SPINAL IMPLANT WITH VARIABLE LINK MECHANISM

Technical Field

[001] The inventive concepts relate generally to spinal implants. More particularly,

the invention concerns apparatus and associated methods for articulating variable

cross-link or transverse connectors or devices for use in spinal implants.

Background [002] Modern spine surgery often involves the use of spinal implants to correct or

treat various spine disorders or to support the spine. Spinal implants may help, for

example, to stabilize the spine, correct deformities of the spine, facilitate fusion, or

treat spinal fractures. Typical spinal implants may include rigid (i.e., in a fusion

procedure) support for the affected regions of the spine. They either limit movement

in the affected regions in virtually all directions (for example, in a fused region).

[003] Fusion or rigid implants typically use longitudinal rods to support parts of

the spine. The rods usually do not provide much protection against torsional forces

or movement. To address that concern, cross-link devices have been used. The

conventional cross-link devices, however, suffer from disadvantages, such as limited

range of motion (to allow the surgeon to adjust the implant to the patient's needs

and anatomy), a relatively large number of fasteners to adjust, etc. A need exists for

a variable cross-link or transverse connector that addresses those deficiencies.

Summary

[004] The inventive concepts relate to apparatus and methods for spinal implants

with variable cross-link devices or poly-axial connectors. In one exemplary

embodiment, an implant includes a locking mechanism. The locking mechanism

includes a rod engaging member. The rod engaging member is configured to

facilitate a compression fit to two implant rods. The implant rods may constitute

two longitudinal rods, or a longitudinal rod and a transverse rod, as desired.

[005] In another exemplary embodiment, a system for supporting a spine includes

two longitudinal rods, and a transverse rod. The system further includes at least one

variable cross-link device, having a body. The variable cross-link device is

configured to simultaneously couple the transverse rod to a respective one of the

longitudinal rods when a plug is engaged with the body of that variable cross-link

device.

[006] Yet another exemplary embodiment concerns a method of coupling a pair of

longitudinal rods in a spinal implant by using a transverse rod and a pair of poly-

axial connectors. The method includes tightening a fastener in one of the poly-axial

connectors in order to couple that connector to one of the longitudinal rods and to

the transverse rod. The method further includes tightening a fastener in the other

poly-axial connector in order to couple that connector to the other longitudinal rod

and to the transverse rod.

Brief Description of the Drawings

[007] The appended drawings illustrate only exemplary embodiments of the

invention and therefore should not be considered or construed as limiting its scope.

Persons of ordinary skill in the art who have the benefit of the description of the

invention appreciate that the disclosed inventive concepts lend themselves to other

equally effective embodiments. Unless noted otherwise, in the drawings, the same

numeral designators used in more than one drawing denote the same, similar, or

equivalent functionality, components, or blocks.

[008] FIG. 1 shows a spinal implant system that includes a variable cross-link

device or transverse connector according to an illustrative embodiment of the

invention.

[009] FIG. 2 illustrates an exploded view of variable cross-link devices according to

an illustrative embodiment of the invention.

[0010] FIG. 3 depicts a perspective view of variable cross-link devices according to

an exemplary embodiment of the invention.

[0011] FIG. 4 shows a side view of a variable cross-link device according to an

exemplary embodiment of the invention.

[0012] FIG. 5 illustrates an end view of variable cross-link devices according to an

exemplary embodiment of the invention.

[0013] FIG. 6 depicts a transverse connection using variable cross-link devices

according to an exemplary embodiment of the invention.

[0014] FIG. 7 shows another transverse connection using variable cross-link devices

according to an exemplary embodiment of the invention.

[0015] FIG. 8 illustrates a cross-section of the variable cross-link device shown in

FIG. 4.

Detailed Description [0016] The disclosed novel concepts relate to spinal implants with variable cross-link

devices or transverse connectors. The cross-link devices provide poly-axial or

variable motion, thus providing several degrees of freedom and facilitating

conforming the implant to the patient's anatomy or desired formation or structure.

[0017] The cross-link devices allow supporting of the spine in fusion procedures.

More specifically, the cross-link devices help to limit or eliminate undesired motion

(e.g., torsional movement) in a fusion implant. In other applications, the variable

cross-link devices help the surgeon to extend a fused portion of the spine to

additional levels. In such cases, the surgeon may use extended longitudinal rods,

and use cross-link devices to provide additional support and to link the new

implants to the existing implants. The novel cross-link devices provide several

advantages over conventional devices, as persons of ordinary skill in the art who

have the benefit of the description of the invention appreciate.

[0018] FIG. 1 shows a spinal implant system that includes a variable cross-link

device or transverse connector according to an illustrative embodiment of the

invention. The implant system may include a pair of longitudinal rods or elongated

members 103. Longitudinal rods 103 are affixed to spine 10 of the patient, disposed

generally in a vertical direction along spine 10.

[0019] The surgeon may use a variety of techniques to affix longitudinal rods 103 to

spine 10, as desired, and as persons of ordinary skill in the art who have the benefit

of the description of the invention understand. For example, the surgeon may use

coupling elements 106, which may include fasteners such as screws, caps, set screws,

hooks, etc. In one embodiment, coupling elements 106 may include pedicle screws,

as persons of ordinary skill in the art who have the benefit of the description of the

invention understand.

[0020] The longitudinal rods 103 immobilize and support one or more levels of spine

10. More specifically, during a surgical procedure, the surgeon uses coupling

elements 106 to affix longitudinal rods 103 to the vertebrae of spine 10. Longitudinal

rods 103 support and/ or immobilize spine 10 and facilitate fusion in one or more

levels, as desired, depending on the nature of the defect or injury in spine 10.

Persons of ordinary skill in the art who have the benefit of the description of the

invention understand the details of the procedures, as well as the instruments and

devices used to affix longitudinal rods 103 to spine 10.

[0021] The spinal implant system also includes a plurality of cross-link devices 112

(or poly-axial connectors), and one or more transverse rods or elongated members

109. Each pair of cross-link devices 112 couples to longitudinal rods 103 and also to

a respective transverse rod 109.

[0022] By using variable cross-link devices 112, the surgeon may also couple

longitudinal rods 103 to each other at one or more locations, as desired. More

specifically, at one or more desired locations, the surgeon may use a pair of variable

cross-link devices 112 (or poly-axial connectors), together with transverse rod 109, to

further support and immobilize the spine.

[0023] Put another way, variable cross-links 112, when used with transverse rod 109,

provide additional rigidity to the spinal implant. The additional rigidity helps to

reduce, limit, or eliminate undesired motions or stresses. For example, the implant

tends to limit or eliminate torsional movements in the affected levels of spine 10,

provides torsional stability to spine 10, and therefore facilitates fusion in one or more

desired levels.

[0024] Compared to conventional approaches, variable cross-link devices according

to the invention offer several advantages. In a typical implant procedure, the

surgeon forms longitudinal rods 103 to conform them to the patient's anatomy, i.e.,

the physical properties and geometry of spine 10. With conventional approaches,

the surgeon also forms longitudinal rods 103 in order to conform them to the cross¬

link device.

[0025] As described below in detail, variable cross-link devices 112 according to the

invention provide the surgeon with more flexibility, and help achieve a better fit

among the various parts of the implant. Viewed another way, by providing variable

transverse cross-linking or coupling between longitudinal rods 103, cross-link

devices 112 more readily conform to the geometry and shape of longitudinal rods

103 and the anatomy of spine 10.

[0026] Accordingly, the surgeon need not contour the cross-link devices and/ or the

rods in order to fit an implant to a particular patient's anatomy. By conforming to

the patient's anatomy, spinal implant systems according to the invention provide

better support and immobilization of spine 10, thus accelerating the healing or

fusion process.

[0027] Furthermore, conventional approaches often involve positioning and

fastening a relatively large number of fasteners in order to situate the cross-link

devices as part of the implant. As described below in detail, the variable cross-link

devices according to the invention, however, use a novel approach of transmitting

force from a relatively small number of fasteners in order to couple to longitudinal

rods 103 and transverse rod 109.

[0028] FIG. 2 shows an exploded view of variable cross-link devices 112 according to

an illustrative embodiment of the invention. The following description discusses

variable cross-link device 112 on the right side of the figure; a similar description

applies to the cross-link device on the left side of the figure.

[0029] Variable cross-link device 112 includes body 115, piston or rod engaging

member 125, and screw or closure top or cap or plug 130. Note that, in one

embodiment, cross-link device 112 may also include transverse rod 109, as desired.

In other words, the cross-link device may comprise either a connector (body 115, rod

engaging member 125, and plug 130), or a combination of a connector with a

transverse rod 109 (e.g., as an integral unit). In another embodiment, one may

provide the variable cross-link as a combination of two variable cross-link devices

112 pre-assembled with a transverse rod 109, as desired.

[0030] Body 115 has an opening or through hole (not shown explicitly) that allows an

end of transverse rod 109 to pass through body 115. The end of transverse rod 109

may protrude from body 115, as shown more clearly in FIG. 2.

[0031] The hole may have a diameter larger than the diameter of transverse rod 109,

as desired. That arrangement allows positioning transverse rod 109 in a number of

positions with respect to body 115 of variable cross-link device 112. Thus, when

affixing the implant in spine 10, the surgeon may rotate body 115 with respect to

transverse rod 109 in order to fit the implant to the patient's anatomy, or fit variable

cross-link device 112 to the shape and structure of longitudinal rod(s) 103 and

transverse rod 109.

[0032] Referring back to FIG. 2, body 115 includes a curved or hook element or

member 120. Curved member 120 outlines an opening or recess 140. Opening 140

engages with longitudinal rod 103 (not shown explicitly), and helps couple body 115

to longitudinal rod 103. Body 115 may be made of a desired suitable material, such

as titanium.

[0033] Body 115 receives piston or rod engaging member 125. Rod engaging

member 125 couples to transverse rod 109, and couples body 115 to transverse rod

109. As described below in detail, rod engaging member 125 also couples curved

member 120 to longitudinal rod 103 (not shown explicitly).

[0034] In the embodiment shown, rod engaging member 125 has a "U"-shaped

portion or slot for engaging or coupling to one end of transverse rod 109. The

exemplary embodiment of rod engaging member 125 in FIG. 2 also has a beveled

portion or face, or conical face, that engages with, or couples to, longitudinal rod 103

(not shown explicitly). Rod engaging member 125 may be made of a variety of

suitable materials, for example, titanium.

[0035] Plug 130 screws or fastens in the top part of body 115. Plug 130 may have a

variety of shapes, for example, it may have a hexagonal head. Plug 130 may be

made of a desired suitable material, such as titanium.

[0036] When fastened in body 115, plug 130 couples to transverse rod 109, and exerts

force onto it. Transverse rod 109 transmits or transfers this force to rod engaging

member 125. In response, rod engaging member 125 provides a compression

coupling or fit to transverse rod 109. Advantageously, rod engaging member 125

also provides a compression coupling or fit to longitudinal rod 103 (not shown

explicitly).

[0037] Note that the implant may include mechanisms to prevent or reduce the

possibility of loosening or dislodging, either during surgery or thereafter, as desired.

For example, the end(s) of transverse rod 109 may be widened to prevent it from

uncoupling from device(s) 112, by expanding the end(s) of rod 109 by applying force

to it and deforming it (e.g., shaping or turning it to a ball or round shape). As

another example, a "stake" may be added to plug 130 to prevent it from loosening or

falling out.

[0038] FIG. 3 depicts a perspective view of a pair of variable cross-link devices

according to an exemplary embodiment of the invention. More particularly, the

illustration shows a pair of cross-link devices 112 coupled to a transverse rod 109.

[0039] Note that, as noted above, in the embodiment shown, body 115 of variable

cross-link device 112 includes an elongated, elliptical, or oblong hole. The topology

of the hole allows rotation of body 115 with respect to transverse rod 109, thus

providing the surgeon with an additional degree of freedom.

[0040] Furthermore, as noted above, body 115 includes curved member or hook 120,

shaped for coupling to longitudinal rod 103 (not shown explicitly). The inside

surface of curved member 120 may be shaped in order to couple to longitudinal rod

103, and provide a compression or friction fit to it.

[0041] The surgeon may position each of variable cross-link devices 112 in a desired

position along transverse rod 109. More specifically, the surgeon may slide each of

variable cross-link devices 112 along transverse rod 109 and fasten it in a position

that accommodates the anatomy of spine 10, the position and shape of longitudinal

rods 103, or both, as desired. In this manner, the inventive variable cross-link

devices provide the surgeon with a degree of freedom in positioning and securing

the implant within the patient's body.

[0042] FIG. 4 shows a side view of a variable cross-link device 112 according to an

exemplary embodiment of the invention. More specifically, the figure shows how

curved member 120 of body 115 of the variable cross-link device 112 couples to

longitudinal rod 103. Put another way, curved member 120 of body 115 "wraps" at

least part-way around longitudinal rod 103, and provides a compression or friction

fit to it (in response to the force exerted by fastening plug 130, as described below in

detail).

[0043] As shown in the figure, rod engaging member 125 has a channeled or "U"-

shaped slot that engages transverse rod 109. The pressure exerted from fastening

plug 130 compresses or presses transverse rod 109 against rod engaging member

125. The "U"-shaped slot of rod engaging member 125 may match the physical

characteristics of transverse rod 109, and thus facilitate a compression or friction fit

to it.

[0044] For example, the width of the opening in the "U"-shaped slot of rod engaging

member 125 may be close to, or the same as, the diameter of transverse rod 109. This

arrangement would result in a relatively tight compression or friction fit between

rod engaging member 125 and transverse rod 109. From a broader perspective, the

compression or friction fit provides a relatively tight coupling of plug 130, rod

engaging member 125, transverse rod 109, and body 115 to one another.

[0045] FIG. 5 illustrates an end view of a pair of variable cross-link devices 112

according to an exemplary embodiment of the invention, coupled to a transverse rod

109. Note that the shape of curved member or hook 120 allows "wrapping" around

a longitudinal rod 103 (not shown explicitly), as described above. Put another way,

curved member 120 receives or wraps around (at least partially) the lateral outside

surface of the longitudinal rod 103 to which it couples.

[0046] Furthermore, note that rod engaging member 125 in each variable cross-link

device 112 protrudes from body 115. The protruding portion of rod engaging

member 125 helps to provide a compression or friction fit to longitudinal rod 103.

[0047] The inventive variable cross-link devices 112 provide flexibility to the surgeon

in shaping an implant system that suits the needs or anatomy of a particular patient.

In an implant system using variable cross-link devices 112, longitudinal rods 103

may be parallel or non-parallel to each other, as desired. Furthermore, longitudinal

rods 103 may be skewed in orientation with respect to each other. Thus,

longitudinal rods 103 may be diverging or converging with respect to each other, as

desired.

[0048] FIG. 6 depicts a transverse connection of longitudinal rods 103, using variable

cross-link devices 112 according to an exemplary embodiment of the invention. In

this configuration, a pair of variable cross-link devices 112 couple to each other a

pair of vertically skewed longitudinal rods 103. In other words, longitudinal rods

103 do not occupy the same plane along spine 10.

[0049] Because of the flexibility that variable cross-link devices 112 provide, the

surgeon may rotate or skew longitudinal rods 103 with respect to each other, as

desired. Thus, the surgeon may rotate each variable cross-link device 112 with

respect to transverse rod 109, and thus accommodate a vertically skewed implant, as

desired.

[0050] FIG. 7 shows another transverse connection of longitudinal rods 103, using

variable cross-link devices 112 according to an exemplary embodiment of the

invention. In this arrangement, a pair of variable cross-link devices 112 couple to

each other a pair of horizontally skewed longitudinal rods 103.

[0051] Put another way, longitudinal rods 103 may occupy the same horizontal plane

(e.g., a plane along spine 10). They, however, may have a non-parallel configuration

and diverge from each other or converge towards each other. As an example, the

surgeon may wish to design converging longitudinal rods 103 in order to

accommodate a progressively narrower spine.

[0052] Variable cross-link devices 112 provide the surgeon with additional flexibility

by allowing the surgeon to skew longitudinal rods 103 with respect to each other, in

either a converging or diverging configuration, as desired. The choice of the

arrangement depends on factors such as the patient's anatomy, the size and

configuration of the components, etc., as persons of ordinary skill in the art who

have the benefit of the description of the invention understand.

[0053] Generally speaking, the variable cross-link devices (or poly-axial connectors)

according to the invention provide five degrees of freedom or variations of

movement. The variations of movement may occur in two axes (i.e., the x, and y

axes), and movement about three axes (i.e., movement or rotation about each of the

x, y, and z axes, 300, 310, 320) as shown in Figures 6 and 7.

[0054] The cross-link provides the capability for horizontal adjustment along the

length of transverse rod 109, vertical adjustment along longitudinal rods 103, and

anterior/ posterior adjustment on longitudinal rods 103. Thus, the variable cross-

link devices allow locking transverse rod 109 and longitudinal rods 103 without

limiting their freedoms of movement (or variations of movement).

[0055] Variable cross-link devices according to the invention provide the additional

advantage that, by fastening plug 130, the surgeon can couple a variable cross-link

device 112 to both longitudinal rod 103 and transverse rod 109. (Note that, to lock

the variable cross-link device at the other end of transverse rod 109, the surgeon may

use a similar procedure.) Locking variable cross-link device 112 to longitudinal

rod(s) 103 and transverse rod 109 prevents or limits further movement or

articulation of the implant.

[0056] Rather than fastening multiple fasteners, as is the case with conventional

cross-link devices, the surgeon fastens plug 130 for each variable cross-link device

112. This feature simplifies the operation, reduces the number of steps that the

surgeon takes, and may reduce the number of physical components.

[0057] FIG. 8 illustrates a cross-section of variable cross-link device 112 shown in

FIG. 4. More specifically, FIG. 8 shows a cross-section along the line marked A-A in

FIG. 4 of variable cross-link device 112. The cross-section shown in FIG. 8 illustrates

the details of how the surgeon may affix variable cross-link device 112 by fastening

plug 130.

[0058] To fasten variable cross-link device 112 to both longitudinal rod 103 and

transverse rod 109, the surgeon fastens plug 130. Fastening plug 130 exerts a force

(labeled "Fl" in FIG. 8) to transverse rod 109, and provides a compression fit

between body 115, plug 130, and rod engaging member 125 of variable cross-link

device 112 and transverse rod 109.

[0059] Fastening plug 130 also pushes transverse rod 109 against rod engaging

member 125. Thus, plug 130 causes rod engaging member 125 to extend downward

into body 115 of variable cross-link device 112.

[0060] The extension of rod engaging member 125 in body 115 causes the beveled

portion of rod engaging member 125 to contact longitudinal rod 103, and exert a

force (labeled "F2" in FIG. 8) against it. The application of this force helps to provide

a compression or friction fit between rod engaging member 125 and longitudinal rod

103.

[0061] The application of force against longitudinal rod 103 causes it to exert a force

(labeled "F3") against curved member 120 of body 115 of variable cross-link device

112. The exertion of force against curved member 120 further causes a compression

or friction fit between it and longitudinal rod 103.

[0062] Thus, by fastening plug 130, the surgeon can simultaneously cause a

compression or friction fit between variable cross-link device 112 and both

transverse rod 109 and longitudinal rod 103. Accordingly, unlike conventional

devices, the surgeon need not fasten separate or individual fasteners.

[0063] Note that, rather than coupling a longitudinal rod 103 to a transverse rod 109,

one may use the poly-axial connectors according to the invention to couple two

longitudinal rods 103, as desired. In such an embodiment, the slot in body. 115 for

accommodating transverse rod 109 may be parallel to longitudinal rod 103 (or a

desired angle with respect to rod 103), rather than being normal (or substantially or

nearly normal) to longitudinal rod 103. Such a configuration allows coupling two

rods 103, or two sections or pieces of rods 103, to be coupled together, including the

advantages of the connectors according to the invention, as described herein.

[0064] The implants according to the invention, including the variable cross-link

devices (or poly-axial connectors) may be used in minimally invasive surgery (MIS)

procedures or in non-MIS procedures, as desired, and as persons of ordinary skill in

the art who have the benefit of the description of the invention understand. MIS

procedures seek to reduce cutting, bleeding, and tissue damage or disturbance

associated with implanting a spinal implant in a patient's body. Exemplary

procedures may use a percutaneous technique for implanting longitudinal rods and

coupling elements. Examples of MIS procedures and related apparatus are provided

in U.S. Patent Application Serial No. 10/698,049, filed October 30, 2003, U.S. Patent

Application Serial No. 10/698,010, October 30, 2003, and U.S. Patent Application

Serial No. 10/697,793, filed October 30, 2003, incorporated herein by reference.

[0065] The variable cross-link devices (or poly-axial connectors) according to the

invention are suitable for use with MIS procedures because plug 130 (used to lock

the rods) is tightened or fastened to the longitudinal rods from above. In such an

MIS procedure, the surgeon may percutaneously position and place the implant

using the same technique and through the same wound exposure as with other

spinal implants, then tighten or fasten plug 130 by inserting. Because plug 130 is

accessible through the wound, one may couple the rods together by tightening plug

130, as described above in detail, without using additional incisions or wounds.

[0066] Implanting the variable cross-link devices (or poly-axial connectors) does not

entail additional exposures or cuts, as all insertion and locking of the poly-axial

connector may be performed through the two existing exposure sites used to

implant the longitudinal rods. Other details of the procedure will be apparent to

persons of ordinary skill in the art who have the benefit of the description of the

invention.

[0067] Various modifications and alternative embodiments of the invention in

addition to those described here will be apparent to persons of ordinary skill in the

art who have the benefit of the description of the invention. Accordingly, the

manner of carrying out the invention as shown and described are to be construed as

illustrative only.

[0068] Persons skilled in the art may make various changes in the shape, size,

number, and/ or arrangement of parts without departing from the scope of the

invention described in this document. For example, persons skilled in the art may

substitute equivalent elements for the elements illustrated and described here, or use

certain features of the invention independently of the use of other features, without

departing from the scope of the invention.