 side.

[0036] More specifically, as shown in FIG. 4, on the outer surface of the proximal end 5a of each inner arm 5, a connecting groove 52 extending in the circumferential direction of the outer sleeve 4 is formed. On the other hand, as shown in FIG. 6, on the inner peripheral surface of the end of the actuator 6, a connecting protrusion 63 that engages with the connecting groove 52 is provided.

[0037] Also, a female thread 45 is formed on the inner peripheral surface of the base 41 of the outer sleeve 4. On the other hand, a male thread 61 that engages with the female thread 45 is formed on the outer peripheral surface of the actuator 6. Therefore, when the actuator 6 receives a rotational operation, both inner arms 5 move in the axial direction of the outer sleeve 4 together with the actuator 6. Note that a notch 62 for engaging with a tool for rotating the actuator 6 is formed at the proximal end of the actuator 6 on the side opposite to the inner arm 5.

[0038] In the present embodiment, as shown in FIG. 7, a predetermined range (for example, a range of 1 / 4 to 1 / 8 of the total length of the inner arm) including the proximal end 5a in each inner arm 5 is bent radially outward of the outer sleeve 4. And the inner arm 5 is arranged in the outer sleeve 4 in a state where the bending of the predetermined range is corrected.

[0039] Returning to FIG. 4, a notch 51 that opens in the direction from the proximal end 5a toward the distal end 5b is formed at the distal end 5b of each inner arm 5 on the side opposite to the actuator 6, and the distal end 5b has a substantially U shape. The ridge 43 of the outer sleeve 4 described above is located within the notch 51.

[0040] As shown in FIG. 8, when the inner arm 5 advances with the ridge 43 of the outer sleeve 4 engaged with the engagement groove 27 provided in the opposing wall 24 of the head 22 of the pedicle screw 2, the support surface 50 located at the bottom of the above-described U shape of the distal end 5b of the inner arm 5 abuts against the end surface of the opposing wall 24, whereby the extender 3 is fixed to the head 22.

[0041] Furthermore, in the present embodiment, the thickness T of the portion of each inner arm 5 that overlaps with the inner surface of the corresponding arm portion 42 is set to be 1.5 times or less the height H of the ridge 43 in the radial direction of the outer sleeve 4. It is more desirable that the thickness T of each inner arm 5 is 1.2 times or less the height H of the ridge 43.

[0042] Thus, in the present embodiment, since the thickness of the inner arm 5 is set to be thin, when the pedicle screw 2 is the tabbed pedicle screw 2A, as shown in FIG. 5(a), when the extender 3 is attached to the tabbed pedicle screw 2A, the tab 28 is disposed inside the inner arm 5. Therefore, the extender 3 can be used for both the non-tabbed pedicle screw 2B and the tabbed pedicle screw 2A.

[0043] (Modification) 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.

[0044] For example, in the above embodiment, a predetermined range including the proximal end 5a of the inner arm 5 was bent radially outward of the outer sleeve 4, but the inner arm 5 may be straight over its entire length. However, with the configuration as in the above embodiment, since the proximal end 5a of the inner arm 5 is pressed against the inner peripheral surface of the actuator 6, it is possible to make it difficult for the connecting protrusion 63 to come off from the connecting groove 52.

[0045] Further, in order to increase the gripping force of the pedicle screw 2 by the extender 3, a predetermined range including the tip of each arm portion 42 of the outer sleeve 4 may be bent radially inward of the outer sleeve 4.

Explanation of Reference Numerals

[0046] 1 Spinal fixation kit 2 Pedicle screw 21 Anchor 22 Head 28 Tab 3 Extender 4 Outer sleeve 41 Base 42 Arm portion 43 Ridge 44 Female thread 5 Inner arm 52 Connecting groove 6 Actuator 61 Male thread 63 Connecting protrusion

Claims

1. A pedicle screw and, an extender attached to the pedicle screw, comprising: The extender is an outer sleeve including a cylindrical base and a pair of arm portions protruding from the base, and a ridge for engagement with the pedicle screw is provided at the tip of each arm portion, a pair of inner arms held by the outer sleeve so as to be slidable in the axial direction of the outer sleeve along the inner surfaces of the pair of arm portions, and when the pedicle screw includes a pair of tabs, the pair of tabs are disposed inside the pair of inner arms when the extender is attached to the pedicle screw, an actuator attached to the base of the outer sleeve and configured to move the pair of inner arms in the axial direction of the outer sleeve upon receiving a rotational operation, A spinal fixation kit, wherein a thickness of a portion of each of the pair of inner arms that overlaps an inner surface of the corresponding arm portion is 1.5 times or less of a height of the ridge in a radial direction of the outer sleeve.

2. A female screw is formed on an inner peripheral surface of a base of the outer sleeve, The actuator is a cylindrical body having a male screw formed on an outer peripheral surface thereof and screwed with the female screw, A connecting groove extending in a circumferential direction of the outer sleeve is formed on an outer surface of a proximal end on the actuator side of each of the pair of inner arms, The spinal fixation kit according to claim 1, wherein a connecting protrusion engaged with the connecting groove is provided on an inner peripheral surface of a terminal on the pair of inner arm sides of the actuator.

3. A predetermined range including the proximal end of each of the pair of inner arms is bent outward in a radial direction of the outer sleeve, and the inner arm is disposed in the outer sleeve in a state where the bending of the predetermined range is corrected. The spinal fixation kit according to claim 2.

4. The pedicle screw includes an anchor, a head, and a pair of tabs. The spinal fixation kit according to any one of claims 1 to 3.

Images