WO2023039398A1

WO2023039398A1 - Ball-nosed pedicle screw

Info

Publication number: WO2023039398A1
Application number: PCT/US2022/076015
Authority: WO
Inventors: Wyatt Drake Geist; Keith ROBY
Original assignee: Integrity Implants Inc.
Priority date: 2021-09-07
Filing date: 2022-09-07
Publication date: 2023-03-16

Abstract

The invention involves a bone screw or pedicle screw for insertion by a surgical robot. The bone screw includes a ball-nose or spherical cutting surface having cutting edges that follow the spherical surfaces. This construction allows the ball-nosed screw to contact the bone at any angle from perpendicular to sixty degrees or more of f of perpendicular with respect to the surface without walking or skiving. The radiused cutting surfaces contact the bone surface and cut away the bone to create a pilot bore for the threads on the shaft of the screw. Flutes are provided along a portion of the screw shaft length to route bone chips away from the ball-nosed end of the screw as it cuts. The shaft of the screw may include any thread arrangement necessary to anchor the screw to the bone.

Description

BALL-NOSED PEDICLE SCREW

FIELD OF INVENTION

The present invention generally relates to spinal implants , and more particularly, to a pedicle screw that is particularly suited for robotic installation due to a tip design that is capable of use on uneven undulating surfaces to provide a desired traj ectory .

BACKGROUND INFORMATION

A normal human spine is segmented with seven cervical , twelve thoracic, and five lumbar segments . The lumbar portion of the spine resides on the sacrum, which is attached to the pelvis . The pelvis is supported by the hips and leg bones . The bony vertebral bodies of the spine are separated by intervertebral discs , which reside sandwiched between the vertebral bodies and operate as j oints , allowing known degrees of flexion, extension, lateral bending and axial rotation .

The intervertebral disc primarily serves as a mechanical cushion between adj acent vertebral bodies , and permits controlled motions within vertebral segments of the axial skeleton . The disc is a multi-element system, having three basic components : the nucleus pulposus ( "nucleus" ) , the annulus fibrosus ( " annulus" ) , and two vertebral end plates . The end plates are made of thin cartilage overlying a thin layer of hard cortical bone that attaches to the spongy, richly vascular, cancellous bone of the vertebral body . The plates thereby operate to attach adj acent vertebrae to the disc . In other words , a transitional zone is created by the end plates between the malleable disc and the bony vertebrae . The annulus of the disc forms the disc perimeter, and is a tough, outer fibrous ring that binds adj acent vertebrae together . The fiber layers of the annulus include fi fteen to twenty overlapping plies , which are inserted into the superior and inferior vertebral bodies at roughly a 40-degree angle in both directions . This causes bi-directional torsional resistance , as about hal f of the angulated fibers will tighten when the vertebrae rotate in either direction .

It is common practice to remove a spinal disc in cases of spinal disc deterioration, disease or spinal inj ury . The discs sometimes become diseased or damaged such that the intervertebral separation is reduced . Such events cause the height of the disc nucleus to decrease , which in turn causes the annulus to buckle in areas where the laminated plies are loosely bonded . As the overlapping laminated plies of the annulus begin to buckle and separate , either circumferential or radial annular tears may occur . Such disruption to the natural intervertebral separation produces pain, which can be alleviated by removal of the disc and maintenance of the natural separation distance . In cases of chronic back pain resulting from a degenerated or herniated disc, removal of the disc becomes medically necessary .

One known technique to address many such spinal conditions is commonly referred to as spinal fixation . Surgical implants are used for fusing together and/or mechanically immobili zing adj acent vertebrae of the spine . Spinal fixation may also be used to improve the position of the adj acent vertebrae relative to one another so as to alter the overall alignment of the spine . Such techniques have been used ef fectively to treat the above-described conditions and, in most cases , to relieve pain suf fered by the patient .

One particular spinal fixation technique includes immobili zing the spine by using orthopedic rods , commonly referred to as spine rods , which run generally parallel to the spine . This is accomplished by exposing the spine posteriorly and fastening bone screws to the pedicles of the appropriate vertebrae . The pedicle screws are generally placed two per vertebra, one at each pedicle on either side of the spinous process , and serve as anchor points for the spine rods . Clamping elements adapted for receiving a spine rod therethrough are then used to j oin the spine rods to the screws . The clamping elements are commonly mounted to the head of the pedicle screws . The aligning influence of the rods forces the spine to conform to a more desirable shape . In certain instances , the spine rods may be bent to achieve the desired curvature of the spinal column .

Drawbacks to the procedure may include infection, blood loss , and nerve damage from accessing the disc space or improper insertion of the bone screws , also referred to as pedicle screws . It has been proposed to eliminate some of the complications associated with these procedures by the utili zation of robots to insert the screws in the top the bones . However, most screw constructions were designed with the thought that a person would be installing the screw . The bones include uneven undulating surfaces that may include small protuberances , arthritic growth or the like on the surface of the bone . These surfaces are extremely di f ficult to get the screw started at the right position and on the right traj ectory . The points of the screws are often deflected requiring the surgeon to react to the deflection and reposition the screw, or adj ust the traj ectory after the point of the screw has been started into the bone . Thus , the screws are often provided with sharp points , which allow the use of a hammer, or hollow shafts that are passed over guide wires to insure the proper positioning and traj ectory of the screw . Thus , surgical robots are also subj ect to skiving of the screw across the bone surface . The robot , however, is often unable to detect the subtle changes that may af fect the outcome of the surgery .

Therefore , there is a need in the art for a bone screw, also known as a pedicle screw that is specially designed for robot insertion . The screw should include a point that is suitable to start from numerous angles without skiving or walking across the surface . The point should also be constructed to cut away protuberances or the angled surfaces to provide the desired positioning and traj ectory programmed into the robot to start the screw into the bone without the need for a pilot bore .

SUMMARY OF THE INVENTION

Briefly, the invention involves a bone screw or pedicle screw for insertion by a surgical robot . The bone screw includes a ball-nose or spherical cutting point having cutting edges that intersect and follow the spherical shape . This construction allows the ball-nosed screw to contact the bone at any angle from perpendicular to sixty degrees or more of f of perpendicular with respect to the surface without walking or skiving . This construction may also provide two points contacting the surface on non- flat surfaces to maintain the positioning and desired angulation of the screw . The radiused cutting surfaces contact the bone surface and cut away the bone to create a pilot bore for the threads on the shaft of the screw . Flutes are provided along a portion of the screw shaft length to allow the threads to cut into the bone and route bone chips away from the ball-nosed end of the screw as it cuts . The shaft of the screw may include any thread arrangement necessary to anchor the screw to the bone .

Accordingly, it is an obj ective of the present invention to provide a bone screw that can be started into bone from various angles without a pilot bore .

It is a further obj ective of the present invention to provide a bone screw that can be started into a bone without a guide wire .

It is yet a further obj ective of the present invention to provide a ball-nosed bone screw that can be inserted with a surgical robot at a desired position and traj ectory .

It is a further obj ective of the present invention to provide a bone screw that can be started into a bone with a guide wire . Because of the uni formity of the bony removal , the screw should follow the guide wire more directly and not kink the guide wire .

It is another obj ective of the instant invention to provide a ball-nosed bone screw having a screw tip constructed and arranged to cut bone without skiving or walking .

It is still another obj ective of the present invention to provide a screw tip that engages the bone surface with a speci fic cutting surface profile across a wide variety of angles .

Still yet another obj ective of the present invention is to provide a bone screw having a cutting tip that includes a single constant radius with no sharp corners in the profile .

An even further obj ective of the present invention is to provide a bone screw having a cutting tip that includes a plurality of blended radii with no sharp corners in the profile .

Other obj ectives and advantages of this invention will become apparent from the following description taken in conj unction with the accompanying drawings wherein are set forth, by way of illustration and example , certain embodiments of this invention . The drawings constitute a part of this speci fication, include exemplary embodiments of the present invention, and illustrate various obj ects and features thereof .

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a partial front view illustrating the shape of the cutting tip of the present ball-nosed bone screw prior to threading;

Figure 2A is a side view showing one embodiment of the ball-nosed bone screw, illustrated as a pedicle screw;

Figure 2B is a partial front view taken along lines 2B-2B of Figure 2A, illustrating the cutting tip of the ball-nosed bone screw with cutting faces and threads ;

Figure 2C is an end view illustrating the machined ball-nosed cutting point ;

Figure 3 is a partial side view illustrating the cutting tip of the ball-nosed bone screw;

Figure 4 is a front view of the ball-nosed bone screw in the form of a pedicle screw inserted into a spinal bone ;

Figure 5 is a section view of the ball-nosed bone screw as taken along lines 5-5 of Figure 6 ; Figure 6 is a perspective view illustrating the ballnosed cutting surface along with the relief angles and flutes ;

Figure 7 is a section view taken along the longitudinal centerline of a cannulated embodiment of the ball-nosed pedicle screw .

Figure 8 is a side view illustrating the cannulated ball-nosed screw being placed over a guide wire ; and

Figure 9 is a section view taken along the longitudinal centerline of the the ball-nosed pedicle screw of Figure 8 .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the present invention is susceptible of embodiment in various forms , there is shown in the drawings and will hereinafter be described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exempli fication of the invention and is not intended to limit the invention to the speci fic embodiments illustrated .

Referring generally to Figs . 1- 9 , a ball-nosed bone screw 100 for attachment to bones is illustrated . The ball-nosed bone screw 100 includes a screw shaft 12 having a first end 14 and a second end 16 . At least one helical thread 18 protruding outwardly and extending along an outer surface 20 of the screw shaft 12 between the first end 14 and the second end 16 ; the first end 14 including a ballnosed cutter 22 having a ball-nosed cutter surface 26 constructed and arranged to provide a single contact point with a bone surface throughout a range of angulation 30 with respect to the bone surface . The range of angulation 30 is defined by a longitudinal axis 24 of the screw shaft 12 with respect to a tangent plane 28 constructed from the contact point. In different embodiments, this range of angulation may vary from at least fifteen degrees to about ninety degrees without departing from the scope of the invention. The second end 16 includes a driving surface 32 for providing rotational force to the ball-nosed bone screw 100. In a most preferred embodiment, the driving surface 32 is a TORX, registered TM, hex socket 34 or the like. It should also be noted that other driving surfaces, not shown, such as cross, polygon, Robertson, tri-point, clutch and the like, may be utilized without departing from the scope of the invention. The driving surface may be internal to a spherical ball portion 36, or may form portions of an external surface of the spherical ball portion 36 or screw shaft 12. In general, the spherical ball portion 36 is utilized for the construction of poly- axial bone screws used for orthopedic spine surgery. The ball 36 may be modified to construct mono-axial, uniplaner, fixed bone screws or the like without departing from the scope of the invention. In general, the ball 36 cooperates with a tulip portion 37 (Fig. 9) to provide polyaxial attachment between a rod member (not shown) and the ball-nosed pedicle screw 100. The tulip 37 is provided with threads 60 and a saddle or seat 62 for the rod member. In this manner, when the threads 60 are used in conjunction with a fastener to secure the rod to the tulip 37, the rod pushes against the saddle 62 to lock the tulip 37 in a desired orientation with respect to the screw shaft 12.

Referring generally to the figures, and more specifically to Figs. 1-3 and 6, the ball-nosed cutter 22 portion of the bone screw is illustrated. Fig. 1 illustrates one embodiment of the ball-nosed cutter profile . The first end 14 of the ball-nosed bone screw 100 is shown in profile before being machined into a screw . Thus , the spherical radius 50 at the spherical distal end 48 is machined to include at least one , and more preferably, two or more flutes 42 . The flutes 42 may be straight as shown, helical , or angled as desired . The flutes 42 may also be cut into the screw shaft 12 to create a rake angle 41 which may be a positive radial rake angle as shown in Fig . 3 , a neutral rake angle , or a negative rake angle on the face of the ball-nosed cutter and/or threads without departing from the scope of the invention . The rake angle is chosen based upon the hardness of the material being cut and the desired load on the cutting surface . Positive rakes typically result in lower loads on the flute face when cutting bone . Negative rakes typically result in higher loads ; however, they force a portion of the bone that would be removed with a positive rake back into the bone at the cutting edge , thereby forming part of the thread instead of simply cutting and removing the material creating the thread . This compressive forming action may make stronger threads in a weak or osteoporotic bone . Blending radii 52 and 54 may be utili zed to transition from the spherical distal end 48 to the screw shaft 12 . In this manner, the transition to the helical thread 18 can be controlled to reduce the amount of rotational force that is required to start the ball-nosed bone screw 100 . Back relief 46 and relief surfaces 40 are used to form spherical land 44 . Spherical land 44 and the flute face 38 are the surfaces that contact and cut away the bone upon rotational contact of the ball-nosed bone screw 100 to the bone . In at least some embodiments , the spherical land 44 may have a relieved back angle that follows and includes the spherical shape of the spherical land 44 . It should be appreciated that the ball-nosed cutter contacts the bone surface with a single point of contact regardless of the angle of the screw shaft to the bone surface . This is particularly advantageous when the present ball-nose screw 100 is utili zed in conj unction with a surgical robot . The surgical robot can establish traj ectory and provide rotation and controlled advancement along the traj ectory to the ball-nosed bone screw 100 . Thus , the ball-nosed screw 100 can machine away the bone as it is advanced, creating a spherical cavity for the screw threads to catch in the bone to pull the screw to the desired depth . The surface of a bone , such as a pedicle , can vary widely with undulations , angles , knobs of bone , arthritic build up and the like . The present ball-nosed bone screw 100 is suitable for dealing with all of these maladies and more to start the screw without walking or deflection of the screw from the desired traj ectory . The construction of the screw therefore provides the same contact to the bone regardless of the angle or deformation of the bone . However, it should be noted that in some instances , when the bone includes suf ficient deformation or shape , the ball-nose may contact at more than one point . In these cases , the bone is cut and removed to create a pilot bore for the threads to start into the bone . Multiple lead threads or threads with decreasing pitch angle may be utili zed without departing from the scope of the invention . The screw shaft 12 is preferably constructed from metal , and most preferably titanium . However, other metals suitable for use in an animal anatomy may be utili zed without departing from the scope of the invention . Various coatings may also be utili zed to reduce friction or reduce the animal ' s reaction to the metal ; such coatings may include but should not be limited to , titanium nitride , titanium carbo-nitride , vanadium carbide and the like .

Referring generally to the figures , and most particularly to Figs . 7- 9 , an embodiment of the ball-nosed bone screw 100 including a cannula 64 or aperture through and along the centerline of the screw shaft 12 is illustrated . This embodiment is particularly suited for use with a guide wire 70 , which may be inserted into the bone 80 prior to insertion of the ball-nosed bone screw 100 . In the preferred embodiment , the cannula 64 is constructed to include a substantially uni form diameter along its length . Substantially in this embodiment means within normal machining tolerances for drilled holes . In this embodiment , the spherical ball-nose is constructed the same as the embodiments without the cannula .

It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the speci fic form or arrangement of parts herein described and shown . It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown and described in the speci fication .

One skilled in the art will readily appreciate that the present invention is well adapted to carry out the obj ects and obtain the ends and advantages mentioned, as well as those inherent therein . Any compounds , methods , procedures and techniques described herein are presently representative of the preferred embodiments , are intended to be exemplary, and are not intended as limitations on the scope . Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the appended claims . Although the invention has been described in connection with speci fic preferred embodiments , it should be understood that the invention as claimed should not be unduly limited to such speci fic embodiments . Indeed, various modi fications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims .

Claims

CLAIMS What is claimed is:

1. A ball-nosed bone screw (100) comprising: a screw shaft (12) having a first end (14) and a second end (16) , at least one helical thread (18) protruding outwardly and extending along an outer surface (20) of the screw shaft (12) between the first end (14) and the second end (16) , the first end (14) including a ballnosed cutter (22) having a ball-nosed cutter surface (26) constructed and arranged to provide a single contact point with a bone surface throughout a range of angulation (30) with respect to the bone surface, the range of angulation (30) defined by a longitudinal axis (24) of the screw shaft (12) with respect to a tangent plane (28) constructed from the contact point.

2. The ball-nosed bone screw of Claim 1 wherein the point of contact is not along the longitudinal axis (24) of the screw shaft (12) .

3. The ball-nosed bone screw of Claim 1 wherein the range of angulation (30) is at least fifteen degrees.

4. The ball-nosed bone screw of Claim 1 wherein the range of angulation (30) is at least thirty degrees.

5. The ball-nosed bone screw of Claim 1 wherein the range of angulation (30) is at least forty-five degrees.

6. The ball-nosed bone screw of Claim 1 wherein the range of angulation (30) is at least sixty degrees.