# Patent

## Title
Tissue splitter

## Abstract

A tissue splitter for creating a subcutaneous cut is disclosed. The tissue splitter includes a retractable blade located at the distal end. The tissue splitter is configured to be insertable into a slotted cannula that is placed via an incision to a location proximate a patient's spine. An actuator at the proximal end of the instrument projects the blade located at the distal end from its retracted state through the slot of the cannula to an extracted state to subcutaneously cut tissue at a location outside the cannula. The instrument is configured such that the blade is movable inside the slot of the cannula by a distance such that the cut created by the blade remains subcutaneous and does not puncture the skin of the patient. The distance is adjustable for the size and depth of the cut and is limited by an adjustment collar. The tissue splitter is ideally suited for creating a pathway for the subcutaneous insertion and implantation of a spinal stabilization rod between two bone anchors placed in vertebral bodies.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to and the benefit of and is a continuation-in-part of U.S. Provisional Patent Application Ser. No. 61/011,478 entitled “Tissue splitter” filed on Jan. 16, 2008 and is incorporated herein by reference in its entirety. This application is a continuation-in-part of U.S. patent application Ser. No. 11/586,849 entitled “Systems and methods for stabilization of bone structures” filed on Oct. 25, 2006 which is a continuation-in-part of U.S. patent application Ser. No. 11/362,366 entitled “Systems and methods for stabilization of bone structures” filed on Feb. 23, 2006 which is a non-provisional of U.S. Provisional Patent Application 60/701,660 entitled “Systems and methods for stabilization of bone structures” filed on Jul. 22, 2005, all of these applications are hereby incorporated by reference in their entireties.


BACKGROUND
Damage to the spine as a result of advancing age, disease, and injury, has been treated in many instances by fixation or stabilization of vertebrae. Conventional methods of spinal fixation utilize a rigid or semi-rigid spinal fixation device to support an injured spinal vertebra relative to an adjacent vertebra and prevent movement of the injured vertebra relative to an adjacent vertebra. These conventional spinal fixation devices include anchor members for fixing to a series of two or more vertebrae of the spine and at least one substantially rigid link element designed to interconnect the anchor members. Typically, the anchor member is a screw and the substantially rigid link element is a rod. The screw is configured to be inserted into the pedicle of a vertebra to a predetermined depth and angle. One end of the rigid link element is connected to an anchor inserted in the pedicle of the upper vertebra and the other end of the rod is connected to an anchor inserted in the pedicle of an adjacent lower vertebra. The rod ends are connected to the anchors via coupling constructs such that the adjacent vertebrae are supported and held apart in a relatively fixed position by the rods. Typically, two rods and two pairs of anchors are installed each in the manner described above such that two rods are employed to fix two adjacent vertebrae, with one rod positioned on each side of adjacent vertebrae. Once the system has been assembled and fixed to a series of two or more vertebrae, it constitutes a rigid device preventing the vertebrae from moving relative to one another. This rigidity enables the devices to support all or part of the stresses instead of the stresses being born by the series of damaged vertebra.
The implantation of a rod requires a pathway to be created through the surrounding tissue between two anchors. Because of the surrounding tissue between two anchors is comprised of muscle and fascia, the pathway, if not cleared, makes passing the rod through muscle and fascia quite difficult. Therefore, there is a need for instrumentation designed to create a pathway for rod implantation. Furthermore, in minimally invasive procedures, the pathway preferably needs to be cleared subcutaneously to minimize the disruption and damage to the surrounding tissue. Therefore, the need extends to instrumentation designed to create a pathway subcutaneously for rod implantations. The present invention sets forth such instrumentation.
SUMMARY
According to one aspect of the invention, an instrument is provided comprising a shaft, an actuator connected to the shaft and a blade connected to the distal end of the actuator. The actuator is configured to extend and retract the blade with respect to the shaft and the shaft is configured to be insertable into a cannula having a longitudinal axis and connectable to the cannula such that the blade is capable of longitudinal movement with respect to the cannula. The longitudinal movement with respect to the cannula is controllable and adjustable by the instrument having adjustable stops such that the cut created by the longitudinal movement does not breach the skin.
According to another aspect of the invention, an instrument comprising a retractable blade at a distal end is provided. The instrument is configured to be insertable into a cannula with the blade in a retracted state. The blade is movable subcutaneously by a distance relative to the cannula to create a subcutaneous cut outside the cannula.
According to another aspect of the invention, a system is provided. The system includes a first cannula connectable to a first bone anchor implanted in a first vertebral body. The first cannula has a longitudinal sidewall opening. A second cannula is connectable to a second bone anchor implanted in a second vertebral body. The system includes an instrument insertable into the first cannula. The instrument includes a shaft, an actuator connected to the shaft, and a blade connected to the distal end of the actuator. The actuator is configured to move the blade through the longitudinal sidewall opening into a deployed configuration such that the blade projects through the longitudinal sidewall opening towards the second cannula and the blade is longitudinally movable inside the longitudinal sidewall opening of the cannula by a distance to subcutaneously cut tissue outside the cannula.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to-scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. All figures herein illustrate a tissue splitter according to the present invention.
FIG. 1a illustrates a perspective view of a tissue splitter according to the present invention.
FIG. 1b illustrates a cross-sectional view of a tissue splitter according to the present invention.
FIG. 2a illustrates a side view of a tissue splitter with blade extended according to the present invention.
FIG. 2b illustrates a cross-sectional view of a tissue splitter with blade extended according to the present invention.
FIG. 3a illustrates a perspective view of an adjustment collar according to the present invention.
FIG. 3b illustrates a side view of an adjustment collar according to the present invention.
FIG. 4 illustrates a perspective view of a tissue splitter in conjunction with an access system connected to a pair of bone anchors implanted into adjacent vertebral bodies of a patient's spine shown in part.
FIG. 5 illustrates a perspective view of a tissue splitter in conjunction with an access system extending through skin and connected to a pair of bone anchors implanted into adjacent vertebral bodies of patient's spine shown in part.
FIG. 6a illustrates a side view of a partially deployed blade of a tissue splitter inserted in one of two cannulas connected to bone anchors implanted in adjacent vertebral bodies of a patient's spine.
FIG. 6b illustrates a side view of a fully deployed blade of a tissue splitter inserted in one of two cannulas connected to bone anchors implanted in adjacent vertebral bodies of a patient's spine.
FIG. 6c illustrates a side view of a fully deployed blade of a tissue splitter inserted in one of two cannulas connected to bone anchors implanted in adjacent vertebral bodies of patient's spine with the blade pulled proximally to dissect tissue between the two cannulas.
FIG. 7 illustrates a perspective view of a fully deployed blade of a tissue splitter inserted in one of two cannulas connected to bone anchors implanted in adjacent vertebral bodies of patient's spine with the blade pulled proximally to dissect tissue subcutaneously between the two cannulas.



DETAILED DESCRIPTION
With reference to FIGS. 1a and 1b, there is shown a tissue splitter 10 according to the present invention. The tissue splitter 10 includes a handle assembly 12 connected to a shaft assembly 14 and an actuator assembly 16 connected to a blade 18 and an adjustment collar 15 and locking collar 20 connected to the shaft assembly 14. The locking collar 20 is placed over the shaft assembly 14 and permitted to free-float between an adjustment collar 15 and the handle assembly 12. The distal end of the locking collar 20 includes a threaded portion for connecting or locking the locking collar 20 and in turn, the tissue splitter 10 to a cannula or other instrument. An adjustment collar 15 is connected to the shaft assembly 14 and also permitted to slide and be locked with respect to the shaft assembly 14.
Referring briefly to FIGS. 3a and 3b, there is shown an adjustment collar 15 according to the present invention. The adjustment collar 15 is substantially cylindrical in shape and includes a longitudinal slot 44 formed in the sidewall with a plurality of side slots 46 having corresponding adjacent graduations 48. The adjacent graduations 48 correspond to various and approximate lengths of spinal stabilization rods implantable between two bone anchors placed in vertebral bodies. A pin 50 (seen in FIG. 2a) formed on the outer surface of the shaft assembly 14 is configured to travel the longitudinal slot 44 relative to the adjustment collar 15 to position the adjustment collar 15 relative to the shaft assembly 14 or the locking collar 20 by a distance approximately equal to the length of a rod selected for implantation. Hence, the adjustment collar 15 is movable with respect to the shaft 14 and its position adjusted and locked from said movement by guiding the pin 50 into any of the side slots 46. For example, after a surgeon measures the pedicle-to-pedicle distance of adjacent vertebrae and determines the rod length suitable for implantation to be 45 mm, the surgeon will slide the adjustment collar 15 longitudinally relative to the shaft assembly 14 such that the pin 50 travels in the longitudinal slot 44. Then, the surgeon will turn the adjustment collar 15 to position the pin 50 in the side slot 46 having the appropriate graduation “45” inscribed next to the side slot 46. So positioned, the pin 50 is approximately the rod length distance from the distal end of the locking collar 20 when connected to a cannula or other instrument through which the instrument is inserted. Hence, a stop is defined by the adjustment collar 15 against which movement of the blade 18 is limited to prevent the blade 18 from breaching skin from its subcutaneous position when creating a cut.
Referring back to FIGS. 1 and 2, a blade housing assembly 17 is connected to the shaft assembly 14. In one variation, the blade housing assembly 17 is threadingly connected to the shaft assembly 14 such that rotation of the proximal end of the blade housing assembly 17 permits the blade housing assembly 17 to longitudinally slide proximally on the shaft assembly 14 to expose, remove and exchange the blade 18. The blade housing assembly 17 is moved distally longitudinally to encase and cover the blade 18 with the proximal end of the blade housing assembly 17 rotated to threadingly re-connect the blade housing 17 to the shaft assembly 14. As a result, disposable blades may be employed.
FIGS. 1a and 1b show the tissue splitter 10 in an undeployed configuration in which the blade 18 is retracted. FIGS. 2a and 2b show the tissue splitter 10 in a deployed configuration in which the blade 18 is extracted or deployed. With particular reference to FIGS. 1b and 2b, the actuator assembly 16 includes a proximal knob 38 connected to an inner shaft 41 which is connected to a back linkage 40 that is connected to the blade 18 which is in turn connected to a front linkage 42. The front linkage 42 is connected to the shaft assembly 14. The inner shaft 41 of the actuator assembly 16 is disposed inside the handle assembly 12. The actuator assembly 16 is in part disposed inside the shaft assembly 14. Rotation of the proximal knob 38 in one direction drives the shaft 41 and connected back linkage 40 toward the distal end of the instrument 10 relative to the handle and shaft assemblies 12, 14 pivoting the blade 18 out from the blade housing assembly 17. Rotation of the proximal knob 38 activates the blade 18 into deployment in which the blade 18 projects outwardly from the distal end of the instrument 10 to expose the blade 18. Rotation of the proximal knob 38 in the opposite direction draws the shaft 41 and connected back linkage 40 proximally, thereby, pivoting the blade 18 to within the confines of the blade housing assembly 17. Rotation of the proximal knob 38 in the opposite direction retracts the blade 18 into an undeployed or retracted position in which the blade 18 is hidden in the blade housing assembly 17. In the variation shown, a serrated blade 18 is employed to advantageously cut tissue when the blade 18 is moved. Also, in one variation, the blade 18 is angled with respect to the shaft assembly 14 or blade housing assembly 17 or cannula when in the extracted deployed state.
Turning now to FIG. 4, there is shown the tissue splitter 10 in conjunction with a minimally invasive, percutaneous rod deployment system 22 attached to a pair of bone anchors 24 that are implanted into adjacent vertebral bodies 26 of a patient's spine 28 shown in part in FIG. 4. The minimally invasive, percutaneous rod deployment system 22, such as that developed by Vertiflex, Inc. and described in detail in U.S. patent application bearing Ser. No. 11/362,366 entitled “Systems and methods for stabilization of bone structures” filed on Feb. 23, 2006 and in U.S. patent application bearing Ser. No. 11/586,849 entitled “Systems and methods for stabilization of bone structures” filed on Oct. 25, 2006, both of which are incorporated herein by reference in their entireties, comprises, in part, of a pair of slotted cannulas 30 with alignment guides 32 seated on top of the cannulas 30. Prior to insertion of a rod, the rod length is determined by the clinician. Also, the outside of the cannulas 30 include depth markers 34 which can be read above the skin 36 (see FIG. 5). The depth that the cannulas are sunk into the patient is typically greater than the length of the rod to be implanted and as such, the cut that the tissue splitter 10 makes at the first cannula is preferably approximately equal to the length of the rod and less than the approximate depth to which the first cannula is sunk into the patient. The adjustment collar 15 is positioned with respect to the shaft assembly 14 by moving the pin 50 along the longitudinal slot 44 and into a side slot 46 that corresponds approximately to the desired length of the cut which may correspond to the length of the rod to be deployed and/or to less than the depth reading at the skin on the outside of the cannulas. In cases where the patient is thin, for example, a depth marking on the cannula may shown 35 millimeters and the surgeon selected rod length may be 45 millimeters. In such cases, the clinician would select the smaller cut, 35 millimeters, so as to not breach the skin. Prior to implantation of the rod, the tissue splitter 10 is inserted into a first alignment guide 32 that is connected to a first cannula 30 or in another variation, inserted into a cannula 30 without an alignment guide 32. The tissue splitter 10 is inserted such that the tissue splitter is aligned with a second cannula. Markers on the tissue splitter 10 are provided to aid the user in properly inserting and aligning the tissue splitter 10 into the first cannula 30. In general, a properly oriented tissue splitter 10 is one in which the blade is deployable in a direction toward the other or second cannula 30. The tissue splitter 10 is connected to the alignment guide 32 or directly to the cannula 30 via the locking collar 20 or other means. In one variation, the tissue splitter 10 is connected by rotation of the locking mechanism 20 which threads to a correspondingly threaded alignment guide 32 or cannula 30.
Still referencing FIG. 5 and turning to FIGS. 6a-6c, the blade 18 is actuated and deployed by turning the proximal knob 38 of the actuator assembly 16. The blade 18 may be actuated by other means known to one skilled in the art including a push type mechanism for deploying the blade. As a result, the blade 18 emerges from the blade housing assembly 17 and through the slot in the first cannula 30 and begins to cut tissue as shown in FIG. 6a. In FIG. 6b, the blade 18 is shown fully deployed. In FIG. 6c and FIG. 7, the handle assembly 12 is pulled upwardly by the user in a longitudinal direction as shown by the arrow in FIG. 7 along the cannula inside the cannula slot. As a result of pulling the handle assembly 12 upwardly, the handle assembly 12 that is connected to the shaft assembly 14 which is in turn connected to the blade housing assembly 17 pulls the deployed blade 18 upwardly, thereby, cutting more tissue in an upwardly direction as shown in FIG. 7 and shown progressively in FIGS. 6a-6c. The handle assembly 12 can then be pushed distally and pulled again to repeat the cutting motion as needed. Upward translation of the blade 18 is limited by at least one stop relative to the cannula. Downward translation of the blade 18 in one variation is also limited by at least one stop. Also, after a cut is made with the tissue splitter 10 in the first cannula, it may be removed and placed into the second cannula and a second cut made. The second cut the same length or the adjustment collar 15 may be adjusted for a shorter cut, which may be determined by the clinician as necessary where skin depth is smaller than the desired rod length or when rod length is longer than the blade length.
The locking collar 20 which is connected to the alignment guide 32 is free-floating with respect to the shaft assembly 14 allowing the shaft assembly 14 to translate longitudinally within the locking collar 20 between a first stop and a second stop, thereby, limiting longitudinal blade movement. One stop is defined by the adjustment collar 15 which, in one variation, is the proximal end 52 of the adjustment collar 15, against which a stop defined by the locking collar 20 abuts arresting further longitudinal translation in the proximal direction of the shaft/blade relative to the locking collar 20. In one variation, another stop is defined the handle assembly 12 which, in one variation, is the distal end of the handle assembly 12 against which a stop defined by the locking collar 20 abuts arresting further longitudinal translation in the distal direction of the shaft/blade relative to the locking collar 20. The blade 18 is allowed limited longitudinally travel relative to the cannula between two stops that are defined by the instrument. One of the stops is adjustable by the user such as the adjustment collar to customly vary the distance traveled by the blade relative to the cannula so as to not breach skin and maintain a subcutaneous incision. The adjustment collar 15 can be moved and locked into position with respect to the shaft assembly 14 and as such the movable adjustment collar 15 advantageously adjusts the distance between the first stop that is defined by the adjustment collar 15 and a second stop. The first and second stops between which the locking collar 20 is allowed to move also limits travel of the blade 18 with respect to the locking collar 20 which when connected to the cannula limits travel of the blade 18 in turn with respect to the cannula 30 as well, thereby, preventing the blade from breaching the skin surface or cutting a length that is too long. The position of the alignment collar 15 is selected to the length of the cut according to the length of the rod to be implanted and/or marker readings on the outside of the cannulas. Adjusting the position of the alignment collar 15 translates the alignment collar 15 along the shaft assembly 14 which thereby varies the stop defined by the alignment collar 15 and hence the travel distance of the shaft and handle assemblies with respect to the locking collar 20.
As shown in FIGS. 6a-6c, the blade 18 is angled downwardly towards the second cannula 30. Also, the blade 18 is also wider proximate to its point of attachment relative to the distal end of the blade which is narrower. As a result of this angle and width of blade, the length of the cut created by the tissue splitter near the first cannula is longer relative to the length of the cut created by the tissue splitter 10 near the first cannula 30. This length differential is advantageous because the rod is first seated in the first bone anchor and rotated through a slot in the first cannula towards the second cannula. As a result of the rotation of the rod having a pivot point at the first anchor, an arc is traced by the rod that requires a shorter cut near the second cannula where the arc ends relative to near the first cannula where the rod is in a substantially vertical orientation inside the first cannula and begins to arc and therefore requires a longer cut or pathway. If needed, the tissue splitter can be placed on the second alignment guide and tissue can be further dissected. With the tissue splitter removed, the rod is inserted into one of the first or second cannulas and rotated through the slotted cannula toward the other of the first or second cannula and connected to the first and second bone anchors.
All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. Although preferred illustrative embodiments of the present invention are described hereinabove, it will be apparent to those skilled in the art that various changes and modifications may be made thereto without departing from the invention. It is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the invention.

## Claims

1. An instrument comprising:
a shaft;
an actuator connected to the shaft;
a blade connected to the distal end of the actuator;
wherein the actuator is configured to extend and retract the blade with respect to the shaft; and
wherein the shaft is configured to be insertable into a cannula having a longitudinal axis and connectable to the cannula such that the blade is capable of longitudinal movement with respect to the cannula;
a locking collar connected to the shaft such that the shaft is capable of longitudinal movement with respect to the locking collar; the locking collar being configured to connect to the cannula such that the instrument is inhibited from removal from the cannula;
an adjustment collar connected to the shaft; the adjustment collar being longitudinally movable with respect to the shaft, wherein the longitudinal movement of the blade with respect to the cannula is limited by a plurality of predetermined stops defined by the adjustment collar.

2. The instrument of claim 1, wherein the longitudinal movement of the shaft is limited by a stop defined by the locking collar.

3. The instrument of claim 1 wherein the shaft is insertable into a cannula having a longitudinal opening in the sidewall of the cannula; the shaft is connectable to the cannula such that the blade is extendable through the longitudinal opening of the cannula and longitudinally movable inside the longitudinal opening of the cannula.

4. The instrument of claim 1, wherein a portion of the adjustment collar engages, during use, a portion of the locking collar such that longitudinal movement of the shaft in a first direction is limited.

5. The instrument of claim 1, wherein the instrument is adapted for creating a subcutaneous pathway for a spinal stabilization rod.

6. The instrument of claim 1, wherein the blade is angled with respect to the cannula when in an extracted state.

7. An instrument comprising:
a shaft;
an actuator connected to the shaft;
a blade connected to the distal end of the actuator;
wherein the actuator is configured to extend and retract the blade with respect to the shaft; and
wherein the shaft is configured to be insertable into a cannula having a longitudinal axis and connectable to the cannula such that the blade is capable of longitudinal movement with respect to the cannula;
a locking collar connected to the shaft such that the shaft is capable of longitudinal movement with respect to the locking collar; the locking collar being configured to connect to the cannula such that the instrument is inhibited from removal from the cannula;
an adjustment collar connected to the shaft; the adjustment collar being longitudinally movable with respect to the shaft, wherein the longitudinal movement of the blade with respect to the cannula is limited by a plurality of predetermined stops defined by the adjustment collar, and wherein at least one of the predetermined stops defined by the adjustment collar defines the distance to be approximately less than the length of a spinal stabilization rod.

8. The instrument of claim 7, wherein the longitudinal movement of the shaft is limited by a stop defined by the locking collar.

9. The instrument of claim 7, wherein the shaft is insertable into a cannula having a longitudinal opening in the sidewall of the cannula; the shaft is connectable to the cannula such that the blade is extendable through the longitudinal opening of the cannula and longitudinally movable inside the longitudinal opening of the cannula.

10. The instrument of claim 7, wherein a portion of the adjustment collar engages, during use, a portion of the locking collar such that longitudinal movement of the shaft in a first direction is limited.

11. The instrument of claim 10, further comprising a handle connected to the shaft, wherein a portion of the handle engages, during use, a portion of the locking collar such that longitudinal movement of the shaft in a second direction is limited, and wherein the second direction is in a direction substantially opposite to the first direction.

12. The instrument of claim 7, wherein the instrument is adapted for creating a subcutaneous pathway for a spinal stabilization rod.

13. The instrument of claim 7, wherein the blade is angled with respect to the cannula when in an extracted state.

14. A system comprising:
a first cannula connectable to a first bone anchor implanted in a first vertebral body; the first cannula having a longitudinal sidewall opening;
a second cannula connectable to a second bone anchor implanted in a second vertebral body;
an instrument insertable into the first cannula; the instrument comprising:
a shaft;
an actuator connected to the shaft;
a blade connected to the distal end of the actuator;
wherein the actuator is configured to move the blade through the longitudinal sidewall opening into a deployed configuration such that the blade projects through the longitudinal sidewall opening towards the second cannula; and the blade being longitudinally movable inside the longitudinal sidewall opening of the cannula by a distance to subcutaneously cut tissue outside the cannula;
a locking collar connected to the shaft such that the shaft is longitudinally movable with respect to the locking collar; the instrument being connectable to the first cannula via the locking collar such that the instrument is inhibited from removal from the first cannula; and
an adjustment collar connected to the shaft; the adjustment collar being longitudinally movable with respect to the shaft, wherein the longitudinal movement of the blade with respect to the first cannula is limited by a plurality of predetermined stops defined by the adjustment collar.

15. The system of claim 14 wherein the instrument is configured to make a cut that is longer at a location proximate to the first cannula relative to the length of the cut at a location proximate to the second cannula.

16. The system of claim 14 wherein the blade is configured to angulate through the longitudinal opening.

17. The system of claim 14, wherein the shaft is longitudinally movable and lockable with respect to the adjustment collar.

18. The system of claim 17 wherein the distance is between a stop defined by the locking collar and at least one of the plurality of stops defined by the adjustment collar.

19. The instrument of claim 4, further comprising a handle connected to the shaft, wherein a portion of the handle engages, during use, a portion of the locking collar such that longitudinal movement of the shaft in a second direction is limited, and wherein the second direction is in a direction substantially opposite to the first direction.

20. The system of claim 14, wherein a portion of the adjustment collar engages, during use, a portion of the locking collar such that longitudinal movement of the shaft in a first direction is limited.