Bone alignment and fixation device and installation method, using guide tab

[0002] This invention relates generally to the alignment and fixation of bone segments as required for appropriate bone healing, for example after fracture or surgical intervention, and specifically to a device, and the tools needed to install the said device, for the alignment and fixation of cranial bone fragments.

[0003] In cases of bone fragmentation where bone fixation is desired, the appropriate alignment of the bone is also a desired result. This is especially true in the cranium, where bone fragmentation can occur as a result of trauma, congenital deformity, or of surgical intervention. In the field of neurosurgery, cranial bone fragments are frequently cut and removed to create defects to allow for access into the cranial cavity and the brain.

[0004] The bony cranium is generally regarded to have two surfaces: the outer surface which is characterized by the outer cortex of the bone and is adjacent to the scalp and soft tissue; and the inner surface which is characterized by the inner cortex of the bone and which is adjacent to the cranial cavity and the brain. Between the inner cortex and the outer cortex, which are dense layers of bone, lies the diploe which generally consists of soft bone and bone marrow. When a bone fragment is created, a cut between the bone fragment (the primary bone zone) and the remainder of the cranium (the secondary bone zone) is present.

[0005] Several methods of alignment and fixation of primary and secondary bone zones are known. Traditional techniques involve the use of several pieces of filament, such as wire, that are tied after being threaded through holes drilled obliquely through the outer cortex to the cut surface of both bone zones. Precise alignment of the two zones can be difficult and the technique can be cumbersome.

[0006] Commonly, the zones of bone can be aligned and fixated with a system of plates and screws (U.S. Pat. Nos.: 5,372,598; 5,413,577; and 5,578,036). A plate made of metal or other substance can be fixated to the outer cortex of the primary bone zone with screws whose penetration of the bone can be limited to the outer cortex. With three or more plates attached to the primary bone in such a way that the plates protrude beyond the edges of the primary bone zone, the primary bone zone can be introduced into a defect and aligned to the outer cortex of the secondary bone zone without danger of the primary bone zone falling too deeply into the defect in the secondary bone zone and exerting pressure on the underlying tissue such as the brain. Fixation can then be achieved by employing additional screws fixating the plates to the outer cortex of the secondary bone zone. Plates and screws systems allow for the alignment and fixation of the zones, while preventing the primary bone zone from falling below the level of the secondary bone zone without actually introducing a component of the device below the secondary bone zone. A plate with a spring clip extension has been described (U.S. Pat. No. 5,916,217). Plate and screw systems can be expensive and time consuming to use.

[0007] Devices that align the two bone zones by way of compressing them between the two disks positioned along the inner and outer cortex have been described. (Foreign Patents: DE 19603887C2, DE 19634699C1, DE 29812988U1, EP 0787466A1.) A pin connects the two disks aligning and securing two bone zones. These devices introduce foreign material that is left below the inner cortex, and they do not protect the underlying tissue from compression during the installation procedure.

[0008] Devices that fixate bone zones using friction forces created by a cam without a component that extends below the inner cortex are known and described (Patent DE 19634697C1). These devices also do not protect the brain from compression during the installation procedure.

[0009] Intramedulary pins are well known in the orthopedic fields for alignment of long bones. Such pins have also been described for cranial fixation (U.S. Pat. No. 5,501,685); however, the bone zones can not be aligned in three dimensions with this technique.

[0010] There is a need for an alignment and fixation device that is simple and rapid to use, versatile, and ultimately cost effective. There is also need for guidance of clip attachment to bone zones.

[0011] One object of the invention is to provide a device and instruments for its use and installation that aligns one cortex of a primary zone with one cortex of a secondary bone zone without extending to the opposing cortex, and which accurately fixates the bone zones to each other. When used in the field of neurosurgery, the device is applied to the primary bone zone and it aligns the outer cortex of the primary bone zone with the outer cortex of the secondary bone zone; it prevents the primary bone zone from entering the cranial cavity; and it provides fixation of the two bone zones. The alignment feature can be used independently from the fixation feature. An example of the use of the alignment feature is in the replacement of a cranial bone fragment which will be held in place by the tissue forces of the scalp, which allows for the bone fragment to be elevated away from the cranial cavity in cases where brain swelling occurs. Fixation can also be applied to attach the alignment device to the bone, using elements alone or in combination such as filaments, screws, rivets, pins, clips, cams, friction or adhesives. The alignment aspect of the invention can also be applied to situations where it is desired to offset the alignment of the bone fragment to the adjacent bone such as where the object is to create a more prominent chin by cutting the bone of the chin and advancing the bone fragment.

[0012] The fixation feature of the invention is likewise independent from the alignment feature. The fixation feature of the device relies on the principle that the device is fixated to the primary bone zone and the fixation feature grips the secondary bone zone by means of spring loaded tab or hook elements engaging the soft areas of the medullary space, irregularities along the cut surface, or a slot cut into the cut surface of the secondary bone zone.

[0013] The invention provides an improved clip meeting the above need or needs.

[0014] As will be seen, the preferred clip is configured to interconnect primary and secondary bone zones having edges spaced apart by a gap, the clip comprising

[0015] a) a tab such as a small plate to extend over and generally parallel to a surface of the secondary bone zone, and above a first level defined by that surface, and

[0016] b) a first projection carried by the tab and configured to penetrate the primary bone zone at the edge thereof, and below said surface level,

[0017] c) and an auxiliary tab associated with the first tab to be positioned to extend over a top surface of the primary bone zone to guide movement of the clip as the first projection penetrates the primary bone zone.

[0018] As will be seen, a second projection may be provided and carried by the tab and configured to engage the secondary bone zone at the edge thereof, and below said surface level, as well as below the level of the auxiliary tab.

[0019] It is another object to provide an extension of the tab projecting below said first level. That extension may carry the first projection, and may carry the second projection, if it is provided. In this regard, the second projection is typically located beneath the tab; and the first projection extends generally parallel to the tab and forwardly from a part of the tab extension below said surface level, and it preferably has a sharp terminal to enable penetration of diploe.

[0020] A further object is to provide the second projection to have a sharp terminal, and to extend at an angle toward the tab, in order to resist removal relative to the secondary bone zone.

[0021] Yet another object is to provide another second projection carried by the tab in sidewardly spaced relation to the first mentioned second projection, and configured to engage the secondary bone zone at the edge thereof, and below said surface level, as well as below the auxiliary tab.

[0022] An additional object is to provide a tab extension as referred to, but having S-shape or configuration, whereby enhanced spring support of one or both projections is realized; and also the S-shape of the extension facilitates its formation or manufacture.

[0023] An additional object is to provide a plate or flap defining the primary bone zone, and to provide multiple of the clips having their first projections penetrating the primary bone zone at different edges thereof, below a surface defined by the plate or flap.

[0024] The method of using the clip as referred to includes the steps

[0025] i) advancing the first projection to penetrate the primary bone zone,

[0026] ii) and locating the tab to extend over the surface of the secondary bone zone, and causing the auxiliary tab to guidingly engage and slide on the top surface of the primary bone zone during said penetration, and attaching the first tab to said surface.

[0027] As will be seen, the step i) preferably includes pushing the clip toward the primary bone zone to effect push-in penetration of the first projection into the primary bone zone. The method may further include providing a second projection carried by the tab and configured to engage the secondary bone zone at the edge thereof, and below its top surface level, the method including displacing the clip and said second projection to engage the secondary bone zone at the edge thereof, below said surface level. An additional step includes displacing the clip in a direction to effect scraping of the edge of the secondary bone zone by the second projection, the second projection oriented to resist reverse displacement of the clip in an upward or opposite direction relative to the secondary bone zone. In this regard, the method may include effecting penetration of the edge of the secondary bone zone by the second projection in an angular direction toward the tab. The bowed or S-shape of the extension provides enhanced spring effect to aid in effecting such penetration.

[0028] These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings, in which:

[0029] FIG. 1 is a plan view of a clip blank in one plane, prior to deformation;

[0030] FIG. 2 is like FIG. 1, but showing folding of an auxiliary tab;

[0031] FIG. 3 is a perspective view of a clip, of the invention;

[0032] FIG. 4 is a top plan view of the FIG. 3 clip;

[0033] FIG. 5 is a front elevation view of the FIG. 4 clip, and taken on lines 5—5 of FIG. 4;

[0034] FIG. 6 is a right side elevation taken on lines 6—6 of FIG. 4;

[0035] FIG. 7 is a view like FIG. 6, but showing use of the clip;

[0036] FIG. 8 is a perspective view showing a bone flap fixated on a skull, employing fixation clips; and

[0037] FIG. 9 shows a flat strip applicable to the clip of FIG. 6.

[0038] Referring to FIGS. 3-7, the illustrated and preferred clip 310 is configured to interconnect primary and secondary bone zones 311 and 312 having opposed and spaced apart edges 311cand 312c. A cut or gap 313 is formed between the opposed edges of the primary and secondary bone zones. Diploe is shown at 315 between the top and bottom surfaces 311aand 311bof zone 311; and at 316 between the top and bottom surfaces 312aand 312bof zone 312. As also seen in FIG. 8, primary bone zones 11 may be defined by bone flap 17; and secondary bone zones 12 may be defined by skull 18 and its zone extents at 12 opposing zones 11. In the adult, cranial bone or skull averages 7 mm in thickness, but varies between 3 and 12 mm.

[0039] The clip 310, is also shown in blank formed condition in FIG. 1, and in.folded condition in FIGS. 2-7. The clip, which is preferably.metallic, includes the following:

[0040] a) a tab 320 to extend over and generally parallel to a surface 312aof the secondary bone zone 312, above surface level;

[0041] b) a first projection or tang 321 directly or indirectly carried by the tab and configured to penetrate the exposed diploe of the primary bone zone 311 at the edge 311cof that zone (and typically into diploe 315); and wherein the tang 321 may have barbed edges at 321dand 321e;

[0042] c) and an auxiliary tab, such as tab 360, associated with the first tab to be positioned to extend over a top surface of the primary bone zone to guide movement of the clip as the first projection penetrates the primary bone zone.

[0043] The clip may include, and preferably does include at least one second projection 322 carried by the tab and configured to engage (for example gouge into) the exposed diploe of the secondary bone zone 312 at its edge 312c, below the level of surface 312a, and below the level of the auxiliary tab 360.

[0044] In the example, two such second projections are provided, as is clear from FIGS. 3-5, and they are located at opposite sides of a lengthwise plane 323 bisecting the clip, including projection 321. Such projections are equally spaced from plane 323, as indicated by dimensions D₁, seen in FIG. 4. The projections 321 and 322 have legs 321aand 322a, and their terminals are sharpened at 321band 322b, to facilitate penetration of the diploe zones, as seen in FIG. 7. Leg 321aand projection 321 extend forwardly in direction 324 from a tab downward extension 320a; and projections 322 extend back upwardly at an angle between 25° and 45° toward the underside of the tab 320. Note that each projection 322 extends from tab ring-shaped extension 320aand is U-shaped. A bend is formed at 322d.

[0045] Four edges 11cof the flap 17 are seen in FIG. 8, and corresponding four edges 12cof the skull face the flap edges and receive penetration of the stabilizing clip projections 322, as described.

[0046] It will be noted that the generally upright extension 320ais bowed to produce an enhanced spring effect for urging one or more of the projections, and also to facilitate ease of manufacture. See extension sections 380 and 381, the former bowed frontwardly in the direction of projection 321; and the latter section 381 bowed in the general direction of the projections 322 extents. Section 380 is curved at 380ato merge with the tab. Projection 321 is carried by section 380, and projections 322 are carried by section or sections 381, whereby movements of the projections 322 are isolated from movements of the projection 321, enhancing completeness and permanence of fastening to bone. See for example FIG. 5, showing such isolation.

[0047] The method of use of the clip or clips includes the following steps:

[0048] i) causing the first projection or projections 321 to penetrate the primary bone zone or zones;

[0049] ii) causing the second projection or projections 322 to grip the secondary bone zone at the edge thereof;

[0050] iii) employing an auxiliary tab to guide the clip during such penetration

[0051] Step i) includes pushing the clip 310 relatively toward the edge 311cof the primary bone zone 311, as in direction 324 seen in FIG. 7, while employing the folded auxiliary tab 360 to engage surfaces 311aand slide forwardly, to effect guiding of push-in penetration of the first projection 321 into the bone zone 11, as for example into diploe 15. See FIG. 7. The auxiliary tab 360 is preliminarily folded forwardly about axis 361, to the position seen in FIGS. 2-3. Push-in is typically completed when bent-down and bowed tab extension 380 closely approaches and/or engages edge 311cof the primary bone zone 311 defined by the plate or flap 17 (or bone zone 311). As described above, four pushed-in clips are seen in FIG. 8, the clips located in opposed pair positions, at four sides of the flap 17. Each tab 320 has a through hole 340 drilled or formed therein to receive a fastener such as a retention screw, indicated at 41 in FIG. 7, to penetrate and attach to the skull proximate the secondary bone regions.

[0052] The step ii) preferably also includes displacing the clip in a direction (typically relatively downwardly toward the skull to bring 322, and 320ainto gap 313 as seen in FIG. 7) to effect scraping of the edge 312cof the secondary bone zone 312 by the tip or tips of the angled second projection or projections. Projection or projections 322 is or are oriented, i.e. angled, to resist displacement of the clip in an upward or opposite direction, relative to bone zone 12. For example, attempted upward and outward displacement would increase the “gouge-in” movement of the second projection, into the diploe 16.

[0053] As described above, the installed spacing d₂of the bone zone edges 11cand 12cis slightly less than the spacing d₃as measured from the sharp terminal of the projection 322 to the surface 332 of the tab extension facing the edge 311c. The width d₂of gap 13 between 311cand 312cis slightly less than the dimension d₃, i.e.

[0054] d₂<d₃,

[0055] to provide a desirably tight installation of plate 17 into the corresponding skull opening.

[0056] Projections 322 can resiliently deflect, as by spring bending of sections 381, to accommodate the multiple clips to the gaps 13 between 11 and 12, as during plate or tab downward installation. In FIG. 5, the lateral spacing of bowed sections 381 enhances clip installed stability.

[0057] As shown in the drawings tab 360 is U-shaped, and has two parallel legs 361 joined at their ends 361ato laterally spaced extents 320aof tab 320. Tab 360 has an edge 363 that flatly and slidably engages surface 311aduring penetration of projection into diploe 315, to guide and stabilize such penetration.

[0058] The clips as referred to above are metallic, and preferably consist essentially of one of the following:

[0059] i) titanium

[0060] ii) titanium alloy

[0061] iii) an alloy consisting essentially of titanium, aluminum and vanadium

[0062] iv) an alloy consisting essentially of:

[0063] about 90% by weight of titanium

[0064] about 6% by weight of aluminum

[0065] about 4% by weight of vanadium.

[0066] Further characteristics of the illustrated auxiliary tab 360 include:

[0067] i) it has substantially U-shape and extends about a major portion of the first tab, before it is folded,

[0068] ii) it has a foldable portion proximate an extension of the tab associated with the projection,

[0069] iii) it is connected to the first tab, and comprises a thin plate.

[0070] As also seen in FIG. 8 primary bone zones 311 may be defined by bone flap 17; and secondary bone zones 312 may be defined by skull 18 and its zone extents at 312 opposing zones 311. In the adult, cranial bone or skull averages 7 mm in thickness, but varies between 3 and 12 mm.

[0071] FIG. 9 shows a flat strip 390 applicable over the tab 320 seen in FIG. 6, to hold it and the clip structure 380 in down position. The rod 390aof strip 390 fits between legs 361 of the auxiliary tab.