Intramedullary nail aiming device

#The present invention generally relates to an aiming device for guiding a drill bit during the drilling of a hole in a bone. More particularly, the present invention relates to an intramedullary nail aiming device for drilling holes in a bone that are suitable for receiving locking screws of an intramedullary nail. Exemplary embodiments of the invention relate to a system comprising an intramedullary nail aiming device and an intramedullary nail and to a method for drilling the holes in a bone for inserting locking screws in an intramedullary nail by using the intramedullary nail aiming device.

#Intramedullary nails including fixation screws inserted through the intramedullary nail in a transverse direction to lock the intramedullary nail relative to the bone are commonly known. In particular, proximal humerus nails comprise multiple fixation screws arranged at different angles relative to each other in the proximal part of the intramedullary nail to securely fixate bone fragments.

#These screws are positioned in the intramedullary nail in corresponding through holes using an aiming arm or aiming block rigidly connected to the proximal end of the intramedullary nail by an intermediate member. These aiming blocks feature guiding holes aligned with the through holes in the intramedullary nail but arranged at a distance from the bone to leave space for the arm and shoulder of the patient. Generally, drilling or guiding sleeves are inserted into the holes in the aiming block drilling tools and screwdrivers guided through the sleeves are exactly aligned with the holes in the intramedullary nail. For anatomical reasons, intramedullary nails are commonly provided in “left” and “right” embodiments, i.e. in a mirrored configuration. Therefore, the aiming blocks generally feature through holes matching the left side and the right side configurations of the intramedullary nail. Because aiming blocks which preferably include radiolucent carbon fibre reinforced PEEK material are very costly, it is preferred to have only one aiming block for both configurations of the intramedullary nail. Known aiming instruments comprise aiming blocks with all the through holes for the left side and the right side configurations of the intramedullary nail in a single aiming block. These known aiming blocks can pose the risk that the wrong through holes may be used when preparing the bone, i.e. drilling the holes in the bone through which the fixation screws will be positioned. For example, a user may inadvertently drill through a hole corresponding to the “right side” configuration of the aiming device while working with a “left side” intramedullary nail. If a wrong hole is selected the drill bit will collide with the intramedullary nail and cause unacceptable debris possibly resulting in a loss of stability of the intramedullary nail and furthermore, an unnecessary hole drilled into the bone. In order to prevent this, the through holes in the aiming block are clearly marked “left” and “right” or are colour coded. In stressful situations, however, mistakes may still be made.

#A plurality of embodiments of the invention will be described in the following by way of example and with reference to the accompanying drawings in which:

#FIG. 1 illustrates a perspective view of an embodiment of the aiming device according to the invention;

#FIG. 2 illustrates a perspective view of the embodiment of FIG. 1 with the drilling bushings inserted in the wrong through holes;

#FIGS. 1 and 2 illustrate an embodiment of the intramedullary nail aiming device 1 used with a left side and a right side configuration of an intramedullary nail 8, wherein the intramedullary nail aiming device 1 comprises an aiming plate 2 with a first surface 5, a second surface 6, a distal end 12 and a proximal end 7 attachable to an aiming arm 9 which is fixed to an intramedullary nail 8. In a left side configuration, the first surface 5 faces away from the bone while the second surface 6 faces toward the bone. In a right side configuration, the first surface 5 faces toward the bone while the second surface 6 faces away from the bone. The aiming plate 2 further includes a plurality of compound openings extending through the aiming plate 2 from the first surface 5 to the second surface 6. In a preferred embodiment, the aiming plate 2 includes four compound openings. However, as would be understood by those skilled in the art, any number of compound openings depending on the characteristics of the intramedullary nails to be used with the aiming plate. Each compound opening comprises a first through hole 3 and a second through hole 13 which are open to one another. The first through holes 3 form a first set of four first through holes 3 and the second through holes 13 form a second set of four second through holes 13.

#The aiming plate 2 comprises a longitudinal central plate portion 29 extending along a longitudinal axis 15, a first lateral side surface 41 and a second lateral side surface 42. Furthermore, the aiming plate 2 includes two parallel first arms 43 protruding laterally from the first lateral side surface 41 of the central plate portion 29 and two parallel second arms 44 protruding laterally from the second lateral side surface 42 of the central plate portion 29. The first arms 43 and the second arms 44 are staggered along the longitudinal axis 15 and have different lengths. A central plane 11 extending between the proximal end 7 and the distal end 12 and cutting the first and second surfaces 5, 6 is substantially perpendicular to the first and second surfaces 5,6. Additionally, a middle plane 28 orthogonal to the central plane 11 extends through the aiming plate 2 substantially parallel to the first and second surfaces 5,6. Each first through hole 3 defines a first hole axis 10 and each second through hole 13 defines a second hole axis 14, wherein the first and second through holes 3, 13 of each compound opening are arranged in such a way that the first hole axis 10 and the second hole axis 14 intersect one another along the middle plane 28. In the present embodiment the first and second hole axes 10, 14 of the first and second through holes 3, 13 of each compound opening intersect one another along the middle plane 28 at an equal distance E from the central plane 11. The first and second hole axes 10, 14 of the first and second through holes 3, 13 of each compound opening define a plane orthogonal to the middle plane 28 and orthogonal to the central plane 11. Further, the four compound openings are arranged so that the first and second hole axes 10, 14 of each of the first and second through holes 3, 13 of one compound opening define a different plane orthogonal to the middle plane 28 and orthogonal to the central plane 11.

#The first through holes 3 are sized and shaped to receive a drill bushing 4 and/or drill bit from the first surface 5 along the central axis 10 aligned with a corresponding locking hole (not shown) in a left side configuration intramedullary nail 8 coupled to the aiming plate 2. The second through holes 13 are sized and shaped to receive a drill bushing 4 and/or drill bit from the second surface 6 along the central axis 14 aligned with a corresponding locking hole in a right side configuration intramedullary nail 8 coupled to the aiming plate 2. The first hole axes 10 of the first through holes 3 converge toward the central plane 11 in a direction from the first surface 5 toward the second surface 6 while the second hole axes 14 of the second through holes 13 diverge from the central plane 11 in the direction from the first surface 5 toward the second surface 6. Thus, each first hole axis 10 of the first through holes 3 forms an angle αi with the central plane 11 while each second hole axis 14 of the second through holes 13 forms an angle βi with the central plane 11. The present embodiment may comprise four compound openings such that i=1 to 4. If identically positioned anterior and posterior locking holes in the intramedullary nail 8 are used in left side and right side intramedullary nails 8, the angle βi=−αi for the first and second through holes 3, 13 of each compound opening.