Snap-in washers and assemblies thereof

[0001] 1. Field of the Invention

[0002] This invention relates to connecting devices for spinal fixation, in particular, for joining a bone anchor with spinal stabilizers such as a spinal rod or spinal plate in a polyaxial fashion.

[0003] 2. Related Art

[0004] It is well know and practiced that when securing and maintaining bones in a preferred alignment, a plurality of bone anchors may be attached to one or more bones and subsequently secured together in a desired orientation with a bone stabilizer. Examples of bone stabilizers include “longitudinal members,” and in some cases, “connectors” as is known in the art. That is, the longitudinal member (e.g. a rod or a plate) connects the bone anchors together, and (if needed), the connectors are used to secure the bone anchor to the longitudinal member. Accordingly, there are at least two criteria that would be desirable to be satisfied when securing bones in a desired alignment using bone anchors and a bone stabilizer:

• [0005] (i) it is desirable to attach each bone anchor to a bone in a manner that will inhibit movement of the anchor relative to the bone. Thus, the orientation of the bone anchor to its attached bone may be dependent on, e.g., the bone configuration, density, and/or fractures therein;
• [0006] (ii) the bone stabilizer must be attached to each bone anchor, and in particular, to an included shaft, in a manner so that the longitudinal member (of the bone stabilizer) is oriented to effectively maintain the desired alignment of bones.

[0007] In order to satisfy the above criteria, it may be preferable that the shafts of the bone anchors are not parallel to each other and/or not perpendicular to the longitudinal member when they are attached to their respective bones. Moreover, for each bone alignment procedure performed using bone anchors and bone stabilizers, the orientations of the shafts relative to one another and the longitudinal member may be substantially unique.

[0008] Accordingly, a preferable position of the longitudinal member can be compromised by the various orientations of the bone anchoring shafts, these various orientations due to, e.g., the preferred positions of the anchors when they are secured to the bones. Thus, it is advantageous to have the ability to firmly secure such bone anchoring shafts to a bone position retainer, wherein the shafts may be at various orientations to the longitudinal member, i.e., in polyaxial or multi-angular orientations.

[0009] U.S. Pat. No. 5,984,924 discloses such a bone alignment system capable of multi-angular orientations with respect to the bone anchor and longitudinal member. Through use of a system of concave or convex arcuate washers, the multi-angular orientations are achieved.

[0010] U.S. Pat. No. 6,315,779 discloses a multi-axial bone fixation implant having an elongated member, one or more bone anchor assemblies, and stabilizer members which are fitted within the elongated member. The stabilizer members are rectilinear in shape and do not include arcuate surfaces. The only use of washers disclosed are ones having an undercut within its oblong aperture on the top of the implant. The implant is locked by a nut and the washer atop the elongated member, the enlarged portion of a bone anchor is forced against an inside wall of the stabilizer, which is in turn locks against the elongated member. Disadvantages of this system are the large number of separate parts and that the washers can be cumbersome to use in that they are not secured to the elongated member.

[0011] The present invention provides an advance in the art by minimizing a number of parts a surgeon has to handle during a surgical procedure while having the advantage of multiple orientations provided by use of the arcuate washers.

[0022] One embodiment of the invention is directed toward a connecting device for joining a spinal stabilizer with a bone anchor comprising:

[0023] a body comprising a bone anchor fastening portion and a spinal stabilizer fastening portion, wherein the bone anchor fastening portion comprises an aperture for receiving and retaining a washer.

[0024] Another embodiment of the invention is directed toward a connecting device for joining a spinal stabilizer with a bone anchor comprising:

[0025] a body comprising a clamp with two projecting arm portions, the clamp portion for fastening a spinal stabilizer in the form of a rod and the arm portions having apertures for fastening the bone anchor.

[0026] Another embodiment of the invention relates to a connecting device for joining two bone anchors comprising a plate having an aperture for receiving and retaining a washer.

[0027] Yet another embodiment of the invention comprises a washer comprising a concave or convex arcuate portion and a fastening portion, wherein the fastening portion comprises flexible projections for receipt and retention in a channel.

[0028] Another embodiment of this invention relates to a systems for spinal stabilization comprising a spinal rod; a bone anchor comprising a bone engaging first portion, a machine threaded second portion for engaging a locking nut, and a third portion, intermediate to the first and second portions, comprising arcuate surfaces for polyaxial engagement with a connector; and a locking nut; wherein, the bone anchor and rod are joined by the connecting devices as hereinafter described and claimed. Additionally, systems of this invention may comprise at least two bone anchors as described above joined by a plate having an aperture for receiving and retaining a washer.

[0029] Generally, this invention deals with devices for spinal fixation especially to those used particularly for joining a bone anchor with spinal stabilizers such as a spinal rod or spinal plate in a polyaxial fashion. The invention is also directed to polyaxial connectors which incorporate arcuate washers. The polyaxial features of this invention are achieved preferably with snap-in washers which minimize the numbers of parts that a surgeon may have to handle during surgery.

[0030] FIG. 1 depicts spinal stabilizer-bone anchor connector 1. Connector 1 comprises spinal stabilizer portion 20 and bone anchor portion 10. Spinal stabilizer portion 20 comprises a stabilizer receiving throughbore 22 and a set screw bore 24. Thus in attaching to a stabilizer, a stabilizer (rod) will pass through bore 22 and be secured into place by the locking of a set screw through bore 22 by securely contacting the stabilizer. Portion 10 of the device includes aperture 12 for receiving a head of a bone anchor and channels 14 for receipt of washers. The bone anchors contemplated for use of this invention are those well known in the art which generally comprise a bone engaging threaded first portion, a machine threaded second portion for engaging a locking nut, and a third portion, intermediate to the first and second portions, comprising arcuate surfaces for polyaxial engagement with the connector, for example, as depicted in FIG. 4 of U.S. Pat. No. 5,984,924 or in FIG. 7 of U.S. Pat. No. 6,315,779, the disclosures of which are incorporated by reference in their entirety.

[0031] FIG. 2 depicts the connector 1 incorporating washer 30.

[0032] FIG. 3 depicts washer 30 comprising aperture 32 for receiving the head of a bone anchor. Projections 34 are sized to engage channels 14. Optionally spacers 36 (shown in phantom) may be employed to provide spacing between the body of the washer and portion 10 of connector 1.

[0033] FIG. 4 is a cross-sectional depiction of connector 1. Portion 10 comprises channels 14 which receive projection 32 of washers 30. Preferably projections 32 of washers 30 are biased to securely fit in channels 14.

[0034] FIG. 5 depicts the band clamp 40 embodiment of this invention. Clamp 40 comprises two projecting arm portions 42 with aperture 44 for engaging a spinal stabilizer in the form of a rod and arm portions 42 having apertures 46 for fastening to a bone anchor. Each arm portion 42 comprises channels 48 for receiving projections of washers (not shown).

[0035] FIG. 6 depicts washer 50 suitable for use with band clamp 40. Washer 50 comprises throughbore 52, concave surface 54 and projects 56 which engage channels 48 (not shown) of band clamp 40.

[0036] FIG. 7 depicts the assembled clamp 40 with washers 50 engaged in channels 48.

[0037] FIG. 8 depicts the bone plate 70 embodiment of this invention. Plate 70 comprises aperture 72 for receiving and retaining washers 50 in channels 74. In this figure, both top and bottom washers are depicted. Engagement of washers 50 into channels 74 are as described for the band clamp embodiment of this invention. Furthermore, bone plate 70 would actually have at least two additional washers (one top and one bottom) for a total of 4 resilient washers so that connection between at least 2 bone anchors may be made.

[0038] FIG. 9 depicts a cross-sectional end view of bone plate 70 shown in FIG. 8. Referring to FIG. 9, channels 74 for receiving washers 50 are more clearly seen.

[0039] Although washers 30 and 50 of this invention have been depicted with concave surfaces, it is apparent to one skilled in the art that washers having other arcuate surfaces, such as convex surfaces, may also be used depending on the nature of engagement with the corresponding bone anchor and locking nut such as through well know bone anchors as depicted, for example, in U.S. Pat. No. 5,984,924 or in U.S. Pat. No. 6,315,779.

[0040] Also the invention relates to systems for spinal stabilization comprising a spinal rod; a bone anchor comprising a bone engaging first portion, a machine threaded second portion for engaging a locking nut, and a third portion, intermediate to the first and second portions, comprising arcuate surfaces for polyaxial engagement with a connector; and a locking nut used in combination with the connecting devices of this invention as described above. Additional systems of this invention include a system for spinal stabilization comprising at least two bone anchors comprising a bone engaging first portion, a machine threaded second portion for engaging a locking nut, and a third portion, intermediate to the first and second portions, comprising arcuate surfaces for polyaxial engagement with a connector; and a locking nut, wherein, the bone anchors are joined by the connecting device comprising a plate having an aperture for receiving and retaining a washer.

[0041] It should be understood that the foregoing disclosure and description of the present invention are illustrative and explanatory thereof and various changes in the size, shape and materials as well as in the description of the preferred embodiment may be made without departing from the spirit of the invention.