Abstract:
A device and method to mechanically strengthen bone matrix and deliver tissue reinforcement material to weakened areas in skeletal structures. A preferred embodiment is an orthopedic screw configured to receive and directionally disperse a therapeutic fluid through the screw&#39;s channels and apertures.

Description:
PRIORITY  
       [0001]    This application claims priority to Provisional Application No. 60/466,487 filed Apr. 29, 2003. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates to orthopedic devices used to reinforce bones in mammals.  
         BACKGROUND OF INVENTION  
         [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.  
         SUMMARY OF THE INVENTION  
         [0007]    A device for entering an area of a host&#39;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&#39;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. 
       
    
    
     BRIEF DESCRIPTION OF THE INVENTION  
       [0008]    [0008]FIG. 1 is side and cutaway view of one embodiment.  
         [0009]    [0009]FIG. 2 is a side and cutaway view of another embodiment.  
         [0010]    [0010]FIG. 3 is a side and cutaway view of a third embodiment.  
         [0011]    [0011]FIG. 4 is a side view of a fourth embodiment.  
         [0012]    [0012]FIG. 5 is a side view of a sleeve.  
         [0013]    [0013]FIG. 6 is a cutaway view illustrating insertion of a sleeve and enlargement of that sleeve.  
         [0014]    [0014]FIG. 7 is a schematic body portion showing bone zones and trabeculae.  
         [0015]    [0015]FIG. 8 is a view of FIG. 7 with a bone screw and bone reinforcing material optimally placed.  
         [0016]    [0016]FIG. 9 is a partial cutaway view of one embodiment of a bone screw assembly deploying bone reinforcing material.  
         [0017]    [0017]FIG. 10 is a partial cutaway view of one embodiment of a bone screw assembly deploying bone reinforcing material.  
         [0018]    [0018]FIG. 11 is a partial cutaway view of one embodiment of a bone screw assembly deploying bone reinforcing material.  
         [0019]    [0019]FIG. 12 is a partial cutaway view of angled proximal apertures.  
         [0020]    [0020]FIG. 13 is a partial cutaway view of one embodiment of a bone screw assembly.  
         [0021]    [0021]FIG. 14 is a view of one embodiment of a sleeve.  
         [0022]    [0022]FIG. 15 is an expanded view of a portion of the sleeve of FIG. 14.  
         [0023]    [0023]FIG. 16 is a partial cutaway view of angled distal apertures.  
         [0024]    [0024]FIG. 17 is a section view of FIG. 1 along lines  17 - 17 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [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]    [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]    [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]    [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]    [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]    [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]    [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]    [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.