Patent Publication Number: US-2007112435-A1

Title: Ball and shaft of joint prothesis

Description:
RELATED APPLICATIONS  
      This application is a continuation-in-part of application Ser. No. 10/799,192, filed Mar. 12, 2004, which is a division of application Ser. No. 09/961,662, filed Sep. 24, 2001, now U.S. Pat. No. 6,755,865, the specification and drawings of application Ser. Nos. 10/799,192 and 09/961,662 are incorporated herein their entirety. 
    
    
     FIELD OF THE INVENTION  
      The field relates to devices for joint replacement, especially hip and shoulder joint prosthetics and procedures.  
     BACKGROUND OF THE INVENTION  
      Arthroplasty, the restoration of normal joint motion, is frequently done by the insertion of a prosthetic joint replacement. Implant technology has improved over the last number of years and provides solutions to problems caused by injury, arthritis and other joint diseases. Frequently, the damage is sufficiently severe to require a total joint replacement. The prior art discloses numerous designs for total hip joint prosthetic devices.  
      Total hip joint replacements require interactive prosthetic femoral and acetabular components to emulate the ball-socket mechanism of a natural hip joint. When the supporting structure is weakened, particularly the femoral head and neck, a prosthetic femoral component with an extended shaft is implanted within the medullary cavity of the femur. Examples of this type total hip replacement prosthetic device are disclosed in U.S. Pat. No. 6,093,208 issued to Enrico Tian and U.S. Pat. No. 5,807,407 issued to England, et al. Many surgeons take this route, even when the underlying bone structure of the femoral head and neck is strong, under the theory that implantation of the shaft within the medullary cavity of the femur is required to obtain the necessary support for the prosthetic femoral head, as the femoral implant is under high stresses that can cause failure of “surface replacement” devices. Such failures frequently occur early in the patient&#39;s recovery, before the bonding of the bone to the metal surfaces of the prosthetic implant has occurred. However, the insertion of the prosthetic device with a long femoral shaft requires the resection of the femoral head and neck to obtain access to the longitudinal cavity within the femur. Such surgery is very stressful to the patient and increases the risk of infection. If the device fails, any further implantation of prosthetic devices becomes exceedingly difficult, as the supporting bone structure has already been appreciably reduced.  
      U.S. Pat. No. 5, 800,558 to Gerald A. LaHaise, Sr., U.S. Pat. No. 5,133,764 to Pappas et al., and U. S. Pat. No. 4,846,841 to Indong Oh, disclose the “surface replacement” technique of a total replacement of a hip joint. “Surface replacement” is aimed at primarily providing replacement of the joint surfaces while preserving as much of the supporting bone structure as possible and preserving the integrity of the medullary cavity. Pappas et al. &#39;764 and Oh &#39;841 each disclose a version of a cap that is implanted over the resected head of the femur. LaHaise &#39;558 discloses a more complex means for attaching the ball to the resected head of a femur. One advantage to the surface replacement type of total hip replacement, is that much of the femur is left intact, so that if the surface replacement method fails, it may be replaced with an intramedullary canal prosthetic component.  
      Each of the above patents disclose a generally solid metal acetabular cup that is fixed, usually by screws, to a prepared surface of the hip bone. An insert, a layer of plastic or metal is frequently attached to the acetabular cup, the insert being sized to receive the ball portion of the prosthetic joint that is attached to the femur.  
      Each of these prostheses mentioned above, are installed during lengthy, invasive, major surgery that requires surgically opening the hip area for full exposure and direct access to the hip joint. During surgery the head of the femur must be removed from the acetabular cup, for resection of the femur head or complete removal of the femur head and neck. This surgery comes at a high cost as it is complex, requiring extensive surgical support staff and operating room equipment.  
      Not withstanding the existence of such prior art prosthetic components and methods for attachment to the human body, it remains clear that there is a need for prosthetic components that may be inserted into the human body without a major incision to gain direct access to the femur and hip bone.  
     SUMMARY OF THE INVENTION  
      The present invention relates to a prosthesis and method for implantation of that prosthesis within the human body as the replacement for a ball joint. Reduced or minimally invasive procedures secure a ball and shaft in the femur and a shell and cup in the acetabulum, for example. A segmented shell may comprise a plurality of separate segments which may be inserted minimally invasively into the patient and assembled and may be attached to the hip bone to form a socket.  
      One advantage is that a shell and cup and a shaft and ball may be implanted without fully opening or exposing the hip joint, directly.  
      An expandable drill bit is disclosed that is capable of removing a portion of the head of the femur and a thin portion of the outer layer of the acetabulum, for example, through a hole bored at an angle through the femur.  
      Another advantage is that the implant may be removed an a traditional implant may be inserted without causing damage or weakness that impairs the subsequent implant. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in connection with the accompanying drawings, in which:  
       FIG. 1  is an isometric view of a hip joint prosthesis;  
       FIG. 2  is a cross-sectional elevational view taken along line  2 - 2  of  FIG. 1 ;  
       FIG. 3  is a top plan view of the segmented first shell of the prosthesis of  FIG. 1 ;  
       FIG. 4  is an exploded cross-sectional view of  FIG. 3  taken along line  4 - 4 ;  
       FIG. 4A  is a detailed view illustrating the use of surgical thread;  
       FIG. 5  is an isometric view of a segmented shell with a key segment exploded;  
       FIG. 6  is a top plan view of a segmented second shell with a portion cutaway in cross-section to illustrate the relationship of the parts;  
       FIG. 7  is a cross-sectional elevational view taken along line  7 - 7  of  FIG. 6 .  
       FIG. 8  is a detailed front elevational view of one of the second group of parts of the segmented shell of this invention;  
       FIG. 9  is a cross-sectional view taken along line  9 - 9  of  FIG. 8 ;  
       FIG. 10  is a side elevational view of one of the first group of parts of a segmented second shell;  
       FIG. 11  is a front elevational view of one of the first group of parts of a segmented second shell;  
       FIG. 12  is an isometric view of a shaft and cup;  
       FIG. 13  is a bottom plan view of a shaft;  
       FIG. 14  is an isometric view illustrating another example of a hip joint prosthesis;  
       FIG. 15  is an isometric view illustrating yet another example of a hip joint prosthesis;  
       FIG. 16  is a detailed view of a hip structure illustrating a placement of the guide wire into a hip bone;  
       FIG. 17  illustrates the placement of a protective hollow blunt guide and a hole bored through a neck and head of a femur and into a acetabulum of a hip bone;  
       FIG. 18  illustrates the placement of a sleeve into a hole bored through a femur;  
       FIG. 19  illustrates the insertion of an expandable bit into a sleeve;  
       FIG. 20  illustrates the extension and expansion of an expandable bit for removal of a portion of an acetabulum of a hip bone;  
       FIG. 21  illustrates the placement of a segmented shell and transportation of one of a plurality of segments through a sleeve guided by a secondary guide wire for placement onto a base and engagement with an adjacent segment;  
       FIG. 22  illustrates a placement of a segmented shell;  
       FIG. 23  illustrates a placement of a cup within a segmented shell of  FIG. 22  and placement of a shaft into a hole bored through a femur;  
       FIG. 24  illustrates the placement of a segmented shell and a second segmented shell liner;  
       FIG. 25  illustrates the placement of a cup into the first and second segmented shells;  
       FIG. 26  illustrates a placement of a shaft into a hole through a femur;  
       FIG. 27  illustrates a placement of a segmented shell, a solid shell liner, a cup and a shaft;  
       FIG. 28  is a front elevational view an the expandable drill bit, illustrating the blades extended outwardly;  
       FIG. 29  is a detailed view of a first end of an expandable drill bit;  
       FIG. 30  is a detailed view of one of the blades of the cutter of  FIG. 28 ;  
       FIG. 31  is a cross-sectional view taken along line  31 - 31  of  FIG. 30 ;  
       FIG. 32  is a detailed top plan view of  FIG. 28 ;  
       FIG. 33  is a detailed view of an attachment of the blades to an expandable drill bit;  
       FIG. 34  illustrates the attachment of the expandable drill bit to a drill motor for rotation of the expandable drill bit.  
       FIGS. 35A and 35B  illustrate two examples of threaded shaft and ball assemblies;  
       FIG. 36  illustrates a sleeve fixed in a femur.  
       FIG. 37  illustrates a tapped bore hole in a femur;  
       FIGS. 38 and 39  illustrate alternative embodiments with and without a nail; 
    
    
      The examples described and drawings rendered are illustrative and are not to be read as limiting the scope of the invention as it is defined by the appended claims  
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      One example of a ball and shaft joint prosthesis is illustrated in  FIGS. 1-13 , in which shows the prosthesis  10  comprised of components capable of being used in a minimally invasive surgery. Based upon the teachings of this patent, a person of ordinary skill in the art is enabled to implant shoulder joint replacement, hip replacement, and other joint replacements with a less invasiveness, quicker recovery times, and fewer complications.  FIG. 1  and  FIG. 2  illustrate an example of a prosthetic joint comprising a socket implant  12  and a ball implant and shaft combination  114 . The ball implant and shaft combination  114  is received by the socket implant  12  replacing the natural joint in a total hip replacement, for example.  
      For a total hip joint replacement, the acetabulum of the patient is prepared for receipt of the socket implant  12  and the femur is prepared for receipt of the ball implant and shaft combination  114 . For a total shoulder joint replacement, the glenoid cavity of the scapula is prepared for receipt of a socket implant  12  and the humorous bone is prepared for receipt of the ball implant and shaft combination  114 . In the case of a shoulder joint, the portion of the socket implant that is attached directly to bone may be solid or segmented, as the shoulder socket implant is much smaller than the hip socket implant, and the size of the humorous bone in comparison with the femur supports a larger access bore for passing a solid shoulder socket implant therethrough, although use of separate segments has the advantage of reducing the size of the borehole needed for inserting the socket  12 .  
      For purposes of illustration, the hip joint will be used to illustrate the apparatus and method of implantation. A socket implant  12  comprises a first segmented shell  16  made of material, such as biocompatible metal, a second segmented shell  70  made from a material, such as a synthetic resin, and a cup  106 , which may be made of any material having a hard surface capable of sustaining wear from a ball, such as a metal or cross-linked, high density polyethylene.  
      Another example is illustrated in  FIGS. 14, 22 , and  23 , the socket implant  312  is comprised of a segmented metal first shell  316  and a cup  406  that is received by the first shell, the cup being made from metal or plastic. In order to use a single segmented shell and a cup, the patient receiving the prosthetic components  310  should have large bones such that the hole bored through the neck of the femur is large enough to allow thicker segments to pass therethrough and/or a greater or lesser number and thickness of segments may be used. Thus, the invention illustrated by the drawings may be modified to accommodate any bone size using minimally invasive surgery or other less invasive procedures.  
      Yet another example is illustrated in  FIGS. 15 and 27 , the socket implant  612  is comprised of a metal segmented first shell  616 , which receives a second shell  670  that is constructed from a single piece of a material made of a ceramic, polymer or metal, which then receives a cup  706  of a synthetic resin, for example. A bore hole through the femur must have an opening large enough to accommodate the separate segments, second shell, ball and cup for use in minimally invasive surgery. Alternatively, a surgical technique may be used that is less invasive than standard procedures but not minimally invasive.  
      Now referring to the examples in  FIGS. 1-13 , the socket implant  12  comprises a segmented first shell  16 , which may be mounted into a prepared hip acetabulum. Herein, the term “segmented shell” refers to a shell having separate segments, which may be inserted through a hole bored through a bone of a patient, which separate segments collectively form the concave surface of the shell when joined together. A first segmented shell  16  is comprised of a base  18  and a plurality of shell segments  20   a - j  that engage one another to form the concave surface of the first segmented shell  16 . Thus, a segment is defined as a separate piece and segmented is defined as something that is comprised of separate pieces. Any convenient number of segments can be used, provided each fits an opening cut into the patient; however, ten segments have been used for illustration purposes. The segmented first shell  16  is comprised of separate pieces or segments  20   a - j  that are joined together to form the segmented first shell  16 . As seen more clearly in  FIG. 4 , the base  18  has at least one ridge  22  that is formed in the top surface  24  of the base  18  proximal to the edge  26  of the base  18  and projects outwardly therefrom. In a preferred embodiment, the ridge  22  is continuous; however, this is unnecessary as long as a portion of the ridge  22  engages each segment  20   a - j . The base  18  has a hole  27  therethrough for receipt of a cannulated screw  29  for attachment of the base  18  to the hip bone. The bottom surface  28  of the base  18  is curved to fit the curvature of the prepared surface on the hip bone. A plurality of flexible secondary guide wires  30 , one for each segment  20   a - j , are threadably mounted to the ridge  22  so that they are spaced apart from one another.  
      Each segment  20   a - j  has an inner surface  32 , having a concave curvature, an outer surface  34 , having a convex curvature, a first longitudinal side  36 , a second longitudinal side  38 , a first end  40  and a second end  42 . The outer surface  34  of each segment  20  may longitudinally and transversely arcuate, with a curvature that will mount to the curvature of the prepared surface of the hip. Each segment has a groove  44  formed in the outer surface  34  proximal the first end  40 , as seen in  FIG. 3  and  FIG. 5 , and a hole  46  that extends from the bottom of the groove to the inner surface  32 . Some of the segments also may have a hole  48  that extends through the inner and outer surfaces of the segment between the first and second ends  40  and  42  of the segment. The holes  48  may receive surgical nails  50  therethrough. An example of a nail  50  is visible in  FIG. 2 , and is used to attach one of the segments  20   a - j  to the prepared bone surface.  
      Also, the example illustrated in  FIG. 2  shows how the cup  106  and shells  70 ,  16  may have an angled, exposed surface, such that the angle X provides for improved range of motion of the joint.  
      As seen most clearly in  FIG. 5 , all but two of the segments  20   a - j  have male and female arms  52 ,  54  providing interlocking lands and grooves. The segments  20   a - g  may be identical. Each male arm  52  extends outwardly from the first side  36  and then inwardly toward the longitudinal axis A of the shell  16 . The arm  52  extends longitudinally from the second end  42  toward and proximal to the first end  40 . A female second arm  54  extends outwardly from the second side  38  of each of the segments  20   a - j  and then away from the longitudinal axis A of the shell  16  to form a groove  58 . The groove  58  is sized and configured to receive the land  56  of the male arm  52  to form a land and groove interlocking connection. Wedge segment  20   i  is the last segment to be attached to adjoining segments; therefore, wedge segment  20   i  is inserted from the inside of the shell  12 . The interior of the shell  12  has a smaller circumference than the exterior; and the wedge segment  20   i  is wedge-shaped having an outer surface  34  narrower than the inner surface  32 . The wedge shapes interlock the wedge segment  20   i  with each of its neighbors. The adjacent sides of the two adjoining segments,  20   h  and  20   j , are shaped to receive the wedge shape of the segment  20   i . In addition, wedge segment  20   i  has two female arms  54  and the adjacent segment  20   h  has two male arms  52  for interlocking with the adjacent segments.  
      For example, the segmented shell  16  may be constructed of titanium or cobalt chrome alloys. However, other materials that are resistant to wear, tough, and stiff may be suitable for the purpose.  
      The segmented shell  16  may be received by the surgeon in disassembled form for thorough disinfecting prior to assembly in the patient by the surgeon or may be packaged in a sterile pack in an assembly or pre-assembled state. During assembly of the segmented shell  16 , each of the segments may be mounted on a respective secondary guide wire  30  and advanced along the wire until the groove  44  engages the ridge  22  on the base  18  as best represented by  FIGS. 4, 44  and  21 . The secondary guide wires  30  guide their corresponding segments to their proper position. These wires  30  are flexible enabling the segments  20   a - j  to easily slide through the bore hole and into position during the surgery, which is described in greater detail herein. After assembly of the shell, the flexible wires  30  are removed from their holes  59 , such as by screwing or unlashing and then removed. For example, holes may be bored through the base  18  to provide a through-hole  60 , as illustrated in  FIG. 4A . The first end  62  of a closed loop  64  of surgical thread, is passed through the hole  60  in the base  18  from the top downwardly. The second end  66  of the loop is then passed through the loop at the first end  62  to connect the thread to the base  18 . The first end of the thread loop  66  is then passed through the hole  46  in one of the segments  20   a - j . Once the segments  20   a - j  are in place, each of the plurality of loops of thread  64  are cut and the thread  64  is pulled from the base  18  through the hole  46  in the segments  20   a - j . Alternatively, the loop may be engaged on each of the segments  20   a - j  and the passed through the base  18 , which allows the segments  20   a - j  to be pulled into place before cutting and removing the thread  64 .  
      As shown in  FIGS. 6-11 , a second segmented shell  70  may be sized and configured such that it may be assembled within the first segmented shell  16 . In this example, the second shell  70  is comprised of a plurality of parts. A total of  10  parts have been used for illustrative purposes, a first group of parts  72   a - e  and a second group of parts  74   a - e ; however, the number and size of the plurality of parts may be determined by the application. Each of the group of parts  72   a - e  have a longitudinal axis B, a first end  76 , a second end  78 , a first face  80 , a second face  82 , a first side  84  and a second side  86 . Each of the second group of parts  74   a - e  have a longitudinal axis C, a first end  88 , a second end  90 , a first face  92 , a second face  94 , a first side  96 , and a second side  98 . The first face  80  and the second face  82  of the first group of parts and the first face  92  and the second face  94  of the second group of parts are each longitudinally and transversely arcuate. The first ends  76  and  88  of each part of the first and second group of parts is linked to one another, preferably by surgical thread passing through the hole  100  in the parts  72   a - e  and the hole  102  in the parts  74   a - e , as seen in  FIGS. 10 and 8  respectively.  
      A portion of the sides  84  and  86  of each of the parts  72   a - d , that is proximal the outer rim  104  of the shell  70  extend radially toward the central axis D. When the parts  74   a - e  are being assembled to form the cup shaped shell  70 , the last part  72   e  is tapered outwardly such that the sides  84  and  86  are angled toward one another. The horizontal arc of the second face  82  is smaller than the horizontal arc of the first face  80 . To ensure that all sides fit tightly, the sides of the adjacent parts,  72   a  and  72   d , are tapered inwardly to match the taper of part  72   e  such that the sides fit tightly when the parts are fully assembled.  
      The sides  84  and  86  of each of the parts  74   a - d  are tapered outwardly so that the first face  92  is much larger than the second face  94 . The transverse dimensions of the second face  94  of the parts  74   a - d  vary along the longitudinal axis C between the first end  88  and the second end  90 . The horizontal width of the second face  94  varies from a sharp edge (where the cross-section of the part would be triangular) proximal the first end  88  to a greater cross-section as seen in  FIG. 9  and then narrows proximal the second end  90  to a generally triangular cross-section. As each of the parts  74   a - e  is inserted between adjoining parts  72   a - e , as illustrated by  FIG. 6 , the curvatures of the adjacent sides match one another to make a tight friction fit, for example.  
      The second shell  70  may be constructed from a synthetic resin or a suitable metal. In one example, the second shell is formed in place by injecting a polymer resin, which hardens when cured, as a alternative to a second segmented shell. The second segmented shell  70  may be made using the same material used for the first segmented shell. The second segmented shell may be comprised of interlocking segments and a base similar to the first segmented shell  16 , as an alternative to the structure illustrated in  FIGS. 6-11 . The primary difference is that the second shell is smaller than the first segmented shell  16 . However, the second shell may be made of a suitable synthetic resin or metal of a different composition than the first shell  16 . The second shell when made of metal may be attached to the first segmented shell  16  by snap rings, for example. A polymer resin shell may be joined to the first segmented shell  16  by heat and pressure or by snap rings. In one example, the inner surface  32  of the first shell  16  may be roughened or otherwise prepared to make a tight bond to a polymer resin shell.  
      As shown in  FIG. 2 , a cup  106  is inserted within the second shell  70 . In one example, the cup  106  is made of a solid titanium or cobalt chrome alloy with a highly polished interior surface  108 . The cup  106  is preferably a metal when the second shell  70  is constructed from a synthetic resin, for example. The cup  106  may be constructed from a synthetic resin, such as a cross-linked high density polyethylene. When comprised of a synthetic resin, the cup  106  may be formed so that when the cup  106  receives the ball  110 , the edge  112  of the cup  106  extends beyond the equator of the ball  110  so that the cup  106  snaps onto and is retained on the ball  110  for easy insertion into the socket implant  12 .  
      The cup  106  may be retained in the second shell  70  by a snap ring, press fit, adhesive bond or other retainer. The shells and the cup may be attached to one another in a number of different ways. Snap rings or drop rings operate simply. Snap ring or drop ring  145 , as seen in  FIG. 25 , is inserted within a groove  146 , as seen in  FIG. 5  that matches a second groove  148  in the second shell  70 , as seen in  FIG. 7 . When the second shell  70  is pressed into place, the snap ring  145  is expands into the groove  146  locking the two shells together. Snap ring  188  in groove  190  may engage the groove  182  in the cup  106 . When a plastic cup or plastic segmented shell is to be attached to an inner metal shell, heat (approximately 400 degrees) and pressure can be applied to the plastic cup or shell so that it bonds to a roughened surface of the metal shell. In other embodiments, it is possible to use well-known biologically tolerable bonding resins to adhesively bond a shell or cup within a shell.  
      A ball implant and shaft combination  114 , as shown in  FIGS. 12 and 13 , has a ball  110  opposite of angled end  118 . A shaft body  120  and a neck  122  are fixed to the ball  110 . The ball  110  may be shaped spherically and may be comprised of highly polished titanium or cobalt chrome, for example. The neck  122  and the body  120  may be comprised of a steel alloy and the body  120  may be coated with a bone growth medium, such as any one of the well-known ingrowth surfaces for encouraging the growth of the bone to that surface for bonding the body  120  to an adjacent bone, such as a femur. The shaft  114  is cannulated, having at least one channel  124  extending from an open first end  126  at a bottom surface  128  of the opposite end  118  of the shaft body  120  to an open second end  130  on a surface of the neck  122  disposed between the shaft body  120  and the ball  110 . The channel  124  may be used to flush and suction the site of the hip joint to remove debris that may have collected in the joint during surgery or due to the wear of the head  110  or cup  106  and may also be used to insert antibiotics to fight infection. A bag constructed from a formulation of silicon and rubber (or other material that is non toxic to the surrounding tissues) may be implanted in the patient&#39;s leg adjacent the second end  118  of the shaft  114  and attached by a ring mechanism or other fastener or adhesive to the shaft  114  so that it is in fluid flow communication with the tube or tubes  124 . The bag will collect debris created by the prosthetic joint to prevent the debris from a toxic interaction with the surrounding tissue. An open second tube  132  also extends inwardly from the bottom of the shaft  114  to a closed second end  133  proximal the neck  122 . The second tube  132  has an open first end  134  that is threaded for attachment of a syringe through which a cement may be injected into the tube  132  to bond the body  120  to the surrounding bone. The threads on the second tube  132  may also be used for attachment of an extraction tool (not shown) to remove the shaft  114 , if the implant is temporary or damaged. A secondary tube  136  may be connected at one point along the second tube  132  and may be in fluid flow communication such that a fluid may be distributed to a surface of the shaft body  120 . For example, the secondary tube  136  extends through the side wall  137  and additional tubes  136 ,  136 ′ provide the channels to the other surfaces the body  120  such that cement may be distributed between the body  120  and the surrounding bone. For an even distribution of the cement around the body  120 , a plurality of secondary tubes  136 ,  136 ′, as illustrated in  FIG. 12  for example, interconnect with the second tube  132 . For example, in  FIGS. 12 and 13 , two channels  124  are formed in the shaft body  12  extending from an opening  124  in the bottom surface  128  to an opening in the neck  130 . The body  120  has holes  184  for screws  138  for attachment to the bone of the femur, as shown in  FIGS. 2 and 12 , for example. As shown in  FIG. 2 , the screws may have expandable ends  188  to prevent loosening and provide a fixed attachment to the bone, which is particularly desirable if the bone is cancellous or otherwise weak.  
      A groove  140  may be formed in the side wall  137  adjacent the bottom  128  to receive a U-shaped shield  142  that has a pair of legs  144  that extend outwardly from the groove. This shield is curved to fit the body  120  so that the legs will engage the comer of the cortical bone along the superior portion of the hole through the femur to reduce the risk that the bone will fail due to stresses applied by the body  120  of the shaft  114 .  
      When the patient&#39;s bone structure is large enough or the prosthesis small enough,  FIGS. 14, 22  and  23  illustrate another example of the invention. Segments  420   a - j  (not all of which are shown), may be inserted and assembled to form a single, segmented shell  416  and cup  406  or a dual shell  616 ,  670  and cup  706 , as illustrated in  FIGS. 14 and 15 , respectively. The socket implant  310  comprises the segments  420   a - j  that are assembled and joined to one another to form the first shell  316 , and a cup  406  is inserted. The cup  406  is sized and configured to be received into the interior cavity of the first shell  416 . The cup  406  is held in the first shell  416  by a snap ring  445 , for example, as illustrated in  FIG. 23 . The cup  406  may be constructed of a metal or a polymer resin. Attachment by a snap ring may be done whether the cup  406  is metal or resin; however a resin may be able to adhere to the surface of the shell  316  without the need for a snap ring, for example. The shaft  414  may be similar in size and shape as shaft  114 , illustrated in  FIGS. 1-13 . The cup  406  is sized to receive a ball  410 .  
      A compound shell  610 , illustrated in  FIGS. 15 and 27 , maybe similar in structure and assembly to the previous examples, except a solid second shell or shell liner  670  is inserted between the first segmented shell  616  and the cup  706 . As shown in  FIG. 15 , the shell liner  670  is formed as a single piece, which is not segmented. The single piece shell liner  670  may have the same general shape as the segmented shell  70 . The maximum diameter of the shell liner  670 , during installation, must be less than the minimum diameter of the channel through which it is inserted during surgery to assemble the compound shell  610  (not shown). The second shell  670  may be made of metal such as a titanium or cobalt chrome alloy. A polymer resin cup  706  may be inserted in the second shell  670  and may be attached by snap rings or heat and pressure, as previously discussed. The combined ball and shaft  714  may be similar in structure to the previously described examples.  
      An advantage of this apparatus and method is that the surgery is much less invasive, takes much less time, requires much less surgical support in the operating room, and is much less expensive. In addition, if these components were to fail, a full hip joint replacement, done in accordance with current practice, is still available, as more than enough of the femur remains and only a small portion of the acetabulum was removed. The steps for implantation of these prosthetic components are discussed below. Thus, the examples are suitable for use as a temporary prosthetic device, for example.  
      The patient is suitably prepared for surgery in accordance with known practice. In an example of a method of using a prosthetic device in a minimally invasive surgery, the patient&#39;s body is aligned so that a longitudinal axis D extending from and neck and head of the femur of the patient passes through the geometric center of the acetabulum of the patient, such as illustrated in  FIG. 16 . The patient&#39;s body is placed in skin traction to prevent movement during surgery. A one inch incision is made to expose the femur at the point at which the longitudinal axis exits the femur, just under the greater trochanter. As seen in  FIG. 16 , a hollow and blunt guide  150  is inserted up against the bone such that its axis is coincident with the longitudinal axis D. A 2 mm smooth guide wire  152  with a threaded tip, as shown in the enlarged view of  FIG. 16 , is passed through the guide  150  and along the longitudinal axis D so that the guide wire  152  is aligned with and driven through the geometric center of the femoral head, across the joint and into the geometric center of the acetabulum  156 . A cannulated drill bit is mounted over the guide wire  152  and a hole is bored through the femur, the neck of the femur, the head, across the joint and  2  mm into the acetabulum. A larger blunt guide  150 ′ is placed over the smaller blunt guide  150 , which is then removed. A second cannulated drill bit may be inserted in the drill to bring the hole  158  to the proper diameter, as shown in  FIG. 17 , for example. The size of the hole  158  will largely be determined by the size of the patient&#39;s femoral neck, in the case of a femoral joint replacement. However, other factors may include the age and athletic activity of the patient and whether the prosthesis is permanent or merely temporary.  
      The hole  158  for example, does not remove the interior of the subchondral plate. To ensure that the bore does not extend beyond the planned depth into the acetabulum, such as 2 mm, the cannulated drill bit and drill ride the guide wire  152  to a stop  153 , as seen in  FIG. 31 .  FIG. 34  demonstrates use of the drill  200  with an expandable drill bit  166 , which is used for forming the cavity in the acetabular. However, a cannulated surgical drill bit may be inserted in the drill motor  200  to bore hole  158 . A guide wire  152  may be received within a tube in the drill motor  200  that has a predetermined length. The guide wire  152  is sized so that when the end of the guide wire  152  reaches the end of the tube, or stop  153 , the proper length of the hole  158  has been reached. In this way, the depth of a hole may be accurately predetermined.  
      As seen in  FIG. 18 , sleeve  160 , having the same exterior diameter of the hole  158 , which is bored in the femur, is now placed around the wire and inserted through the blunt guide  150 ′ and into the femur until the first end  162  of the sleeve  160  lies proximal the neck  164 . The blunt guide  150 ′ may be removed. An expandable drill bit  166 , as illustrated in  FIG. 28 , for example, is mounted on the guide wire  152  and inserted through the sleeve  160 . As shown in  FIG. 19 , the expandable bit is capable of holding to less than the inner diameter of the sleeve  60 . This drill bit  166  has multiple blades  168  that can be expanded so that the outer cutting edges  170  of the blades  168 , when fully expanded, match the shape of the outer surface of the segmented shell  16 . As seen in  FIG. 20 , once the blades have exited the sleeve  160  they may begin cutting away the head of the femur  154 . The expandable drill bit  166  is advanced until the drill blades  168  remove approximately 2 mm of the acetabulum  156 , for example. The expandable drill bit  166  includes a mechanism for measuring the distance that has been bored. Once the predetermined distance for movement of the drill along the guide wire has been reached the expandable drill bit  166  is drawn inwardly so that the inner cutting edge  172  of the blades  168  can remove additional portions of the head  154  such that adequate clearance for full movement of the joint is accomplished. In one example, a portion of the femoral head and neck remains, in order to provide a structure for a later procedure greater stability to the shaft body. The expandable drill bit  166  is advanced again until the blades  168  can be closed and then the expandable drill bit  166  is retracted through the sleeve  160 . The drilling operation may be controlled through fluoroscopy. While drilling is being accomplished a flushing fluid may be injected into the site through a tube  174  in the expandable drill bit  166  and suction may be applied to the central portion of expandable drill bit  176  for removal of debris.  
      Once debris is removed, a socket implant may be attached to the hipbone of the patient. A ball  110  is sized to be inserted through the hole  158 , and the acetabulum site on the hipbone has been enlarged by the expandable drill bit  166 . Therefore, the cup  106  is sized to receive the ball and the cup  106  is supported by one or more shells attached to the hip bone. The larger the cross-section of the neck of the femur the larger the hole  158  that can be bored through the femur, without damage to the subchondral plate, through which the socket implant is passed. The surgeon, based upon measurements of the patient&#39;s bone structure, may determine the particular size and structure of the socket implant.  
      In one example, prosthetic component  10  comprises a segmented first shell  16 , a segmented second shell  70 , a cup  106 , and a shaft  114  of  FIG. 1 . In  FIG. 14 , a second example comprises a socket implant  312  comprised of a metallic segmented first shell  316  and a metallic or polymer resin cup  406 . A third example comprises a segmented first shell  616 , a single piece, metal second shell  670 , and a cup  706 , such as illustrated by  FIG. 15 . The fewer parts needed to complete the socket implant, the easier the placement and the more quickly the operation can proceed, which is better for the surgeon and the patient.  
      In one example, the surgeon selects the example using two segmented shells. The next step is to implant the first segmented shell  16 . The base  18  having the cannulated screw  178  inserted therein, is mounted on the guide wire  152  so that the cannulated screw and base  18  passes along the guide wire  152  and is therefore centered in the acetabulum . With the base  18  centered by the guide wire the self-tapping cannulated screw  29  is driven into the bone of the acetabulum of the patient by a cannulated screw driver. The ends of the plurality of flexible wires  30  attached to the base  18  may extend outwardly through and beyond the sleeve  160 . First a segment having two male arms  52 , which in  FIG. 5  is segment  20   h , is inserted. A flexible secondary guide wire  30  is received through the hole  46  in the first segment  20   h  so that the segment  28  may slide downwardly on the guide wire until the groove  44  on the first segment  20   h  engages the ridge  22  of the base  18 , as seen in  FIGS. 4 and 5 . Once the segment is seated in place a surgical nail  50  is driven through the hole  48  in the segment  20   h  to attach the segment  20   h  to the hip bone. As seen in  FIG. 21 , some of the segments are already in place and one segment is shown mounted on one of the flexible secondary guide wires  30 , such that the flexible secondary guide wire  30  passes through the hole  46  in the segment. Thus, the guide wire  30  directs and aligns the segment  20   c  to the proper location.  
      After positioning of segment  20   h , segment  20   g  is then mounted on its corresponding flexible secondary guide wire  30  and installed so that the female land  56  engages the groove  58  of the segment  20   h . The next segments are inserted in the same manner until the next to last segment  20   j  is in place. The last segment, segment  20   i , has two female arms  54  that engage with the male arms  52  on segments  20   h  and  20   j  interlocking the segments  20   a - j  of the segmented first shell  16  in place. In addition, as discussed previously, the segment  20   i  is tapered so that it may be inserted in place from the inside of the first shell  16 . A surgical nail is driven through the hole  48  of segment  20   i  to secure the segments. As seen in  FIG. 21 , surgical nails may be driven in more of the holes  48  in the segments  20   a - j  if the surgeon believes it is desirable. The location of the nails will be determined by the surgeon based upon the thickness and density of the bone in the adjacent area; however, nails are often driven into the superior, posterior superior or the straight posterior portions of the hipbone, as needed. If nails are driven in segments  20   h  and  20   i , then these segments should be located adjacent to bone that is thick and dense.  
       FIG. 21  illustrates the method for placement of a segment, and it illustrates the implantation of the first segmented shell  16 , with the plug  180  screwed into place. An asymmetric surface contour  3  is shown that provides a greater angle ({acute over (α)} in  FIG. 2 ) in one direction than another, improving range of motion in at least one direction requiring greater range of motion. As discussed previously, a loop of surgical thread  64 , as shown in  FIG. 4A , may be used as a guide wire or may be used in addition to a guide wire to deliver the segments to their proper location.  
      A second segmented shell  70  is likewise positioned within the first shell  16 .  FIG. 24  schematically illustrates a second segmented second shell  70  inserted within the first segmented shell  16 .  
      As shown in  FIGS. 25 and 26 , the second shell  70  lies between the first shell  16  and the cup  106 . As shown in  FIGS. 6-11 , the segmented second shell  70  comprises a plurality of parts, a first group of parts  72   a - e  and a second group of parts  74   a - e . The first group of parts  74   a - e  each have a hole  100  therethrough and the second group of parts each have a hole  102  therethrough. The parts are alternatingly strung on a surgical thread that is passed through the holes  100  and  102  and tied in a loop. The parts are then inserted through the sleeve  160  so that the guide wire  152  passes through the loop of surgical thread. The surgeon places the first group of parts within the first shell  16  beginning with part  72   a  and ending with part  72   e . The last part  72   e  is tapered to provide a friction fit between part  72   d  and  72   a , forcing the other parts into position forming a cup-shaped shell. The second group of parts  74   a  through  74   e , which are held in proper orientation by the surgical thread, are then each inserted between the adjacent pair of the first group of parts  72   a - 72   e . As seen in  FIG. 6  and  9 , the second group of parts are tapered and may be readily placed in position and then firmly pushed into place. The parts  72   a - e  and  74   a - e  are then placed under pressure and high temperature (approximately 400 degrees), thereby bonding the plurality of parts  72   a - e  and  74   a - e  to one another and to the first shell  16 .  
      Alternatively, if the second segmented shell  70  has a similar interlocking arm structure as the first segmented shell  16 , the segments are inserted through the sleeve  160  and assembled in the first segmented shell  16  in the same manner that the first segmented shell  16  was inserted through the sleeve  160  and assembled in the acetabulum. Of course, the first and last segments of the second shell may be attached or bound to the first shell  16  by heat and pressure or using a snap ring, for example.  
      The next step is to insert a cup  106  through the sleeve  160  and fit it to the second shell  70  such as by using a snap ring  188  that is inserted in the groove  190  in the parts  72   a - e . As the cup is pushed into the interior cavity of the first shell  16 , the exterior sides of the cup  106  engage the snap ring  188  pushing it into the groove  190  until the groove  190  aligns with the groove  182  in the cup  106 , at which time the snap ring  188  expands outwardly and engages the groove  182  locking the cup  106  within the second shell  70 , as seen in  FIG. 25 . If the cup is made from a polymer resin it may be installed on the ball  110  prior to the shaft  114  being inserted in the hole  158 . The shaft  114  may be pressed into the hole in the femur, and the ball  110  with the cup attached seats the cup  106  in the second shell  70 . The cup  106  may be locked by a snap ring in the second shell  70 , for example. As discussed previously the plastic cup  106  snaps on the ball as the edge  112  of the synthetic resin cup curves around the ball beyond its equator.  
      The sleeve  160  may be removed from the hole  158  prior to inserting the ball and shaft assembly  114 . As illustrated in  FIG. 23 , the shaft  114  may be implanted in the femur of the patient. The shaft  114  may be driven into the hole  158  so that the ball  110  is seated within the cup  106  for free movement between the ball and the cup. As the shaft  114  is inserted, a shield  142  is placed around the superior portion of the hole  158  and is held in place by the groove  140  formed in the body  120 . To stabilize the shaft  114  during the healing process, a surgical screw  138  may be inserted through a hole  184  in the shaft  114 . The surgical screw  138  may have a first end  186  that is capable of expanding after it has entered into the femur to more tightly hold the shaft  114  in place. This may be especially desirable if the bones are soft. Additional screws may also be inserted through other holes. If the patient has very soft bones, such as due to osteoporosis, a syringe may be threadably attached to the tube  132  and a fluid cement may be forced into a channel the tube  132  and out secondary channels  136  and  136 ′ between the sidewall of the shaft body  120  and femoral bone. Also, if the bones are soft a shaft with a larger diameter may be driven into the femur for a better bond, as long as the subchondral plate of the bone, the hard exterior layer of bone, is drilled to the size of the shaft.  
      The shaft  114  may be cannulated by at least one tube  124  which permits flushing and suctioning of the hip joint site prior to closing the incision and at a later date, if infection or other difficulties occur. At this time, the surgeon may attach and implant a drainage bag constructed from a formulation of silicon and rubber, not shown, to catch any drainage after the incision is closed. The incision may now be closed. At a later date it may be necessary to remove and replace the drainage bag.  
      If the surgeon determines, through measurements of the patient&#39;s bone structure and other factors such as age, athleticism and purpose of the prosthetic, that the bone structure can support an alternative prosthetic component  310 , the surgeon may select a prosthetic component  310  having fewer parts, reducing the complexity of the procedure. The steps for implantation of the prosthetic component  310  will largely be the same as the previous procedure, except a second segment shell is not inserted. All the steps leading up to and for installing the first segment  316  are the same as described above.  
      The next step is to insert a cup  406  through the sleeve  460 , the cup being sized and configured to be received into the interior cavity of the segmented shell  316 . The steps for attachment of the cup  406  to the shell  316 , by snap ring  445  are the same as discussed above for attaching the cup  106  to the second shell  70 , except the snap ring  445  is positioned in the segmented shell  316 .  
       FIG. 23  shows the completed installation of the prosthetic component  310 , with similar steps for inserting and fixing the shaft body  414  in the hole  458 .  
      The surgeon may determine that a second shell or shell liner may be formed as a single piece, as shown in  FIGS. 15 and 27 , that will pass through the hole  458  as shown in  FIG. 27 . Therefore, he may select the prosthetic component  610 , as shown in  FIG. 15 . The steps for installation of the prosthetic component  610  change only to the extent that the shell liner  6   f   70  (or second shell) is inserted and fixed in place prior to insertion of the cup  706 . The steps for installing the single piece second shell  670  will require that the shell  670  be sized to pass through the hole  458  for minimally invasive surgery. However, a reduced invasiveness may be obtained by inserting a shell or a cup through a separate incision providing limited access to the joint of a patient for introducing the shell or cup at the site of the joint, for example. The shell  670  will then be inserted into the interior of the first shell  616  and attached thereto by a snap ring, or otherwise, in the same manner that the cup  106  was attached to the second shell  70 , as discussed above. In one example, a solid (single piece) shell liner  616 , is made of polymer resin, which may be bonded to the first shell by pressure and temperature. The shaft  714  is installed by the same steps used to install the shaft  114 , as described above.  FIG. 27  shows the completed installation of a prosthetic component, with the ball  710  inserted into the cup  706 . In the example illustrated in  FIG. 27  the shaft body  714  is symmetric, providing a greater range of motion of the joint in one direction than in another.  
      The surgeon may determine that none of the segmented acetabulums will be appropriate and may insert any of the well known acetabulums directly into the prepared hip socket. These acetabulums may be selected that have a cup sized to receive the ball  110 ,  710 . The surgeon may determine that minimally invasive surgery is not preferred, but the surgeon may use a reduced invasiveness, as previously discussed. For example, the femoral head may be partially resected and the neck and head portion may be extended through an incision without fully and directly exposing the joint.  FIGS. 35A and 35B  illustrate two examples of ball and shaft assemblies  3510  and  3520 . These assemblies may be inserted by tapping and/or threading the femur, such as shown in  FIG. 37 , after removing a portion of the femoral head.  
      In  FIGS. 35A and 35B , the shaft and ball assembly  3510 ,  3520  may be inserted directly into a hole  3700  bored int the femur  3701 . Threads  3514  may be self-tapping or may mate with tapped threads. Holes  3516  may be used to inject adhesive and bone growth stimulant between threads  3514 , using one or more channels  3518  extending from a neck region. An exit hole  3519  may be used for injecting cement at the base of the shaft  3512 . In  FIG. 35B , the base  3529  is dome-shaped. The dome-shaped base  3529  may be made of flexible material, such as silicone rubber or may be rigid.  
      In  FIG. 36 a  tube  3530  is inserted in a hole bored into the femur by screwing the self tapping threads  3534  into the hole. Additional holes  3536  are located between threads for injection of a biocompatible adhesive and bone growth promoting material between the tube  3530  and the bone. A ball and shaft assembly may be mechanically or adhesively fixed in the sleeve formed by the tube  3530 .  
       FIGS. 28-33  disclose a preferred embodiment of an expandable drill bit  166 . In  FIG. 28 , the expandable drill bit is shown extending through the sleeve  160 . The expandable drill bit  166  comprises a plurality of blades  168 , a body  190  and a central hollow shaft  192  that includes a plurality of supports  194 . As seen in  FIG. 29 , the top plan view of the apparatus of  FIG. 32 , a support  194  is attached to the first end  196  of the shaft  192 , and at least one additional support  194 , as seen in  FIG. 28 , is spaced along the length of the shaft  192 . The support  194  has a hole  193  therethrough for receiving the guide wire  152  therethrough and a plurality of holes  195  that permits water to pass therethrough for flushing the site. The second end  198  of the shaft  192  is insertable in a drill motor  200 , as shown in  FIG. 34 , for rotation of the shaft  192  and the blades  168  of the expandable drill bit  166 .  
      Annular plate  202 , as shown in  FIGS. 32 and 33 , is attached to the first end  196  of the shaft  192  for attachment of the blades  168  to the shaft  192 . Each blade  168  has one end of a stiff wire  204  attached to a hole  206  in a respective blade of the plurality of blades  168 . The other end of the stiff wire  204  is attached to the end support plate  208  which is mounted to the first end  210  of the body  190 . The body  190  is slideably mounted on the shaft  192  for expansion and retraction of the blades  168 . A flexible wire  212  is passed through the holes  214  of the blades  168  as a safety measure to prevent the blades from expanding beyond a predetermined arc with a radius matching the finished radius of the acetabulum.  
      The hollow shaft  192  provides a means for delivering a flushing fluid to the cutting site through the port  216 , which is connected to a pressurized water supply, (not shown). The port  216  is connected to a fixed annular ring  218 , as seen in detail FIG.  29 , that is sealingly attached to an annular cavity  217  that extends about the body  190  so that the body  190  may rotate inside the ring and maintain the port  216  in fluid flow communication with annular cavity  217  and the hollow shaft  192 . A water source is attached to the port  216  by any well known means. Suction may be applied to port  220  by any well known suction device (not shown). Port  220  is connected in fluid flow communication with the interior of the body  190  through a fixed annular ring  224 , for rotation of the body  190  therein, and an annular cavity  222 . This permits suctioning the flush water and debris from the hip joint site through the plurality of holds  226  through the end plate  208  and the hollow body  190 .  
      As the body  190  is free to slide longitudinally on the shaft  192 , it is also free to rotate about the longitudinal axis of the shaft  192 . During a cutting operation the body  190  must rotate with the shaft  192  to maintain the wires  204  in proper orientation. Therefore, thumbscrew  228  is tightened to rotate the body  190  with the shaft  192  and is loosened when adjustments are made to the angle of the blades  168 . For adjustments to be made to the blades  168 , the drilling must be stopped, the thumb screw  228  loosened, and the body moved along the shaft  192 .  
      As discussed previously, each blade  168  has an outer cutting edge  170  and an inner cutting edge  172 . The outer cutting edge is used primarily for cutting through the head of the femur and cutting the acetabulum to its predetermined curvature. The inner cutting edge is used to further trim the neck and head of the femur to ensure adequate clearance for free movement of the prosthetic joint.  
      In  FIGS. 38 and 39 , two alternative examples are shown for fixing a shaft and ball assembly  3512  in a femur  3701 . In  FIG. 38 , threads and an adhesive cement injected between the threads are used to fix the femoral implant, while in  FIG. 39 , a nail  3910  is inserted through a hole  3590  and one or more pins, nails or screws  3912  may be used to further secure the nail  3910 , such as gamma nail. This procedure is less invasive than traditional total joint replacement. The addition of a nail  3910  may be desirable when there are fractures or substantial bone loss, for example.  
      The foregoing examples are not limiting and should not be used to limit the claims. Instead, the claims should be read in light of the specification as a whole according to their plain meaning to a person of ordinary skill in the field.