Patent Publication Number: US-2005143837-A1

Title: Arthroplasty devices configured to reduce shear stress

Description:
This application is a continuation in part of U.S. patent application Ser. No. 10/608,616, filed Jun. 27, 2003, which application claims benefit from U.S. Provisional Patent Application Ser. No. 60/392,234, filed Jun. 27, 2002, which applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention is directed in general to arthroplasty devices and, in particular, to arthroplasty devices which improve bone growth into said devices.  
      2. Description of the Related Art  
      The use of arthroplasty devices to replace damaged or defective joints within the body is commonplace in the medical field. The prosthetic replacement of joints has evolved over the years from early relatively crude models to current prostheses which closely replicate functions and motions of a natural joint. Prosthetic arthroplasty devices have been used as replacements for the shoulder, hips, knee, ankle and invertebral disc.  
      One problem encountered with prosthetic joints includes movement of the implant with respect to the patient&#39;s bones. This motion often compromises fixation. Another problem that occurs is an abnormal stress transference from the implant to the bone.  
      The most common method of holding the implant in the bones is “press-fitting” the device into the intramedullary cavity of the bone. This often causes abnormal stress distribution, leading to premature failure.  
      These devices also rely on the ingrowth of the patient&#39;s bone to hold these devices in place. The difficulty of achieving true growth of a patient&#39;s bone into a metal prosthesis is a well known problem in the surgical field.  
     SUMMARY OF THE INVENTION  
      It is, therefore, an object of the present invention to provide an arthroplasty device which has improved bone ingrowth capabilities.  
      It is a further object of the present invention to provide an arthroplasty device configured to reduce shear stress.  
      It is a still further object of the present invention to provide an arthroplasty device having a resorbable component which restricts motion in a joint for a period of time to allow for improved bone ingrowth.  
      It is a still further object of the present invention to provide an arthroplasty device configured to receive bone growth promoting substances.  
      These and other objects and advantages of the present invention will be readily apparent in the description the follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a lateral view, partly in cross section, of a femur and a prior art impacted femoral component of a hip replacement;  
       FIG. 2  is a lateral view, partly in cross section, of a femur and an embodiment of the present invention showing a femoral hip replacement device having a threaded component;  
       FIG. 3  is a cross-sectional view of the embodiment of the present invention shown in  FIG. 2 ;  
       FIG. 4  is an exploded view of the device of  FIG. 2 ;  
      FIGS.  5 A-D, taken together, show the sequence of installation of the device of  FIG. 2 ;  
       FIG. 6  is a lateral view, partly in cross section, of the device of  FIG. 2  which includes a collared rod component;  
       FIG. 7  is a cross-sectional view of the device of  FIG. 2  which includes an anti-rotation feature;  
       FIG. 8A  is a cross-sectional view of the femur and another embodiment of the device of the present invention having an expandable component shown in the contracted position;  
       FIG. 8B  is a cross-sectional view of the device of  FIG. 8A  showing the expandable component in the extended position;  
       FIG. 9A  is a lateral view of another embodiment of the present invention;  
       FIG. 9B  is a cross-sectional view of the device of  FIG. 9A ;  
       FIG. 9C  is a cross-sectional view of another version of the device of  FIG. 9A ;  
       FIG. 10A  is a lateral view of another embodiment of the present invention;  
       FIG. 10B  is a cross-sectional view of the device of  FIG. 10A ;  
       FIG. 10C  is a different cross-sectional view of the device of  FIG. 10A ;  
       FIG. 11A  is a lateral view, partly in cross section, of another embodiment of the present invention;  
       FIG. 11B  is a lateral view, partly in cross section, of the device of  FIG. 11A  after a period of time;  
       FIG. 11C  is a lateral view of another embodiment of the present invention;  
       FIG. 11D  is a cross-sectional view of the device of  FIG. 11C ;  
       FIG. 11E  is a lateral view of another embodiment of the present invention;  
       FIG. 12A  is a lateral view of an alternative device according to the present invention for use in prosthetic disc replacement shown in the unassembled position;  
       FIG. 12B  is a lateral view of the device of  FIG. 12A  in the assembled position;  
       FIG. 13  is a lateral view of a femoral component according to the present invention;  
       FIG. 14  is a perspective view of another embodiment of the present invention;  
       FIG. 15A  is a perspective view of the device of  FIG. 14  with a portion of the device removed and a syringe shown for injecting a bone growth promoting substance into the device;  
       FIG. 15B  is a perspective view of  FIG. 15A  showing the device of  FIG. 14  partially filled;  
       FIG. 16A  is a lateral view of a section of the spine showing the device of  FIG. 14  installed in position between the vertebrae;  
       FIG. 16B  is a lateral view of a drill bit which may be used to create a hole in the device of  FIG. 14 ;  
       FIG. 17  is a perspective view of an alternative embodiment of the device of  FIG. 14 ;  
       FIG. 18A  is an end view of an alternative artificial disc replacement device for use in the present invention;  
       FIG. 18B  is a sectional view of the device of  FIG. 18A  positioned between vertebrae of the spine;  
       FIG. 19  is a perspective view of an acetabular component for use in an embodiment of the present invention;  
       FIG. 20  is a perspective view of a femoral component for use in an embodiment of the present invention;  
       FIG. 21  is a perspective view of an alternative acetabular component similar to the device of  FIG. 19 ;  
       FIG. 22A  is a perspective view of an alternative femoral component similar to the device of  FIG. 20 ;  
       FIG. 22B  is a perspective view of another alternative femoral component similar to the devices of  FIG. 20  and  FIG. 22A ;  
       FIG. 23A  is a lateral view of an alternative embodiment of the device of  FIG. 12A ;  
       FIG. 23B  is a lateral view of the device of  FIG. 23A  shown in the deployed position;  
       FIG. 23C  is a lateral view of an alternative embodiment of the device shown in  FIG. 23A ;  
       FIG. 23D  is a sectional view of the device of  FIG. 23C ;  
       FIG. 24A  is an exploded view of an alternative embodiment of a device according to the present invention;  
       FIG. 24B  is a cross-sectional view of the device of  FIG. 24A  in the assembled position;  
       FIG. 24C  is a cross-sectional view of the device of  FIG. 24A  installed in the femur;  
       FIG. 24D  is a cross-sectional view of an alternative embodiment the threaded component shown in  FIG. 24A ;  
       FIG. 25A  is a cross-sectional view of a device according to the present invention installed in the tibia;  
       FIG. 25B  is a cross-sectional view of an alternative embodiment of the device of  FIG. 25A ;  
       FIG. 26  is a cross-sectional view of a device according to the present invention installed in the proximal femur;  
       FIG. 27A  is a cross-sectional view of a device according to the present invention installed in the distal femur;  
       FIG. 27B  is a cross-sectional view of an alternative embodiment of the device of  FIG. 27A  installed in the distal femur;  
       FIG. 28A  is an exploded view of a device according to the present invention for use in a long bone;  
       FIG. 28B  is a cross-sectional view of the device of  FIG. 28A  invention installed in a long bone;  
       FIG. 28C  is a cross-sectional view of an alternative embodiment of the device of  FIG. 28A ;  
       FIG. 29A  is an anterior view of an alternate embodiment of the prosthetic femoral device shown in  FIG. 10A ;  
       FIG. 29B  is a sagittal cross-sectional view of the device of  FIG. 29A ;  
       FIG. 30A  is an axial cross-sectional view of the device of  FIG. 29A ;  
       FIG. 30B  is an axial cross-sectional view of an alternative embodiment of the device of  FIG. 29A ;  
       FIG. 31A  is a lateral view of an alternative embodiment of the device of  FIG. 29A ;  
       FIG. 31B  is a cross-sectional view of the device of  FIG. 31A ;  
       FIG. 32A  is an anterior view of an alternative embodiment of the device of  FIG. 29A ;  
       FIG. 32B  is a cross-sectional view of the device of  FIG. 32A ;  
       FIG. 33  is an axial cross-sectional view of the device of  FIG. 32A ; and  
       FIG. 34  is an axial cross-sectional view of an alternative embodiment of the device of  FIG. 32A . 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       FIG. 1 . represents a typical prior art impacted femoral component of a hip replacement commonly used in the surgical field today. Referring now to  FIG. 1 , there is shown a femoral component  10  having an elongated tapered portion  12 , an extended stem portion  14  for connecting component  10  to the prosthetic femoral head, and a textured surface area  16 . In use, tapered portion  12  is driven into a femur  20  which has been prepared to receive component  10 . Surface area  16  of component  10  is configured to encourage bone ingrowth to assist in the permanent attachment of component  10  within femur  20 . Surface area  16  may contain small beads, fibrillar wires or other structures known in the art to promote bone ingrowth. This type of arthroplasty device relies on impaction of the device into patients&#39; bones for stability.  
      The difficulty of achieving true growth of a patient&#39;s bone into metal prostheses is well known in the medical field.  FIGS. 2-4  show a device according to the present invention which assists in overcoming this problem. Femoral hip replacement device, generally designated as  30 , includes an upper outer sleeve  32  which contains a textured surface area  34 , a tubular inner component  36  having a threaded lower portion  38 , and an elongated rod component  42  having an outwardly extending stem  44 . In operation, threaded portion  38  of component  36  engages an internally threaded area which has been previously incorporated into femur  20 . Alternatively, portion  38  may contain self tapping threads for attachment within femur  20 . Sleeve  32  is then installed on the tubular portion of component  36  such that it is held against threaded portion  38  and the inner walls of femur  20 . Elongated rod component  42  is then inserted through tubular component  36  such that it is tightly held in place by sleeve  32  and femur  20 , as can be best seen in  FIG. 2 .  
      Although device  30  contains surface area  34  to assist bone ingrowth, threaded section  38  helps to stabilize device  30 , as threaded components are less likely to allow motion between the device and bone. Bone ingrowth, which is dependent upon the surface features of the device and motion between the device and the bone, is thus facilitated by decreasing motion between the arthroplasty device and a patient&#39;s bone.  
      The process for installing device  30  is shown in FIGS.  5 A-D. Referring now to  FIG. 5A , a tap  50  having a thread cutting end  52  is used to chase threads within femur  20  in the area in which threaded portion  38  of component  36  is to be affixed within femur  20 . Alternatively, portion  38  may be manufactured as a self-tapping device. After this has been performed, portion  38  is brought into threaded engagement with femur  20 , with tubular portion  36  positioned above the threaded connection (FIG. sleeve  5 B). Next, outer sleeve  32  is forced over tubular portion  36  until the edge of sleeve  32  contacts threaded portion  38  ( FIG. 5C ). Finally, elongated rod component  42  is inserted through tubular portion  36  captured within sleeve  32  such that outwardly extending stem  44  is properly positioned for attachment within the prosthetic femoral head. This construction decreases the possibility of motion between device  30  and femur  20 , potentially enhancing bone ingrowth.  
       FIG. 6  represents another embodiment of device  30  which a collar  60  positioned on rod component  42  between stem  44  and sleeve  32  to aid in the positioning of device  30  within femur  20 . In this embodiment, rod component  42  is inserted through tubular portion  36  within sleeve  32  until collar  60  contacts sleeve  32 . In this manner, forces within rod component  42  are transferred to sleeve  32  having textured surface  34  for bone ingrowth, adding additional stability to device  30 .  
       FIG. 7  is a sectional view of an alternative embodiment of device  30  which adds an anti-rotation feature for additional stability. Referring now to  FIG. 7 , rod component  62  contains outwardly extending edges  62   a ,  62   b . Tubular component  64  contains a pair of channels  64   a ,  64   b  within its inner walls corresponding to edges  62   a ,  62   b . In this manner, rod component  62  cannot rotate within tubular component  64 , adding additional stability to the arthroplasty device, which potentially promotes bone ingrowth. Rod component  62  may also contain a cruciform shape, with tubular component  64  having a corresponding shape.  
      Square threads, buttress threads, or reverse buttress threads may be used in the embodiments requiring threaded devices, as these decrease hoop stress on the bone. Hoop stress can lead to fracture of the bone. Taper threads may also be used. In addition, the threads can be either left or right handed.  
      FIGS.  8 A-B represent another alternative embodiment for an arthroplasty device according to the present invention. In this embodiment, an adjustable component  68  having a first section  68   a  and a second section  68   b  which are movable relative to each other by a pair of adjusting screws  70  is inserted into femur  20  in order to fit a patient&#39;s bone anatomy better. Screws  70  are adjustable to shift component  68  between a contracted position ( FIG. 8A ) and an expanded position ( FIG. 8B ). Screws  70  are adjusted by a corresponding pair of screws  72  which, when turned, control the adjusting motion provided by screws  70 . Alternatively, a wrench may be used to turn a screw, or gear, which cooperates with a toothed component to force sections  68   a  and  68   b  apart.  
      Component  68  is placed into the intramedullary canal of a bone and expanded. The tighter fit provided by component  68  decreases motion between the prosthesis and the patient&#39;s bone. Adjustable component  68  also allows for compaction of the cancellous bone with the cortical bone into which the prosthesis device is inserted. Cancellous bone is rich in cells that promote bone ingrowth. Prior art impacted devices are generally inserted into the cortical bone after the removal of most of the cancellous bone. Thus, expanding components such as component  68  will aid in the immobilization of the prosthesis and preserve the healing characteristics of cancellous bone. While the device shown in FIGS.  8 A-B show expansion of one component in one direction, multiple components may be used that expand in multiple directions. A torque wrench may be used to control the force and help prevent fracture of the bone into which the device is to be inserted. In addition, shape memory materials may be used to change the shape of components within the device. For example, a sleeve made of nitinol could be inserted in its contracted shape and then open to the expanded shape after insertion into the base.  
      Alternative expansion mechanisms could be used for component  68 . For example, a scissor jack-like mechanism or inclined planes could be used to move the sections to its expanded position. In addition, multiple sections can be used that expand in multiple directions.  
      In another embodiment, a rod component similar to that shown in  FIGS. 2-6  is inserted between sections of component  68  in its expanded expansion. The implanted rod may be held in position within component  68  by adding a taper to the interior surfaces of sections  68   a  and  68   b.    
      Upper outer sleeve  32  which contains textured surface area  34  in  FIG. 2  can be adapted to further enhance bone ingrowth in devices according to the present invention. FIGS.  9 A-C demonstrate several alternative embodiments which may be used to further promote this growth. Referring now to  FIG. 9A , upper outer sleeve  34  contains a plurality of wells  80  along its outer surface which replaces the textured surface. Wells  80  are filled with collagen sponges  82  which have been soaked with Bone Morphogenetic Protein (BMP). Sponges  82  are inserted into wells  80  prior to insertion of device  30  into femur  20 . In  FIG. 9C , sleeve  34  contains a plurality of channels  84  which extend along the length of sleeve  34 . In this embodiment, BMP could be injected into channels  84  after insertion of device  30 , or BMP soaked collagen sponges  82  may be forced into channels  84 .  
      Another alternative embodiment of an arthroplasty device according to the present invention is shown in FIGS.  10 A-C. A femoral rod component  90  having an outwardly extending stem  92  and a collar stop  94  is installed through a sleeve  96  having a textured area  98  for promoting bone ingrowth. The interior of sleeve  96  contains of pair of grooves  100  which correspond to a pair of wings  102  extending from the outer surface of component  90  such that the interaction of wings  102  and grooves  100  allow small amounts of motion between rod component  90  and sleeve  96  to decrease the shear stress on textured area  98  where bone ingrowth occurs. Shear stress can cause motion between the device and the patient&#39;s bone, decreasing the chance of bone ingrowth. Devices using anti-rotation features, such as shown in  FIG. 10C  and  FIG. 7 , will have rods with varying degrees of version, including antiversion and retroversion.  
      FIGS.  11 A-E show an alternative embodiment of the device according to the present invention which uses resorbable components to temporarily decrease or remove the stress on the bone ingrowth surfaces of the device. Referring now to  FIG. 11A , an arthroplasty device  100  similar to the device of  FIG. 1A -C is shown, having a femoral rod component  102  with a outwardly extending stem  103 , a positioning sleeve  104  having a textured area (not shown) for promoting bone growth, and a solid disc  106  having an threaded outer surface  108 . Disc  106  is initially positioned within a femur  20 . Disc  106  has been installed into position within femur  20 , after its interior has been threaded in the appropriate area by using a tool similar to that shown in  FIG. 5A . Alternatively, outer surface  10 B may contain self-tapping threads. Resorbable material  110  is threaded into femur  20 , contacting disc  106 , and then rod component  102  is introduced into sleeve  104 . Note that component  102  is supported by resorbable material  110  and not sleeve  104 . Preferably, device  100  contains the anti-rotation features shown in  FIG. 1  ° C. Additionally, anti-rotation features can also be added between disc  106 , resorbable material  110  and the end of rod component  102  for additional stability. Suitable resorbable materials include a high molecular weight poly-L-lactic acid (PLLA) polymers, calcium hydroxyapatite, tricalcium phosphate. Other potentially useful resorbable materials include polydiaoxanone (PDS), oxidized regenerated cellulose and various forms of collagen.  
      In this relationship, resorbable material  110  temporarily decreases or removes the stress on the bone ingrowth surfaces of sleeve  104 . The forces on device  100  are transferred from resorbable material  110  to the ingrowth surfaces of sleeve  104  as resorbable material  110  disappears. Disc  106  may also contain a through hole  111  to aid in the drainage of resorbable material  110 . This resorption process generally takes months. Bone will grow into the ingrowth area of sleeve  104  while device  100  is supported by resorbable material  108 . Eventual transfer of the forces to the ingrowth area of device  100  is important to prevent bone resorption that occurs with stress shielding. Resorbable material  110  may also temporarily eliminate movement through device  100 . Eliminating movement across device  100  decreases forces on the bone ingrowth surfaces. Motion through device  100  is permitted once resorbable materials  110  has dissolved, as rod component  102  now contacts sleeve  104 , as can be seen in  FIG. 11B .  
      A prosthetic hip device according to the present invention is shown in FIGS.  11 C-D. Hip device  112  includes a femoral rod component  114  having an outwardly extending stem  115 , a head  116  mounted on stem  115 , an inner acetabular component  117 , and an outer acetabular component  118 . A resorbable component  120  is located between component  118  and rod component  114  to restrict motion between the acetabular and femoral components of device  112  until resorbable component  120  disappears, allowing time for bone ingrowth to firmly take hold.  
       FIG. 11E  shows prosthetic disc replacement device  122  according to the present invention. Device  122  includes an upper plate  123  and a lower plate  124  connected by a pivot  125 . Resorbable material  126  is placed between plates  123  and  124  before insertion of device  122  into a position between vertebrae of the spine.  
      FIGS.  12 A-B show an alternative embodiment of a prosthetic disc replacement device  130 . Device  130  contains an upper plate  131  and a lower plate  132 . Each plate contains a keel-like ingrowth extension component  134  attached for rotation through plates  131 ,  132  at a pivot  135 . An activation device  136  consisting of a flat plate is also shown. To install device  130 , the device is placed between vertebrae in the spine of a patient. Activation device  136  is pushed between plates  131  and  132  to force extensions  134  away from plates  131 ,  132  to affix device  130  in its proper location between the vertebrae. Extensions  134  are exposed to the cancellous bone of the vertebrae, immobilize device  130  and help prevent its extrusion.  
       FIG. 13  shows another embodiment of a method for restricting motion of the prosthesis relative to the bone when using an arthroplasty device. Referring now to  FIG. 13 , there is shown a femoral component  140  positioned within femur  20 . Component  140  is held firmly in place by a first screw  142  which is affixed crosswise through component  140  and femur  20 . A second screw  144  is affixed through component  140  and femur  20  in a direction oriented approximately 90° to first screw  142 . A guide is preferably removably attached to femur  20  or component  140  to help direct a drill bit through femur  20  and to thread screws  142  and  144  through the structure. Use of screws  142  and  144  assist in minimizing motion of component  140  with respect to femur  20 , allowing bone ingrowth between component  140  and femur  20 .  
       FIG. 14  shows a device which promotes bone ingrowth in a spinal fusion procedure. Implant  200  consists of a box-like structure having top and bottom surfaces  200   a ,  200   b , front and rear surfaces  200   c ,  200   d , and side surfaces  200   e ,  200   f . In this embodiment, surfaces  200   a  and  200   b  are essentially parallel,  200   c  and  200   d  are essentially parallel, and  200   e  and  200   f  are essentially parallel; however, implant  200  can consist of any shape which will fit between adjacent vertebrae. Surface  200   c  contains an aperture  202  which allows access to the interior of implant  200 . Aperture  202  allows for the injection of a bone growth promoting substance into implant  200 . Possible substances include Platelet Rich Plasma (PRP), bone morphogenetic protein (BMP), or concentrated leukocytes. Other substances which are available are discussed in my co-pending patent application Ser. No. 09/897,000, which application is incorporated by reference herein. Although implant  200  is preferably manufactured from bone, it could also be constructed from other compatible materials such as metal or polymers. Alternatively, the metal or polymer devices could be filled with bone.  
      FIGS.  15 A-B show how implant  200  can be filled with an appropriate bone growth promoting substance. A syringe  206  filled with a suitable substance  207  is positioned with its needle  208  inserted through aperture  202 . As syringe  206  is operated, substance  207  fills implant  200  with the bone growth promoting fluid, as can be seen clearly in  FIG. 15B .  FIG. 16A  shows implant  200  in position between adjacent vertebrae  210 ,  212  while syringe  206  injects growth substance  207  into the implant.  
      A drill bit  216  is shown in  FIG. 16B  which may be used to create aperture  202  in implant  200 . Bit  216  contains a smooth cylindrical section  216   a , a fluted end  216   b  having a point for drilling, and a collar stop  216   c . Drill bit  216  is particularly suited for drilling aperture  202  into implant  200 , as collar stop  216   c  acts to prevent bit  216  from traveling too far into implant  200 , possibly damaging the device. Drill bit  216  may be helpful when drilling aperture  202  into a device such as implant  200   a , which has a different shaped structure, as can be seen in  FIG. 17 . Aperture  202  can be aligned in any suitable direction within the device. While aperture  202  can be drilled into implant  200  before inserting the device into position in the spine, it may be advantageous to drill aperture  202  into implant  200  after it is positioned between vertebrae  210 ,  212 . This would avoid weakening of implant  200 , as the device is under compressive forces when in position. Alternatively, implant  200  could be manufactured with aperture  202  in place in the device.  
      Bone growth promoting substances can be used in many other arthroplasty devices. FIGS.  18 A-B show its use in connection with an artificial disc replacement (ADR) procedure. An ADR device  220  similar to the device of FIGS.  12 A-B contains a pair of extensions  221  for fixing device  220  in the spine and a pair of end plates  222   a ,  222   b  each having an aperture  223 . End plates  222   a ,  222   b  are separated by an activating structure  226 . End plates  222   a ,  222   b  may contain a series of channels which are connected to apertures  223 . When device  220  has been positioned in place between vertebrae  210 ,  212 , syringe  206  can be located with needle  208  inserted into apertures  223  of end plates  222   a ,  222   b  to input growth substance  207  into device  220  to promote bone ingrowth between the device and the vertebrae.  
      FIGS.  19  to  22 A-B depict different arthroplasty devices which can be used in conjunction with bone growth promoting substances to maximize bone ingrowth between the body and the implants. An acetabular component for use in hip replacement is shown in  FIG. 19 . Component  240  is a cup-shaped device having a spherical outer surface  242  and a hollow curved inner surface  244 . A front surface  246  contains a plurality of apertures  248 . Apertures  248  are connected to a series of channels which are connected to a series of outlets  250  which are scattered along outer surface  242  of device  240 . When component  240  is placed in position during hip replacement surgery, bone growth substance  207  can be injected into apertures  248  such that the substance can travel through the channels to outlets  250 , where it can contact the hip bone to promote bone ingrowth between device  240  and the bone. An alternative embodiment to implant device  240  is shown in  FIG. 21 . This acetabular component  260  has a spherical outer surface  262 , a hollow curved inner surface  264  and a flat front surface  266 . Along the periphery of surface  266  a series of grooves  268  are channeled into outer surface  262 . Grooves  268  may be parallel channels along outer surface  262 , or they may spiral around outer surface  262 . When component  260  is positioned in the bone during hip surgery, growth substance  207  may be injected into grooves  268  such that the fluid can flow between component  260  and the bone to promote bone ingrowth.  
      Examples of the present invention for use with femoral components are shown in  FIGS. 20 and 22 A-B. Referring now to  FIG. 20 , a femoral component  280  is shown having a body  282  having an outer surface  283 , a flat top surface  284 , and an outwardly extending stem  286 . A plurality of apertures  288  are located on flat surface  284 .  
      A series of channels within body  282  are connected to apertures  288  at one end, while the other ends are connected to a series of outlets  290  located on outer surface  283 . When component  280  is implanted in position within a femur, bone growth substance  207  is injected into apertures  288  such that it will travel through body  282  and exit through outlets  290  between component  280  and the bone to promote bone ingrowth. Alternative versions of this device are shown in FIGS.  22 A-B. In  FIG. 22A , femoral component  280   a  contains a body  282   a  having an outer surface  283   a , a flat top surface  284   a , and an outwardly extending stem  286   a . Along the periphery of surface  284   a , a plurality of grooves  292  are channeled into the outer surface  283   a . Grooves  292  may be straight along outer surface  283   a , or they can spiral around component  280   a . When component  280   a  is fixed in place within a femur, growth substance  207  can be injected into grooves  292  such that the fluid can flow between the implant  280   a  and the bone to promote bone ingrowth.  FIG. 22B  shows a similar device  280   b , except that grooves  294  are equally spaced around the periphery of upper surface  284   b  and are oriented in a parallel fashion along outer surface  283   b.    
      The principles of the present invention taught in  FIGS. 19-22B  can be applied to other prosthetic devices such as knee replacements, shoulder replacement, and spinal fusion cages.  
      FIGS.  23 A-D teaches several alternative embodiments of the present invention for use in spinal procedures similar to those taught in FIGS.  12 A-B and FIGS.  18 A-B. Referring now to  FIG. 23A , there is shown a spinal device generally indicated at  300  having a pair of end plates  302   a ,  302   b . Each end plate contains a keel-like fixation component  304  which is fixed for rotation about a pivot  306  through the interior area of the end plate. Component  304  are offset from each other with respect to device  300  such that component  304  rest side by side between end plates  302   a ,  302   b  when device  300  is in the unactivated position. This orientation allows for larger fixation components to be used in device  300  for better fixation in position between vertebrae. An activating component  308  is shown alongside device  300 . Component  308  consists of a pair of spherical pusher plates  310 . In operation, activating component  308  is forced between end plates  302   a ,  302   b , causing fixation components  304  to rotate about pivot points  306  outwardly through end plates  302   a ,  302   b , to extend from device  300  and holding the device firmly between vertebrae of the spine, as is shown in  FIG. 23B .  
      FIGS.  23 C-D show spinal device  300   a  in which slots  316  are incorporated into end plates  302   a ,  302   b  such that fixation components  304  rest within slots  316  when device  300   a  is in the unactivated state. Slots  316 , which may be shaped such that the end of each fixation component  304  just fits within said slot, or may extend along a longer portion of each end plate, to allow for the use of a larger fixation component with device  300   a , improving the holding power of spinal device  300   a  when positioned between Vertebrae.  
      FIGS.  24 A-D show an alternative embodiment for an arthroplasty device according to the present invention for use in hip surgery. Referring now to FIGS.  24 A-C, there is shown a device  329  having a femoral component  330  with a outwardly extending stem  332 , and a hollow passageway  334  extending through the central area of component  330 . Passageway  334  is square shaped in this embodiment, but it may be shaped in any configuration in which a component inserted into said passageway cannot rotate, such as an ellipse, a triangle, pentagon, or hexagon. Component  330  also contains a recess  336  on its upper surface. Passageway  334  and recess  336  are connected by a channel  338 . An attachment component  340  contains an upper section  342  having a square shape with a threaded aperture  344  at its upper end and a lower threaded cylindrical section  346 . A screw  348  is also provided with the device.  
      To install femoral component  330  into a femur in a hip replacement procedure, the inner surface of femur  20  is threaded at the proper depth using a tool similar to that shown in  FIG. 5A . Attachment component  340  is installed within femur  20  by threading section  346  into the femur. Component  330  is then located upon upper section  342  of attachment component  340  by matching the shape of section  342  with recess  334  in the proper orientation. Screw  348  is then inserted into recess  336  of component  330  through channel  338  and threaded into aperture  344  to hold the device in its proper position within femur  20 . This procedure “pulls” the device into the femur, helping to prevent fracturing the bone. A torque wrench may be used to adequately tighten screw  348  to its proper tightness to prevent splitting femur  20 . Attachment component  342  may be composed of a polymer such as carbon fiber, or alternatively may be composed of a resorbable material. Device  329  minimizes motion between the implant and bone, as the matched shape connection between passageway  334  and upper section  342  of attachment component  340  allows for virtually no movement.  
      An alternative attachment component  340   a  for component  340  is shown in  FIG. 24D  Component  340   a  contains a similar upper section  342  containing a threaded aperture  344 ; however, lower cylindrical threaded section  346   a  contains a hollow internal section  352 . Hollow section  352  gives threaded section  346   a  more flexibility than a solid component. Hollow threaded components and polymer threaded components are less likely to cause thigh pain from excessive stress transfer to the femur at the level of the threaded component. Furthermore, resorbable components, in particular, are less likely to cause stress shielding of the proximal femur.  
      FIGS.  25 A-B show an embodiment of the present invention for use in a prosthetic knee device. Device  400  includes a cylindrical component  402  having a threaded outer surface and a recess  404  having a threaded inner surface. An articulating component  406  includes a planar section  408  having an extension  410  with a treaded end  412 .  
      To install device  400 , the internal surface of tibia  416  is threaded internally using a device similar to that shown in  FIG. 5A  at the desired depth. Component  402  is then threadably engaged within tibia  416 . Articulating component  406  is then threadably affixed to component  402  by threading end  412  of extension  410  into recess  404  until surface  408  contacts tibia  416 .  
      Referring now to  FIG. 25B , prosthetic device  420  includes a cylindrical component  422  having a threaded outer surface and an aperature  423  having a threaded inner surface, and an upper component  424  having a planar surface  426  and an aperture  428  in the central region. The upper surface of component  424  is sized such that a cover  430  may be snapped into position on the upper surface. Cover  430  may be constructed of polyethylene. A bolt  432  having a head  433  is also included with device  420 .  
      To install device  420 , the internal surface of tibia  416  is threaded internally using a device similar to that shown in  FIG. 5A  at the desired depth. Upper component  424  is placed on the upper surface of tibia  416  and bolt  432  is placed through aperture  428  and is threaded into aperture  423  of component  422  until head  433  contacts the upper surface of component  424 . Cover  430  is then snapped into position on component  424 .  
      In FIGS.  25 A-B, components  402  and  422  may be composed of metal or a polymer, or could also be made from a resorbable material. Components  406  and  429  may be constructed from titanium or chrome cobalt.  
       FIG. 26  shows a device  444  embodying the present invention for use in treating the hip socket. In this embodiment, a fracture  450  of a femur  451  is shown at the base of the femoral head  452 . Device  444  includes a femoral repair component  453  consisting of a cylindrical member  454  having a threaded end section  456 . Component  453  also contains an aperture  458  which is oriented angularly toward femoral head  452 . Aperture  458  may be threaded internally. A second component  460  of device  444  consisting of a connecting rod  461  having a threaded end  462  is connected to femoral head  452  by a threaded aperture  464  within femoral head  452 .  
      To install device  444  for repair of the fractured femur, threaded end section  456  is located within femur  451  using the techniques previously discussed. The correct angular position of component  460  relative to component  453  and femoral head  452  is determined, and threaded end  462  is affixed within femoral head  452 . Rod  461  is sized such that the end can be inserted into aperture  458  of component  453  using a small amount of force to overcome the friction fit between the components. Rod  461  is then inserted into aperture  458  until femoral head  452  is positioned against femur  451 . The interaction between rod  461  and component  453  acts to hold head  452  in the correct position to heal.  
       FIG. 27A -B show an embodiment of the present invention for use in repairing a fracture of the distal end of the femur. Repair device  480  includes a component  482  having a solid first section  484  with a threaded outer surface and a narrower cylindrical second section  486 . To install repair device  480 , the internal surface of femur  488  is threaded at a section on the opposite side of fracture  490  from distal end  492  of femur  488  using a device similar to that shown in  FIG. 5A . Threaded section  484  of component  482  is affixed within femur  488  such that section  486  is spaced apart from distal end  492  of femur  488  when the two sections of femur  488  are held together tightly along fracture  490 . A hole  496  is then drilled across the distal end  492  of femur  488 , passing through section  486  of component  482 . A screw  498  is then placed into hole  496 , passing through section  486  of component  482  and is threaded into femur  488  as shown at  500 . This device holds the sections of femur  488  tightly together to aid in the healing process. Threaded section  484  can be made from a resorbable material, non-resorbable polymers, metal, or a combination of materials. For example, section  484  could be made with a metal core surrounded by a resorbable component.  
      The device  480   a  of  FIG. 27B  is similar to device  480  shown in  FIG. 27A  except for the design of component  482 . Component  482   a  is constructed like the component shown in  FIG. 24D  in that first section  484   a  is hollow with a threaded outer surface. As discussed previously, the hollow section allows more flexibility than a solid component. The installation of device  480   a  follows the same methods of that taught for device  480 .  
      FIGS.  28 A-C show a fixation device  500  for use in long bones. Referring now to  FIG. 28A , a first component  502  contains a solid cylindrical portion  504  having an outer threaded surface  506 , and a cylindrical portion  508  having a lesser diameter than portion  504  and containing a threaded portion  510  located along its length. A second component  512  comprises a cylindrical disc having a threaded outer surface  514  and a central aperture  516  which is threaded. In addition, a pair of screws  520  are provided.  
      Fixation device  500  is shown on its installed position in  FIG. 28B . A long bone  540  is shown having a fracture  542 . Threads are made on the internal surfaces of bone  540  in the appropriate positions in the manner previously described. Component  502  is then positioned within the upper section  540   a  of bone  540  by engaging outer threaded surface  506  into the threaded position in section  540   a  to fix component  502  in its proper location. Component  512  is then positioned onto threaded portion  510  of cylindrical portion  508  while component  512  is being threaded into lower section  540   b  of bone  540 . Component  512  is rotated until it is firmly coupled to both component  502  and bone  540 . In this embodiment, left handed threads may be used for threaded  510  and also for threaded outer surface  514  and threaded aperture  516 . In this manner, the action of installing component  502  of device  500  acts to pull the components together. After device  500  has been installed in bone  540 , holes may be drilled into upper section  540   a  and lower section  540   b  through the upper and lower ends of component  502  and screws  520  inserted to prevent rotation of long bone  540  about device  500 .  
       FIG. 28C  shows device  500  installed within long bone  540  without the use of screws  520 .  
      Another embodiment for use with the arthroplasty devices according to the present invention involves the use of bone cells. Bone and bone cells are grown onto the prosthesis prior to implanting the device into a patient. To accomplish this task, bone cells are initially harvested from a patient. Osteoblasts could be harvested from a patient&#39;s iliac crest; a piece of iliac crest bone could be surgically removed. In “Culture of Animal Cells” by R. Ian Freshney, Wiley-Liss New York 2000, which is incorporated herein by reference, techniques for harvesting osteoblasts are described on pps. 370-372. Also described in the article are cell culture techniques. U.S. Pat. No. 6,544,290, which issued on Apr. 8, 2003, to Lee et al, which patent is hereby incorporated by reference, teaches a method culturing cells onto a resorbing calcium phosphate material. The present invention contemplates the culturing of cells onto arthroplasty devices made of titanium, chrome, cobalt, ceramic, or other non-resorbable materials.  
      In the present invention, bone is harvested from a patient, and the bone then treated to remove the cells. The cells are cultured and grown onto the prosthesis in a lab. The device, now covered with living bone cells, is subsequently implanted into the patient. These cells, which include osteoblasts, osteocytes, donor bone cells, stem cells or other pluripotential cells, and other cells that are capable of transforming into osteoblasts or osteocytes, will promote the bone ingrowth to improve the stability of the device in the body. Alternatively, the bone cells could be added to the device at the time of surgery.  
      To foster the improved bone ingrowth, the titanium components would have surface treatments. For example, the surfaces could be porous, beaded, plasma sprayed, or covered with fibrillar wire to promote ingrowth. Alternatively, the cells could be cultured onto arthroplasty devices made of other metals, or materials such as ceramic and hydroxyapatite coated metals. In addition, to attempt to improve the ingrowth characteristics of this process, bone growth promoting substances such as TGF-α,β1, -2; EGF, IGF-I; PDGF, FGF, BMP-1, VEGF and other similar substances may be added to the cell culture medium.  
      It is contemplated that features of the various embodiments may be combined. For example, the expandable component taught in FIGS.  8 A-B could be used with the threaded component of  FIGS. 2-7 . Also, although the drawings are directed primarily to the use of the invention in prosthetic hips, the principles may be applied to other prosthetic joints, such as knees, shoulders, ankles and wrists. In addition, bone cells harvested from the patient could be added to the bone growth promoting substance used in other embodiments. These cells could also be combined with a cell culture media or a synthetic matrix.  
      The devices shown in FIGS.  10 A-C of the present invention are directed to prosthetic hip devices which reduce shear on bone ingrowth components. In addition, these devices reduce the risk of dislocating the prosthetic joint. Dislocation occurs when the ball on the femoral component pops out of the socket of the acetabulum. Dislocations may occur when the components are misaligned; however, dislocations often occur when the patient accidentally moves his leg into a prohibited position, as prior art hip replacements do not allow rotation between the portion of the femoral component that is affixed to the femur and the ball of the femoral component. The ball of the femoral component can be levered out of the socket when positioning the leg in the prohibited position.  
      The devices taught in FIGS.  10 A-C permit rotation between the portion of the sleeve component that is affixed within the femur and the ball portion that is attached to the rod component. Movement between the two components reduces the lever arm of the leg. The joint between the two components allows rotation between the two components as the leg is moved into prohibited position. For example, prosthetic hips may be dislocated in a posterior direction as the hip is flexed and internally rotated. The risk of posterior dislocation increases if the prosthetic hip is placed in a retroverted alignment. The risk of posterior dislocation is decreased if the prosthetic hip is fixed in an anteverted alignment. The risk of an anterior dislocation is increased if the prosthetic hip is fixed in excessive anteversion. The devices taught in FIGS.  10 A-C allow change in version (anteversion and retroversion) as a reaction to force placed on the prosthetic hip. The novel hip is free to rotate into additional anteversion when the leg is moved into a position that causes posterior dislocation. Similarly, the novel femoral components are free to rotate into additional retroversion when the leg is moved into a position that causes anterior dislocation.  
      Several other alternative embodiments of arthroplasty devices similar to the devices taught in FIGS.  10 A-C are shown in  FIGS. 29-34 . Referring now to  FIG. 29A , device  600  comprises a femoral rod component  602  having an outwardly extending stem  604  for affixing a ball joint. Rod component  602  is installed within a passageway or channel  606  of a sleeve component  608 . Note that rod component  602  is completely contained within sleeve  608 , as can be clearly seen in  FIG. 29B .  
      Sleeve  608  is permanently affixed within the femur in this embodiment. Sleeve  608  may be press fitted into the femur for bone ingrowth, or, alternatively, polymethylmethacrylate (PMMA) may be placed between the femur and the outer surface of sleeve  608  to cement the sleeve tightly in place.  
       FIG. 30A  shows a cross-sectional view of an embodiment of device  600  in which channel  606  of sleeve  608  and the outer surface  610  of rod component  602  both contain essentially circular shapes. Channel  606  and rod component  602  are sized to fit together snugly such that articulation between components  602  and  608  allows unlimited rotation when sleeve  608  is implanted into the femur when normal forces are placed on device  600  by the body.  
      An alternative embodiment of device  600  is shown in  FIG. 30B . In this embodiment, outer surface  610  of rod component  602  consists of a rounded portion  612  connected to an extension  614 , while channel  606  within sleeve  608  contains a rounded section  616  connected to an open area  618 . When device  600  is implanted into the femur, limited axial rotation is allowed, as extension  614  of rod component  602  can rotate within the confines of open area  618 . This rotation is limited by the size of extension  614  of rod component  602  within open area  618  of channel  606  within sleeve component  608 .  
      FIGS.  31 A-B show another embodiment of the device shown in  FIG. 29A . In this embodiment, channel  606  within sleeve component  608  extends completely through sleeve  608 . Rod component  602  is sized such that its end  619  extends just beyond the bottom edge of sleeve component  608 , as can be clearly seen in  FIG. 31A . This arrangement will prevent the tip of rod  602  from striking the femur, even in patients with bowed femurs.  
      FIGS.  32 A-B show yet another embodiment of the device shown in  FIG. 29A . In this embodiment, rod component  602  has a conical shape, and channel  606 , which does not extend through sleeve component  608 , is also conically shaped. Components  602  and  608  are sized with tolerances such that articulation between components allows rotation. The conical shape reduces the risk of device  600  developing a fatigue fracture.  
       FIGS. 33 and 34  are directed to embodiments of the device shown in  FIG. 32A  in which the rod component and channel are sized to allow limited rotation of the components. Referring now to  FIG. 33 , channel  606  of sleeve component  608  contains a central section  630  having a smaller groove  632  located on either side of central section  630 . Rod component  602  is constructed with a central section  634  corresponding to central section  630  of channel  606 , and a pair of wings  636  on either side of central section  630  which are contained within grooves  632  of channel  606 . Wings  636  are sized such that they are smaller than grooves  632 , thus allowing small amounts of motion between rod component  602  and sleeve component  608  to decrease shear stress on device  600 .  
       FIG. 33  shows the cross section of a device as shown in  FIG. 32A  in which channel  606  is a trapezoidal shape, and rod component  602  is a similar shape, but smaller. In this design, small amounts of motion between components  602  and  608  is possible to decrease shear stress.  
      While the present invention has been shown and described in terms of preferred embodiments thereof, it will be understood that this invention is not limited to any particular embodiment, and that changed and modifications may be made without departing from the true spirit and scope of the invention as defined in the appended claims.