Bone screw with fluid delivery structure

[0001] This application claims priority to Provisional Application No. 60/466,487 filed Apr. 29, 2003.

[0002] The invention relates to orthopedic devices used to reinforce bones in mammals.

[0003] In any number of medical procedures it becomes necessary to deliver therapeutic material to an anatomic location. For example, it can be desirable to deliver materials usually as a fluid to particular locations within bone. This is particularly desirable when using bone screws. Materials such as calcium phosphate, hydroxyapatite, etc. are often needed to be delivered to aid in the fixation applied by an orthopedic screw.

[0004] Within the context of the present invention, which will be discussed in greater detail below, the inventors have discovered a method and apparatus which offer advantages over the currently known techniques. For convenience of explanation, the present invention will be described in conjunction with various applications, but principally bone screw and therapeutic material delivery systems. Various other applications and embodiments will be apparent in view of the following disclosure.

[0005] In the context of bone screws, bone screws may be applied to bone matrix for any number of reasons but usually such devices are attached for the purposes of repair of a weakened bone matrix in order to support bone or bone structure which has become fractured or weakened. In many cases, the fracturing of bone is in whole or in part due to disease. The bone breaks or weakens as a result of disease, for example, osteoporosis. Current techniques do not usually take into consideration that condition in the context of repair. The technique often used to repair bone may fail to address the situation under which the bone was fractured in the first place.

[0006] For example, in accordance with the conventional methods of attaching bone screws to bone, bone cement is injected through a pilot hole drilled into the bone prior to inserting the bone screw. After the bone screw is inserted into the site, the bone site theoretically hardens to strengthen the fixation site. This method lacks control over the location and the amount of bone cement applied. Often, difficulty in controlling the placement of a bone adhesive near tissues, specifically in the spinal cord region, allows improper placement resulting in injury. Too little bone cement or improper placement of the bone cement may result in a weak fixation site, which may lead to an undesirable extraction of the bone screw from the fixation site. For example, if the bone has been broken because of a chronic medical condition the use of cement in this fashion will not materially enhance fixation. Specifically, if the bone is weakened due to osteoporosis, then merely adding adhesive to the area may not necessarily address the pre-existing condition.

[0007] A device for entering an area of a host's bone matrix to mechanically strengthen the matrix and deliver tissue reinforcement material comprising; a shaft with a first external threaded portion, said shaft having a distal end, a middle portion and a proximal end; said shaft's proximal end configured to receive a fluid supply of tissue reinforcement material within walls of said shaft forming a lumen extending therethrough; walls forming at least one channel extending directionally from said lumen to at least one aperture formed by shaft walls to an outer surface of said device; and a sleeve sized to fit inside said lumen to selectively guide delivery of tissue reinforcement material.

[0025] In general, the present invention provides a device and method that enhances delivery of a reinforcement material to improve fixation without deleteriously affecting the performance of the device. The material applied to a weakened bone matrix would be more useful if it enhanced the fundamental integrity of the bone. Delivering calcium phosphate, hydroxyapatite, bone growth factors, or similarly functioning materials would strengthen the fundamental structure of the bone matrix. Controlled delivery of the therapeutic fluid as to location, rate, and dispersion of equally effective amounts would be of benefit to the patient. This could be achieved by carving a larger chamber slightly beyond that created by an orthopedic screw giving better access for the fluid into the bone matrix. Apertures along the screw shaft would also allow more fluid dispersion between screw and bone matrix, particularly where such apertures are angled to deliver fluid so that distal or proximal motion of the screw is specifically minimized and controlled.

[0026] A sleeve positioned within a central lumen of a screw would also control the fluid delivery to external apertures thereby achieving a more precise application. Furthermore, to decrease application pressure inherent in pushing fluid through a channel, the lumen and the channels connecting to outside apertures could be coated with a material to decrease friction between fluid and walls formed by such a screw.

[0027] Various bone screw configurations are known. For example, cannulated screws are known and typically used for conventional applications. Alternatively, such cannulated screws are utilized in connection with various techniques. For example, U.S. Pat. No. 6,214,012, issued 10 Apr. 2001, teaches a bone screw with apertures for delivery of bone cement or other medicaments to allow reinforcement of the surrounding bone. This patent also discloses a special adaptor at the head of the screw in order to make a connection for delivery of the cement or medications. However, such device does not enable the therapeutic fluid delivery with through-enlarging of a chamber in the bone matrix, selection of exterior apertures on a screw, precise delivery of material using specially angled apertures, or controlling screw channel flow of the fluid.

[0028] To aid in describing preferred embodiments of the present invention, reference will be made to the term “bone screw”. The term “bone screw” is intended to refer to screws of all types which are presently known or will be devised to be used for internal fixation of fractures of mammalian bone. This includes cortical screws, cancellous screws, ASIF screws and machine screws which are contemplated as being useful in connection with the present invention. The combination with plates, pins, nails and the like used in internal or external fixation are contemplated in combination with this invention.

[0029] FIG. 1 is a partially cut away schematic of one embodiment of the bone screw device 10 of this invention. There is the shaft 12 with threads 30 and cutting edge 40. Elevation line 42 shows the height of the kerf or cutting edge 40 above the root 44 reference point. Elevation line 46 illustrates the diameter height of threads 30, in this embodiment. It may be appreciated therefore, that cutting edge 40 forms an excavated zone above root 44 reference location around the device upon insertion into bone. This feature is designed to cut a pathway to allow dispersion of tissue reinforcement material. The height, shape and angle of the cutting edges of this structure control the direction that the material is dispersed. Preferably, this results in the removed material/tissue being directed away from the excavation site and allows for insertion of the reinforcing material in an even distribution to aid in the purchase of the screw in anchoring within weakened bone tissue. Cut away distal portion “A” shows an internal lumen 20 and an optional open tip 50 that communicates with the lumen 20, as shown also in FIG. 17.

[0030] FIG. 2 is a partial cutaway view of another embodiment of the invention where an aperture 60 is positioned on the shaft 112 with nearby cutting edge 140 protruding between threads 130 on device 110. The distal portion “A” of the device is a cutaway showing aperture 60 in conjunction with channel 70 which communicates with the lumen 120, and the relative position of the cutting edge 140. This figure also illustrates a closed tip 55 as one embodiment of the invention.

[0031] FIG. 3 is a third embodiment of the invention that shows apertures 160 positioned on a middle portion of a shaft 212 without threads. The threads are confined to a distal portion in this embodiment; and the relationship of thread 230 with cutting edge 240 is illustrated with a cutaway portion “A” showing the relationship to lumen 220 and an open tip 150.

[0032] FIG. 4 shows a proximal portion of the device with differently sized threads 80, a middle portion of a shaft 312 which is without threads, but with apertures 260, and cutting edges 340. A distal portion of the device comprises threads 330 around shaft 312 with a closed tip 155.

[0033] FIG. 5 shows a sleeve 90 designed for insertion in lumen 320 (shown in FIG. 6) inside shaft 412 positioned to block a channel 170 which connects to an aperture 360. FIG. 6 also illustrates the proximate relation of threads 430 and cuttings edges 440 with a closed tip 255. Also in this figure is a truncated enlargement of the sleeve 90 showing a lumen 95 throughout the sleeve for delivery of fluid material through the lumen, channels, and apertures and into the region around the device which was evacuated or created by action of the cutting edges.

[0034] FIG. 7 is a schematic view of a body portion 501 comprising a bone 504 having a plurality of zones 1, 2, and 3 adjacent to tension and compression trabeculae 510, 511 representative of such zones and trabeculae in certain body portions. When bone damage occurs through trauma or degenerative processes, the strength of these trabeculae is compromised. It is therefore quite important to reinforce those natural strengthening members through proper placement and selective fixation of any bone screw utilized for repair or strengthening. FIG. 8 shows bone screw 512 and bone reinforcing material placed across each of the main trabeculae and at the triangulated intersection region 517. This placement of bone screw 512 is enhanced by deployment of bone reinforcing material which is dispersed away from the outer surface of the screw and at an angle directionally distally and proximally, from the distal and proximal portions of the screw respectively. The structure and methodology which enables this dispersion pattern not only fills bone voids more effectively, but also prevents migration of the screw by directly locking the screw mechanically and by use of distal and proximal anchoring blocks 522, 523 of set material. This feature is accomplished by using either angled apertures or deflecting the flow from the threads or other features of the screw. This improved purchase of the screw in the bone by proper placement of the screw and use of proximally and distally directed flow of bone reinforcing or strengthening material enables improved outcomes for the patient by truly strengthening at the natural locations for strengthening members and by preventing migration of the screw. These phenomena occur virtually simultaneously with dispersion of the material.

[0035] FIGS. 9-11 show the use of movable sleeve 528 used within screw 512 to enable controlled directional dispersal of bone reinforcing material 533 through channels or via 535, 537 in the walls of the sleeve and the screw. As shown, one advantageous pattern of dispersal includes distally oriented flow from the distal end at about a 30° to about a 60° angle α. Further use of such a dispersal pattern in the proximal direction from the proximal portion of the screw, shown in FIG. 11, provides further strengthening function. In one embodiment, angle α is preferably about 45°. A radially oriented dispersal of material may also be helpful from the medial portion of the screw, as shown in FIG. 10. FIGS. 12-16 further illustrate embodiments of these structures which enable the advantages of this invention. It is recognized various combinations of the features disclosed may be utilized to achieve the advantages of the embodiments of this invention.