The present invention relates to bone anchoring devices and their methods of use. More specifically, the invention relates to an anchor for securing a cable within a hole or opening in a bone, and, a method of attaching the cable to the anchor.
A wide variety of techniques are available to surgeons for securing sutures or cables within a hole or opening in a bone. Conventionally, such an opening may be a bone tunnel with open ends or a bore hole with one open end and an opposed closed end. Screws, rivets, vertebral straps, suture anchors, and other types of interference fitting anchors are commonly used. In all cases a solid and secure attachment between the suture, or cable, and the anchoring member for anchor devices is key.
The prior art is replete with implantable bone fasteners that include screw members having a threaded body. Typically, the cable, or suture, may be directly attached to the screw member in a variety of conventional manners including threading the suture through an internal channel in the body of the screw or threading the suture through an attached eyelet. One type of known bone fastener includes an expandable member having an axial channel and an elongated insertion element insertable therein. When the insertion element is driven into the axial channel in the expandable member, an interference or interlocking fit secures the insertion element to the expander, thereby securing the suture within the bone bore hole. Load forces exerted on the suture act directly on the insertion element so that the security of the suture within the bone bore hole depends on the security of the engagement between the insertion element and the expandable member.
In one known device, an expandable sheath in which the cable load (bearing force) acts directly on an expandable sheath that is expanded by an expander member for an interference fit within a bore hole in a bone. In such a device the cable load (bearing force) acts directly on the expandable sheath so that the fastening strength of the anchor is independent of the axial security of engagement between the expander member and the expandable sheath. Such a bone anchoring device avoids the failure mode of expander separation from the expandable sheath under suture loading.
In general, methods to attach or secure cables to anchoring members are insert molding, or passing the cables through eyelets or small holes in the anchoring members. The disadvantage of the former methods is low pullout strength of the cable from the anchoring member because insert-molding processes cannot form a secure attachment between the cable and anchoring device. In the latter method, the hole or eyelet is related to the removal of material from the anchoring member that may result in mechanical strength lost, or it may be difficult or not possible to place a hole or eyelet at the anchoring member due to a low profile configuration or limited space. Thus, there is a need for a device where the cable can be securely attached without compromising the structural integrity of the anchoring member.
The problems and disadvantages of the prior art devices described above are overcome by the present invention through the provision of a novel bone anchoring device. The bone anchoring device has an anchor member, a cable, and a cover. The anchor member is provided with a series of engagement ribs to form an interference fit with the surface of a bone hole and pins for attaching the cable. The cable is attached to the anchor member by penetrating the cable using the pins and securing it in place by welding. A cover may be mounted to the anchoring member, and optionally the cover and pins are welded together.
These and other aspects and advantages of the present invention will become more apparent by the following description and accompanying drawings.
Referring to
The bone anchoring device 10 includes an anchor member 20 and a cable member 50. Anchor member 20 is seen to have proximal end 22, distal end 24, engagement ribs 26 extending outward from anchor member surface 21 and axial cutout 30 extending into surface 21. Engagement ribs 26 further include bone engagement edges 28. The axial cutout 30 further includes bottom 31 adjacent to cutout surface 32 and at least one pin 40 that extends radially outward from the cutout surface 32. Preferably, and as shown in
Though pins 40 preferably extend perpendicularly from cutout surface 32, one skilled in the art, will appreciate that pins 40 may extend at any angle from cutout surface 32. Though pins 40 are shown in
Each pin 40 is seen to have a proximal end 42 and a distal end 44. The distal ends are seen to have optional pointed piercing tips 45, but the tips may have any configuration including blunt, rounded, squared-off, and the like. Cable 50 is seen to have proximal end 52 and distal end 54. In the embodiment shown in
Cable member 50 may be tipped as described below to reinforce the section of cable member 50 attached to anchor member 20 of bone anchoring device 10. The purpose of tipping cable member 50 is to encapsulate the end of the cable with a material, such as a polymer, for a predetermined length, typically as long as the section to be attached to the anchor member 20. During the tipping operation, which can be done by several methods including compression and injection molding, holes for pins 40 on anchor member 20 are incorporated. This is done by having posts in the tipping mold to create the holes in cable member 50. During the tipping process these holes are permanently formed in cable member 50. The tipping process may strengthen the cable member 50 to help eliminate “cheese wire” damage to cable member 50 under axial loads.
The bone anchoring devices 10 of the present invention may be used to secure suture or cable within a bone bore hole for a variety of uses in surgical procedures. Typically, the surgeon will form a pilot hole for device 10 using a conventional surgical drill. The diameter of the pilot hole is preferably slightly smaller than the diameter of anchoring device 10. Device 10 would then be deployed in the pilot hole through the application of force resulting in the device being maintained in the pilot hole via an interference fit.
The anchoring devices of the present invention have a variety of uses in surgical procedures. These uses include reattachment of ligaments or tendons to bone. Optionally, cable member 50 of bone anchoring device 10 could be connected to a second bone anchor (not shown), which would be secured within a second bore hole in bone. This arrangement could be used, for example, to hold a bone block between adjacent vertebrae in spinal fusion procedures.
Referring to
Optionally, expandable anchor member 120 contains a wall hinge to aid in the expansion of expandable anchor member 120. Preferably, the wall hinge is an inner wall hinge 142 (see
As shown in
With reference to
Deployment stabilization unit (DSU) 300 is seen in
Bone anchoring device 110, is shown in combination with expander 180 and DSU 300 in
As shown in
Use of DSU 300 in combination with bone anchoring device 110 is advantageous because the forces on DSU 300 counter the forces on the expander element (see
Uses of bone anchoring device 110 include reattachment of ligaments or tendons to bone. Furthermore, cable member 160 of bone anchoring device 110 could be connected to a second bone anchoring device (not shown), which is secured within a second hole opening in bone. This arrangement could be used, for example, to hold a bone block between adjacent vertebrae in spinal fusion procedures.
Bone anchoring device 110, expander 180 and deployment stabilization unit (DSU) 300 may be available separately, or can be in combination as part of a bone anchoring kit. The pieces may be fully, or partially, assembled prior to use, and preferably packaged and sterilized prior to being made available.
Suitable materials from which bone anchoring devices 10 and 110 may be formed include biocompatible polymers such as aliphatic polyesters, polyorthoesters, polyanhydrides, polycarbonates, polyurethanes, polyamides and polyalkylene oxides. The present invention also can be formed from absorbable glasses or ceramics comprising calcium phosphates and other biocompatible metal oxides (i.e., CaO), metals, combinations of metals, autograft, allograft, or xenograft bone tissues.
In the preferred embodiment, the bone anchoring device is formed from aliphatic polyester polymers, copolymers or blends thereof. The aliphatic polyesters are typically synthesized in a ring opening polymerization. Suitable monomers include but are not limited to lactic acid, lactide (including L-, D-, meso and D,L mixtures), glycolic acid, glycolide, epsilon-caprolactone, p-dioxanone(1,4-dioxan-2-one), trimethylene carbonate(1,3-dioxan-2-one), delta-valerolactone, beta-butyrolactone, epsilon-decalactone, 2,5-diketomorpholine, pivalolactone, alpha-diethylpropiolactone, ethylene carbonate, ethylene oxalate, 3-methyl-1,4-dioxane-2,5-dione, 3,3-diethyl-1,4-dioxan-2,5-dione, gamma-butyrolactone, 1,4-dioxepan-2-one, 1,5-dioxepan-2-one, 6,6-dimethyl-dioxepan-2-one, 6,8-dioxabicycloctane-7-one and combinations thereof. These monomers generally are polymerized in the presence of an organometallic catalyst and an initiator at elevated temperatures. The organometallic catalyst is preferably tin based, e.g., stannous octoate, and is present in the monomer mixture at a molar ratio of monomer to catalyst ranging from about 10,000/1 to about 100,000/1. The initiator is typically an alkanol (including diols and polyols), a glycol, a hydroxyacid, or an amine, and is present in the monomer mixture at a molar ratio of monomer to initiator ranging from about 100/1 to about 5000/1. The polymerization typically is carried out at a temperature range from about 80° C. to about 240° C., preferably from about 100° C. to about 220° C., until the desired molecular weight and viscosity are achieved.
In another embodiment of the present invention, the polymers and blends can be used as a therapeutic agent release matrix. Prior to forming the bone anchoring device, the polymer would be mixed with a therapeutic agent. The variety of different therapeutic agents that can be used in conjunction with the polymers of the present invention is vast. In general, therapeutic agents which may be administered via the pharmaceutical compositions of the invention include, without limitation: anti-infectives such as antibiotics and antiviral agents; chemotherapeutic agents (i.e. anticancer agents); anti-rejection agents; analgesics and analgesic combinations; anti-inflammatory agents; hormones such as steroids; growth factors, including bone morphogenic proteins (i.e. BMP's 1-7), bone morphogenic-like proteins (i.e. GFD-5, GFD-7 and GFD-8), epidermal growth factor (EGF), fibroblast growth factor (i.e. FGF 1-9), platelet derived growth factor (PDGF), insulin like growth factor (IGF-I and IGF-II), transforming growth factors (i.e. TGF-beta I-III), vascular endothelial growth factor (VEGF); and other naturally derived or genetically engineered proteins, polysaccharides, glycoproteins, or lipoproteins.
Matrix materials for the present invention may be formulated by mixing one or more therapeutic agents with the polymer. Alternatively, a therapeutic agent could be coated onto the polymer, preferably with a pharmaceutically acceptable carrier. Any pharmaceutical carrier can be used that does not dissolve the polymer. The therapeutic agent may be present as a liquid, a finely divided solid, or any other appropriate physical form. Typically, but optionally, the matrix will include one or more additives, such as diluents, carriers, excipients, stabilizers or the like.
The amount of therapeutic agent will depend on the particular drug being employed and medical condition being treated. Typically, the amount of drug represents about 0.001 percent to about 70 percent, more typically about 0.001 percent to about 50 percent, most typically about 0.001 percent to about 20 percent by weight of the matrix. The quantity and type of polymer incorporated into the drug delivery matrix will vary depending on the release profile desired and the amount of drug employed.
Upon contact with body fluids, the polymer undergoes gradual degradation (mainly through hydrolysis) with concomitant release of the dispersed drug for a sustained or extended period. This can result in prolonged delivery (over, say 1 to 5,000 hours, preferably 2 to 800 hours) of effective amounts (say, 0.0001 mg/kg/hour to 10 mg/kg/hour) of the drug. This dosage form can be administered as is necessary depending on the subject being treated, the severity of the affliction, the judgment of the prescribing physician, and the like. Following this or similar procedures, those skilled in the art will be able to prepare a variety of formulations.
The following examples are illustrative of the principles and practice of this invention, although not limited thereto.
Forming cable/cover/anchor assemblies In this example, a general ultrasonic welding process was used to form strap, anchor, and cover assembly.
The cover was formed by compression molding (Model 2696, Carver, Inc., Wabash, Ind.). The material used to form the cover was 95/5 poly(lactide-co-glycolide) (95/5 PLGA) from PURAC (Gorinchem, The Netherlands), with an Inherent Viscosity (I.V.) of 2.33 dl/gm (measured in chloroform at 25° C. and a concentration of 0.1 gm/dl). The cover was cut to a square piece with the dimensions of 2×4.5 millimeter.
The cable was a three dimensional woven cable made using 95/5 poly(lactide-co-glycolide) (95/5 PLGA) fibers. The fibers are sold under the tradename PANACRYL, (Ethicon, Inc., Somerville, N.J.). The cable was 3D woven with 100 Denier fiber and a thickness of 1 millimeter and width of 2 millimeter at Fiber Concepts, Inc. (Conshohocken, Pa.).
The anchor was made using 95/5 poly(lactide-co-glycolide) by injection molding (Model NN35M14, Niigata Machinery Plant, Tokyo, Japan).
The anchor was placed into a fixture. The cable was cut to 25 millimeter in length and placed on the anchor by penetrating the cable using the pins of the anchor. The cover is placed to cover the cable. The horn of an ultrasonic welding machine (Model SureWeld 70, Sonobond, West Chester, Pa.) was applied to the pins and the cover, and melted the pins and the cover. The welding time was set to 2.35 seconds, the holding time was set to 1.5 seconds, and the amplitude was set to 9.
The pullout strength of the assembly was tested. Pullout tests were performed using an Instron 4501 test frame. The anchor was first loaded on a polyurethane foam block with a pre-drilled hole with diameter of 5.1 mm, which was fixed in place by a clamp that allows movement in the X-Y plane but not the Z (pulling) direction. The cable end was held tightly by the grips and then a tensile testing procedure was performed with a cross-head rate of 0.1 millimeter/second. The pullout strength of the control was 12.5 pounds-force (Ibf).
Surgical Procedure A patient is prepared for spinal fusion surgery in a conventional manner. The surgery will fuse one or more levels of the spinal column. The patient is anesthetized in a conventional manner. The tissue repair site is accessed by making an incision through the abdominal cavity and dissecting down to the spinal column. A sterile device of the present invention is prepared for implantation into the patient, the device having anchor members mounted to each end of the cable. The operative site is prepared to receive the anchor members of the repair device by dissecting through the ligamentous structure attached to the vertebral bodies of the spinal column that will be fused. A discectomy procedure is performed to remove the disc of the vertebral level to be fused and a bone graft is inserted into the discs space. A bore hole is drilled into the vertebral body above and below the disc space. The anchor bodies are then inserted into drilled bore holes in the adjoining vertebrae to be fused. The cable of the device is used to prevent migration of the bone graft in order to complete the tissue repair. The incision is approximated in a conventional manner using conventional surgical sutures.
The incision is bandaged in a conventional manner, thereby completing the surgical procedure.
The novel devices and method of the present invention provide the patient and surgeon with multiple advantages. The advantages include increased pull-out strength of the anchor member from the cord.
It should be understood that the embodiments described herein are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the present invention. All such variations and modifications are intended to be included within the scope of the invention as defined in the appended claims.