Patent Publication Number: US-2010114101-A1

Title: Method of resecting a femoral head for implantation of a femoral neck fixation prosthesis

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 10/779,353, filed Feb. 14, 2004, which is a continuation of U.S. patent application Ser. No. 10/228,907, filed Aug. 27, 2002, now U.S. Pat. No. 6,695,883, which claims priority to U.S. Provisional Application No. 60/371,837, filed Apr. 11, 2002. Priority is claimed to all of the above-mentioned applications and patents, and each application and patent is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention The present application relates generally to hip prostheses and more specifically to an improved method of implanting a femoral neck fixation prosthesis in the femoral neck. 
     2. Description of Related Art 
     A widely used design for replacement of the proximal portion of a femur employs an elongate, often curved, shaft that extends into the medullary canal of the femur. This design has the tendency to place unnatural stresses on the femur, which lead to pain and the consequent curtailment of activity for the patient. Further, present techniques can lead to proximal bone loss and call for the resection of the majority of the femoral neck. Current designs also call for fixing the prosthesis in the proximal third of the femur. The useful life of an intramedullary implant is often less than the expected life span of a young patient. 
     Previously known prostheses for replacing a femoral head that do not extend into the medullary canal have been mechanically complex or have proven troublesome in actual use. Huggler, U.S. Pat. No. 4,129,903 and Grimes, U.S. Pat. No. 4,795,473 are examples of prosthetic implants having a side plate attached to the exterior lateral side of the femur opposite the femoral head. Screws are used to secure the plate to the femur and one or more holes are drilled into the femur for securing the plate to the bone. The additional holes and the stresses at the site of fixation are believed to cause trauma to the bone. 
     Masini, U.S. Pat. No. 5,571,203 discloses a device having a shaft that extends through a resected portion of the proximal femur, positioned co-axially relative to the longitudinal axis of the femur. The device is secured by a screw or similar locking device that extends into the femur from the lateral side, just below the greater trochanter. It is believed that the natural forces applied to the prosthesis during normal hip motion result in the application of shear forces to the greater trochanter. The shear forces can be harmful to the greater trochanter and can permit micro-movement of the prosthesis on the unsecured side. 
     A conventional method for implanting the above types of femoral head implants is described in Campbell&#39;s Operative Orthopaedics, (Mosby, 7th ed., 1987) and typically includes making a large incision in the patient&#39;s lateral side at the hip joint and through the skin and muscle, dislocating the hip and then sawing off the femoral head. This method is considered invasive because of the need to dislocate the hip and cut through muscle surrounding the hip joint. Invasive procedures increase the trauma to the patient, the potential for complications, recovery time and the cost. 
     Replacement of the proximal portion of the femur is sometimes necessary due to degenerative bone disorders or trauma to otherwise healthy bone caused by accidental injury. In the latter instance it is desirable to replace the traumatized portion of the bone without causing further trauma to healthy bone. There is a need, therefore, for an implant that replaces a traumatized portion of the femur, but also significantly minimizes stress to the remaining healthy bone and that can be implanted by a method that is less invasive. 
     There are several other significant problems and issues relating to hip arthroplasty. One problem is encountered with the young, active patient. Younger patients are more likely to have failure of their primary arthroplasty both due to increased demand on the mechanical construct, and from a pure life expectancy standpoint. It follows that they are more likely to require a revision and a second revision, which may lead to a catastrophic bone loss situation. 
     Another problem relates to instability of the hip following implantation of the prosthesis. This problem still occurs at the same rate that it did 50 years ago. Larger femoral heads may decrease the incidence, but no other significant technical changes have occurred to effect the incidence of this serious complication. 
     Still another problem is related to bone loss in patients receiving hip prostheses. The overwhelming majority of present successful femoral prostheses achieve fixation at least as far distal as the proximal femoral metaphysis. When these prostheses fail, the next step usually involves diaphyseal fixation, often with a large diameter, stiff stem. 
     Leg length inequality is another problem associated with hip arthroplasty. An average lengthening of the leg of 1 centimeter is common. Lengthening is sometimes accepted for the sake of improved stability; however, leg length inequality has been reported as the primary reason why surgeons are sued after hip arthroplasty. 
     Finally, another problem associated with hip arthroplasty is surgical morbidity. The surgery usually involves significant blood loss, body fluid alterations, and pain. Shortly, the surgery is a big operation that hurts. It should be the goal of every compassionate surgeon to minimize these issues. If the operation can be made smaller, with less blood loss and less pain without diminishing long term results, every effort should be made to do so. 
     It would therefore be desirable to provide a femoral neck prosthesis and method for implanting the prosthesis that overcomes these significant disadvantages. 
     BRIEF SUMMARY OF THE INVENTION 
     It is therefore one object of the present invention to provide an improved apparatus and method for hip replacements. 
     It is another object of the present invention to provide an improved and less-invasive prosthesis and implantation method that replaces the femoral head while retaining a substantially intact femoral neck. 
     The foregoing objects are achieved as is now described. A femoral neck fixation prosthesis and method of implanting the prosthesis according to the principles of the present invention, reduce bone loss and avoid the other shortcomings of the prior art by allowing the fixation of a stable femoral head replacement while reducing the amount of the femur that must be removed and reamed for the insertion of the prosthesis. The preferred embodiment provides that the femoral head is attached to a fixation prosthesis, which extends coaxially through the central canal of the femoral neck, into the femur, and is then attached to the opposite lateral wall of the femur. In this manner, the prosthesis serves to imitate the original structure of the femoral neck. No other support members, either crosspins or arms extending into the length of the femur, are required. 
     The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a schematic of an anterior view of a prosthesis in accordance with the principles of the present invention; 
         FIGS. 2A-2H  depict a schematic of the cross-section at various levels of the body of a prosthesis in accordance with the present invention; 
         FIG. 3  illustrates joining members used with a prosthesis in accordance with the present invention; 
         FIG. 4  depicts a centering guide for placement of a starting pin in accordance with the present invention; 
         FIG. 5  illustrates how the center of rotation of the femoral head can be reproduced in accordance with the present invention; 
         FIG. 6  depicts a prosthesis in accordance with the principles of the present invention; 
         FIG. 7  illustrates a prosthesis in accordance with the principles of the present invention; 
         FIG. 8  depicts a posterior view of a human femur having a femoral head and a femoral neck; 
         FIG. 9  illustrates multiple cross-sectional views of the femoral head and femoral neck of  FIG. 8  taken at A-A, B-B, and C-C; 
         FIG. 10  depicts a perspective view of a femoral neck clamp according to the principles of the present invention positioned at an isthmus of the femoral neck of  FIG. 8 ; 
         FIG. 11  illustrates a perspective view of the femoral neck clamp of  FIG. 10 ; 
         FIG. 12  depicts a posterior view of a human femur with the femoral neck clamp of  FIG. 10  shown installed at an isthmus of the femoral neck, the handle members of the femoral neck clamp being omitted for clarity; 
         FIG. 13  illustrates a cross-sectional distal view of the femur and femoral neck clamp of  FIG. 12  taken at XIII-XIII; 
         FIG. 13A-13C  depict alternative shapes of an inferior clamping member of the femoral neck clamp of  FIG. 13 ; 
         FIG. 14  illustrates a posterior view of the femur and femoral neck clamp having superior and inferior clamping members, the inferior clamping member having a proximal clasp attached to a distal clasp by a connecting member according to principles of the present invention; 
         FIG. 15  depicts a posterior view of a femur and femoral neck clamp similar to those of  FIG. 14 , the femoral neck clamp having an alternative connecting member according to the principles of the present invention; 
         FIG. 16  illustrates a posterior view of a femur and femoral neck clamp similar to those of  FIG. 14 , the femoral neck clamp having an alternative connecting member according to the principles of the present invention; 
         FIG. 17  depicts a side view of a femoral neck clamp according to the principles of the present invention; 
         FIG. 18  illustrates a side view of a femoral neck clamp according to the principles of the present invention; 
         FIG. 19  depicts a posterior view of a human femur having a femoral neck clamp attached to a femoral neck of the femur, a locator shaft connected to the femoral neck clamp, and a pin locator guide slidingly received on the locator shaft; 
         FIG. 20  illustrates a perspective view of a human femur having a cutting guide positioned on pins placed in the femoral head using the pin locator guide of  FIG. 19 ; 
         FIG. 20A  depicts a method of resecting a femoral head according to the principles of the present invention; 
         FIG. 21  illustrates a perspective view of a starter guide according to the principles of the present invention and a human femur having the femoral head of the femur resected; 
         FIG. 22  depicts a posterior view of a human leg, including a human femur, and a drilling guide according to the principles of the present invention for preparing the femur for implantation of a femoral neck prosthesis; 
         FIG. 23  illustrates a side view of the drilling guide of  FIG. 22 ; 
         FIG. 23A  depicts a method of preparing a femur for implantation of a prosthesis according to the principles of the present invention; 
         FIG. 24  illustrates a posterior view of a femoral neck liner and a reamer path protector according to the principles of the present invention, the femoral neck liner being positioned within a femoral neck, and the reamer path protector being threadingly received by the femoral neck liner; 
         FIG. 25  depicts a side view of the reamer path protector and femoral neck liner of  FIG. 23 ; 
         FIG. 25A  illustrates a method of preparing an acetabulum according to the principles of the present invention; and 
         FIG. 26  depicts a method of implanting a prosthesis in a femur according to the principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof and in which is shown by way of illustration specific preferred embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is understood that other embodiments may be utilized and that logical mechanical, structural, and chemical changes may be made without departing from the spirit or scope of the invention. To avoid detail not necessary to enable those skilled in the art to practice the invention, the description may omit certain information known to those skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. 
     The present invention provides a femoral neck fixation prosthesis and a method of implanting the prosthesis which reduces bone loss and avoids the other shortcomings of the prior art by allowing the fixation of a stable femoral head replacement while reducing the amount of the femur, that must be removed and reamed for the insertion of the prosthesis. The preferred embodiment provides that the femoral head is attached to a fixation prosthesis, which extends coaxially through the central canal of the femoral neck, into the femur, and is then attached to the opposite lateral wall of the femur. In this manner, the prosthesis serves to imitate the original structure of the femoral head while substantially retaining the natural femoral neck. No other support members, either crosspins or arms extending into the length of the femur, are required. 
     A femoral neck fixation prosthesis in accordance with the principles of the present invention is designed to achieve fixation in the femoral neck with or without cement. Therefore, revision of the disclosed femoral neck fixation prosthesis would essentially become the complexity of a present day primary hip arthroplasty for the femoral component. The improved femoral neck fixation prosthesis would require an operation equivalent to a primary arthroplasty on the femoral side. Therefore it would be ideal for the younger patient, but would also be recommended for the older patients with accommodating anatomy. 
     The innovative method for implanting the femoral neck fixation prosthesis would allow less muscular dissection, and the capsule can be repaired anteriorly at the end of the procedure. The disclosed femoral neck fixation prosthesis is designed to be used with larger diameter femoral heads. The combination of these factors would significantly improve stability of the hip. The goal is to minimize the need for hip position precautions postoperatively. 
     One advantage of the preferred embodiment is that less bone would be resected initially using the femoral neck fixation prosthesis, and the stress would be transferred to the bone in the femoral neck. The metaphysis and the diaphysis of the proximal femur would be minimally disturbed. Only the femoral head itself will be resected. 
     Another advantage of the preferred embodiment, is that the femoral neck length and offset would be accurately measured and reproduced when using the femoral neck fixation prosthesis. Leg length inequality due to hip arthroplasty could be minimized, and muscle mechanics could be accurately restored. 
     Further, an operation using the femoral neck fixation prosthesis would be less invasive with less blood loss, less post operative pain, and less perioperative morbidity than an operation that employs the vast majority of commonly used prostheses. 
     The economic implications of a shorter hospital stay, fewer blood transfusions, and fewer medical complications are significant. 
     A femoral neck fixation prosthesis according to the principles of the present invention is shown in  FIG. 1 , wherein femur  100  is shown with femoral neck  105 , joining member  115 , and prosthetic head  110 . 
     An uncemented porous coated femoral prosthesis body  125  with a modular head  110  and joining member  115  is provided. The metal used is preferably either titanium or chrome-cobalt based, and can be any metal commonly used in hip prosthesis construction. The modulus of elasticity of such a short segment will be of less significance than in a standard femoral stem. The coating is preferably either sintered beads or plasma sprayed, depending on the type of metal used for the body of the prosthesis. 
     The body  125  of the prosthesis will preferably be available in various diameters, approximately every 1-1.5 mm. The length of the prosthesis will preferably be chosen from one or two lengths, approximately 30 mm. Most of the fixation and ingrowth of the bone to the prosthesis will occur in the first 10-20 mm. 
     As described in more detail below, fixation to the femur will be achieved by reaming the femoral neck  105  to accommodate a cylindrical porous coated sleeve body  125 , which is supported by a proximal collar and given distal stability with a compression screw  120  through the lateral wall of the femur just distal to the greater tuberosity (location  140 ). Reaming will be progressive until the cortex of the femoral neck is encountered. A femoral component ½ mm greater than the last diameter reamed will then be selected. 
     After insertion, the long axis of the body of the component body  125  will coincide with a longitudinal axis in the preoperative femur  100  corresponding to an imaginary line connecting the center of the femoral neck  105  with the center of the femoral head  110 . Resection of the femoral head will be measured such that the center of rotation of the femoral head  110  can be measured and reproduced. The femoral neck  105  will be reamed with a planar reamer that fits in the reamed canal of the femoral neck  105  to establish a flat surface. The proximal body  125  of the prosthesis will have the female end of a morse taper to allow the attachment of the joining member  115 . 
     A compression screw  120  passes through the center of the body of the prosthesis. This screw attaches to a barrel nut  130  in the lateral wall of the femur at point  140  and preferably has a hexagonal head. The screw  120  is preferably smooth in the segment within the body of the prosthesis and has threads on the distal end. The tunnel through the body of the prosthesis forms a snug fit around the smooth portion of the screw  120 . The barrel nut  130  is preferably angled to be flush with the lateral side of the femur at point  140 . The head of the screw  120  is preferably located in the base of the morse taper in the body  125  of the femoral component. This screw  120  adds stability to the construct by giving antero-posterior and varus-valgus stability to the body  125  of the prosthesis and by compressing the prosthesis on the neck  105  of the femur  100 . These screws will be available in various lengths. 
     It is important to note that this innovative design allows the prosthesis to be installed and used without requiring any other fastener on the femur. In particular, the preferred embodiment does not require any additional screws or other fasteners to be placed in the femur, and does not require any sort of support plate on the lateral wall of the femur. 
     Male-male morse taper joining member  115  acts as a joining portion in connecting the body  125  of the prosthesis to the femoral head  110 . Adjustments in joining member length will occur in this segment with several lengths of joining member segments available for each femoral body and femoral head. The joining member segment needed to exactly reproduce the center of rotation of the femoral head will be known based on the amount of bone resected. In this embodiment, the joining member  115  has male morse tapers  135  on each side, and will have a variable-length section in between the morse tapers to fit the specific patient. 
     The femoral head  110  will have a female morse taper to connect to the joining member  115 . Femoral heads  110  will be of various diameters depending on the acetabulum, and several exemplary sizes are shown in  FIG. 1 . Ideally, larger femoral head diameters (e.g., 36 mm to 50 mm) are used to both improve stability and prevent impingement of the neck on the acetabular rim. The femoral head  110  is preferably polished chrome-cobalt, as the industry standard, but other materials can be used. 
     In another embodiment of the present invention, a de-rotation component is added to reduce the likelihood of the rotation of the prosthesis within the femoral neck. This can be accomplished with a pin or stem with grooves or slots that passes through the lateral cortex into the body of the prosthesis. This would then be compressed with a screw, which would be put through the head end of the body of the prosthesis into the stem. 
     It should be clear that the femoral neck fixation prostheses described herein can be used with or without cement. 
       FIGS. 2A-2C  show several cross-sectional views of the cylindrical porous coated body  225  of the prosthesis of the preferred embodiment.  FIG. 2A  shows a longitudinal cross-section of the body  225 . In this view, a collar  248  at the proximal end of the body  225  is illustrated, as is the female morse taper cavity  246 , which is fit to receive the joining member. The collar  248  is configured to abut the proximal end of the resected femoral neck. Communicating with cavity  246  is tubular channel  247  which will receive the compression screw. Below the collar  248 , the exterior of the body  225  has a porous coated layer  249 . 
     While the preferred embodiment has a substantially circular cross-section, as shown in  FIGS. 2A-2C , the body member  225  can also be configured with a triangular ( FIG. 2E ), scalloped ( FIG. 2F ), oval ( FIG. 2H ), or fluted ( FIG. 2G ) cross-section. 
       FIG. 2B  shows a lateral cross-section of body  225  as cut across line B of  FIG. 2A . In  FIG. 2B , the cavity  246  is shown, and the proximal collar  248  is also illustrated. 
       FIG. 2C  shows a lateral cross-section of body  225  as cut across line C of  FIG. 2A . In  FIG. 2C , channel  247  for the compression screw is shown passing through the center of body  225 . On the exterior of body  225  is shown the porous coated layer  249 . A cross-section across line D of  FIG. 2A  is the same as described for line C of that FIG. 
       FIG. 3  shows joining members  316 / 317 / 318  of various sizes, which can be used for patients with differing requirements. Each joining member  316 / 317 / 318  has a morse taper on each end, and a variable-length straight section connecting the morse tapers. 
       FIG. 4  depicts the centering guide for placement of the starting pin in accordance with the principles of the present invention. In this FIG., femoral neck gripping clamp  405  is to grip and hold the femoral neck after the femoral head centering device  410  has been placed over the patient&#39;s femoral head. 
     The femoral neck gripping clamp  405  is expanded or contracted using adjustment piece  420 , which operates gears  415 . Cannulated rod  425 , which is connected to femoral head centering device  410 , allows pin insertion into the cannula at  435 . 
     Free nut  430  is used to tighten the femoral head centering device  410 . The centering guide shown in  FIG. 4  is preferably made of a stiff metal, and can also be used as a retractor to expose the femoral head. 
       FIG. 5  depicts how the center of rotation of the femoral head can be reproduced in accordance with a preferred embodiment of the present invention. First, distance A from the head to the lateral cortex is measured. After the femoral head is removed, distance B, from the cut surface to the lateral cortex, is measured. The diameter D of the femoral head is also measured. When these measurements are known, distance C is calculated using the formula 
         C =( A−D/ 2)− B    
     Distance C then represents the distance from the cut surface of the femoral neck that the prosthetic femoral head center-of-rotation should be placed in order to reproduce the pre-operative femoral head center-of-rotation. 
     In another embodiment shown in  FIG. 6 , compression screw  620 , preferably with washer  645 , is inserted through the lateral wall of the femur at location  640  and screwed into the body  625  of the femoral component. This simplifies the barrel nut portion of the design shown in  FIG. 1 . It would require that the screw  620  be of various lengths that would engage the body  625  of the prosthesis without reaching the depth of the hole in the femoral prosthesis. The body of the prosthesis would preferably be longer, using optional extension  650  to provide enough length so that the compression screw will be stable within the body of the prosthesis. 
     The remainder of  FIG. 6  is similar to  FIG. 1 . In this FIG., femur  600  is shown with femoral neck  605 , joining member  615 , and prosthetic head  610 . 
     This embodiment provides an uncemented porous coated femoral prosthesis body  625  with a modular head  610  and joining member  615 . The body  625  of the prosthesis include threads  655  for receiving screw  620 . 
     As described in more detail below, fixation to the femur will be achieved by reaming the femoral neck  605  to accommodate a cylindrical porous coated sleeve body  625 , which is supported by a proximal collar and given distal stability with a compression screw  620  through the lateral wall of the femur just distal to the greater tuberosity (location  640 ). 
     After insertion, the long axis of the body of the component body  625  will coincide with a longitudinal axis in the preoperative femur  600  corresponding to an imaginary line connecting the center of the femoral neck  605  with the center of the femoral head  610 . Resection of the femoral head will be measured such that the center of rotation of the femoral head  610  can be measured and reproduced as discussed with reference to  FIG. 5 . The femoral neck  605  will be reamed with a flat reamer that fits in the reamed canal of the femoral neck  605  to establish a flat surface. The proximal body  625  of the prosthesis will have the female end of a morse taper to allow the attachment of the femoral neck  615 . 
     Compression screw  620  passes through the center of the body of the prosthesis. The screw  620  is preferably smooth in the segment within the body of the prosthesis and has threads on the proximal end, for engaging threads  655 . The tunnel through the body of the prosthesis forms a snug fit around the smooth portion of the screw  620 . Screw  620  adds stability to the construct by giving antero-posterior and varus-valgus stability to the body  625  of the prosthesis and by compressing the prosthesis on the neck  605  of the femur  600 . These screws will be available in various lengths. 
     Male-male morse taper joining member  615  connects the body  625  of the prosthesis to the femoral head  610 . Adjustments in joining member neck length will occur in this segment with several lengths of joining member segments available for each femoral body and femoral head. The joining member segment needed to exactly reproduce the center of rotation of the femoral head will be known based on the amount of bone resected. 
     The femoral head  610  will have a female morse taper to connect to the joining member  615 . Femoral heads  610  will be of various diameters depending on the acetabulum. Ideally larger femoral head diameters (e.g., 36 mm to 60 mm) are used to both improve stability and prevent impingement of the neck on the acetabular rim. The femoral head  610  is preferably polished chrome-cobalt, as the industry standard, but other materials can be used. 
       FIG. 7  shows a preferred embodiment of the femoral neck fixation prosthesis of the present invention. If the compression screw  720 , with washer  745 , is inserted through the lateral wall of the femur at  740 , the length of the body  725  of the prosthesis may not be long enough to provide adequate stability for the compression screw  720 . In order to provide this stability for the compression screw, a fixed length joining member  760  on the body of the prosthesis would be necessary to act as a joining member, abandoning the modular joining member ( 115  in  FIG. 1 ). The varied lengths required on the joining member would be incorporated into the femoral head either with separate individual lengths for each head diameter (2 to 3 for each diameter femoral head) or by using an interposing piece of metal to provide additional neck length. The latter is done with several femoral components available on the market today. 
     The femoral neck fixation prosthesis is implanted by first preparing the femur for reception of the prosthesis. Referring to  FIG. 8 , several orientations and anatomical features relative to a femur  811  should first be defined to more easily understand the process of preparing the femur and implanting the prosthesis. As used herein, the term “medial” shall mean “pertaining to the middle,” while the term “lateral” shall mean “pertaining to the side.” The femur  811  includes a medial side  813  and a lateral side  815 . The term “proximal” shall mean “nearest the point of attachment, center of the body, or point of reference,” while the term “distal” shall mean “the opposite of proximal, or farthest from the center, from a medial line, or from the trunk.” The terms proximal and distal are generally used to convey positional or directional information relative to a particular feature, so it would not be entirely proper to refer to a proximal “side” of the femur or a distal “side” of the femur. However, these terms can be demonstrated by comparing some of the basic anatomy of the femur. Femur  811  includes a femoral head  821 , a femoral neck  823 , a shaft  825 , a greater trochanter  827 , and a lesser trochanter  829 . Since the femoral head  811  serves as a point of attachment when it is received by the acetabulum (not shown), the femoral head  821  is located proximal to the femoral neck  823  and the shaft  825 . The shaft  825  is located distal to both the femoral neck  823  and the femoral head  821 . As used herein the term “superior” shall mean “higher than or situated above something else,” while the term “inferior” shall mean “beneath or lower.” The term “anterior” shall mean “before or in front of” and shall generally refer to the ventral or abdominal side of the body. The trem “posterior” shall mean “toward the rear” and shall generally refer to the back or dorsal side of the body. A posterior side  831  of the femur  811  is shown in  FIG. 8 , while the anterior side is hidden from view in  FIG. 8 . 
     A longitudinal axis  845  of the femoral neck is difficult to precisely define because the geometry of the femoral neck  823  is usually not perfectly cylindrical. Theoretically speaking, if the femoral neck  823  were sectioned along its length at a finite number of cross-sectional planes (e.g. B-B and C-C in  FIG. 8 ), and the center of each cross-section were determined, the line passing through the center of rotation of the femoral head (described previously with reference to  FIG. 5 ) and passing through an average of the centers of the cross-sections would likely represent the longitudinal axis  845  of the femoral neck  823 . In reality, it is difficult to locate the center of each cross-section of the femoral neck  823 . It is also difficult to locate the plane at which each cross-section would be taken. Theoretically, each cross-section is located at a plane perpendicular to the longitudinal axis  845 , but this presents a somewhat circular method for determining the orientation of the cross-sectional planes and the longitudinal axis  845 . 
     One method for determining the proper orientation of the cross-sectional planes would be to envision an isthmus  849  of the femoral neck  823 . The isthmus  849  is the narrowest point on the femoral neck  823  when viewed from the anterior or posterior side of the femur  811 . Visualization of the posterior side  831  of the femur  811  allows a lateral line to be constructed across the femoral neck  823  at the isthmus  849 . In  FIG. 8 , the line at section C-C represents an isthmus plane  851 , which is a cross-sectional plane extending through the femur in an antero-posterior direction. The visualization of this plane at the isthmus  849  of the femoral neck  823  allows a close approximation of a plane that would be perpendicular to the longitudinal axis  845  of the femur  811 . Other cross-sectional planes visualized through the femoral neck  823  would be parallel to the isthmus plane at the isthmus  849 . 
     In practice, the femoral neck  823  is not actually cut at each of the cross-sectional planes discussed above. Rather, the visualization of these planes is helpful in determining, theoretically, where the longitudinal axis  845  of the femoral neck  823  would lie. It would be sufficient to define the longitudinal axis  845  as the line passing through the center of rotation of the femoral head  821  and the center of the femoral neck  823  at the isthmus  849 . However, as previously mentioned, it would also be appropriate and perhaps more accurate to define the longitudinal axis  845  as the line passing through the center of rotation of the femoral head  821  and the average of the centers of the femoral neck  823  taken at several cross-sections, all of which are parallel to the isthmus plane  851 . It should also be noted that for some patients, the center of rotation of the femoral head may not necessarily coincide with the longitudinal axis  845 . 
     Referring to  FIG. 9 , the visualization of the “center” of the femoral neck is not necessarily simple due to the varying geometry of the femoral neck  823 . For example, a cross-section taken at A-A in a region of transition between the femoral head  821  and the femoral neck  823  is approximately round. However, the cross-sectional shapes of the femoral neck  823  taken at B-B and C-C are not perfectly round, and instead have various protrusions and other anatomical features that make it difficult to locate the center point of the cross-section. A cross-section from a more proximal portion of the femoral neck  823  is illustrated at B-B and demonstrates that this portion of the neck is somewhat circular in shape. Cross-section C-C at the isthmus  849  of the femoral neck  823  illustrates several prominent features that cause the femoral neck  823  to deviate from a perfectly round shape. The features of the femoral neck at C-C include an antero-superior ridge  850  and a postero-inferior ridge  855 . The antero-superior ridge  850  is a pronounced feature of the femoral neck  823  at this part of the femoral neck  823  and joins the greater trochanter  827  in a region distal to the isthmus  849 . The postero-inferior ridge  855  is less pronounced and joins the lesser trochanter  829  in a region distal to the isthmus  849 . The femoral neck  823  includes a relatively flat superior surface  857 , while an inferior surface  859  is more rounded. These anatomical features of any particular femur will vary slightly and could vary greatly from person to person. 
     Referring still to  FIGS. 8 and 9 , the center of any given cross-section will be at the mean geometric center for any particular cross-section. When several cross-sections are visualized along the femoral neck  823 , the mean geometric centers of all the cross-sections may not be aligned such that the centers can be connected by a line. In this particular instance, a line representing longitudinal axis  845  could be drawn through the center of rotation of the femoral head and through the plurality of cross-sectional centers so as to minimize deviation with respect to the plurality of cross-sectional centers. If the femoral head is misshapen, the longitudinal axis  845  may be considered only with respect to the cross-sectional centers and not the center of rotation of the femoral head. 
     Alternatively, the center of each cross-section could be located based on the shape of the cancellous bone at that cross-section. Since the prosthesis according to the principles of the present invention is to be implanted within the cancellous bone, it may be more appropriate to define the center of the femoral neck  823  based on the shape and location of the cancellous bone. The center of each cross-section would be the point at which a circle circumscribed around the point would most fully contact the surrounding cortex. 
     The “location” and/or “visualization” of the longitudinal axis  845  of the femoral neck  823  is theoretical and is discussed to more easily explain how the femoral neck fixation prosthesis is oriented and implanted within the femur  811 . It is not necessarily required that the longitudinal axis  845  be found prior to implanting the prosthesis; however, it is important to note that in most cases, the femoral neck fixation prosthesis will be installed in the femur such that a longitudinal axis of the prosthesis is substantially coaxial to the longitudinal axis  845  of the femoral neck  823  as described above. This implantation could be accomplished by using non-invasive techniques such as X-rays or magnetic resonance imaging (MRI) to visualize and locate the longitudinal axis  845  of the femoral head  823 , but in most instances, the prosthesis will be implanted using specialized tools that properly orient the prosthesis based on anatomical landmarks on the femoral neck. We believe that the use of these tools and anatomical landmarks will closely align the prosthesis with the longitudinal axis of the femoral neck, thereby obviating the need for calculating or identifying the longitudinal axis during the procedure. 
     It will be appreciated by those of ordinary skill in the art that certain femoral anatomical variations among patients may result in the prosthesis being implanted such that the longitudinal axis of the prosthesis is not coaxial to the longitudinal axis  845  of the femoral neck  823 . In fact, the implantation of the prosthesis in some patients could result in the longitudinal axis of the prosthesis being located as much as 5 to 10 degrees from the longitudinal axis  845  of the femoral neck  823 . 
     Implantation of the femoral neck fixation prosthesis is accomplished by resecting the femoral head  821 , reaming at least one passage through the femoral neck, reaming the acetabulum, and implanting the femoral neck fixation prosthesis into the reamed passage. Access to the femoral head and femoral neck is accomplished by making a small incision in the gluteus maximus to expose the hip joint. The femoral head  821  is dislocated from the acetabulum in a manner similar to that employed in current hip arthroplasty procedures. The leg of the patient is then internally rotated (i.e. rotated such that the toe of the patient&#39;s foot are rotated toward a medial plane of the body) to expose the femoral head and neck through the incision. Following exposure, the femoral head may be resected as explained below from the internally rotated position. The remaining procedures (i.e. reaming the passages, reaming the acetabulum, and implanting the femoral neck fixation prosthesis) are performed as described below with the patient&#39;s leg in either the internally-rotated position or in a neutral position (i.e. non-rotated position). The procedures for preparing the femur and implanting the prosthesis could alternatively be accomplished by rotating the patient&#39;s leg externally if the location of the initial incision were moved. 
     Referring to  FIGS. 10-13 , a femoral neck clamp  1011  according to principles of the present invention assists in locating the cutting plane at which the femoral head  821  is to be resected. The femoral neck clamp  1011  does this by locating the isthmus  849  of the femoral neck  823  by grasping anatomical landmarks on the femoral neck, such as the antero-superior ridge  850  and the inferior region of the femoral neck  823 . Again, the isthmus  849  defines a line that is substantially perpendicular to the longitudinal axis  845  of the femoral neck  823 . 
     The femoral neck clamp  1011  includes an inferior clamping member  1013  and a superior clamping member  1015 . A locator shaft guide member  1021  includes a cylindrical passage  1023  and is attached to either the inferior clamping member  1013  or the superior clamping member  1015 . The superior clamping member  1015  preferably includes an arcuate region  1025  for securely gripping the antero-superior ridge  850  (see  FIG. 9 ) of the femoral neck  823 ; however, the superior clamping member  1015  could be substantially flat with no arcuate region. The inferior clamping member  1013  preferably includes a proximal clasp  1031  and a distal clasp  1033  that are connected by a connecting member  1035 . The inferior clamping member  1013  cradles the inferior region of the femoral neck  823  with preferably at least two points of contact occurring between the femoral neck  823  and each of the proximal and distal clasps  1031 ,  1033 . It is important to note that while it is preferred that the shape of the proximal and distal clasps  1031 ,  1033  is V-shaped, the shape could be hemi-circular (see  FIG. 13A ), square (see  FIG. 13B ), polygonal (see  FIG. 13C ), or any other shape that provides adequate contact with the femoral neck  823 . While the preferred embodiment includes the presence of a proximal and distal clasp, the inferior clamping member  1013  may include only one clasp that is preferably aligned with the superior clamping member  1015  to locate the isthmus  849  of the femoral neck  823 . 
     Referring still to  FIGS. 10 and 11 , the femoral neck clamp  1011  preferably includes a handle portion  1041  having a pair of handle members  1043  biased apart by a spring member  1045 . The spring member  1045  is preferably made from sheets of spring steel and shaped to hold the handle members  1043  apart in an open position. However, the spring member  1045  could be any device used to apply such a force, including without limitation a helical spring, a leaf spring, or a resilient bushing. A pair of rods  1047  is rigidly attached to one of the handle members, and each rod  1047  passes through an aperture  1049  in the other handle member  1043 . Since the handle members  1043  are not pivotally attached, the rods  1047  assist in guiding the movement of the handle members  1043  relative to one another. By applying a force to each handle member  1043  directed toward the other handle members  1043  (i.e. by squeezing the handle members  1043 ), a surgeon can decrease the distance between the inferior and superior clamping members  1013 ,  1015  in order to position the clamping members securely around the femoral neck. When the squeezing force applied to the handle members  1043  is released or relaxed, the spring member  1045  pushes the handle members  1043  apart, thereby returning the femoral neck clamp  1011  to the open position. The configuration of the handle members  1043 , rods  1047 , and spring member  1045  allow the inferior and superior clamping members  1013 ,  1015  to move in translational, parallel fashion relative to one another when the handle members  1043  are squeezed. Since rotation of the handle members  1043  relative to one another is avoided, the inferior and superior clamping members  1013 ,  1015  are allowed to more effectively grip the appropriate anatomical features of the femoral neck  823 . A locking member  1051  may be attached to the handle portion  1041  to lock the inferior and superior clamping members  1013 ,  1015  once positioned around the femoral neck  823 . The locking member  1051  shown in  FIG. 11  is pivotally attached to one of the handle members  1043  and is rotatably positionable to engage a plurality of teeth  1053  on at least one of the rods  1047 . In  FIG. 11 , two locking members  1051  are shown. 
     The femoral neck clamp  1011  is used to locate the isthmus plane  851 , which is represented by a line in  FIG. 12  at the isthmus  849  of the femoral neck  823 . To find the isthmus plane  851 , the inferior and superior clamping members  1013 ,  1015  are first positioned on inferior and superior sides of the femoral neck  823 , respectively, with the superior clamping member  1015  and the proximal clasp  1031  visually aligned with an area of the femoral neck  823  that appears to be the isthmus  849 . As the handle members  1043  are squeezed, the superior clamping member  1015  and the proximal clasp  1031  grip the femoral neck  823  in the area of the isthmus  849 . Further squeezing of the handle members  1043  and gentle side-to-side manipulation of the femoral neck clamp  1011  in a direction approximately parallel to the longitudinal axis  845  of the femoral neck  823  allows the superior clamping member  1015  and the proximal clasp  1031  to settle at the isthmus  849  of the femoral neck  823 . Further alignment of the femoral neck clamp  1011  is ensured by the distal clasp  1033 , which prevents the femoral neck clamp  1011  from rotating about the line representing isthmus plane  851  in  FIG. 12 . The distal clasp  1033  accomplishes this by providing a second point of contact for the inferior clamping member  1013  in the inferior region of the femoral neck  823 . Preventing rotation of the femoral neck clamp  1011  about the line representing isthmus plane  851  in  FIG. 12  could also be accomplished by having an inferior clamping member  1013  that included a single clasp with a wider area of contact on the inferior region of the femoral neck  823 . However, widening either the inferior clamping member  1013  or the superior clamping member  1015  too much will decrease the ability of the femoral neck clamp  1011  to find the isthmus  849  since the inferior and superior clamping members  1013 ,  1015  will be unable to properly settle into the concave portions of the femoral neck  823  as illustrated in  FIG. 12 . 
     Both the inferior and superior clamping members  1013 ,  1015  take advantage of anatomical landmarks present on the femoral neck  823  to locate the isthmus  849  and the isthmus plane  851 , which is typically substantially perpendicular to the longitudinal axis  845  of the femoral neck  823 . As previously mentioned, the superior clamping member  1015  primarily contacts and, depending on whether it includes an arcuate region  1025 , cradles the antero-superior ridge  850  (see  FIG. 13 ). The inferior clamping member  1013 , including the proximal and distal clasps  1031 ,  1033 , preferably is formed in one of the shapes previously described (see  FIGS. 13-13C ) to cradle the postero-inferior ridge  855  and other portions of the inferior region of the femoral neck  823 . The distal clasp  1033  of the inferior clamping member  1013  provides stability to the femoral neck clamp  1011  to prevent rotation of the femoral neck clamp  1011  about the line representing isthmus plane  851  in  FIG. 12 . The distal clasp  1033  is preferably not directly connected to either handle member  1043 , but rather is connected to proximal clasp  1031  by the connecting member  1035 , which allows rotation of the distal clasp  1033  relative to the proximal clasp  1031 . By connecting the distal clasp  1033  to the proximal clasp  1031  (as opposed to the handle members  1043 ), the application of force through the handle members  1043  is directed primarily to the superior clamping member  1015  and the proximal clasp  1031 . This allows the superior clamping member  1015  and the proximal clasp  1031  to more easily locate the isthmus  849  of the femoral neck  823 , while the distal clasp  1033  maintains rotational stability of the femoral neck clamp  1011  without causing the superior clamping member  1015  and the proximal clasp  1031  to shift positions along the femoral neck  823 . 
     Referring to  FIGS. 14-16  in the drawings, several different variations of the connecting member  1035  are shown, each of which would be suitable to allow rotation of the distal clasp  1033 . In  FIG. 14 , a connecting member  1411  is rigidly connected to the distal clasp  1033  and pivotally connected to the proximal clasp  1031 . A torsion spring (not shown) is operably connected to the proximal clasp  1031  and the connecting member  1411  to bias the distal clasp  1033  toward the femoral neck  823  in a counter-clockwise direction (with respect to the view shown in  FIG. 14 ). In  FIG. 15 , a connecting member  1511  is rigidly connected to both the proximal and distal clasps  1031 ,  1033 . The connecting member  1511  is preferably made from a resilient material such as spring steel that allows rotation of the distal clasp  1033  relative to the proximal clasp  1031 , but provides sufficient force to the distal clasp  1033  to firmly contact the femoral neck  823 . In  FIG. 16 , a connecting member  1611  is rigidly attached to the distal clasp  1031  and is pivotally attached to the proximal clasp  1031 . The connecting member includes a slot  1615 ; and a fastener  1617 , preferably a screw, a bolt, or a locking pin, is received through the slot  1615  and is attached to the proximal clasp  1031 . The fastener  1617  allows rotation of the distal clasp  1033  to be selectively chosen. After rotating the distal clasp  1033  enough to firmly contact the femoral neck  823 , the fastener can be tightened or locked in place to prevent further rotation of the distal clasp  1033  relative to the proximal clasp  1031 . 
     Referring again to  FIGS. 10-12 , the locator shaft guide member  1021  of the femoral neck clamp  1011  is connected to the superior clamping member  1015  or the handle member  1043  adjacent the superior clamping member  1015 . The locator shaft guide member  1021  is oriented such that the cylindrical passage  1023  of the locator shaft guide member  1021  is substantially parallel to the longitudinal axis  845  of the femoral neck  823  when the femoral neck clamp  1011  is finally positioned at the isthmus  849 . Typically, the locator shaft guide member  1021  will be rigidly connected to the superior clamping member  1015  because the anatomy of most femurs is such that the positioning of femoral neck clamp  1011  at the isthmus  849  will provide automatic, parallel alignment of the locator shaft guide member  1021  relative to the longitudinal axis  845  of the femoral neck  823 . However, it is conceivable that certain anatomical features of some femurs may prevent proper alignment of the locator shaft guide member  1021 , so the locator shaft guide member  1021  may be adjustably mounted to the superior clamping member  1015  to allow for rotational adjustment and visual alignment of the locator shaft guide member  1021  relative to the longitudinal axis  845 . 
     Referring to  FIG. 17 , a femoral neck clamp  1711  according to the principles of the present invention includes an inferior clamping member  1713  and a superior clamping member  1715  similar to those of femoral neck clamp  1011 . Femoral neck clamp  1711  includes a parallelogram, four-bar-linkage mechanism  1721  to provide translational movement (as opposed to rotational movement) of the inferior clamping member  1713  relative to the superior clamping member  1715 . Linkage mechanism  1721  includes an inferior handle member  1743  pivotally connected to a superior handle member  1745 . Superior handle member  1745  is pivotally connected at one end to a coupler link  1747  that is rigidly connected to the superior clamping member  1715 . A side link  1751  is pivotally connected at one end to the coupler link  1747  and at another end to the inferior handle member  1743 . The side link  1751  and the portion of the superior handle member  1745  extending between the inferior handle member  1743  and the coupler link  1747  are preferably parallel and equal in length. The coupler link  1747  and the portion of the inferior handle member  1743  extending between the superior handle member  1745  and the side link  1751  are preferably parallel and equal in length. A torsion spring  1753 , or other spring mechanism, may be operably connected to the inferior handle member  1743  and superior handle member  1745  to bias the handle members  1743 ,  1745 , and thus the inferior and superior clamping members  1713 ,  1715 , apart. A locking member  1755  may be pivotally attached to an end of either the inferior or superior handle members  1743 ,  1745 . Preferably, the locking member  1755  includes a plurality of teeth  1759  adapted to engage the other handle member  1743 ,  1745  and thus lock the inferior clamping member  1713  relative to the superior clamping member  1715 . A locator shaft guide member  1765  is connected to either the inferior clamping member  1713  or the superior clamping member  1715  similar to locator shaft guide member  1021  of  FIG. 12 . Alternatively, the locator shaft guide member  1765  could be connected to coupler link  1747 , inferior handle member  1743 , or superior handle member  1745  near the inferior and superior clamping members  1713 ,  1715 . 
     Referring to  FIG. 18 , a femoral neck clamp  1811  according to the principles of the present invention includes an inferior clamping member  1813  and a superior clamping member  1815  similar to those of femoral neck clamp  1011 . Femoral neck clamp  1811  further includes an inferior handle member  1843  pivotally connected to a superior handle member  1845 . A torsion spring  1853 , or other spring mechanism, may be operably connected to the inferior handle member  1843  and superior handle member  1845  to bias the handle members  1843 ,  1845 , and thus the inferior and superior clamping members  1813 ,  1815 , apart. A locking member  1855  may be pivotally attached to an end of either the inferior or superior handle members  1843 ,  1845 . Preferably, the locking member  1855  includes a plurality of teeth  1859  adapted to engage the other handle member  1843 ,  1845  and thus lock the inferior clamping member  1813  relative to the superior clamping member  1815 . A locator shaft guide member  1865  is connected to either the inferior clamping member  1813  or the superior clamping member  1815  similar to locator shaft guide member  1013  of  FIG. 12 . 
     Referring to  FIG. 19 , the femoral neck clamp  1011  (could also be femoral neck clamp  1711  or  1811 ) has been positioned around the femoral neck  823  at the isthmus  849  such that the superior clamping member  1015  and the proximal clasp  1031  of the inferior clamping member  1013  are aligned with the isthmus plane  851 . The distal clasp  1033  also engages the femoral neck  823  to prevent rotation of the femoral neck clamp  1011  about the line representing isthmus plane  851 . Following positioning of the femoral neck clamp  1011  at the isthmus  849 , the locator shaft guide member  1021  is automatically aligned such that a longitudinal axis of the cylindrical passage  1023  of the locator shaft guide member  1021  is oriented at an angle of approximately ninety (90) degrees to the isthmus plane  851 . 
     A locator shaft  1911  is positioned within the cylindrical passage  1023  of the locator shaft guide member  1021  after the femoral neck clamp  1011  has been positioned at the isthmus  849  of the femoral neck  823 . A base plate  1915  is rigidly connected to an end of the locator shaft  1911  such that following insertion of the locator shaft  1911  in the cylindrical passage  1023 , the locator shaft  1911  can be advanced in a distal/lateral direction until the base plate  1915  abuts the femoral head  821 . Indicia  1921  in the form of ruled demarcations is printed along the locator shaft  1911  for accurately positioning a pin locator guide  1925 , which is slidingly received on the locator shaft  1911 . Pin locator guide  1925  preferably includes at least two spaced apart holes  1931  that may be located on one side of the locator shaft  1911 , or as illustrated in  FIG. 19 , may be located on opposite sides of the locator shaft  1911 . Holes  1931  are positioned on the pin locator guide  1925  such that a line connecting the center of the holes  1931  is preferably parallel to the isthmus plane  851 . 
     Referring to  FIGS. 19 and 20 , by slidably positioning the pin locator guide  1925  along the locator shaft  1911  a selectable distance from the proximal end of the femoral head  821 , pins  2011  can be inserted through the holes  1931  on the pin locator guide  1925 . The placement of the pins  2011  in the femoral head  821  fixes the previously determined orientation of the isthmus plane  851 , which allows the femoral neck clamp  1011  to be removed from the femur. In  FIG. 20 , a cutting guide  2021  includes a pair of holes  2027  that are spaced apart the same distance as the holes on the pin locator guide  1925 . The cutting guide  2021  is placed over the pins  2011  such that the pins  2011  are received by the holes  2027 . A cutting slot  2025  is positioned on the cutting guide  2021  such that it is oriented substantially parallel to a line connecting the centers of the two holes  2027 . When installed on the pins  2011  as shown in  FIG. 20 , the cutting guide  2021  places the cutting slot  2025  a known distance from the pins  2011  to allow resection of the femoral head  821  along a cutting plane (not shown) that is substantially parallel to the isthmus plane  851 . The femoral head  821  is resected from the femur  811  by inserting a cutting blade or other cutting tool through the cutting slot  2025  and cutting through that portion of the femur  811 . 
     As mentioned previously, the locator shaft  1911  includes indicia  1921  in the form of ruled demarcations that are spaced apart precise distances. These demarcations can be used to precisely locate the cutting plane relative to the proximal end of the femoral head  821 . The amount of resection that will be performed depends on several factors. A prosthetic femoral head will be chosen to match the measured diameter of the patient&#39;s native femoral head. This is done to insure that the center of rotation is closely matched by the prosthesis and that the length of the patient&#39;s leg is not significantly lengthened or shortened. Based on the diameter chosen for the prosthetic femoral head, a height of the prosthetic femoral head (measured along longitudinal axis  845 ) will be known. This height equates to the amount of bone resected from the proximal end of the native femoral head  823 . Since the distance between the holes  2027  on the cutting guide  2021  and the cutting slot  2025  is known, the pin locator guide  1925  can be accurately positioned along the locator shaft  1911  using the indicia  1921  to place the pin locator guide  1925  according to the amount of bone that needs to be resected. The placement of the pins  2011  using the pin locator guide  1925  then allows the cutting slot  2025  to be accurately positioned at the correct location to remove the correct length of bone. 
     It will be apparent to one of ordinary skill in the art that the cutting guide  2021  of the present invention could be combined with the femoral neck clamp  1011  to eliminate the need for a locator shaft  1911  and a pin locator guide  1925 . The combination clamp and cutting guide would allow the clamp to be positioned at the isthmus  849  of the femoral neck  823  as previously described, but would provide a slot or other guide to allow resection of the femoral head along a cutting plane substantially parallel to the isthmus plane  851 . The slot or guide would be adjustable relative to the isthmus plane  851  to allow a measured amount of bone to be resected from the femur  811 . A cutting guide that aligns the cutting plane a measured distance from the isthmus plane  851  would be particularly useful in the event that the femoral head is missing, deformed, substantially misshapen, or broken. Measurements could be performed preoperatively using radiographic measurement techniques (e.g. X-ray). 
     Referring to  FIG. 20A , a method of resecting a femoral head from a femur having a femoral neck  2051  is illustrated. The first step at  2055  includes positioning a locator shaft adjacent an exterior surface of the femoral head and substantially parallel to a longitudinal axis of the femoral neck. At step  2059  a pin locator guide having a least two holes is positioned along the locator shaft. At step  2063  a pin is inserted through each of the two holes in the pin locator guide and into the femoral head. The femoral head is resected by aligning a cutting guide relative to the pins at step  2065 . 
     Following resection of the femoral head  821 , a proximal neck surface  2111  is exposed that is substantially parallel to the isthmus plane  851 . Progressive reaming and drilling of the femoral neck  823  is needed to prepare passages between the proximal neck surface  2111  and the lateral side  815  of the femur  821 . With the patient&#39;s leg still in an internally rotated position (or alternatively in an externally rotated position), a starter guide  2121  having a positioning portion  2125  and a guide portion  2127  is placed against the proximal neck surface  2111  such that the surface of the positioning portion  2125  opposite the guide portion  2127  mates with the proximal neck surface  2111 . The starter guide  2121  further includes a guide passage  2131  that passes through both the guide portion  2127  and the positioning portion  2125  such that a longitudinal axis of the guide passage  2131  is substantially perpendicular to the proximal neck surface  2111  when the starter guide  2121  is placed against the proximal neck surface  2111 . A starter passage, or main passage, or primary passage  2141  (represented in  FIG. 21  by dashed lines) is formed in the femoral neck  823  from the proximal neck surface  2111  by first drilling a small hole  2145  using a drill bit or other boring tool placed in the guide passage  2131 . The starter passage is preferably drilled only partially into the femoral neck, and not through the lateral side  815  of the femur. When placing the starter guide  2121  and drilling the hole  2145 , it is preferred to visualize the approximate center of the femoral neck on the proximal neck surface  2111  so that the hole  2145  is approximately centered within the femoral neck  823 . 
     After drilling the hole  2145 , the starter guide  2121  is removed from the proximal neck surface  2111 , and the femoral neck  823  is progressively reamed until the hole  2145  extends to the cortical bone of the femoral neck  823 , thereby forming the starter passage  2141 . In practice, depending on the anatomical shape of the patient&#39;s femoral neck  823 , it may only be possible to form the starter passage  2141  to contact the cortical bone at two points of contact. It is of course preferable to maximize the number of contacts of the cortical bone, and in most instances, it will be possible to contact the cortical bone in at least three locations without significantly decreasing the wall thickness of the cortex in any location, The starter passage  2141  is reamed to a depth that is preferably equal to the longitudinal length of the body  125 ,  625 ,  725  (see  FIGS. 1 ,  6  and  7 ) of the femoral neck prosthesis. The final diameter of the starter passage  2141 , which is determined by how much reaming is needed to contact the cortical bone, will be slightly less than the chosen diameter of the body  125 ,  625 ,  725  of the prosthesis. 
     The method for forming the starter passage  2141  described above is largely based on visualization of the center of the femoral neck and formation of a hole  2145 . In an alternative embodiment, a guide may be placed flush against the proximal neck surface  2111  to orient a reamer at a ninety (90) degree angle to the proximal neck surface  2111  and center the reamer relative to the longitudinal axis of the femoral neck. The neck is sequentially reamed until the starter passage  2141  extends to the cortex. In another embodiment, a guide pin may be inserted into the femoral neck substantially parallel to the longitudinal axis of the femoral neck. The pin may be placed based on visualization or guided into place with a guide that is fixed relative to the femoral neck. The guide pin would be used to direct sequential reaming of the starter passage  2141 . 
     Referring to  FIGS. 22 and 23 , a drilling guide  2211  having an anchor member  2215  rigidly connected by a connecting member  2217  to an alignment sleeve  2219  is used to drill a distal passage, or fastener passage, or secondary passage  2221  (represented in  FIG. 22  by dashed lines) from the lateral side  815  of the femur  811 . The alignment sleeve  2219  includes an alignment passage  2225  for receiving a drill bit or other boring tool. The connecting member  2217  may be C-shaped and connects the anchor member  2215  to the alignment sleeve  2219  such that a longitudinal axis of the alignment passage  2225  is coaxial to the longitudinal axis of the anchor member  2215 , both of which are coaxial to a longitudinal axis  2227  of the drilling guide  2211 . The anchor member  2215  is cylindrical and sized to fit within the starter passage  2141 . The anchor member  2215  could be interchangeable to allow different diameters to be used to properly fit within the starter passage  2141  of a particular patient. Alternatively, the anchor member  2215  could be tapered to allow a snug fit within starter passages  2141  of several different diameters. The anchor member  2215  may also include a collar  2231  for further stabilizing the drilling guide  2211  against the proximal neck surface  2111  when inserted into the starter passage  2141 . 
     After positioning the anchor member  2215  within the starter passage  2141 , the alignment sleeve  2219  is located on the lateral side  815  of the femur  811 . The patient&#39;s skin and other soft tissue  2233  are located between the alignment sleeve  2219  and the femur  821 . The leg of the patient is then rotated to a neutral position, and an incision  2235  is made through the soft tissue of the patient in the vicinity of the alignment sleeve  2219 . A drilling bit  2241  or other boring tool is inserted through the alignment passage  2225  of the alignment sleeve  2219  for drilling the distal passage  2221  to join the starter passage  2141 . Because the alignment sleeve  2219  is coaxial to the anchor member  2215  and because the anchor member  2215  is securely positioned within the starter passage  2141 , the distal passage  2221  is easily formed coaxial to the starter passage  2221 . 
     As shown in  FIG. 22 , the distal passage  2221  is typically smaller in diameter than the starter passage  2141 , since the distal passage  2221  will receive the fastener  120 ,  620 ,  720  (see  FIGS. 1 ,  6 , and  7 ) for securing to the body  126 ,  625 ,  725  of the femoral neck fixation prosthesis. 
     The primary reason for using a drilling guide  2211  to complete drilling through the femur is that it is less desirable to drill a hole completely through the femur from the proximal neck surface  2111  toward the lateral side  815  of the femur  811 . When drilling from the proximal neck surface  2111 , the patient&#39;s leg would be in the internally rotated position. It is not as safe to drill through the lateral side  815  of the femur  811  when the leg is internally rotated because the drill bit may contact and sever vital anatomy, such as the femoral artery or other vessels and nerves, upon exiting the femur  811 . Since use of the drilling guide  2211  allows the leg to be rotated back to the neutral position, drilling can proceed from the lateral side  815  of the femur  811  without fear of contacting vital anatomy. 
     Referring to  FIG. 23A , a method of preparing a femur for implantation of a femoral neck fixation prosthesis  2321  includes two steps. The first step at  2325  includes first forming a main passage in the femoral neck from a medial side of the femur substantially coaxial to a longitudinal axis of a femoral neck. The second step at  2329  includes second forming a secondary passage from a lateral side of the femur that is coaxial to and joins the main passage. 
     Although the preparation of the femur for implantation of the prosthesis includes forming two separate passages from different sides of the femur, the starter and distal passages could be formed from the same side of the femur. Following the formation of the starter passage  2141 , a guide may be placed within the starter passage  2141  to guide drilling of the distal passage  2221  from the proximal side of the femoral neck  823 . Since the leg of the patient would likely be in an internally rotated position during this drilling procedure, care would be taken to only slightly penetrate the cortex on the lateral side of the femur  821 . This would help avoid major arteries and nerves in the patient&#39;s leg. After forming both the starter and distal passages  2141 ,  2221  from the medial side of the femur, the drilling guide  2211  could be used to place the fastener  120 ,  620 ,  720  in the femur during the implantation of the femoral neck prosthesis, which is described in more detail below. 
     After forming both the starter passage  2141  and the distal passage  2221 , the femur  811  is capable of receiving the femoral neck fixation prosthesis. However, prior to implantation of the prosthesis, it may be desirable to prepare the acetabulum for receipt of an acetabular component (not shown) that will mate with the head of the femoral neck fixation prosthesis. The starter and distal passages  2141 ,  2221  may be used to guide the preparation of the acetabulum, which initially involves reaming. 
     Referring to  FIGS. 24 and 25 , a reamer path protector  2411  includes an insertion end  2415  and a handle end  2419 . The insertion end preferably includes a plurality of threads  2421 , while the handle end  2419  includes a hand guard  2425 . A passage  2427  passes through the reamer path protector  2411 . A femoral neck liner  2431  is also provided and includes a main body  2435  having a passage  2437  and a collar  2439 . The passage  2437  includes internal threads  2441  at an end of the main body  2335  opposite collar  2339 . 
     In operation, the reamer path protector  2411  is inserted from the lateral side  815  of the femur  811  and into the distal passage  2221 . The femoral neck liner  2431  is inserted from the proximal neck surface  2111  into the starter passage  2141  until the collar  2439  mates with the proximal neck surface  2111 . The femoral neck liner  2431  is sized in diameter the same as or slightly less than the diameter of the starter passage  2141 . As is the case with the anchor member  2215  (see  FIG. 22 ) discussed previously, the femoral neck liner  2431  could be provided in different sizes to fit variously sized starter passages  2141 , or the femoral neck liner  2431  could be tapered. After inserting the femoral neck liner  2431 , the reamer path protector  2411  is advanced further into the distal passage  2221  until it contacts the femoral neck liner  2431 . The reamer path protector  2411  is then rotated to engage the threads  2421  with internal threads  2441 . The attachment mechanism between the reamer path protector  2411  and the femoral neck liner  2431  is not required to be accomplished by a threaded connection. The connection could be formed by any mechanism that would allow the components to be easily disassembled following reaming of the acetabulum. 
     When the reamer path protector  2411  is securely fastened to the femoral neck liner  2431 , a sufficient portion of the reamer path protector  2411  remains extending outside of the femur  811  to allow gripping by the surgeon or other person who will ream the acetabulum. The reamer path protector  2411  is therefore gripped in this area, and a reamer shaft  2451  is inserted through the passage  2427  and the passage  2437  to connect to a reamer head  2453  near the proximal neck surface  2111 . The acetabulum is then reamed by rotating the patient&#39;s leg into a neutral position and applying power to rotate the reamer shaft  2451  and reamer head  2453  from the lateral side  815  of the femur  811 . Some internal rotation of the femur  811  may also be necessary depending on the position of the femur  811  relative to flexion/extension and abduction/adduction. The acetabulum is progressively reamed until enough material has been removed to accommodate the acetabular component of the prosthesis. By reaming the acetabulum through the distal and starter passages  2221 ,  2141  formed in the femur  811 , a highly effective reaming process is accomplished. Since the patient&#39;s leg is positioned in the neutral position during the reaming process, and since the reamer head  2353  is connected to the reamer shaft  2451  along the same axis as that about which the head and body of the prosthesis will be oriented, the acetabulum can be efficiently reamed to closely match the shape of the head of the prosthesis. 
     Following the reaming process, the reamer head  2453  is removed from the reamer shaft  2451 , and the reamer shaft  2451  is removed from the femoral neck liner  2431  and the reamer path protector  2411 . An impactor shaft (not shown) may be inserted into the reamer path protector  2411  and the femoral neck liner  2431  similar to the original insertion of the reamer shaft  2451 . The impactor shaft is releasably connected to an impactor head (not shown) near the proximal neck surface  2111 . The impactor shaft and impactor head are used to apply force to and seat the acetabular component of the prosthesis in the reamed acetabulum. After the acetabular component is firmly seated, the impactor shaft, impactor head, femoral neck liner  2431 , and the reamer path protector  2411  are disassembled and removed from the femur  811   
     Referring to  FIG. 25A , a method for preparing an acetabulum for receiving a head of a femoral prosthesis  2521  is illustrated. A first step  2525  includes forming a primary passage within the femur substantially coaxial to a longitudinal axis of the femoral neck. At step  2529 , a secondary passage is formed from a lateral side of the femur that joins and is coaxial to the primary passage. Step  2531  includes inserting a reamer path protector having a reamer passage within the secondary passage. A reamer shaft is inserted through the reamer passage at step  2535 . A reamer head is attached to the reamer shaft at step  2539 , and the acetabulum is reamed at step  2541 . 
     The femoral neck fixation prosthesis is implanted into the femur  811  by inserting the body  125 ,  625 ,  725  of the prosthesis into the starter passage  2141 . Preferably, the diameter of the body  125 ,  625 ,  725  is sized slightly larger than the diameter of the starter passage  2141  such that a secure fit within the starter passage  2141  is obtained when the body  125 ,  625 ,  725  is driven into the starter passage  2141 . The starter passage  2141  is deep enough to accommodate the body  125 ,  625 ,  725  of the prosthesis and allow the collar of the body  125 ,  625 ,  725  to mate with the proximal neck surface  2111 . 
     The fastener  120 ,  620 ,  720  is then inserted into the distal passage  2221  from the lateral side  815  of the femur  811 . To properly feed the fastener  120 ,  620 ,  720  through the soft tissue  2233  (see  FIG. 22 ) of the patient&#39;s leg and into the distal passage  2221 , a small diameter pin can be used to locate and mark the passage when the leg is in the neutral position. The fastener  120 ,  620 ,  720 , which may be canullated (i.e. having a passage down the center of the shaft), can then be placed onto the pin and fed into the distal passage  2221 . The fastener  120 ,  620 ,  720  is advanced into the distal passage  2221  until it contacts the body  125 ,  625 ,  725  of the prosthesis, at which time the fastener  120 ,  620 ,  720  is threadingly connected to the body  125 ,  625 ,  725  to secure the body within the femur  811 . The head  110 ,  610 ,  710  of the prosthesis is then installed on the morse taper  115 ,  615 ,  760  of the prosthesis be impacting the head of the prosthesis. 
     Referring to  FIG. 26 , a method of implanting a prosthesis in a femur  2611  according the principles of the present invention is illustrated. At step  2615  a main passage is formed in the femoral neck from a medial side of the femur substantially coaxial to a longitudinal axis of the femoral neck. At step  2619  a fastener passage is formed from a lateral side of the femur that is coaxial to and joins the main passage. Step  2623  includes providing a femoral neck prosthesis having a body member connected to a head member. At step  2627  a portion of the body member is inserted in the main passage. A fastener is inserted into the fastener passage at step  2633 . At step  2637  the fastener is connected to the body member to secure the femoral neck prosthesis within the femur. 
     As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a tremendous range of applications, and accordingly the scope of patented subject matter is not limited by any of the specific exemplary teachings given. 
     While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.