Abstract:
The tibia nail comprises a tube including a continuous longitudinal bore and includes a proximal anchoring portion with several cross-bores, an adjoining connecting portion which is flexurally resilient in an anterior and posterior direction, a shank adjoining it, and a distal anchoring portion. The anchoring portion is bent away with respect to the shank and has an elongated hole through which a locking screw may be placed. The tibia may be compressed by means of a compression screw inserted into a longitudinal threaded bore. The tibia nail enables retrograde implantation, which has been considered to be impossible for the tibia up to now.

Description:
BACKGROUND OF THE INVENTION 
     The retrograde implantations of medulla nails in the femur and the humerus already are routine osteosynthetic treatments presently. In contrast, the implantation of a medulla nail into the tibia in a retrograde direction has seemed to be impossible as yet because of anatomic and implant-related technical considerations. Therefore, osteosynthetic plates, for example, have been used up to now, particularly for fractures in the proximal region of the tibia. 
     SUMMARY OF THE INVENTION 
     From FR-A-2 646 078, a bone nail has become known which also is referred to as a locking nail. The bone nail, which also can be employed as a tibia nail and, for this purpose, has a bent-off portion at its end, exhibits cross-bores in each of the end portions to receive a bone screw. The shank of the bone nail is provided with groves axially parallel thereto and with an axially extending slot in the wall of the hollow nail, which increases the resiliency of the shank altogether. 
     It is the object of the invention to provide a tibia nail which specifically is suited for retrograde use. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the invention will now be explained with reference to the drawings. In the drawings: 
     FIG. 1 shows a side view of a tibia nail, 
     FIG. 2 shows a plan view of the nail, 
     FIGS. 3 through 7 show sections along lines III—III through VII—VII in FIG. 1, and 
     FIG. 8 shows a front view in the direction of the arrow VIII in FIG.  1 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The intramedullary tibia nail  1  is manufactured from a bio-compatible metal. It serves for treating broken bones in the proximal portion of the tibia and for temporarily stabilizing high tibia osteotomies. The nail  1  comprises four sections: a flexurally rigid most proximal portion  2 , a proximal portion  3  which is flexurally resilient in an anterior and posterior direction, a medial shank  4 , and a distal flared portion  5  to receive the distal locking screws  6 . The whole nail is designed cannularly (bore  7 ) to enable insertion by means of a target wire or guide wire. As a rule, it is configured in a rotationally symmetric way. The diameters of the individual portions  2 - 5  vary and typically are about 9 mm in the proximal portion  2 , about 7 mm in the shank  4 , and about 10 mm in the distal portion  5 . The nail  1  is manufactured in a length ranging from about 200 to 400 mm with the length of the shaft  4  substantially being varied. 
     The most proximal portion  2  which is flexurally rigid has at least two angularly offset screw holes  12 ,  13  for proximal locking screws (not shown) which have their threads cut up to the screw head unlike the screws  6  of FIG.  3 . At least one hole  12  is located in a medio-lateral direction. The embodiment of FIGS. 1 and 2 illustrates four holes  12 ,  13  with the most proximal and most distal ones being located in a medio-lateral direction and each of the two holes  13  therebetween being rotated through an angle about the axial direction of the nail, which is about 45° in the embodiment shown. The arrangement of the holes  12 ,  13  permits to fix several fragments at their positions in the region of the tibia plateau. The cross-section is approximately the same across the whole length in the flexurally rigid portion  2 . Flexural rigidity is largest at the level of the holes  12 ,  13  whilst the connecting elements between the holes  12 ,  13  will absorb any contingent deformation. This portion  2  is configured in a rotationally symmetric manner about the longitudinal axis  9  of the nail  1 . The proximal tip  14  has a skid-shaped milled area  15  of a large radius on the posterior side  16 , which makes insertion easier. The radius of the milled area  15  is larger than half the diameter d of the portion  2 . 
     The axially adjoining portion  3  has two holes  21  in a medio-lateral direction with the adjacent portions have tangential milled areas  22 ,  23  on the anterior side  17  and the posterior side  16 , which impart greater flexibility to the nail  1  in these directions. This is particularly important because the nail  1  is introduced from the anterior side  17  of the tibia and needs to be moved around a corner in a way. In this flexurally resilient portion  3 , the milled areas  23  are deeper on the anterior side  17  and intersect the bore  7  (FIG. 5) because flexion will be in the anterior direction during insertion. Flexural resiliency is significantly larger in the anterior and posterior direction than in the direction perpendicular thereto. In a realized embodiment, e.g. in the section according to FIG. 5, the area moment of insertia I x =20.75 mm 4  about the axis which is shown horizontally and I y =137.01 mm 4  in a direction perpendicular thereto. In the section of FIG. 4, the respective values are I x =29.0 mm 4  and I y =66.68 mm 4 . Hence, the area moment of inertia in an anterior and posterior direction is smaller by at least a factor  2  than in a direction perpendicular thereto across at least one region of the flexurally resilient portion  3 . This factor is about 6.6, i.e. between 4 and 10, in the region of the section of FIG.  5 . The portion  3  is circularly cylindrical in the surroundings of the holes  21 . These regions  24  serve as supports and prevent the portion  3  from kinking when under a pressure. 
     The shank  4  of the nail  1  which lies contiguous to the flexurally resilient portion  3  consists of a tube  28  which connects the portion  3  and the distal locking portion  5  to each other. This tube  28  typically is of a diameter between 5 and 15 mm. In the embodiment shown, the diameter was chosen so that the tube  28 , when of a sufficient strength, was configured to be as soft (resilient) as possible. The distal end of this tube  28  has disposed thereon a bend  29  which passes over into the distal locking portion  5 . The angle α between the axis  9  in the tube  28  and the axis  30  in the distal portion  5  may range between 5° and 30°. It is 15° in the embodiment shown. In the further course, the cross-section of the tube  28  increases in the bend  29  so that there is a steady transition from the smaller diameter of the tube  28  to the larger diameter of the distal locking portion  5 . 
     This distal locking portion  5  has at least two cross-bores  31 ,  32  with the distal bore  32  being made as an elongated hole in an axial direction. These bores  31 ,  32  serve for receiving the distal locking bolts  6 , the proximal bore  31  is for static locking bolts, the elongated hold  32  is for dynamic or compression-locking bolts  6 . 
     The distal end has a disposed thereon a groove  33  about 3 to 5 mm in depth, which radially runs through the diameter of the nail  1 . The axially bored hole of the nail  1  is largest here. Adjacent to this groove  33 , a female thread  34  begins at a minor inside diameter in an axial, proximal direction and ends just in front of the most distal cross-bore  32 . The distal groove  33  and the female thread  34  serve as an interface with the target apparatus during introduction, as a docking point during extraction, and for receiving a compression or closure screw  35 . 
     The longitudinal bore of the distal locking portion, moreover, is of a larger diameter than the cannular bore  7  in the rest of the nail  1  in order that a compression screw  35  can be received, which perpendicularly pressed the bolt  6  disposed in the distal bore  32 . Thus, a compression of the tibia may be achieved by turning in the screw  35 . Furthermore, the distal anterior end of the nail  1  has disposed thereon a chamfer  36  which is to avoid damage to soft body parts if the nail should slightly come out of the bone because of compression. 
     For surgery, the patient is positioned on its back with his blood circulation blocked on his thigh and his leg covered and freely movable. Access is made via a longitudinal incision 5 to 7 cm in length at the front of the distal lower leg and the upper ankle joint. After the subcutis and the fascia are cut open the retinacula of the extensors is cut open in the longitudinal direction. The musculus extensor halluzis longus is retracted medially, the tibialis anterior vessels and the nervous peronaeus profundus are retracted laterally by means of a vein hook. The anterior cortex of the distal tibia is exposed subperiostally. Great care is taken not to open the articular capsule of the upper ankle joint. 
     A pricker is used to open the cortex of the distal tibia closely above the lug of the articular capsule. A guide wire having a slightly bent tip is introduced into the medullary space and, across the fracture and the osteotomy, is advanced upwards into the proximal tibia and is moved on into the emminentia intercondylaris. The medullary canal is opened by means of flexible boring shanks in a retrograde direction. The boring operation begins at a 6 mm diameter of the boring heads, is continued at 0.5 mm steps, and ends once the diameter is by 1 mm larger than the medulla nail  1  which was selected. 
     The isthmus of the tibia will remain the region for the firm, intromedullary fixation of the medulla nail here. The selected medulla nail  1  may be advanced by hand in most cases. If necessary, a slight hammer blows may make it easier to insert the nail  1 . If resistance becomes too large during its insertion a smaller diameter is chosen for the nail. The end of the nail  1  (the chamfer  36 ) should be introduced so as to be somewhat deeper than the surface of the ventral tibia edge. After the compression screw  35  is inserted and compression is performed the nail  1  will then be flush with the bone surface. 
     The proximal locking in the tibia head is effected by the free-hand technique through the tibia head. Self-tapping 5 mm screws are preferably used for this purpose. The locking screws in the tibia head preferably are inserted from the medial to lateral points and from the ventral to dorsal points. The distal locking screws  6  are inserted by means of a target apparatus. 
     The advantages of the tibia nail are as follows: 
     It enables insertion in a retrograde direction and is specifically employed in very high tibia head fractures where a medulla nail implantation has been completely impossible as yet. 
     Being an intramedullary force carrier, the nail is adapted to be loaded at an early time and is by far more sturdy than in conventional types of fixation. This makes possible a better physiotherapeutic after treatment of the patient and gives him a quick recovery. 
     The tibia nail allows a minimally invasive operation technology. 
     It improves the patient&#39;s comfort. 
     The tibia nail in the medullary space does not impair periostal blood supply. 
     It avoids neuronal lesions. 
     The tibia nail described is primarily suited for use in proximal tibia fractures, revision osteotomies, callus distractions, segment transfer, knee joint transplantations, etc. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.