Abstract:
A pin allows for convenient and noninvasive adjustment and tightening relative to the bone to correct and/or avoid loosening of the pin and attached external fixator. In one embodiment, the pin includes a shank extending from a head toward a distal tip end of the pin. Adjacent to the distal tip of the pin is a threaded region with a varying pitch and the shank of the pin is tapered or conical having an increasing minor and/or major diameter along the pin from the tip end. In an alternative embodiment, an anchor is provided on the distal tip for engagement with the far cortex of the bone. The anchor includes a tapered region proximate the tip that decreases in diameter. A split ferrule, expansion bushing or collar is seated on the tapered region. The shank of the pin also includes a threaded region on which a washer and nut are engaged for rotational movement longitudinally on the shank. The pin is initially inserted through a hole in the bone so that the tapered region adjacent the distal tip projects through the distal edge of the bone and the expansion ferrule is seated within the far cortex of the bone. The ferrule advances along the tapered region and expands to securely seat within the far cortex of the bone for anchoring the external fixator. In either embodiment, subsequent to initial pin installation into the bone, if the pin becomes loose relative to the bone, additional rotation of the pin re-establishes a secure pin-bone interface.

Description:
This is a divisional of U.S. patent application Ser. No. 10/891,270, filed Jul. 14, 2004, which in turn claimed the benefit of U.S. Provisional Patent Application Ser. No. 60/490,215, filed Jul. 25, 2003 and each of these prior applications is hereby incorporated by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   This invention relates generally to an external fixation system for bones, and more specifically, to a pin assembly for use in attachment of the external fixation system to the bones and an associated method of use. 
   In the practice of medicine, and particularly orthopedic medicine, treatment of certain injuries or conditions is accomplished with a system including an external frame that is attached to the bones with pins or wires. Such systems are commonly referred to as orthopedic external fixators or external skeletal fixators. External fixators are commonly utilized to treat acute fractures of the skeleton, soft tissue injuries, delayed union of the skeleton when bones are slow to heal, non-union of the skeleton when bones have not healed, mal-union whereby broken or fractured bones have healed in a mal position, congenital deformities whereby bones develop a mal position, bone infections, bone tumors and bone lengthening, widening or twisting applications. Well known types of external fixators generally include the Ilizarov fixator that is often used for repair of heavily damaged or heavily traumatized bone, the Taylor frame and the limb reconstruction system (LRS). 
   The use of many external fixators requires multiple pins that are placed through the skin and into the bone. The ends of the pins that stick out from the skin are attached to a rigid framework thereby holding the fractured bone stable so that it can heal. 
   In many applications, external fixators of this type are preferred over plaster casts because an external fixator can hold the bone fragments much more rigidly than a cast. The advantages of external fixators are that the external frames are quick and easy to apply and provide excellent rigidity and support for specific fractures. If the fracture is open or compound (meaning the skin over the fracture is penetrated) many orthopedic surgeons prefer external fixators because they reliably and securely position the traumatized bone. Examples of external fixators are shown in U.S. Pat. Nos. 5,067,954; 4,978,348; 4,978,347; and 4,615,338 each listing Gavriil Ilizarov as inventor and incorporated herein by reference. Other well known external fixation devices are commercially available from Orthofix Srl of Verona, Italy and Smith &amp; Nephew, Inc. of Memphis, Tenn. 
   External fixator frames vary considerably in design and capabilities, and may include multiple or single bars, rods or rings and a number of pins or wires connecting the frame to the bony skeleton. The pins or wires may extend completely through the bony skeleton and out each side of the limb or may extend through the bony skeleton and out only one side of the limb. Pins that extend completely through the bony skeleton and out both sides of the limb are commonly referred to as “transfixation pins.” Pins, which extend through the bony skeleton and out only one side of the limb are commonly referred to as “half pins.” 
   The exact location and orientation of the wires and pins are determined by the physician according to anatomic and mechanical factors. In the course of treatment with external fixation, the precise placement of the external fixator and the associated pins and wires is critical for the proper positioning and healing of the traumatized bone. Even slight movement or repositioning of the pins and associated external fixator frame may result in misalignment and repositioning of the traumatized bone often requiring corrective measures by the treating physician including removal, replacement or readjustment of the pins and/or external fixator in a subsequent surgical or similar procedure. 
   While external fixators of this type have proven to be very beneficial in many applications, certain disadvantages associated with external fixators are readily acknowledged. Specifically, infection is a primary concern with the use of such devices. The pins protrude through the muscle, subcutaneous tissue and skin. Because biological tissue does not adhere to the metal pins, a chronic break remains in the skin around the pins. Healthy skin, by its nature, is an effective barrier to bacteria entry. During insertion of the pin this barrier is compromised. Scar tissue formed around a pin or wire during healing lacks the blood vessels normally found in healthy tissue. The lack of blood flow at the pin or wire insertion site hinders systemic antibiotic delivery to the site where bacteria can freely enter the body. As a result, a rather common complication involving external fixators is infection occurring around the pins. 
   Investigations have shown that some superficial infection occurs in approximately fifty percent of the pins used in external fixators. A single external fixator utilizes numerous pins (about 6-12 pins typically) thereby increasing the opportunity for infection. The severities of the infections range from a superficial skin infection to a deep bone infection, i.e., osteomyelitis. Deep bone infections, however, resulting in loosening of the pin-bone interface necessitating return to the operating room occur more rarely. 
   In addition to the obvious problems associated with the infection that must be addressed, pin tract infection for external fixators commonly leads to pin loosening and, in some cases, requires premature pin removal and replacement with a return to the operating room for sterile pin insertion. The pins securing the external fixator to the bones work loose in the bone that leads to failure of the device. If the external fixator is removed or additional pins are required, the healing process can be significantly compromised. This significantly undermines the effectiveness of the external fixator for proper bone/soft tissue healing. 
   In addition to infection, pin loosening can result from a number of factors including pin design and placement, bone necrosis due to surgical trauma during pin insertion, abnormal contact pressure at the pin-bone interface from unfavorable axial loading on the pins due to faulty frame design, or delay in fracture healing. 
   As a result, an external fixator and associated pin attachment system which avoids the above-described problems associated with loosening and provides consistently reliable and secure attachment of the fixation device to the bone is required even in potentially infectious environments. 
   SUMMARY OF THE INVENTION 
   These and other objectives of the invention have been attained by a pin for use with an external fixator and the associated combination and method of use. The pin according to this invention allows for convenient and noninvasive adjustment and tightening of the pin relative to the bone to correct and/or avoid loosening of the pin and attached external fixator. Advantageously, this is readily accomplished without the requirement of adding additional pins to the external fixator or returning to the operating room for removal or replacement of the pins that have become loose as a result of infection or any other cause. Moreover, the pins according to this invention are compatible with standard insertion, installation and adjustment hardware, techniques and procedures for known pin designs. Furthermore, pin designs according to this invention accommodate a variety of coatings that further minimize the likelihood of loosening of the pin relative to the bone. Pin designs according to this invention can be manufactured from a variety of materials that are more compatible with the physical characteristics of the bone structure, external fixator and other criteria, including the modulus of elasticity of the bone being repaired. 
   In certain embodiments of this invention, the pin is a half pin that extends into the proximal bone cortex through the muscles and skin to the outside of the body for attachment to the external fixator. In one embodiment, the pin according to this invention includes a head for securely mounting to the external fixator and a shank extending from the head toward a distal tip end of the pin. Adjacent to the distal tip of the pin in one embodiment is a threaded region in which the shank of the pin is tapered or conical having an increasing minor and/or major diameter along the pin from the tip end. Moreover, the threaded region of the pin includes a varying pitch thread such that the spacing between adjacent threads increases. Therefore, subsequent to initial pin installation into the bone and attachment of the external fixator, if the pin becomes loose relative to the bone, additional rotation of the pin advances the insertion of the pin into the bone and the increasing pitch of the threads and the conical shape of the pin increases the grip of the pin in the bone to re-establish a secure pin-bone interface. As the pin is inserted further into the bone, the threads engage portions of the bone that are not infected or worn as a result of movement of the pin in the bone. Advantageously, the distal tip of the pin according to one embodiment includes a self-tapping flute to assist in the insertion into the bone and advancement of the pin therein. 
   In an alternative embodiment of the pin according to this invention, an anchor is provided on the distal tip for engagement with the far cortex of the bone. In one form according to this invention, the anchor includes a tapered region proximate the tip that decreases in diameter. A split ferrule, expansion bushing or collar is seated on the tapered region adjacent a bulk head on the shank of the pin. The shank of the pin also includes a threaded region on which a washer and nut are threadably mounted for movement longitudinally on the shank. The pin is initially inserted through a hole in the bone so that the tapered region adjacent the distal tip projects through the distal edge of the bone and the expansion ferrule is seated within the far cortex of the bone. The washer and nut combination are seated on the proximal surface of the near cortex of the bone and rotation of the nut relative to the pin retracts the pin relative to the bone and expands the ferrule. The ferrule advances along the tapered region and expands to securely seat within the far cortex of the bone for anchoring the external fixator. 
   Subsequently, if the pin becomes loose relative to the bone as a result of an infection or other factors, an adjustment of the pin through rotation relative to the nut further retracts the pin and expands the ferrule to re-establish a secure pin-bone interface in the far cortex of the bone. Advantageously, the anchor according to this invention provides for secure initial installation of the pin and reliable, non-invasive adjustment of the pin for a continued stable pin-bone interface and positioning of the external fixator throughout the healing process. 
   In any embodiment according to this invention, a cannula may be provided through the longitudinal centerline of the pin to assist in the initial positioning and placement thereof. Additionally, pins according to this invention may be advantageously manufactured from materials that are consistent with the physical properties of the bone and associated external fixator. Specifically, the pin may be manufactured from not only stainless steel, but also titanium, nitonol, ceramics, bioabsorbables, carbon fiber composites and the like. These materials provide for more strength, less weight and a more comparable modulus of elasticity with respect to the bone structure to provide a more natural and consistent flexure of the pin-bone union to assist in healing of the traumatized bone. Moreover, the pin material may be coated with hydroxyapatite or an antibiotic as is well known. 
   Therefore, as a result of a pin according to this invention and associated external fixators, reliable and secure attachment of the fixator is provided throughout the entire length of the installation of the fixator. Pin loosening as a result of infection or other sources is avoided through noninvasive and easily accomplished adjustment of the pin to maintain secure and stable positioning of the fixator and attached bone structure without resort to the operating room, additional pin installation or other drastic treatment options. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of an exemplary external fixator mounted to a bone with a pin according to one embodiment of this invention; 
       FIGS. 2 and 3  are plan views of first and second alternative embodiments of the pin for use with the external fixator according to this invention; 
       FIG. 4  is a cross-sectional view of a bone with the pin of  FIG. 2  inserted therein for mounting the external fixator; 
       FIG. 5  is a view similar to  FIG. 4  of the pin shown in  FIG. 3 ; 
       FIG. 6  is a view similar to  FIG. 5  with the pin adjusted to overcome loosening of the pin relative to the bone; 
       FIG. 7  is a plan view a third alternative embodiment of the pin for use with the external fixator according to this invention; 
       FIG. 8  is a cross-sectional view of a bone, surrounding tissue and associated bodily components with the pin of  FIG. 7  inserted therein before deployment and tightening for mounting the external fixator frame; and 
       FIG. 9  is a view similar to  FIG. 8  with the pin securely deployed in the bone for mounting the external fixator frame. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , an exemplary fixator  10  mounted to a bone  12  via pins  14  according to this invention is shown. The external fixator  10  is used in orthopedic surgery for stabilizing fractured bones  12 . However, it should be understood that the invention is not limited to use with any specific external fixator design or associated device. The pin  14  of this invention is readily employed in other bone, spine, or other applications with or without a fixator  10 . 
   External fixators  10  can be used as an external skeletal fixation system to secure or affix a first bone element relative to a second bone element in the event of a break, trauma, fracture, nonunion, malunion or the like. As shown in  FIG. 1 , the external fixator  10  may include a pair of rings  16  surrounding the bone  12 . The rings  16  are connected together by adjustable struts  18 . Examples of representative external fixators which are compatible with this invention are disclosed in U.S. Pat. Nos. 5,961,515; 4,978,348; 4,978,347; 4,615,338; 5,062,844; 4,662,365; 5,951,556; 6,102,911; 6,461,358; 6,491,694; and 5,971,984, each of which is hereby incorporated by reference in its entirety. 
   The rings  16  and/or adjustable struts  18  as well as other components in combination provide an external fixator frame adapted to be mounted to the bone  12  by a number of pins  14 . The pins  14  are coupled to clamp blocks  20  mounted on the rings  16 . The word “pin” is used herein to encompass standard transfixation pins, half pins, wires, screws, bolts, spine implants and the like. 
   As shown particularly in  FIGS. 1 ,  4 - 6  and  8 - 9 , the pins  14  of this invention are intended to be coupled to the external fixator  10  frame and inserted into the bone  12 . Generally, the bone  12  includes a near cortex  22  and a far cortex  24  spaced therefrom. Between the near and far cortex portions  22 ,  24  of the bone  12  is a cancellous bone region  26 . While the bone  12  shown and generally described herein is referred to as a cortical bone that makes up most of the long bones in the arms and legs, this invention is readily used with both cortical and spongy (cancellous) bone structures. Additional applications for this invention include use as a rotator cuff anchor in the proximal humerus or soft tissue anterior cruciate ligament (ACL) reconstruction of the knee. 
   Despite substantial improvement in metallurgy, design and understanding of the biomechanical forces acting on the fixator frame  10 , the pin-bone interface has remained a major site of complications leading to treatment failure in known fixator and pin-bone interface connections. The pin-bone interface is the most critical component of the fixator system. The biomechanical factors that influence the “rigidity” of an external fixation frame include the pin diameter, pin design, location of the pins in relation to the bone fracture site, as well as to each other, the location of the connecting bar/strut and its distance from the underlying bone, the degree of osseous contact, which influences how much of a physiological load would be borne by either the fixator frame alone or by the bone and frame together. Pin loosening can result from a number of factors including pin design and placement, bone necrosis due to surgical trauma during pin insertion, abnormal contact pressure at the pin-bone interface from unfavorable loading on the pins due to faulty frame design, or delay in fracture healing. 
   Three embodiments of the pin  14  according to this invention are shown in  FIGS. 2 ,  3  and  7 . Each pin  14   a ,  14   b ,  14   c  in  FIGS. 2 ,  3  and  7 , respectively, includes a head end  28  with an operational configuration such as a D flat  30  or other configuration for mating compatibility with drills or the like commonly found in operating rooms such as an AO Quick Connect for convenient and ready attachment to a drill, powered operator (not shown) or the like. Each pin  14   a ,  14   b ,  14   c  likewise includes an elongated shank  32  having a threaded region  34  with a helical thread  36  projecting from the shank  32  and a terminal region  38  including a tip  40  of the pin  14 . 
   Preferably, the pins  14   a ,  14   b ,  14   c  according to this invention as shown in  FIGS. 4-6  and  8 - 9  each include a longitudinal, centrally positioned cannula  42 . A cannula passage  42  in the pin  14  assists in proper alignment and initial positioning and insertion of the pin  14  through an established technique. Additionally, the cannula  42  of any embodiment of the pin  14  is in communication with each of a number of fenestrations  70 , as shown in pin  14   c  of  FIG. 7 , extending at least a portion of the length of the shank  32  of the pin  14   c  for convenient delivery of fluids or gases to the bone  12  and/or surrounding tissues. This can be very beneficial for treatment of infections through the delivery of antibiotics or other medications in either a hospital, operating room, out patient facility or doctor&#39;s office environment. 
   Preferably each pin  14  according to this invention includes a hydroxyapatite (HA) or antibiotic coating  44  to aid in a secure pin-bone interface. The HA coating  44  may extend a substantial portion of the length of the pin  14 , including the threaded region  34  as well as other regions of the pin  14 . Moreover, the pin  14  according to this invention is preferably manufactured from steel, stainless steel and more preferably from titanium, nitonol, ceramic, bioabsorbable or composite (carbon fiber) materials. Most preferably, the pin material has a modulus of elasticity closely matching that of the modulus of elasticity of bone to provide a more natural flex and consistent reaction to stress and movement between the bone  12  and pin  14  materials. 
   In a first embodiment of the pin  14   a  shown in  FIG. 2 , the threaded region  34  of the pin  14   a  is tapered or conical such that a minor diameter of the shank  32  decreases along the shank  32  toward the tip  40  of the pin  14   a . The major diameter of the thread  36  on the shank  32  may likewise decrease toward the tip  40 . Advantageously, the pitch or spacing  46  between adjacent portions of the helical thread  36  on the pin  14   a  of  FIG. 2  increases from the tip  40  toward the head end  28 . The pitch  46  increases in the threaded region  34  to provide for a secure and stable attachment of the pin  14   a  to the bone  12 . 
   The increasing pitch and conical tapered shape of the threaded region  34  of the pin  14   a  in  FIG. 2  advantageously overcomes many of the sources of pin  14   a  loosening. After initial insertion of the pins  14   a  in the bone, periodic adjustment of the pins  14   a  is available without returning to the operating room for additional procedures or more invasive office/out-patient procedures. Rotation of the pin  14   a  relative to the bone  12  to further insert the pin  14   a  into the bone  12  corrects any loosening that may have occurred after initial insertion. The pin  14   a  may loosen within the original hole  48  ( FIG. 4 ) in the bone  12  and continued rotation and adjustment of the pin  14   a  will advance the pin  14   a  in the hole  48  thereby increasing the diameter of the hole  48  in each portion of the bone  12  and consequently re-establishing a secure pin-bone interface and secure attachment of the fixator  10 . The increased pitch  46  of the thread  36  alone or in combination with the conical, tapered configuration of the pin  14   a  allows the pin  14   a  to achieve increased holding power and overcome potential infected regions IF ( FIGS. 4 &amp; 5 ) of the bone that may have resulted in pin  14  loosening. Removal of the pin  14   a  of FIG.  2  is easily accomplished by reverse rotation of the pin  14   a  for retraction out of the bone  12 . 
   The pin  14   a  of  FIG. 2  also includes a self-tapping flute  50  proximate the tip end  40  for easier initial insertion into the bone  12 . The self-tapping flute  50  provides the advantage that predrilling a hole in the bone  12  for insertion of the pin  14   a  is not required. 
   Referring to  FIG. 3 , an alternative embodiment of the pin  14  according to this invention is shown. The pin  14   b  includes the head end  28  as well as the threaded region  34 . The threaded region  34  of the pin  14   b  has a generally constant diameter and constant pitch for the helical thread  36 . The threaded region  34  is compatible with internal threads on a nut  52  and washer  54  combination that may be separate pieces or welded together. Adjacent the terminal tip  40   b  of the pin  14   b  according to this embodiment is an anchor  56 . In one embodiment, the anchor  56  includes a blunt tip  40   b  and a tapered region  58  extending from the blunt tip  40   b . The tapered region  58  has a larger circumference and diameter adjacent the blunt tip  40   b , each of which decreases axially toward a circumferentially extending bulkhead  60 . A split ferrule, bushing or collar  62  which may be constructed of a more ductile material than the pin  14   b  for ease of expansion/contraction is mounted circumferentially around the pin  14   b  on the tapered region  58 . The ferrule  62  is split circumferentially and includes a gap  64 . 
   The pin  14   b  of  FIG. 3  is initially inserted after the skin (not shown) is incised and the subcutaneous tissue, deep fascia and muscle are dissected to the bone  12 . Preferably, the bone  12  is drilled and tapped so that a hole  48  is drilled into the near and far cortex  22 ,  24  and cancellous regions  26  of the bone  12 . The blunt tip  40   b  and anchor  56  of the pin  14   b  are then inserted together to the target depth in either cortical or cancellous bone until the ferrule  62  is deployed at the target depth. Likewise, the washer and nut  54 ,  52  combination are juxtaposed to the proximal surface of the near cortex  22  of the bone  12  as shown in  FIG. 5 . The nut  52  is then rotated relative to the threaded region  34  of the pin  14   b  to initially retract the shank  32  of the pin  14   b  relative to the bone  12 . Rotation of the nut  52  relative to the shank  32  to advance the nut  52  toward the blunt tip  40   b  end of the pin  14   b  retracts the pin  14   b  and thereby moves the tapered region  58  of the pin  14   b  relative to the ferrule  62  seated in the far cortex  24  of the bone  12 . As a result, the ferrule  62  advances slightly on the tapered increasing diameter region  58  and the diameter and circumference of the ferrule  62  and size of the gap  64  likewise increases to securely seat the ferrule  62  and pin  14   b  within the far cortex  24  of the bone  12 . As such, the pin  14   b  is securely anchored in the bone  12  for attachment of the external fixator  10 . The most common loosening mechanism is infection at the pin-bone interface. 
   However, loosening may occur as is common in many situations. The region of the far cortex  24  proximate the ferrule  62  may become infected is indicated by region IF of  FIG. 5  thereby loosening the pin-bone interface. In addition to treating the infection, the pin-bone interface loosening presents a significant problem to the stability of the fixator  10  and ultimate success of the bone union because the infected region IF affords a less severe interface with the pin  14 . 
   Advantageously, according to this invention, the pin-bone interface is re-secured by additional rotation of the pin  14   b  relative to the nut  52  thereby further advancing the ferrule  62  seated within the far cortex  24  relative to the blunt tip  40   b  and increasing the diameter and circumference of the ferrule  62  to engage unaffected regions of the cortex  24  for a secure pin-bone interface. One major advantage of the blunt design of the tip  40   b  is minimal risk to neurovascular structures past the bone cortex  24 . Throughout the use of the external fixator  10 , adjustment of the pin  14   b  through rotation of the nut  52  relative to the threaded region may be required to maintain secure fixation. Comparison between  FIGS. 5 and 6  of the position of the ferrule  62  on the tapered region  58 , size of the gap  64  and position of the nut  52  on the threaded region  34  demonstrates the adjustment. 
   Removal of the pin  14   b  is easily accomplished through reverse rotation of the pin  14   b  relative to the nut  52  to advance the nut  52  toward the head end  28  thereby initially projecting the blunt tip  40   b  further into the body relaxing stress on the ferrule  62  for disengagement with the far cortex  24  and removal of the pin  14   b . Advantageously, the anchor  56  which securely engages the far cortex  24  provides a stable pin-bone interface without trauma or damage to blood vessels, nerves or other soft tissue adjacent the bone  12  and particularly at the far side of the far cortex  24 . The tip  40   b  of the pin  14   b  is blunt and thereby less likely to pierce, puncture or otherwise damage bodily components adjacent the bone  12  into which the anchor  56  is engaged. As such, the pin  14   b  of this invention is not only uniquely suited for use in external fixator applications but also spine or vertebrae related applications in which insertion of prior art pins or screws potentially damages the aorta and/or other bodily vessels or components proximate the spine. 
   Referring to  FIG. 7 , a further alternative embodiment of the pin  14  according to this invention is shown. The pin  14   c  includes the head end  28  as well as the threaded region  34 . The threaded region  34  of the pin  14   c  has a generally constant diameter and constant pitch for the helical thread  36 . The threaded region  34  is compatible with internal threads on a nut  52  and washer  54  combination that are preferably welded or otherwise united together. Preferably, the length of the nut  52  extends from the near cortex  22  of the bone  12  and through a muscle layer  72 , a region of fat  74  and the epidermis or skin layer  76  to be exposed outside of the body for access by the doctor or clinician for adjustment and manipulation as required. 
   Adjacent the terminal tip  40   c  of the pin  14   c  according to this embodiment is an anchor  56 . In one embodiment, the anchor  56  includes a dome shaped, hemispherical tip  40   c  and a tapered region  58  extending from the tip  40   c . The tapered region  58  has a larger circumference and diameter adjacent the tip  40   c , each of which decreases axially toward a circumferentially extending bulk head  60 . A split ferrule, bushing or collar  62  which may be constructed of a more ductile material than the pin  14   c  for ease of expansion/contraction is mounted circumferentially around the pin  14   c  on the tapered region  58 . The ferrule  62  is split circumferentially and includes a gap  64 . The ferrule  62  may include serrations or threads  78  on the outer surface thereof to aid in engaging the cortex  24  of the bone  12 . Moreover, the tip  40   c  of the pin  14   c  is preferably integral with the tapered region  58 . Preferably, the ferrule  62  is mounted for free rotation relative to the tapered region  58  prior to engagement with the bone  12 . 
   The pin  14 C of  FIG. 7  is initially inserted after the skin  76  is incised and the subcutaneous tissue, deep fascia and muscle  72  are dissected to the bone  12 . Preferably, the bone  12  is drilled and tapped so that a hole  48  is drilled into the near and far cortex  22 ,  24  and cancellous regions  26  of the bone  12 . The blunt tip  40   c  and anchor  56  of the pin  14   c  are then inserted together to the target depth in either cortical or cancellous bone until the ferrule  62  is deployed at the target depth. Likewise, the washer and nut  54 ,  52  combination are juxtaposed to the proximal surface of the near cortex  22  of the bone  12  as shown in  FIG. 8 . The nut  52  is then rotated relative to the threaded region  34  of the pin  14   c  to initially retract the shank  32  of the pin  14   c  relative to the bone  12 . Rotation of the nut  52  relative to the shank  32  to advance the nut  52  toward the blunt tip  40   c  end of the pin  14   c  retracts the pin  14   c  and thereby moves the tapered region  58  of the pin  14   c  relative to the ferrule  62  seated in the far cortex  24  of the bone  12 . As a result, the ferrule  62  advances slightly on the tapered increasing diameter region  58  and the diameter and circumference of the ferrule  62  and size of the gap  64  likewise increases to securely seat the ferrule  62  and pin  14   c  within an expansion/contraction region of the far cortex  24  of the bone  12  adjacent to the ferrule  62 . As such, the pin  14   c  is securely anchored in the bone  12  for attachment of the external fixator  10 . 
   However, loosening may occur as is common in many situations. The most common loosening mechanism is infection at the pin-bone interface. The region of the far cortex  24  proximate the ferrule  62  may become infected is indicated by region IF of  FIG. 9  thereby loosening the pin-bone interface. In addition to treating the infection via the administration of antibiotics through the fenestrations  70 , the pin-bone interface loosening presents a significant problem to the stability of the fixator  10  and ultimate success of the bone union because the infected region IF affords a less severe interface with the pin  14 . 
   Advantageously, according to this invention, the pin-bone interface is re-secured by additional rotation of the pin  14   c  relative to the nut  52  thereby further advancing the ferrule  62  seated within the far cortex  24  relative to the blunt tip  40   c  and increasing the diameter and circumference of the ferrule  62  to engage unaffected regions of the cortex  24  for a secure pin-bone interface. 
   One major advantage of the design of the tip  40   c  is minimal risk to neurovascular structures past the bone cortex  24 . The dome shaped configuration of the tip  40   c  upon initial installation of the pin  14   c  creates a safe zone adjacent the far cortex  24  proximate the pin  14   c . The dome shaped tip  40   c  pushes away any veins, nerves, arteries or other bodily components that might otherwise be damaged by pins or other devices inserted into the bone  12 . 
   Throughout the use of the external fixator  10 , adjustment of the pin  14   c  through rotation of the nut  52  relative to the threaded region may be required to maintain secure fixation. Comparison between  FIGS. 8 and 9  of the position of the ferrule  62  on the tapered region  58 , size of the gap  64  and position of the nut  52  on the threaded region  34  demonstrates the adjustment. 
   Removal of the pin  14 C is easily accomplished through reverse rotation of the pin  14 C relative to the nut  52  to advance the nut  52  toward the head end  28  thereby initially projecting the blunt tip  40   c  further into the body relaxing stress on the ferrule  62  for disengagement with the far cortex  24  and removal of the pin  14   c . Advantageously, the anchor  56  which securely engages the far cortex  24  provides a stable pin-bone interface without trauma or damage to blood vessels, nerves or other soft tissue adjacent the bone  12  and particularly at the far side of the far cortex  24 . The tip  40   c  of the pin  14   c  is blunt and thereby less likely to pierce, puncture or otherwise damage bodily components adjacent the bone  12  into which the anchor  56  is engaged. As such, the pin  14   c  of this invention is not only uniquely suited for use in external fixator applications but also spine or vertebrae related applications in which insertion of prior art pins or screws potentially damages the aorta and/or other bodily vessels or components proximate the spine. 
   From the above disclosure of the general principles of the present invention and the preceding detailed description of at least one preferred embodiment, those skilled in the art will readily comprehend the various modifications to which this invention is susceptible. Therefore, we desire to be limited only by the scope of the following claims and equivalents thereof.