CH707804A2 - Two-piece shaft for a hip joint prosthesis. - Google Patents

Abstract

A two-piece stem (10) for a hip joint prosthesis comprises a base stem (1) and a stem tip (5) detachably connected to the base stem. The base shaft (1) has a continuous longitudinal bore (3) which opens at its distal end into a recess (4) for the connection of a subsequently inserted femoral intramedullary nail, wherein the recess has an inner lateral surface (4b) into which the thigh Mark nail is usable. The shaft tip (5) is inserted into the recess (4) of the base shaft (1) and closes the recess (4). The inner lateral surface (4b) of the recess (4) extends axially parallel to the longitudinal axis (4a) of the recess (4), and the distal end of the base shaft (1) has a shoulder (1a) on which the shaft tip (5) in the inserted state lies flat and thereby continues the outer surface of the base shaft (1).

Description

The invention relates to a two-part shaft for a hip joint prosthesis, which comprises a base shaft and a stem tip removably connected to the base shaft, wherein the base shaft has a continuous longitudinal bore, which at its distal end in a recess for the connection of a later to be inserted thigh Intramedullary pin leads, wherein the recess has an inner circumferential surface into which the femoral intramedullary nail is inserted, wherein the stem tip is inserted into the recess of the base shaft and closes the recess.

Hüftprothesenträger with weak, porotic bone or after traumatic events, can suffer femur shaft fractures in fixed prosthesis, which lie below the distal end of the prosthesis. Prosthetic care for such cases is often very difficult. The common surgical procedure is usually done over a long-flat plating with a long bone plate and cortical screws. The disadvantage here is in principle that the operation can not be performed covered, because the bone must be exposed for the creation of the plate. Conflicts between prosthesis, plate and screw can lead to the failure of the Ostheosynthese because sufficient stability could not be achieved.

The search for other solutions, in particular, in a muted way, i. without the exposure of the femur bone to perform the treatment of the fracture leads to the creation of a connection between the prosthesis and a retrograde introduced intramedullary nail to achieve a new stability of prosthesis and femur bone.

Such an idea is based on the Austrian patent AT 502 137, which discloses an axial bore in the prosthesis, through which a lag screw can be introduced, which establishes a connection between the prosthesis and a retrograde introduced into the prosthesis intramedullary nail. It is proposed to adapt the prosthesis tip and the proximal head of the intramedullary nail to each other, as far as the dimensioning and design of the prosthesis tip permit at all. This creates a conical or truncated pyramidal connection between the prosthesis and the intramedullary nail or the prosthesis tip. At first glance, this solution seems to be sufficiently stable.

However, extensive tests and experiments have shown that this compound is not sufficiently stable according to AT 502 137, when a stronger force is effective for a long time. For example, the lag screw may bend, making the conical or truncated pyramid-shaped connection unstable. Subsequently, the connection can break at the transition from the prosthesis to the intramedullary nail. Another problem of the known shaft is that the preparation of the conical or truncated pyramidal connection between the shaft and shaft tip or intramedullary nail in relation to the required low tolerances is extremely delicate and expensive and in practice at the transition between the shaft and stem tip no continuous continuation of Shank surface can be achieved.

There is therefore still a need for a shaft for a hip joint prosthesis and its safe, stable and durable connection with an intramedullary nail. The shaft should be designed in two parts and produced with low tolerances and provide a smooth continuation of the outer surface of the base shaft to the shaft tip out. In particular, abrasion by micro-movements between the shaft and shaft tip should be largely eliminated in this shaft, so that a successful certification of the prosthesis produced therefrom is possible.

The present invention solves this problem by further developing the above-mentioned base shaft of the shaft for a hip prosthesis by the inner lateral surface of the recess of the base shaft is formed axially parallel to the longitudinal axis of the recess and the distal end of the base shaft has a shoulder on which the shaft tip when applied, it rests flat and continues the outer surface of the base shaft.

A very stable connection between the base shaft and the shaft tip or a subsequently inserted intramedullary nail is achieved when the inner circumferential surface of the recess is formed as a cylinder. A cylindrical inner circumferential surface can be produced by drilling or milling, offers a large contact surface for the shaft tip or intramedullary nail, absorbs transverse forces excellently and can be made very deeply into the base shaft. The lateral surface of a cylinder is geometrically defined so that it is formed by parallel straight lines. When the base is a circle, the cylindrical inner surface recess in the base shaft can be easily formed by drilling. If the base is an ellipse or a general surface, results in positive connection with the stem tip or intramedullary nail a rotationally fixed connection. A prism is a special case of a general cylindrical recess and also allows a stable rotationally fixed connection between the base shaft and the shaft tip or the intramedullary nail.

Experiments have shown that an exceptionally high stability of the connection between the base shaft and the shaft tip or the intramedullary nail is achieved.

If the base shaft has a shoulder surface which is substantially normal to the longitudinal axis of the recess, the shaft tip can rest safely and tightly on the base shaft and fixed.

For the secure fixing of the shaft tip in the base shaft, the shaft tip preferably has a guide surface, which is formed at least partially opposite to the inner circumferential surface of the recess.

In order to achieve a rotationally secure attachment of the stem tip in the base shaft, it is further provided that in the recess surrounding the wall of the base shaft projections or grooves are formed, which engage with grooves or projections of the shaft tip.

For the fixation of the stem tip in the base shaft, the stem tip fixing on. These fixing means preferably comprise spreading elements for pressing against the inner circumferential surface of the recess and a screw rotatable through the through-bore in the base shaft. Depending on the direction of rotation, the screw increases the spreading of the spreading or reduces it. The screw is preferably mounted captive in the shaft tip.

The invention further comprises a hip prosthesis with a shaft according to the invention and a joint ball connected to the shaft. In this case, a neck is integrated at the proximal end of the base shaft, on which the joint ball can be mounted.

The invention further comprises a hip prosthesis set with an inventive hip prosthesis and with an insertable through the longitudinal bore of the base shaft guide rod whose distal end is connected to the stem tip being, in particular by means of pierced hex wrench, the shaft tip to solve and distally from the base shaft of the Is to shift away from the base. According to the preferred fixing means described above, the guide rod engages in the screw for adjusting the spreading of the spreading elements. Preferably, the guide rod is bendable.

The inventive hip prosthesis set comprises in one embodiment of the invention at least one, selectable by size and use case intramedullary nail with a proximal coupling surface, which is insertable into the recess of the base shaft and at least partially opposite to the inner surface of the recess is formed. Preferably, the proximal end of the intramedullary nail is connectable to the distal end of the stylet to pull the intramedullary nail into the recess of the base shaft.

In a further embodiment of the invention, the hip prosthesis set comprises an insertable from the proximal end of the through hole of the base shaft tension screw, which is screwed to the proximal end of the intramedullary nail, whereby the intramedullary nail is held extremely stable in the base shaft.

The invention will now be explained in more detail using an exemplary embodiment with reference to the drawings. <Tb> FIG. 1 <SEP> shows the shank according to the invention for a hip prosthesis with removed stem tip in plan view. <Tb> FIG. FIG. 2 shows a section through the shaft and shaft tip along the line A-A of FIG. 1. FIG. <Tb> FIG. Fig. 3 shows a perspective view of the distal end of the shaft with partially inserted shaft tip. <Tb> FIG. 4 shows the shaft according to the invention for a hip prosthesis with inserted shaft tip in plan view. <Tb> FIG. 5 <SEP> shows a section through the shaft and the shaft tip along the line B-B of FIG. 4. <Tb> FIG. 6 <SEP> shows the stem tip in side view. <Tb> FIG. 7 <SEP> shows a section through the shaft tip along the line C-C of FIG. 6. <Tb> FIG. 8 <SEP> shows the stem tip in side view. <Tb> FIG. 9 <SEP> shows the stem tip in a perspective view from the proximal end. <Tb> FIG. 10, 11 and 12 <SEP> show a hip prosthesis set according to the invention in plan view, in section along the line D-D of Fig. 10 and on the basis of a detail E.

In the drawings, reference numeral 10 generally designates the two-part shaft according to the invention for a cementless implantable hip prosthesis. The two-part shaft 10 comprises a base shaft 1 and a stem tip 5 which is detachably connected to the base shaft 1. The base shaft 1 is provided in one piece with a neck 2 for the attachment of a joint ball (not shown). Provided inside the base shaft 1 is a continuous longitudinal bore 3 with a longitudinal axis 3 a, which opens at the distal end of the base shaft 1 into a recess 4 with a longitudinal axis 4 a, see in particular FIGS. 2 and 5. The longitudinal axes 3 a and 4 a of the longitudinal bore and the recess are preferably coaxial with each other, but are at least as far as close to each other that a pressure and tension rigid, preferably flexible guide rod easily through the longitudinal bore 3 and the recess 4 can be guided. The recess 4 is designed for the connection of a subsequently inserted femoral intramedullary nail. In the recess 4, a shaft tip 5 can be used, which is shown in Fig. 1 and Fig. 2 in the removed state, and in Fig. 4 and Fig. 5 is shown in the inserted state in which it closes the recess 4 and the distal tip of the shaft 10 forms. The base shaft 1 is implanted with inserted shaft tip 5. The inner circumferential surface 4b of the recess 4 extends axially parallel to the longitudinal axis 4a of the recess 4. In this embodiment, the inner circumferential surface 4b is formed as a circular cylindrical surface. Other embodiments may comprise elliptical or general cylindrical surfaces or, as a special case of the general cylinder, a prism, all these other embodiments offering the advantage of a rotationally secure connection to the shaft tip 5 or to an intramedullary nail to be inserted into the recess 4. Furthermore, the distal end of the base shaft 1 has a shoulder 1a, on which the shaft tip 5 abuts flatly in the inserted state and thereby continues the outer surface of the base shaft 1, see FIGS. 4 and 5. The heel area of the heel 1a lies substantially normal to the longitudinal axis 4a of the recess 4.

The shaft tip 5 has a guide surface 5a, which is formed in sections opposite to the inner circumferential surface 4b of the recess 4. As a result, a secure fit of the shaft tip 5 is ensured in the recess. Thus, despite the circular-cylindrical recess 4 in this embodiment, a rotationally secure seat of the shaft tip 5 is ensured in the recess, 1 grooves 1b are formed in the surrounding the recess 4 wall of the base shaft, which engage with projections 5c of the shaft tip 5. Alternatively to this embodiment could be formed on the inner surface 4b projections which engage with grooves of the shaft tip.

For fixing the stem tip 5 in the recess 4 5 Fixiermittel are provided on the stem tip, the spreading elements have 5b for pressing against the inner circumferential surface 4b of the recess 4. The expansion elements 5b are biased, preferably resilient, in a non-splayed position and are brought by means of a captive arranged in the shaft tip 5 screw 6 in the spread position by the screw is rotated axially, and is moved along inclined surfaces of the expansion elements 5b , so that depending on the direction of rotation, the screw 6, the spreading elements 5b further spread apart or reduces the spread in cooperation with the spring action of the expansion elements 5b. As an alternative to the fixing cone designed as fixing means, the shaft tip could also be screwed by means of an insertable from the proximal end of the through hole 3 of the base shaft 1 lag screw.

10, 11 and 12, a hip prosthesis set is shown, which includes a hip prosthesis, comprising the shaft 10 with the base shaft 1 with integrated neck 2 and a connectable to the neck 2 joint ball, the selected from a number of different sized joint balls has been. The selected joint ball, not shown, has a blind hole with which it can be pushed onto the neck 2 along the axis 40 of the neck. Furthermore, the hip prosthesis set comprises a non-illustrated, insertable through the longitudinal bore of the shaft, pressure and tensile guide rod whose distal end is connected to the shaft tip by being inserted into the screw 6, whereby the stem tip can be solved by turning the guide rod. Furthermore, the hip prosthesis set comprises an intramedullary nail 20 with a proximal coupling surface 21, which is insertable into the recess 4 of the base shaft 1 and at least partially opposite to the inner lateral surface 4b of the recess 4 is formed. The proximal coupling surface 21 of the intramedullary nail 20 is connectable to the distal end of the guide rod to pull the intramedullary nail 20 into the recess 4 of the base shaft. After the intramedullary nail 20 has been introduced into the recess 4, it can be screwed to a pull-in screw 30 which can be introduced from the proximal end of the through-hole 3 of the base shaft 1. For this purpose, the lag screw 30 at its distal end an external thread 32 which is screwed with an internal thread of a formed at the proximal end of the intramedullary nail 20 blind hole 22. The proximal end of the tension screw 30 is formed as a hexagon socket 31.

The use of the hip prosthesis set according to the invention is carried out as follows:

First, the hip prosthesis according to the invention is implanted without cement, with stem tip 5 attached to the base shaft 1. If the case arises that in the person equipped with such a hip prosthesis a thigh fracture occurs, which must be fixed by a femoral intramedullary nail 20, then the stem tip 5 is released by means of the pressure-resistant guide wire from its fixation in the recess 4 of the base shaft 1, by inserting the guidewire from the proximal end of the through hole 3 of the shaft 1 until it engages the screw 6 and then rotating it in such a direction until the fixation of the shaft tip 5 is released by means of a hexagonal wrench. Thereafter, the stem tip 5 is pushed by the guidewire in the distal direction through the medullary canal of the femur bone until it is expelled from a previously drilled in Notch (between the femoral condyles) hole from the femur and then removed from the guide wire. After removal of the stem tip 5, the distal end of the guidewire is connected to the proximal end of the femoral intramedullary nail (eg threaded through the double threaded blind hole 22 of the intramedullary nail 20) and then inserted with the guidewire through the hole in the notch into the medullary canal of the femur and pulled in the proximal direction until it slides with its proximal coupling surface 21 into the recess 4 of the base shaft 1, where it finds a secure fit due to its opposite to the inner surface 4b of the recess 4 formed outer surface. Thereafter, the guide wire is removed. Subsequently, the intramedullary nail 20 is firmly screwed with an inserted through the longitudinal bore 3 of the base shaft 1 lag screw 30. After this determination, as required in corresponding transverse bores 23 of the intramedullary nail 20 fastening screws are used, which are inserted into the bone material of the femur for fixation.

The main advantages of the subject invention over the known embodiments are a much more durable and stable connection between base shaft and intramedullary nail, improved handling during the operation and a feasibility for a variety of different sizes.

Claims (12)

A two-piece stem (10) for a hip joint prosthesis comprising a base stem (1) and a stem tip removably connected to the stem stem (5), the stem stem (1) having a longitudinal longitudinal bore (3) formed at its distal end in FIG a recess (4) for the connection of a subsequently inserted femoral intramedullary nail opens, wherein the recess has an inner lateral surface (4b) into which the femoral intramedullary nail can be inserted, wherein the stem tip (5) into the recess (4) of the base shaft (4) 1) is inserted and the recess (4) closes, characterized in that the inner lateral surface (4b) of the recess (4) axially parallel to the longitudinal axis (4a) of the recess (4) and the distal end of the base shaft (1) has a paragraph ( 1a), on which the shaft tip (5) rests flat in the inserted state and thereby continues the outer surface of the base shaft (1). 2. Shank according to claim 1, characterized in that the inner lateral surface (4b) of the recess (4) is designed as a cylinder. 3. Shank according to claim 1 or 2, characterized in that the inner circumferential surface of the recess is formed as a prism. 4. Shank according to one of the preceding claims, characterized in that the shoulder (1a) has a shoulder surface which is substantially normal to the longitudinal axis (4a) of the recess (4). 5. Shaft according to one of the preceding claims, characterized in that the shaft tip (5) has a guide surface (5a) which is at least partially opposite to the inner circumferential surface (4b) of the recess (4). 6. Shaft according to one of the preceding claims, characterized in that in the recess (4) surrounding wall of the base shaft (1) projections or grooves (1 b) are formed, which engage with grooves or projections (5 c) of the shaft tip (5) , 7. shank according to one of the preceding claims, characterized in that the shank tip (5) has fixing means, which preferably comprise spreading elements (5b) for pressing against the inner circumferential surface (4a) of the recess and a screw arranged in the shaft tip (6), wherein depending on the direction of rotation, the screw (6), the spread of the expansion elements (5 b) is increased or decreased. 8. hip prosthesis with a shaft (10) according to any one of the preceding claims and a shaft connected to the shaft (10) ball. 9. hip prosthesis set with a hip prosthesis according to claim 8 and with a through the longitudinal bore (3) of the base shaft (1) insertable guide rod whose distal end with the stem tip (5) is connectable to the stem tip (5) to solve and distally from the To move out base shaft (1). 10. Hip prosthesis set according to claim 9, characterized by at least one intramedullary nail (20) with a proximal coupling surface (21) which is insertable into the recess (4) of the base shaft (1) and at least partially opposite to the inner lateral surface (4 b) of the recess (4 ) is trained. 11. Hip prosthesis set according to claim 10, characterized in that the proximal end of the intramedullary nail (20) with the distal end of the guide rod is connectable to pull the intramedullary nail in the recess (4) of the base shaft (1). 12. hip prosthesis set according to claim 9 or 10, characterized by a proximal end of the through hole (3) of the base shaft (1) insertable lag screw (30) which is screwed to the proximal end of the intramedullary nail (20).