Abstract:
An alignment guide for setting the position and depth of a guide pin to be inserted into a bone. The alignment guide includes a mechanical assembly for deploying a calibrated guide rod along a selected external surface of the bone and for adjusting the guide rod so it lies parallel to a desired path extending through the bone for a selected distance. The position and orientation of the guide rod may be adjusted using imaging means for viewing the location of the desired path extending through the bone parallel to the guide rod. The alignment guide is mechanically linked to apparatus for subsequently inserting a guide pin into the bone parallel to the guide rod. In one embodiment the alignment guide is designed to aid a surgeon in centering the guide pin to be inserted in the femoral head and neck without repeated trial-and-error drilling. This shortens the operation time and reduces the radiation due to prolonged exposure to fluoroscopic equipment and reduces the risk of possible complications from the surgery.

Description:
BACKGROUND OF INVENTION 
   This invention relates to apparatus and methods for more precisely aligning guide rods and guide pins into bones for bone fixation. 
   To better understand the problem faced by the inventor and resolved by the invention reference will first be made to the prior art shown in  FIGS. 1-4 . 
   Currently available femoral nail systems for the fixation of femoral or certain types of hip fracture and the prophylactic fixation of pending hip or femoral fracture have been described in several trade publications including: (a) The Titanium Femoral Nail System (Synthes); (b) TRIGEN® IM Nail System (Smith+Nephew, Inc.); (c) Intramedullary Hip Screw Nail (Smith+Nephew, Inc.); (d) M/DN® Intramedullary Fixation (Zimmer, Bristol Myers Squibb Co.); (e) AIM® Titanium Femoral Nail System (DePuy ACE, Johnson &amp; Johnson Co); (f) GAMMA Locking Nail (Howmedica); and (g) UNIFLEX Nailing System (BIOMET). These known systems have design features, as shown in  FIGS. 1A ,  1 B, and  1 C, which allow insertion of metal rods (e.g.,  102 ), also referred to herein as an intramedullary nail (IM nail), into the medullary canal of the femur (e.g.,  104 ) and insertion of additional lag screws (e.g.,  106 ) or blades (e.g.,  108 ) through slots in the intramedullary nail (IM nail),  102 , into the femoral head ( 110 ) and neck ( 112 ) for additional stability of fracture fixation.  FIG. 1A  shows the use of two lag screws in the femoral head.  FIGS. 1B and 1C  show the use of a single blade  108  or screw  106  along the center line of the femoral head and neck. As shown in  FIG. 2 , known fixation systems include a device commonly called a drill guide, a targeting device, or aiming arm ( 120 ) attached to the top end of the IM nail to ensure the correct insertion of lag screws ( 106 ) or blades ( 108 ) through slots in the IM nail. 
   Correct positioning of the IM nail  102  is critical to ensure the lag screws or blades are placed in the center of the femoral head  110  and neck  112  in both anteroposterior (AP) and lateral planes for the single screw or blade. For the two screw system as shown in  FIG. 1A , the IM nail  102  must also be positioned to cause the two screws to be placed parallel to each other in the AP view and in the center of the femoral head and neck in the lateral view. However, no device or guide is available at this time to aid in the correct placement of lag screws or blades in the center of the femoral head and neck. As shown in the cross-sectional diagram of  FIG. 3  (AP view), since the depth of the IM nail  102  is not exactly defined relative to the femoral head and neck, a guide pin  130  driven by means of guide  120  (see  FIG. 2 ) into the femoral head may be too high (position A) or too low (position B), rather than being in the correct center position C. Likewise, as shown in the top (lateral) view of  FIG. 4 , since the rotation of the IM nail  102  is not exactly defined relative to the femoral head and neck, a guide pin  130  driven via the drill guide  120  into the femoral head may be too anterior (position D), or too posterior (position E), rather than being in the correct center (position F). Thus, in order to obtain correct placement of the guide pin in the center of the femoral head and neck, the surgeon must perform fine-tuning, trial-and-error adjustment by changing the depth and rotation of the IM nail to vary the position at which the guide pin is inserted and repeatedly drilling with the guide pin  130  under fluoroscopic image intensification until a correct guide-pin position is confirmed by anteroposterior (vertical) and lateral (horizontal) views. 
   This trial-and-error adjustment increases the length of time a patient has to undergo an operation. It also increases the risk of bleeding, wound contamination and subsequent infection. It also increases the likelihood of bone damage from repeated drilling and potential iatrogenic fractures. This also adds unnecessary radiation exposure to the patient, surgeon, and other operating room personnel. 
   It should also be noted that inadvertent drilling beyond the articular surface of the femoral head is a problem with the presently available systems. 
   Also, it is frequently difficult to confirm the position of the guide pin in central axis or near the central axis line of the femoral neck and head because the drill guide and its handle hide the true lateral view of the femoral head and neck even where a radio-lucent drill guide is used. 
   It is an object of the invention to provide apparatus and methods to overcome the problems discussed above. 
   SUMMARY OF THE INVENTION 
   Apparatus and methods embodying the invention include an alignment guide for setting the position and depth of a guide pin to be inserted into a bone. The alignment guide includes means for deploying a guide rod along a selected external surface of a bone, and for adjusting the guide rod so it lies parallel to a desired path extending through the bone and for a selected distance along the length of the bone. The apparatus includes means for subsequently enabling a guide pin to be inserted within the bone along the desired path, parallel to the guide rod. The means for adjusting the guide rod may include imaging means for viewing the location of the desired path extending through (e.g., the center line) the bone and the spatial relationship between the desired path (e.g., the center line) of the bone and the guide rod whereby the apparatus may be used to drill a hole through and along the desired path (e.g., the center) of the bone for a distance also identified by the guide rod. Note that in the discussion to follow the term “guide pin” refers to a pin driven into, or through, a bone producing a path which functions as the axis and guide for a screw or blade to be subsequently inserted into the bone. The term “guide rod” as used herein and in the appended claims refers to a rod positioned externally (over, below or on either side, but not within the bone) to a bone to enable a drill guide to be properly positioned to propel the guide pin in the corresponding bone. 
   In one embodiment an alignment guide mounted on a drill guide is used to control the position or point at which the guide pin is inserted into the bone and the distance to which guide pin is drilled/inserted into the bone. The alignment guide includes a guide rod which is deployed externally to and along the bone to be drilled (i.e., non-invasively to the bone) and includes adjusting means for positioning the guide rod until it lies parallel to a desired plane running through the bone to be drilled. A drill can then be used to propel a guide pin along a desired (anticipated) path. 
   One embodiment of the invention is directed to a new alignment guide to aid a surgeon in centering the guide pin to be inserted in the femoral head and neck without repeated trial-and-error drilling. This shortens the operation time and reduces the radiation due to prolonged exposure to fluoroscopic equipment and reduces the risk of possible complications from the surgery. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawing like reference characters denote like components; and 
       FIGS. 1A ,  1 B and  1 C are cross-sectional diagrams showing an intramedullary nail (IM nail) inserted into the medullary canal of a femur with nails, blades and screws positioned through the IM nail and the femoral neck and head; 
       FIG. 2  is a cross sectional diagram of a prior art drill guide coupled to an IM nail; 
       FIG. 3  is a cross sectional anteroposterior (AP) view of a hip bone; 
       FIG. 4  is a cross sectional lateral view of the femoral neck and head; 
       FIGS. 5A ,  5 B,  5 C, and  5 D are various perspective views of an alignment guide embodying the invention; 
       FIG. 6A  is a perspective diagram of the alignment guide embodying the invention mounted on the prior art drill guide; 
       FIG. 6B  is a perspective diagram of the alignment guide embodying the invention mounted on the prior art drill guide; and 
       FIG. 7  is a lateral view of a guide rod positioned in accordance with the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 5-7  show various aspects of the apparatus embodying the invention. Different views of the alignment guide  10  embodying the invention are shown in  FIGS. 5A ,  5 B,  5 C and  5 D. The alignment guide  10  is designed to be mounted on a drill guide  120  (see  FIGS. 6A ,  6 B) to help determine the positioning and orientation of the drill guide  120  to ensure that a guide pin  130  is inserted into a selected bone at the appropriate angle (laterally and vertically) and for the desired distance (depth). The alignment guide  10  includes a mechanical assembly for deploying a calibrated guide rod  24  along the surface of a selected bone. The tip of the guide rod  24  may be pointed to enable it to penetrate soft tissue surrounding the selected bone; but the tip of the guide rod is blunt enough to avoid injury to neurovascular structures. The alignment guide  10  is linked to the drill guide  120  so that when the drill guide is used to insert a guide pin into the selected bone, the guide pin is inserted into the selected bone along a path parallel to the guide rod. 
   The alignment guide  10  includes a base  12  with positioning slots  14   a  and  14   b  and a post  16  extending vertically upwards from the base. Base fastening screws  15  may be used to secure the alignment guide  10  to drill guide  120 . The base  12  is designed to enable the alignment guide  10  to be attached to an existing drilling guide  120 , also denoted as a targeting device, or an aiming arm, and includes means (slots  14   a ,  14   b ) for producing fine longitudinal adjustment to obtain correct AP (vertical) alignment between a guide rod  24  and a guide pin  130 . 
   The alignment guide also includes a guide rod holder  18  with two tubes  20  and  22  for holding one or two calibrated guide rods  24 . In a single blade or lag screw system (see  FIG. 1B  or  1 C), one of the two guide holder tubes ( 20 ,  22 ) holds one guide rod  24 . In a double lag screw system (see FIG.  1 A), each one of the two tubes ( 20 ,  22 ) of the guide rod holder  18  holds a guide rod  24 . The guide rod holder  18  can be moved up and down post  16  and can be fixed in position via a set screw  181 , or any suitable pinning arrangement. As discussed below, moving the guide rod holder  18  enables the guide rod to be moved closer to, or away from, the selected bone in order to image the guide rod and guide pin path within a selected viewing screen and/or to accommodate persons having more or less soft tissue about the selected bone. Thus, the post  16  includes means for vertical height adjustment of the guide rod holder  18  to enable the obtaining of a correct lateral alignment between a guide rod  24  and a guide pin  130  and the long axis of the selected bone (e.g., femoral head and neck). 
   The tip of the guide rods which extends beyond the guide holder  18  may be positioned to within a given distance (e.g., 5 mm see  FIG. 6B ) of the articular surface of the femoral head. The guide rod  24  is calibrated to measure the maximum desired distance to the articular surface and to then use that information to set the maximum allowable penetration depth of the guide pin  130  into the femoral head to avoid inadvertent penetration into the hip joint. 
     FIG. 6A  is a perspective diagram showing the alignment guide  10  mounted on the drill guide  120 . Note that when the alignment guide  10  is mounted on the guide drill, the guide rod  24  held in tube  20  (or  22 ) will run parallel to the anticipated line that the guide pin  130  will follow when inserted into the bone. A drill (not shown) is coupled to the guide pin  130  to impel it forward as further discussed below. The handle  123  of the drill guide  120  is connected to an arm  124  which at its distal end is coupled to the IM nail  102  and secured thereto via a screw  125 . The drill guide  120 , the handle  123  and the arm  124  are secured to each other by means of a screw  122 . As already noted, in the apparatus shown in  FIGS. 6A and 6B , the guide rod  24  is coupled to the drilling guide  120  such that the anticipated path of the guide pin  130  runs parallel to the path defined by guide rod  24 . For the single screw or blade system, using an imaging device to view the femoral head  110  and the neck  112  and the projection of guide rod  24 , the drilling device  120  may be moved up and down and rotated until the AP (vertical) view and the lateral view indicate that the anticipated path of guide pin  130 , which will be parallel to guide rod  24 , would in fact pass through the center of neck region  112  and femoral head  110 . Furthermore, by using a calibrated guide rod  24 , it is possible to determine how far the guide pin  130  should be inserted into the bone to be within the predetermined distance (e.g., 5 or 10 millimeters) of the articular surface of femoral head  110 . 
   A method for using the alignment guide  10  linked to the drill guide unit  120 , as shown in  FIGS. 6A and 6B , may be as follows:
     1 The medullary canal of the femur  118  is prepared for the insertion therein of an IM nail  102 . The IM nail-drill guide unit  120  is assembled and the IM nail  102  may be introduced into the prepared medullary canal of the femur, as shown in FIG.  2 .   2. The alignment guide  10  is attached to the drill guide as shown in  FIGS. 6A and 6B  by use of base fasteners  15  in slots  14   a ,  14   b , as shown in  FIGS. 5A and 5D .   3. A calibrated guide rod  24  is inserted into the tube  20  or  22  of guide rod holder  18  mounted on post  16  of base  12  as shown in  FIGS. 5C and 5D . Using the base fastener arrangement (slots  14   a ,  14   b  and base fasteners  15 ) of alignment guide  101  fine longitudinal adjustment may be made until the guide rod  24  is aligned with the center line of the drill sleeve  26 , or partially inserted guide pin  130 , as shown in  FIGS. 6A and 6B . The alignment between the guide rod  24  and the guide pin  130  remains fixed during the remainder of the procedure. This is significant since guide pin  130  will then follow an anticipated path through the neck and femoral head bone section which is parallel to the guide rod  24  as deployed along the bone.   4. The length of the guide rod  24  extending over the bone is adjusted to position its tip within, for example, 5 mm of the articular surface of the femoral head as shown in  FIGS. 6A and 6B . Using a calibrated guide rod enables the determination of the preferred distance the guide pin has to be inserted within the selected bone.   5. The IM nail  102  may be raised or lowered or rotated by, for example, applying manual pressure to handle  123  and/or arm  124  and/or tapping on screw  125 . For a single screw or blade system (see  FIGS. 1B and 1C ) the IM nail  102  is slowly advanced under fluoroscopy, or under any similar imaging system, until the guide rod  24  is aligned with the center line of the femoral head  110  and neck  112 , as shown in  FIGS. 6A and 6B . For a two screw system, as shown in  FIG. 1A , two parallel guide rods would be mounted in tubes  20  and  22  to produce the two parallel paths for the guide pins to follow.   6. To achieve lateral (rotational) adjustment, the guide rod holder  18  is lowered along post  16  (see  FIGS. 5A ,  5 D) until the guide rod rests on the skin surface of the anterior aspect of the patient&#39;s hip joint as shown for position A in FIG.  7 . The lateral (top) view of the femoral head and neck and the guide rod may be displayed on a screen (not shown) which would display an image as shown in FIG.  4 . From the lateral display and knowing the projection of the guide rod  24  onto the bone, the anticipated line which the guide pin will take when inserted into the femoral head and neck may be deduced. [Note: If it is not possible to obtain a lateral view of the femoral head and neck and the guide rod in the same screen, the guide rod is withdrawn and reintroduced through the soft tissue along the anterior aspect of the femoral head and neck as shown for position B in  FIG. 7 , without going into the bone.]   7. The IM nail drill guide  120  with the alignment guide  10  is rotated until the guide rod  24  is parallel to the long axis of the femoral head and neck as shown in FIG.  7 .   8. The distance the guide pin  130  is driven into the selected bone is set according to the measurement obtained from the calibrated guide rod.   9. The IM nail drill guide unit  120  with the alignment guide  10  is now positioned to provide correct placement of the guide pin  130  in the center of the femoral head and neck in both the AP (elevation) and lateral (horizontal) planes.   10. A drill attached to the guide pin can then propel the guide pin through the bone along the anticipated path for the desired length. Subsequently, a reamer may be used to increase the size of the hole and a screw or a blade may be superimposed over the guide pin to hold together the trochanter, the neck  112  and the femoral head  110 .   

   The invention has been illustrated by showing how the alignment guide  10  is attached to an existing drill guide  120 . However, it should be appreciated that the invention may be practiced using any specially designed piece of equipment incorporating the function of the drill guide  120  and the alignment guide  10 . That is, the invention is directed to a guide rod which may be manipulated to lie in a plane parallel to a bone through which a guide pin is to be inserted. The guide rod is coupled to a guide-drill in such a manner that the guide pin, propelled through the bone by a drill (not shown), follows a path through the bone which is parallel to that of the guide rod. 
   The invention has been illustrated for the case of the hip bone. But it should be appreciated that the invention is suitable to take care of any other bone (e.g., the humerus). 
   The invention has been illustrated with the path of the guide pin going through the center of a selected bone. But it should be understood that other paths may be selected, as in the case of the two screw system.