Anchorage nail for the treatment of hollow bone fractures

Abstract: An anchorage nail for the treatment of fractures of hollow bones is disclosed. It has a hollow shaft (10) with at least one transverse hole (28,30) disposed in a first end region (12), for receiving bone screws. In a second region (18), adjacent the driving end (24), a further transverse opening (26) is disposed. The nail is characterised in that the shaft is straight, with an other diameter smaller than the inner diameter of the cortical bone, and in that the transverse opening (26) in the second end region is elongated along the nail axis. An inner thread is formed in the second end region, extending into the transverse opening, for receiving a threaded pin (54,62) which may be brought into contact with the shaft of a bone screw (82) introduced through the transverse opening (26).

Description: The present invention refers to a locking nail for the medical care of hollow bone fractures according to the preamble of claim 1. For the first time DE-U-77 12 901 discloses a locking nail which is used for the osteosynthesis. The locking nail is driven distally or proximally into the hollow bone after preparing the bone cavity. Using conventional nails, the bone cavity is often enlarged by drilling. The ends of the nail are provided with cross bores to receive cortical screws to fix the locking nail in both the axial and rotational direction. This effectively stabilizes the fracture. The known locking nail is axially slotted which is a drawback when the nail is subjected to a torsion by being driven in so that bony material is damaged. For mounting the cortical screws it is necessary to drill the corticalis in alignment with the cross bores of the nail. There are known numerous positioning means to find the cross bores in the nail and to drill the bores in the corticalis. A number of positioning means use X-rays and a monitor. Other positioning means cooperate with the driving-in end of the nail. The distance of the cross bores from the nail end is known; accordingly this determines the position of the cross bores in the bone. Since, however, the known locking nails are mounted by exerting substantial forces, the nail shaft may twist or bend so that the expected position of the cross bore deviates from the actual position. Up to now the locking nails have been primarily used for leg bones, wherein a special shape and dimension of the nail shafts have been provided for the femur and the tibia. In particular the shafts have been subjected to a curvature corresponding to the bone shape. It is of course expensive to store a variety of locking nails to be used for different bones. A locking nail of the kind indicated above has become known from the DE-U-85 33 134. The hollow nail shaft has a first and a second end. At least one cross bore for receiving a bone screw is provided at the first end, and an oblong hole for a bone screw is provided at the second end adjacent to the driving end of the nail. The driving end is provided with an inner threaded portion for the accommodation of a screw bolt which may be brought into contact with the shaft of the bone screw extending through the oblong hole. The known locking nail is to form a nail which is either to act as a static means for stabilizing fractures or as a dynamic means. In the latter case, the screw bolt must be removed or moved away from the bone screw in the oblong hole to allow movement of the bone fractures relative to each other. From the WO-A-91/00065 a locking nail has become known defined as distraction means. The known nail uses a rod which is rotatably supported by specific bearing means located in the interior of the nail. The rod has an external thread which engages an internal thread of the solid portion of the rod which is displaceably, however, non-rotatably located inside the nail shank. The object of the invention is to provide a locking nail for the medical care of hollow bones capable of three application purposes, namely static stabilization, compression or distraction. This object is attained by the features of patent claim 1. The locking nail according to the invention provides a nail shaft which is straight and which has an outer diameter which is for the most part smaller than the inner diameter of the corticalis. Therefore, enlarging the bone cavity by drilling is not necessary in most cases. This facilitates not only the implantation, but reduces the damage of the bone. For the bone growing process the bone tissue should be damaged as least as possible. The smaller diameter reduces the stability of the nail, but by providing the nail with a straight, unslotted shaft, the nail may transmit substantial forces even having a smaller diameter. This smaller diameter may be selected such that identical dimensions are selected for the femur and tibia and even for the humerus. Due to the reduced diameter the curvatures of the bone may be disregarded. For increasing stability, a circular cross section is preferred, at least for the most part of the nail shaft. The cross bore facing the driving end is formed as an oblong hole and in this portion the nail shaft includes an inner thread to receive a screw bolt. The inner end of the screw bolt may be pressed against a bone screw extending through the oblong hole. The screw bolt thus defines an axial abutment for a static locking. However, when after the implantation or at a later time the fracture shall be dynamized, the screw bolt may be somewhat released so that the bone segments joined through the bone nail have a relative play. Contrarily, by tightening the screw bolt, the fracture may be compressed. The telescopic sleeve is pushed onto the nail shaft from the driving end which sleeve cooperates with axial stop means of the nail shaft and is fixed against rotation on the shaft. The sleeve includes at least a cross bore which is aligned with respect to the oblong hole. Preferably, the cross bore of the telescopic sleeve is aligned with the end of the oblong hole facing away from the driving end when the sleeve contacts the axial stop means. The range of application of the locking nail is thus extended by using the telescopic sleeve. A static support of the fracture is obtained if the cortical screw is located at the end of the oblong hole facing away from the driving end and if the inner end of the screw bolt abuts the cortical screw. However, it is necessary that the telescopic sleeve is axially fixed. To obtain a compression, the nail shaft is further driven in when the telescopic sleeve is locked. By turning a compressing screw with respect to the inner thread of the nail shaft, the nail shaft and the telescopic sleeve may be displaced towards each other to urge the bone fragments against each other after the free end of the nail shaft has been locked. When a distraction is to be obtained, the nail shaft and telescopic sleeve are locked by the cortical screws. By turning a distracting screw within the thread of the telescopic sleeve, nail shaft and telescopic sleeve are displaced away from each other to move the bone fragments apart. Nail shaft and sleeve are held non-rotatably with respect to each other. Accordingly, the nail shaft may comprise a pair of opposite flats cooperating with a corresponding inner profile of the sleeve. The ends of the flats preferably form stop means for the sleeve. The outer diameter of the sleeve gradually tapers towards the stop means. Thus the transition between the nail shaft and the sleeve is formed by a relatively small step which causes no problem for driving and handling the device. It is of course possible to provide a constant diameter over the whole length of the nail shaft. For forming the flats and for increasing the stability within the region of the oblong hole it is preferred to slightly enlarge the diameter in the region covered by the sleeve. A standard nail may have a diameter of preferably 9 mm. The region covered by the telescopic sleeve is selected to be 10 mm for example. The cross bore of the nail shaft facing away from the driving end must be detected in a conventional manner when the nail is mounted in the bone. The telescopic sleeve including a cross bore cooperates with a position device engaging at least a recess at the free end of the telescopic sleeve, for example. When the nail according to the invention is applied for example to the humerus by being distally driven in, the telescopic sleeve is not needed. But even then, the position of the bone screw with respect to the oblong hole in the nail shaft may have a different position when used for the femur or the tibia for example. Thus, the telescopic sleeve or, respectively, the nail shaft must have a different relative position with respect to the first leg of a positioning device. As mentioned before, the diameter of the locking nail may have a standard size disregarding the application. The same applies to the cortical screws. However, the length of the nail shaft and the cortical screw should be suitably selected. An embodiment of the invention is described in more detail in referring to the drawings which show: Fig. 1 a section of a locking nail according to the invention along line 1-1 in Fig. 2. Fig. 2 a side view of the locking nail of Fig. 1. Fig. 3 a section of a nail of Fig. 1 along line 3-3. Fig. 4 a section through a telescopic sleeve for the nail of Fig. 1. Fig. 5 a part section of Fig. 4 turned 90° around. Fig. 6 an end view of the sleeve of Fig. 1 in the direction of arrow 6 in an enlarged scale. Fig. 7 a side view of a first embodiment of a compression screw for the nail of Fig. 1. Fig. 8 a second embodiment of a compressing screw. Fig. 9 a side view of a distraction screw for the nail of Fig. 1. Fig. 10 a side view of a cortical screw for the nail of Fig. 1. Fig. 11 an end view of the cortical screw in the direction of arrow 11 in Fig. 10. Fig. 12 a section of the part of the screw in Fig. 10 indicated by the circle 12. Before describing the embodiments in detail it should be mentioned that the dimensions shown in the Figures do not correspond to the actual size of the components and are not in proper scale with respect to each other. A hollow nail shaft 10 comprises a first end 12 which is slightly drawn in. The nail shaft 10 comprises a first portion 14 of circular cross section having an outer diameter of 9 mm, for example. The portion 14 passes over a tapered portion 16 to a second portion 18 including opposite flats 20 and 22. Close to the second end 24, an oblong hole 26 extends through the portion 18. The axis of the oblong hole extends in the same plane as the cross bores 28 and 30 at the first end of the nail shaft 20. The flats 20, 22 in combination with the tapered portion 16 form small stop means 32, 34. It is to be seen that the portion 18 in front of hole 26 has a somewhat larger wall thickness than within the region of the hole. In the region of the oblong hole 26 up to end 24 there is provided an inner thread 36. A telescopic sleeve 40 shown in Figs. 4 to 6 has a circular cross section and at least partly an inner profile which corresponds to the profile of the nail portion 18, i.e. internal flats as shown at 42. Still further, the outer diameter gradually decreases from one end to form a tapered portion 44. The telescopic sleeve 40 includes a pair of cross bores 46 and 48 as well as an internal thread portion 50 at the other end. At the end of the end portion a pair of opposite recesses 52 is formed. The sleeve 40 is pushed over the nail portion 18 up to stop means 32, 34. The sleeve then is non-rotatably mounted on nail shaft 10. In this position bore 48 is aligned with the end of oblong hole 26 facing away from end 24. A first compression screw 54 comprises a shaft portion 56 free of threads and a threaded portion 58, the end thereof including an inner hexagon 60. The threaded portion 58 can be screwed in the inner thread portion 36 of nail shaft 10. The free end of the shaft portion 56 coacts with a bone screw extending through oblong hole 26. When the screw is located between the ends of hole 26, it is possible to subject the fractured segments to a compressing force. For example this is necessary when the nail (without telescopic sleeve) is distally driven in the humerus. A second compression screw 62 comprises a relatively long threaded portion 64 and a head 66, cylindrical portion 68 formed below head 66. Head 66 is provided with an inner hexagon 70. The threaded portion 64 is screwed in the inner thread portion of nail shaft 10. The head 66 cooperates with the telescopic sleeve 40 in as much the cylindrical portion 68 enters the sleeve 40 whereas the outwardly projecting head portion contacts the end of telescopic sleeve 40. By actuating the compression screw 62, the sleeve 40 may be shifted along the nail portion 18 under the condition that the sleeve end is remote from the stop means 32, 34. For example this is true when after locking sleeve 40 by inserting bone screws through the bores 46, 48, the nail shaft 10 is further driven into the bone and then fixed. By turning the compression screw 62, nail shaft 10 and sleeve 40 are moved towards each other to apply a compression force to the bone fragments. A distraction screw 72 shown in Fig. 9 comprises a head 74 including an external thread portion 76 and an internal hexagon 78 as well as a short shaft portion 80. The head 74 cooperates with the internal thread portion 50 of the sleeve 40, while the shaft portion 80 cooperates with a bone screw extending through the bore 46 to move the sleeve 40 and the nail shaft 10 apart when both are fixed in the bone. Thus, it is possible to exert a distracting force on the bone fragments. Figs. 10 to 12 illustrate a cortical screw 82 to be inserted through the cross bores 28, 30 and through oblong hole 26 in the nail shaft and the cross bores 46, 48 of the sleeve 40. The screw comprises a head 84 including an inner hexagon, a threaded portion 86 of relatively short length below head 64 and a cutting groove 88 formed at the free end. A relatively long threadless shaft portion 90 ending in a conical tip 92 including opposed drilling grooves 94 extends from the threaded portion 86. Fig. 12 shows that the thread of the portion 86 comprises first flanks 96 extending perpendicularly to the screw axis and second flanks 98 extending under an angle of 60° which facilitates easily turning the thread pofile in the drilled bore in the corticalis, whereas the steep flanks 96 serve to create a high back-holding force.

Claims: A locking nail for the medical care of hollow bone fractures comprising a hollow nail shaft (10) having a first and a second end (12, 24), at least one cross bore (28, 30) for receiving a bone screw at the first end (12) and an oblong hole (26) for a bone screw at the second end (24) adjacent to the driving end, an inner threaded portion (36) being formed at the second end for receiving a screw bolt (54, 62) which may be brought into contact with the shaft of the bone screw (82) extending through the oblong hole (26), characterized in that a telescopic sleeve (40) is provided to be pushed onto the nail shaft (10) from the driving end (24) which co-operates with axial stop means (32, 34) of the nail shaft (10) which restrict movement of the sleeve (40) towards the first end (12), the sleeve (40) being non-rotatably connected to the shaft (10), in that further the telescopic sleeve (40) comprises at least a cross bore (46, 48) to be brought in alignment with the oblong hole (26), and in that the telescopic sleeve (40) has an internal thread portion (50) at its end facing away from the stop means (32, 34) adapted to receive a distracting screw (72). The locking nail of claim 1, characterized in that a headless screw bolt (54) is provided comprising an inner hexagon (60) for applying a rotating tool. The locking nail of claim 1 or 2, characterized in that the threaded portion (36) extends into the area of the oblong hole (26). The locking nail of one of the claims 1 to 3, wherein the cross bore (46, 48) of the telescopic sleeve (40) is aligned with the end of the oblong hole (26) facing away from the driving end (24) when the telescopic sleeve (40) contacts the stop means (32, 34). The locking nail of one of the claims 1 to 4, wherein the nail shaft (10) comprises a pair of opposed flats (20, 22) in the area of the telescopic sleeve (40) and in that the internal profile of the telescopic sleeve (40) corresponds at least partially in shape thereto. The locking nail of claim 5, wherein the ends of the flats (20, 22) form the stop means (32, 34). The locking nail of one of the claims 1 to 6, wherein the area of the nail shaft (10) being beyond the telescopic sleeve (40) has a slightly smaller diameter than the remaining nail shaft (10). The locking nail of one of the claims 1 to 7, wherein the diameter of the nail shaft (10) is 9 mm. The locking nail of one of the claims 1 to 8, wherein the wall thickness of nail shaft (10) in the area of the stop means (32, 34) up to the oblong hole (26) is larger than that of the remaining area. The locking nail of claims 7 and 8, wherein the diameter in the area of the telescopic sleeve is 10 mm. The locking nail of one of the claims 1 to 10, wherein the outer diameter of the telescopic sleeve (40) gradually tapers towards the stop means (32, 34). The locking nail of one of the claims 1 to 11, wherein the free end of the telescopic sleeve (40) comprises at least a recess (52) for allowing engagement of a positioning device. The locking nail of one of the claims 1 to 12, wherein the head (66) of the screw bolt (62) co-operates with the free end of the telescopic sleeve (40).

Inventors: BEHRENS KLAUS FRIEDRICH ADOLF, STAPERT JOUWERT WILHELMUS JACO, BEHRENS, KLAUS FRIEDRICH ADOLF, DIPL.-ING., STAPERT, JOUWERT WILHELMUS JACOBUS LUCAS, DR. MED.
Applicants: HOWMEDICA GMBH
Application year: 1992
Main classification: A61B17
IPC codes: A61B17