Abstract:
An external fixation system having a fixation component ( 20 ) comprising: a) a first capture member ( 24 ) adapted to capture a second element ( 26 ) of an orthopedic fixation system; and (b) a second capture member ( 22 ) adapted to capture a second element ( 28 ) of an orthopedic fixation system and coupled to the first capture member such that the coupling ( 86,94,110 ) allows the first capture member and the second capture member to rotate about three axes relative to each other element and move along that axis; wherein the coupling is adapted to secure the first and the second capture members from rotation with an activation ( 100 ); and wherein the second capture member is adapted to capture the second element by snapping onto the second element from substantially perpendicular to longitudinal axis of the second element

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national phase of International Application No. PCT/US03/02712 filed on Jan. 30, 2003 and published in English as International Publication No. WO 03/065911 A1 on Aug. 14, 2003, which application claims priority to U.S. application Ser. No. 10/172,654 filed on Jun. 14, 2002 which is a continuation-in-part of U.S. application Ser. No. 10/067,052 filed on Feb. 4, 2002, the contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     This invention relates generally to methods, systems, and devices for orthopedic external fixation and more particularly to an external fixation system having an improved fixation component for constructing a stable, adjustable fixation system that cooperates with other systems, and methods of use thereof. 
     BACKGROUND OF THE INVENTION 
     Surgeons use external fixation systems regularly to treat certain bony skeletal injuries or conditions, such as acute fractures of the skeleton, soft tissue injuries, delayed union of the skeleton when bones are slow to heal, nonunion of the skeleton when bones have not healed, malunion of broken or fractured bones, congenital deformities resulting in malposition of bone, and bone lengthening, widening, or twisting. Treatment of these conditions often includes stabilization and reduction using an external fixation system. These systems may include a frame comprised of one or more of fixation components and one or more fixation elements. As used herein, fixation component refers to a device for positioning one or more parts of an external fixation system, and fixation element refers to one or more of a bar, rod, wire, or pin used in an external fixation system. Wires may be threaded, beaded, or smooth, and pins may be threaded or smooth. Generally, one or more bone pins or wires are inserted into the tissue and bone and then the remainder of the fixation system is assembled. It is often important that a surgeon is able to place the external fixation system on the patient and then reduce the fracture in an expedited manner. Fracture patterns are infinite and may require the fixation system to move in multiple planes simultaneously in order to stabilize and reduce the fracture properly. 
     Current external fixation system designs vary, but generally include a mechanism for attaching at least one fixation element to a fixation component to form a construct, or frame, to support a fracture. In general, at least one pin or wire is drilled into the bone. Bone pins typically have one end that is either or both self-drilling and self-tapping, and have a diameter sufficient to resist bending. Bone wires are generally smaller in diameter. Bone pins or wires may be drilled completely through the bone, exiting the skin on the opposite side of the bone, called “transfixation pins,” or may extend through the bony skeleton and out only one side of the limb, called “half pins.” Current fixation components generally either connect a bar to a bar, a bar to a wire, or a bar to a pin. The frame of an external fixation system may include unilateral bars, which extend along the side of a patient&#39;s body, or circumferential or half rings, which encircle a patient&#39;s body member entirely or in part. Systems designed to use a circumferential ring or half ring include the ILIZAROV™ brand system and the SPATIAL FRAME™ brand system. The SPATIAL FRAME™ brand system is described in U.S. Pat. No. 5,702,389, which is hereby incorporated by reference. Generally, circumferential and half rings have a rectangular cross-section. 
     When stabilizing and reducing a fracture using an external fixation system, it is important to properly align the bone fragments. Such alignment requires a fixation component that securely joins the pins and wires to the bars, but that is readily adjustable. In many cases, two pins are inserted below the fracture and two pins are inserted above the fracture. The surgeon then attaches a fixation component to each pin, bridging the fixation components together with rods, or bars. These bars form the frame of the external fixation system. As additional fixation components are added to the system in different planes, the frame becomes less adjustable. Current fixation systems permit a surgeon to choose the positioning of only two fixation components because after placement of two components, additional fixation components will only fit into set positions. During a procedure, it is often necessary to further reduce a fracture, which requires removal of the bars (and loss of positioning) and then replacement of the bars in the frame. Thus, additional reduction is difficult to achieve and requires reestablishment of optimal position. Current systems are also highly dependent on accurate pin or wire placement. For example, if the pins or wires are angled incorrectly, the frame cannot be properly constructed. 
     One current external fixation component design includes two clamps that rotate in one plane to allow limited manipulation of the external fixation component. One jaw of each clamp of this design includes a toothed chip mechanism that has a surface with teeth similar to a poker chip. The teeth mate and lock when compressed, and thereby resist rotation in one plane after the clamps are in place. This poker chip design requires that the two fixation elements retained by the component are parallel to each other in at least one plane that is parallel to the poker chip surface, so that the angular relationship between the two fixation elements is always zero in that plane. Therefore, this system requires a parallel plane between the pin or wire and bar (or between two bars) for each fixation component This requirement limits the system, as the positioning of each clamp is inhibited. Similar to other current designs, this design becomes substandard when several fixation components are used because it becomes constrained. 
     In addition, the clamps of many current designs are adjacent a central shaft and are both locked upon tightening of a single screw, further constraining the system. Many current designs also allow for placement of the pins in the pin clamp of a fixation element only from the side and require a bent bar for placement of the system proximate the patient, if it is necessary to conform the system to the patient&#39;s anatomy. In addition, current designs use compression to hold the bar or pin in place, and may allow dislodgement of the pin or bar upon application of a great amount of pressure to the system when being placed. 
     Other prior art designs include circumferential rings or half rings, such as those in the ILIZAROV™ and SPATIAL FRAME™ brand systems. These specialized systems are often used for reduction of a fracture of the proximal tibia or distal femur. Generally, wires connected to half rings are used to stabilize a fracture. These specialized systems do not cooperate with general external fixation systems, and must be used separately. 
     Thus, there is a need for an external fixation system that provides a greater degree of freedom of rotation of the fixation components and therefore a more flexible frame construct, sequential locking of capture members, allowing greater adjustability, and cooperation with specialized fixation systems. 
     SUMMARY OF THE INVENTION 
     An external fixation system according to one embodiment of this invention allows manipulation of an external fixation component in any plane independent of the number of fixation components used, which is provided by the ability of the fixation component to rotate in multiple planes. Further, an improved fixation component according to one embodiment of this invention provides an external fixation system that does not bind or become constricted when numerous fixation components are used, providing the surgeon a stable system that is adjustable. 
     One embodiment of a fixation component according to this invention includes two capture members, a first capture member adapted to capture a first fixation element and a second capture member adapted to capture a second fixation element. The capture members are coupled such that the coupling allows the first capture member and second capture member to rotate about three axes relative to each other and the second capture member to rotate about one axis of the second fixation element and move along that axis. The coupling is adapted to secure the first and second capture members from rotation and secure the second capture member from rotating about and moving along the axis of the second fixation element with a single activation. The second capture member is adapted to capture the second fixation element by snapping onto the second element from substantially perpendicular to the longitudinal axis of the second element. 
     One feature of one embodiment of this invention is a fixation component that provides a greater degree of freedom of rotation. 
     Another feature of one embodiment of this invention is a fixation component that simultaneously locks a capture member to a fixation element and locks the joint between two capture members. 
     Another feature of one embodiment of this invention is a modular design whereby at least one of the two capture members of a fixation component may be interchangeable with another capture member. For example, if a fixation component has two capture members each for receiving a bar, the two capture members may be separated at the joint, and another capture member, for receiving a pin, may be attached to one of the original two capture members to form a fixation component with one capture member for receiving a bar and the other capture member for receiving a pin. 
     Yet another feature is a fixation component that allows one capture member to be locked to retain a fixation element without forcing the second capture member also to be locked, allowing additional adjustment of position of the second capture member. 
     Another feature of one embodiment according to this invention is a fixation component having a locking mechanism that is not dislodged by application pressure. 
     Yet another feature of one embodiment of this invention is a fixation component that cooperates with specialized fixation systems. 
     According to the present invention there is provided an external fixation component comprising (a) a first capture member adapted to capture a first element of an orthopedic fixation system; and (b) a second capture member adapted to capture a second element of an orthopedic fixation system and coupled to the first capture member such that the coupling allows the first capture member and the second capture member to rotate about three axes relative to each other and the second capture member to rotate about one axis of the second element and move along that axis; wherein the coupling is adapted to secure the first and second capture members from rotation with an activation; and wherein the second capture member is adapted to capture the second element by snapping onto the second element from substantially perpendicular to the longitudinal axis of the second element. 
     According to the present invention there is provided a method of treating a skeletal condition or injury using an external fixation system, the method comprising: (a) inserting a first fixation element into a bone; (b) capturing the first fixation element in a first fixation component by snapping onto the first fixation element from substantially perpendicular to the longitudinal axis of the first fixation element, the first fixation component comprising: (i) a first capture member adapted to capture an element of an orthopedic fixation system; and (ii) a second capture member adapted to capture an element of an orthopedic fixation system and coupled to the first capture member such that the coupling allows the first capture member and the second capture member to rotate about three axes relative to each other; wherein the coupling is adapted to secure the first and second capture members from rotation with a single activation; (c) capturing a second fixation element in the first fixation component by snapping onto the second fixation element from substantially perpendicular to the longitudinal axis of the second fixation element; and (d) engaging the single activation to secure the first and second capture members from rotation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a fixation component according to one embodiment of this invention. 
         FIG. 2  is an exploded perspective view of the fixation component of  FIG. 1 . 
         FIG. 3  is a perspective view of the fixation component of  FIG. 1  with a pin and bar inserted. 
         FIG. 4  is a cross-sectional view of the fixation component taken along lines  4 - 4  in  FIG. 1 . 
         FIG. 5  is a cross-sectional view of the fixation component taken along lines  5 - 5  in  FIG. 1 . 
         FIG. 6  is an exploded perspective view of the second capture member of  FIG. 1 . 
         FIG. 7  is a perspective view of a fixation component according to an alternative embodiment of this invention. 
         FIG. 8  is an exploded perspective view of the fixation component of  FIG. 7 . 
         FIG. 9  is a perspective view of the fixation component of  FIG. 7 , with bars inserted in the capture members. 
         FIG. 10  is a perspective view of a fixation component according to an alternative embodiment of this invention. 
         FIG. 11  is an exploded perspective view of the fixation component of  FIG. 10 . 
         FIG. 12  is a perspective view of an external fixation system according to one embodiment of this invention. 
         FIG. 13  is an enlarged fragmentary perspective view of selected fixation components of  FIG. 12 . 
         FIG. 14  is an exploded perspective view of an alternative embodiment of this invention. 
         FIG. 15  is a plan view of the fixation component of  FIG. 14 . 
         FIG. 16  is a cross-sectional view of the fixation component of  FIG. 14  taken along lines  16 - 16  of  FIG. 15 . 
         FIG. 17  is an exploded perspective view of an alternative embodiment of this invention. 
         FIG. 18  is a plan view of the fixation component of  FIG. 17 . 
         FIG. 19  is a cross-sectional view of the fixation component of  FIG. 17  taken along lines  19 - 19  of  FIG. 18 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Methods, systems, and devices according to this invention seek to provide improved external fixation, including an improved fixation component allowing an increase in freedom of rotation, independent locking of capture members, a more stable, yet more flexible frame, and cooperation with specialized fixation systems. External fixation systems according to embodiments of this invention may include fixation components designed to retain one or more fixation elements. In general, the fixation components either connect a bar to a bar; a bar to a pin; a bar to a wire; or a bar to a circumferential or half ring. Each fixation component generally includes two capture members, and each capture member includes a base and a head. 
     One embodiment of a fixation component according to this invention includes a first capture member and a second capture member connected by a joint. Each capture member includes a channel, which allows attachment of a fixation element from the side. Prior to being locked down, each fixation element can slide (back and forth) and rotate within the channel providing two degrees of freedom between the fixation element and the capture member. The first and second capture members are connected by a joint that allows each capture member to rotate with respect to the other capture member. The joint also allows rotation of up to 50° in any plane (25° each way), increasing the degree of freedom of rotation. In one embodiment, angulation is limited to 50° due to profile height constraints. However, in another embodiment more angulation may be provided. Thus, each capture member is provided three degrees of rotational freedom relative to the other capture member. An external fixation system including fixation components according to this invention allows movement of the bone along six separate axes, a combination of three orthogonal translational axes and three orthogonal rotational axes. 
     In one embodiment according to this invention, a fixation component having a unique joint allows simultaneous locking of one capture member and the joint. In addition, one capture member may be locked in place while the second capture member continues to freely rotate. In this manner, the surgeon is able to lock one capture member and continue to rotate the second capture member for final positioning. The surgeon is also able to loosen only one capture member to gain additional reduction, if required, without losing placement, as occurs with current systems when additional reduction is required. 
     Consider one example of systems and devices according to this invention. As shown in  FIGS. 1-6 , a bar-to-pin fixation component  20  includes a first capture member  24  and a second capture member  22 . First capture member  24  retains a pin  26 , while second capture member  22  is configured to retain a bar  28 , as shown in  FIG. 3 . A base  30  of first capture member  24  includes a groove  32 , while a head  34  of first capture member  24  contains a wedge  36 , which together are adapted to retain pin  26 . Likewise, a base  38  and a head  40  of second capture member  22  include a groove  42  and a wedge  44 , together adapted to retain bar  28 . In one embodiment, groove  42  of second capture member  22  has splines  46 , which provide rotational stability of bar  28  and penetrate the surface of bar  28  when second capture member  22  is tightened. Alternatively, the second capture member may be adapted to retain a pin and the first capture member may be adapted to retain a bar. In an alternative embodiment, both the first and second capture members are configured to retain a bar, as shown in  FIGS. 7-9  . In another embodiment, one capture member is adapted to retain a wire, while the other capture member is adapted to retain a bar. In another embodiment, the capture members are modular allowing for each capture member to be connected to a similarly designed capture member. Additional embodiments are further described below. 
     As shown in  FIG. 2 , head  34  of first capture member  24  has a recess  48  adapted to receive a spring  50 , while base  30  of first capture member  24  includes a stop  52 . A first track  54  on each side of head  34  slides in a second track  56  on each side of base  30 , allowing head  34  and base  30  of first capture member  24  to translate with respect to each other. In an alternative embodiment, second track  56  slides in first track  54 . In one embodiment, one of first and second tracks  54 ,  56  is an L-shaped track, while the other track is shaped to receive the L-shaped track. As a force in a direction perpendicular to the pin is exerted against groove  32  and wedge  36  of first capture member  24 , head  34  moves, compressing spring  50  against the extended portion of base  30 . Spring  50  compresses until it exerts a force in a direction perpendicular to pin  26  that is equal and opposite to the force exerted against wedge  36 . At that point, head  34  stops moving and holds pin  26  in groove  32  and wedge  36 , which together form channel  58 . 
     The angular position of channel  58  is set by tightening a first fastener  60 . Prior to tightening of first fastener  60 , the cartridge mechanism, in the loosened state, does not allow pin  26  to passively separate or detach from capture member  24 . Base  30  of first capture member  24  includes an elevated portion  61 , as shown in  FIG. 4 , forcing two points of contact between base  30  and head  34  in order to increase the holding power of first capture member  24 . Base  38  of second capture member  22  also includes an elevated portion  63 , also shown in  FIG. 4 , which increases the holding power of second capture member  22  in the same manner. 
     Second capture member  22  also includes a cartridge mechanism for retaining bar  28 . Head  40  of second capture member  22  has a recess  62  adapted to receive a spring  64 , while base  38  of second capture member  22  includes a stop  66 . A first track  68  on each side of head  40  slides in a second track  70  on each side of base  38 . In an alternative embodiment, second track  70  slides in first track  68 . In one embodiment, one of first and second tracks  68 ,  70  is an L-shaped track, while the other track is shaped to receive the L-shaped track. Groove  42  and wedge  44  of second capture member form a second capture member channel  72 , which receives a bar  28 . Bar  28  is retained in second capture member  22  in the same manner as first capture member  24  retains pin  26 . 
     In an alternative embodiment, one or both capture members may include two recesses for receiving two springs and two spring stops. In the embodiments shown, the recess, spring, and stop are located on one side of the capture member. In an alternative embodiment, the recess, spring, and spring stop are in the middle of the capture member, or are on the other side of the capture member. In one embodiment, heads  40  and  34  of capture members  22  and  24 , respectively, include grip surfaces  74  and  76  for gripping and sliding heads  40  and  34  in relation to bases  38  and  30 , respectively. In one embodiment, grip surfaces  74  and  76  include ridges. 
     A threaded end  78  of first fastener  60  is adjacent a biasing element, such as a center spring  80 , and passes through a keyhole aperture  82  in head  34  of first capture member  24 , mating to internal threads  84  in base  30  of first capture member  24 . Keyhole aperture  82  of head  34  if first capture member  24  allows a reduced diameter neck  85  of first fastener  60  to translate within the aperture  82 . Tightening of first fastener  60  locks first capture member  24  and rigidly retains pin  26 . In an alternative embodiment, aperture  82  is circular, or any other suitable shape. 
     A connector  86  having an end  88  and a shaft  90  extends through a keyhole aperture  92  in base  30  of first capture member  24 . In one embodiment, connector  86  is a ball stud, as shown in  FIG. 2 , having a spherical end. End  88  of connector  86  is received in a planetary member  94  of base  30  of first capture member  24 . As used herein, a planetary member refers to an object that is received in another object, and that receives another object within itself. In one embodiment, planetary member  94  is an outer sphere, as shown in the figures. Shaft  90  of connector  86  extends through an aperture  96  in base  38  of second capture member  22  and an aperture  98  in head  40  of second capture member  22 , and mates with a second fastener  100 . Threads  102  on shaft  90  of connector  86  mate with internal threads  104  of second fastener  100 . 
     A slot  106  in aperture  96  of base  38  of second capture member  22  is adapted to receive a key  108  on shaft  90  of connector  86 . Key  108  and slot  106  thus prevent rotation of connector  86  within second capture member  22 . In another embodiment, any suitable mechanism for preventing rotation of the connector is used. In other words, the connector fits through the base of the first capture member and the end is received in the planetary member of the base, while the shaft of the connector extends through both the base and head of the second capture member and threads to a second fastener. A planetary member, for example outer sphere  94 , fits within a cooperating surface  110 , which is machined into the one side of base  38  of second capture member  22 . Tightening of second fastener  100  on second capture member  22  draws connector  86  into planetary member  94 , locking the second capture member and the joint to make it rigid. In one embodiment, one or both of the planetary member and cooperating surface may be tapered. For example, a taper of 10°, 15°, 20°, or 30° may be used on each. 
     The joint mechanism described above allows the second capture member to rotate with respect to the planetary member of the first capture member, and allows the first capture member to grasp and lock a pin while permitting the second capture member to continue to rotate. Independent tightening of the capture members provides the surgeon flexibility to snap a fixation element to a capture member and then to manipulate the second capture member before locking the second capture member in order to achieve a more stable frame. In this manner, independent tightening of each capture member of the external fixation component allows more precise angular positioning. Alternative embodiments of a joint mechanism between two capture members are described below with reference to  FIGS. 14-19 . 
     Other embodiments, such as a bar-to-bar fixation component, shown in  FIGS. 7-9 , and a bar-to-wire fixation component, also may contribute to a more stable, more adjustable external fixation system. These embodiments function similarly to the bar-to-pin fixation component, with the capture members having a wedge and groove adapted to form a channel sized for receiving either a bar or a wire, depending on the component. 
     In one embodiment, a cartridge locking of the pin and bar is provided, as described above. However, in alternative embodiments, other one-piece designs may be used. For example, a solid piece of aluminum metal having the shape of the two part head and base cartridge construct of the two capture members may be used. This one-piece design includes a channel in each one piece capture member and a slot that extends close to the rear portion of the capture member. The slot causes the material to behave similar to a spring and allows the capture member to open when pressure is placed against it, so that a fixation element may be snapped into place in the channel. 
     Several mechanisms may be used to improve the locking capabilities of the joint. Coatings or elastic materials or alternate taper shapes may be applied to any of the articulating surfaces. For example, coatings or elastic materials or alternate taper shapes may be applied to one or both of the planetary member and cooperating surface so that a textured surface on either or both improves locking. In one embodiment, the cooperating surface is coated with SC729, a coating manufactured by Hitemco. In this embodiment, the cooperating surface is very rough and is made from tungsten cobalt carbide. In this embodiment, the value for slip increases to about 240 in.-lb., from about 140 in.-lb. without the coating. In an alternative embodiment, a mechanical locking pattern is applied. For example, splines and dimples may be added to one or both of planetary member and cooperating surface, providing teeth to grab when locking, thereby improving the locking function. A 30 degree chosen taper configuration on the inside of the planetary member mating surface uses a taper design to achieve torque strength of up to 200 in.-lb. 
     In an alternative embodiment, a fixation component is designed for attachment to a circumferential external fixator system, such as an ILIZAROV™ brand system, a SPATLAL FRAME™ brand system, or other spatial frame, to achieve a hybrid external construct. In this embodiment, shown in  FIGS. 10-11 , the fixation component includes a capture member for retaining a bar and a capture member for retaining a half or circumferential ring having a generally rectangular cross-section. Use of a fixation component having a capture member for retaining a ring allows a surgeon to create a hybrid frame, using both a standard external fixation system and a system that includes a circumferential external frame. This hybrid system is very useful in adapting a system for treating a shaft fracture, or typical in-line fracture, to one for treating a plateau fracture, which is a fracture in a joint space. 
     Referring to  FIGS. 10 and 11 , a T-component  112  according to one embodiment of a fixation component of this invention includes a second capture member  114  that is similar to the second capture member described above with respect to the bar-to-pin fixation component. A head  116  of second capture member  114  has a recess  118  adapted to receive a spring  120 , while a base  122  of second capture member  114  includes a stop  124 . Recess  118  and spring  120  function as described above. Second capture member  114  also includes a first track  126  and a second track  128  so that head  116  and base  122  translate and retain a bar in a groove  130  and a wedge  132  in the same manner as described above. 
     Base  122  of second capture member  114  also includes a cooperating surface  134 , which is adapted to receive a planetary member  136  of a first capture member  156 . A connector  138 , which, as described above and shown in  FIG. 11 , may be a ball stud, has a shaft  140  that extends through apertures  142  and  144  in base  122  and head  116 , respectively, of second capture member  114 . A slot  146  in aperture  142  of base  122  is adapted to receive a key  148  on shaft  140  of connector  138  in order to prevent rotation of connector  138  within second capture member  114 . Threads  150  on shaft  140  mate with a second fastener  152 , while an end  154  is received in planetary member  136 . 
     First capture member  156  includes a base  158  and a head  160 , each having a recess  162  and  164 , respectively, that together form a channel  166 , adapted to receive a ring having a rectangular cross-section. Head  160  has an extension  168  that fits into a rim  170  of base  162 . A rod  172  includes second threads  174  that mate with internal threads  176  of an aperture  178  of base  158  after extending through an aperture  180  of head  160 . A biasing element  182 , such as a spring, passes over rod  172  and also into an aperture  184  of a first fastener  186 . First threads  188  of rod  172  mate with internal threads  190  of first fastener  186 . Tightening of first fastener  186  thus locks base  158  and head  160  of first capture member  156 . Second capture member  114  is free to rotate about planetary member  136  of base  158  of first capture member  156  until second fastener  152  is tightened, at which time both second capture member  114  and planetary member  136  and cooperating surface  134 , which form the joint, are locked. 
     In an alternative embodiment, other locking mechanisms may be used, such as a universal joint mechanism, which allows independent movement in different directions. In yet another alternative embodiment, the capture member may include a flip through for the bar or pin, rather than a snap-on from the side as described above. 
     One embodiment of a fixation component of this invention is made from titanium and aluminum. In this embodiment, the heads of the capture members are made from aluminum and the remaining parts from titanium. In alternative embodiments, fixation components are made from metals, alloys, plastics, composites, ceramics, or any other suitable material. 
     As noted above, additional alternative embodiments of capture members and a joint mechanism between two capture members are shown in  FIGS. 14-19 . One alternative joint mechanism is shown in  FIGS. 14-16 , while another alternative is shown in  FIGS. 17-19 . The capture members shown in  FIGS. 14-19  generally perform in a similar manner as the capture members described above with regard to the receipt of fixation elements and engagement of the base and head of each capture member. 
     As shown in  FIGS. 14-16 , a fixation component  200  includes a first capture member  202  and a second capture member  230 . Capture members  202  and  230  may be designed to retain one of any of a pin, wire, bar, at least a partial ring, or other fixation element. As shown in  FIGS. 14-16 , each capture member is designed to receive a bar. A base  204  of first capture member  202  includes a groove  206 , while a head  208  of first capture member  202  contains a wedge  210 , which together are adapted to retain a fixation element. Likewise, a base  232  and a head  234  of second capture member  230  include a groove  236  and a wedge  238 , together adapted to retain a fixation element in the same manner as described above. 
     Head  208  of first capture member  202  has a recess (not shown) adapted to receive a spring  214 , while base  204  of first capture member  202  includes a stop  216 . The recess, spring  214 , and stop  216  function in the same manner as described above. First capture member  202  also includes a first track  218  and a second track  220  so that head  208  and base  204  translate and retain a fixation element in a channel  222  formed by groove  206  and wedge  210  in the same manner as described above. The angular position of channel  222  is set by tightening a first fastener  224 . Prior to tightening of first fastener  224 , the cartridge mechanism, in the loosened state, does not allow an inserted fixation element to passively separate or detach from capture member  202 . 
     Second capture member  230  also includes a cartridge mechanism for retaining a fixation element. Head  234  of second capture member  230  has a recess  240  adapted to receive a spring  242 , while base  232  of second capture member  230  includes a stop  244 . Second capture member  230  also includes a first track  246  and a second track  248  so that head  234  and base  232  translate and retain a fixation element in a channel  250  formed by groove  236  and wedge  238  in the same manner as described above. The angular position of channel  250  is set by tightening a second fastener  252 . Prior to tightening of second fastener  252 , the cartridge mechanism, in the loosened state, does not allow an inserted fixation element to passively separate or detach from capture member  230 . 
     In the embodiments shown, the recess, spring, and stop are located on one side of the capture member. In an alternative embodiment, the recess, spring, and spring stop are in the middle of the capture member, or are on the other side of the capture member. In one embodiment, heads  208  and  234  of capture members  202  and  230 , respectively, include grip surfaces  226  and  254  for gripping and sliding heads  208  and  234  in relation to bases  204  and  232 , respectively. In one embodiment, grip surfaces  226  and  254  include ridges. 
     A threaded end  256  of second fastener  252  passes through an aperture  258  in head  234  of second capture member  230 , mating to internal threads  260  in base  232  of second capture member  230 . Tightening of second fastener  252  locks second capture member  230  and rigidly retains an inserted fixation element. 
     A connector  270  having an end  272  and a shaft  274  extends through bore  276  in base  204  of first capture member  202 . In one embodiment, connector  270  is a ball stud, as shown in  FIG. 14 , having a spherical end. End  272  of connector  270  is received in a spherical collet  278  of base  204  of first capture member  202 . Shaft  274  of connector  270  extends through bore  276  in base  204  of first capture member  202  and an aperture  280  in head  208  of first capture member  202 , and mates with first fastener  224 . Threads  282  on shaft  274  of connector  270  mate with internal threads  228  of first fastener  224 . A slot  284  in bore  276  of base  204  of first capture member  202  is adapted to receive a key  286  on shaft  274  of connector  270 . Key  286  and slot  284  thus prevent rotation of connector  270  within first capture member  202 . 
     The end of bore  276  may be tapered or countersunk. When connector  270  is inserted through the countersunk end of bore  276  and aperture  280  of head  208  of first capture member  202 , end  272  rests against the countersunk end of bore  276 . First fastener  224  is threaded onto shaft  274  so that as first fastener  224  is tightened against capture member  202 , end  272  is pulled through base  204  and head  208  of capture member  202 , forcing spherical collet  278  to expand. 
     A spherical pocket  290  of base  232  of second capture member  230  receives spherical collet  278 . In a loosened state (i.e., first fastener  224  is not fully tightened and spherical collet  278  is not fully expanded), spherical collet  278  may be retained within spherical pocket  290 , and spherical collet  278  may or may not be biased against spherical pocket  290  to provide resistance for the joint mechanism. When end  272  of connector  270  is not expanding spherical collet  278 , capture members  202  and  230  may be rotated about or detached from each other. When first fastener  224  is tightened and spherical collet  278  fully expanded, capture members  202  and  230  cannot be rotated about each other or detached from each other. The tightening of first fastener  224  locks first capture member  202  and the joint to make it rigid. In one embodiment, one or both of the spherical collet and spherical pocket may be tapered. For example, a taper of 10°, 15°, 20°, or 30° may be used on each. Several mechanisms may be used to improve the locking capabilities of the joint, including coatings, elastic materials, or alternate taper shapes as discussed above. 
     The joint mechanism shown in  FIGS. 14-16  allows the first capture member to rotate with respect to the spherical pocket of the second capture member, and allows the second capture member to grasp and lock a fixation element while permitting the first capture member to continue to rotate. Independent tightening of the capture members provides the surgeon flexibility to snap a fixation element to a capture member and then to manipulate the first capture member before locking the first capture member in order to achieve a more stable frame. In this manner, independent tightening of each capture member of the external fixation component allows more precise angular positioning. 
     In addition to increasing the degrees of freedom of movement of fixation components and allowing for more precise angular positioning, the use of the joint mechanism shown in  FIGS. 14-16  provides a modular external fixation system for use by surgeons. Rather than providing pre-assembled fixation components in a surgical tray, separate capture members, not yet attached to other capture members to form fixation components, may be provided. For example, instead of providing a predetermined number of bar-to-bar fixation components and bar-to-pin fixation components in a surgical tray, a system may include a specified number of capture members for receiving bars and capture members for receiving pins. The capture members may be connected by the surgeon, or an assistant, using the joint mechanism shown in  FIGS. 14-16  to form specific fixation components (e.g., bar-to-bar, bar-to-pin, bar-to wire, etc.) as desired based upon the surgery being performed. This provides better inventory control and should reduce the number of capture members and/or fixation components required to be provided in a surgical tray. 
     Another alternative embodiment is shown in  FIGS. 17-19 . Similar to the embodiment shown in  FIGS. 14-16 , the embodiment shown in  FIGS. 17-19  also provides better inventory control by using capture members that may be easily detached and interchanged with other capture members to form the type of fixation component desired. However, the embodiment shown in  FIGS. 17-19  also provides independent locking of the joint and each capture member rather than providing the simultaneously locking of the joint and one of the two capture members as discussed with regard to several other embodiments. 
     As shown in  FIGS. 17-19 , a fixation component  300  includes a first capture member  302  and a second capture member  330 . Capture members  302  and  330  may be designed to retain one of any of a pin, wire, bar, at least a partial ring, or other fixation element. As shown in  FIGS. 17-19 , each capture member is designed to receive a bar. A base  304  of first capture member  302  includes a groove  306 , while a head  308  of first capture member  302  contains a wedge  310 , which together are adapted to retain a fixation element. Likewise, a base  332  and a head  334  of second capture member  330  include a groove  336  and a wedge  338 , together adapted to retain a fixation element in the same manner as described above. 
     Head  308  of first capture member  302  has a recess (not shown) adapted to receive a spring  314 , while base  304  of first capture member  302  includes a stop  316 . The recess, spring  314 , and stop  316  function in the same manner as described above. First capture member  302  also includes a first track  318  and a second track  320  so that head  308  and base  304  translate and retain a fixation element in a channel  322  formed by groove  306  and wedge  310  in the same manner as described above. The angular position of channel  322  is set by tightening a first fastener  324 . Prior to tightening of first fastener  324 , the cartridge mechanism, in the loosened state, does not allow an inserted fixation element to passively separate or detach from capture member  302 . 
     Second capture member  330  also includes a cartridge mechanism for retaining a fixation element. Head  334  of second capture member  330  has a recess  340  adapted to receive a spring  342 , while base  332  of second capture member  330  includes a stop  344 . Second capture member  330  also includes a first trick  346  and a second track  348  so that head  334  and base  332  translate and retain a fixation element in a channel  350  formed by groove  336  and wedge  338  in the same manner as described above. The angular position of channel  350  is set by tightening a second fastener  352 . Prior to tightening of second fastener  352 , the cartridge mechanism, in the loosened state, does not allow an inserted fixation element to passively separate or detach from capture member  330 . 
     In the embodiments shown, the recess, spring, and stop are located on one side of the capture member. In an alternative embodiment, the recess, spring, and spring stop are in the middle of the capture member, or are on the other side of the capture member. In one embodiment, heads  308  and  334  of capture members  302  and  330 , respectively, include grip surfaces  326  and  354  for gripping and sliding heads  308  and  334  in relation to bases  304  and  332 , respectively. In one embodiment, grip surfaces  326  and  354  include ridges. 
     A threaded end  356  of second fastener  352  passes through an aperture  358  in head  334  of second capture member  330 , mating to internal threads  360  in base  332  of second capture member  330 . Tightening of second fastener  352  locks second capture member  330  and rigidly retains an inserted fixation element. 
     A set screw  370  including threads  372  is inserted into bore  376  in base  304  of first capture member  302 . In one embodiment, set screw  370  is tapered. End  374  of set screw  370  is received in a spherical collet  378  of base  304  of first capture member  302 . Threads  372  on set screw  370  mate with internal threads  388  of bore  376  of base  304  of first capture member  302 . 
     A spherical pocket  390  of base  332  of second capture member  330  receives spherical collet  378 . When set screw  370  is tightened, spherical collet  378  expands and the joint between first and second capture members  302  and  330  is rigid. In a loosened state, when set screw  370  is not tightened, spherical collet  378  may be retained within spherical pocket  390 , and spherical collet  378  may or may not be biased against spherical pocket  390  to provide resistance for the joint mechanism. Locking of the joint between the two capture members prevents rotation of either capture member about each other, but neither capture member is locked by tightening of set screw  370 . When set screw  370  is partially threaded onto internal threads  388  of base  304  of first capture member  302  and spherical collet  378  is within spherical pocket  390  but not fully expanded, capture members  302  and  330  may be rotated about each other. Several mechanisms may be used to improve the locking capabilities of the joint, including coatings, elastic materials, or alternate taper shapes as discussed above. 
     First fastener  324  includes a bore  392  and threads  394 . First fastener  324  extends through an aperture  380  in head  308  of first capture member  302  and threads  394  are threaded onto internal threads  388  of base  304  of first capture member  302 . Tightening of first fastener  324  locks capture member  302 . Bore  392  extends through first fastener  324 , allowing for insertion of a tool  396  to tighten or loosen set screw  370  in spherical collet  378 . 
     One method of using one form of structure according to this invention, shown in  FIG. 13 , is as follows: 
     At least two half pins are self-drilled into a bone, one on either side of a bone fracture. One bar-to-pin fixation component is connected to each pin by placing each pin into the capture member of each fixation component sized to receive a pin, such as the first capture member of the bar-to-pin fixation component shown in  FIG. 1 . Each fixation element is placed into the fixation component from the side for easy placement. After a pin is in place, the first fastener is tightened, so that the pin is retained in the capture member, while the second capture member and joint continue to freely rotate. Bars are then snapped into the bar capture member of the fixation components, forming a frame for the system. As each bar is added, the fixation components are adjusted as required by loosening the joint and second capture member, so that optimal positioning may be obtained. Bar-to-bar fixation components and bar-to-pin fixation components may be added to expand and connect the frame as required. If it is necessary or desirable to utilize a circumferential ring or half ring with a system for complex fractures, as shown in  FIG. 13 , additional fixation components having capture members designed to retain the rectangular bar of a ring are used to join the standard system to the specialized frame. A T-component is used to capture the rectangular bar of a ring and link it to a bar of the original frame, forming a hybrid system. If additional reduction is required, one capture member of any component may be loosened without losing placement of the system. A T-component may also be used to provide stability to an existing system that has. already been placed using standard fixation component designs. A plurality of clamps may be used in various configurations to achieve stability for different fractures. 
     Similar instrumentation and devices may be used in other areas, such as to provide a fixed reference to a pin. Constructs made under the present invention are stable and provide for a wide variety or placements. Embodiments of an external fixation component according to this invention may also be adapted for use with an image guided surgery system to provide stability to a reference frame or other guidance target or mechanism. 
     The foregoing description of certain exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. 
     The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and certain exemplary embodiments described therein.