Abstract:
The kit for implanting a cementable endoprosthesis comprises a fitting instrument ( 3 ) and at least two components to be implanted, namely an endoprosthesis shaft ( 4 ) and a proximal centering and/or sealing element ( 1 ), the shaft ( 4 ) and the fitting instrument ( 3 ) being designed to be able to be coupled to each other, and the centering and/or sealing element ( 1 ) being designed to be placeable on the shaft ( 4 ) and to be displaceable in the direction of extension of the latter, and either the fitting instrument ( 3 ) comprising a limit stop part ( 3   e ) which forms a limit stop relative to the centering and/or sealing element ( 1 ), or a marking ( 6 ) being arranged on the fitting instrument ( 3 ) and on the shaft ( 4 ) in order to ensure a defined mutual position between the centering and/or sealing element ( 1 ) and the shaft ( 4 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to a kit for implanting a cementable endoprosthesis according to the preamble of claim 1. 
     BACKGROUND OF THE INVENTION 
     Document DE 195 18 391 A1 discloses a proximal centering and sealing element for implanting a cementable endoprosthesis shaft, which element on the one hand serves as a proximal centering aid and on the other hand prevents escape of the cement in the proximal direction, as a result of which, when inserting the endoprosthesis shaft into the medullary cavity, there is an increase in the pressure of the bone cement located therein. 
     This known combination of endoprosthesis shaft and suitably adapted centering and sealing element has the disadvantage that the depth of insertion of the endoprosthesis shaft in the medullary cavity of the femur in the proximal-distal direction can be set only with difficulty and therefore inexactly. In addition, the centering and sealing element has only a limited sealing effect and inadequate centering in the medial-lateral direction. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to make available a set of instruments permitting more precise implantation of a cementable endoprosthesis shaft. 
     This object is achieved by means of a kit having the features of claim  1 . Dependent claims  2  through  17  relate to further advantageous embodiments of this kit. 
     The object is achieved in particular by means of a kit for implanting a cementable endoprosthesis, comprising a fitting instrument and at least two components to be implanted, namely an endoprosthesis shaft and a proximal centering and/or sealing element, the shaft and the fitting instrument being designed to be able to be coupled to each other, and the centering and/or sealing element being designed to be placeable on the shaft and to be displaceable in the direction of extension of the latter, and either the fitting instrument comprising a limit stop part which forms a limit stop relative to the centering and/or sealing element, or a marking being arranged on the fitting instrument and on the shaft in order to ensure a defined mutual position between the centering and/or sealing element and the shaft. 
     This embodiment according to the invention has the advantage that the depth of fitting of the endoprosthesis shaft in the medullary cavity of the femur can be adjusted even during implantation. Therefore, it is still possible during implantation to adjust, for example, the length of the femur or depth of fitting of the endoprosthesis shaft in such a way that after the operation has been completed, both legs are the same length. In a preferred embodiment, the kit comprises a manipulating instrument which is inserted into the medullary cavity of the femur before fitting the shaft, in order to determine the optimum depth of fitting, so that in particular an optimum leg length or optimum ligament tensioning is achieved. The optimum depth of fitting which is determined in this way is read off and the endoprosthesis shaft is then inserted into the femur corresponding to this depth of fitting. 
     The proximal centering and/or sealing element has, in the proximal area of the femur, the task of centering the endoprosthesis shaft in the medullary cavity or sealing off the gap between medullary cavity and shaft, in order to ensure that the bone cement located in the medullary cavity cannot flow out, or of providing centering and sealing at the same time. This centering and sealing element which ensures both centering and sealing is preferably adapted in design to the geometry of the shaft in such a way that a displacement of the shaft along the sealing element in the distal direction is possible while maintaining the sealing effect. 
     The centering and sealing element can be placed on the resected femoral neck and can be inserted at least partially into the medullary cavity in the proximal area thereof so that the endoprosthesis shaft to be inserted subsequently is inserted in the medullary cavity with all-round centering, the element additionally exerting a sealing effect so that the bone cement located in the medullary cavity is prevented from escaping. 
     In an advantageous embodiment, the proximal centering and sealing element consists of a sleeve-shaped body extending in a proximal-distal direction, the body having two broad-side boundaries and two narrow-side boundaries which enclose an essentially rectangular inner space, and the two broad-side boundaries each forming inner side surfaces extending essentially parallel in the proximal-distal direction. This centering and sealing element is especially suitable for endoprosthesis shafts of blade-type design whose broad sides extend approximately parallel in the proximal-distal direction. In this way, a particularly good sealing effect is achieved between the centering and sealing element and the endoprosthesis shaft. A centering and/or sealing element is designed as a sleeve-shaped body whose inner space, in an advantageous embodiment, is designed such that a movement of the shaft in the proximal-distal direction is also possible during implantation of the endoprosthesis shaft. If this is desired, then the shaft would be able to settle even some time after implantation since the movement in the proximal-distal direction is not impeded. 
     The centering and/or sealing element advantageously consists of a polymerized bone cement, in particular polymethyl methacrylate (PMMA). During implantation, this centering and/or sealing element binds chemically to the bone cement present to form a particularly homogeneous connection. However, the centering and/or sealing element can also consist of another material, in particular of a metal such as a biocompatible titanium alloy. 
     The centering and/or sealing element satisfies either a centering or a sealing function, or both functions simultaneously, said functions being: 
     to center the shaft in the proximal section of the medullary cavity; 
     to guide the shaft centrally in the proximal-distal direction during fitting of the shaft; 
     to prevent tilting in the medial-lateral direction and also twisting of the shaft; 
     to seal off the gap occurring between the shaft and the femur in the proximal area so that pressure is exerted on the bone cement located in the medullary cavity. 
     The centering and/or sealing element has, in the proximal direction, an end face which is advantageously used as a reference surface. The centering and/or sealing element is preferably inserted into the medullary cavity in such a way that said reference surface is flush with the resected surface of the femoral neck. The endoprosthesis shaft is secured on a fitting instrument prior to insertion, a spacer element additionally being secured on the fitting instrument, said spacer element being designed in such a way that with the endoprosthesis shaft inserted deep in the medullary cavity, it lies on the reference surface of the centering and/or sealing element and prevents any further insertion of the shaft. By means of this spacer element which is available in different sizes, the depth of fitting of the endoprosthesis shaft can be adjusted exactly with respect to the resected surface. A spacer element corresponding to the desired depth of fitting is chosen and is secured on the fitting instrument prior to insertion of the endoprosthesis shaft. 
     A kit is understood as comprising the mutually adapted parts of centering and/or sealing element, endoprosthesis shaft and fitting instrument, if appropriate in combination with one or more spacer elements, and of this kit only the centering and/or sealing element and the endoprosthesis shaft are intended to remain as implants in the body. 
     A number of illustrative embodiments of the invention are described below with reference to figures, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of a proximal centering and/or sealing element; 
     FIG. 2 a  shows a side view of a further proximal centering and/or sealing element; 
     FIG. 2 b  shows a cross section through the element according to FIG. 2 a;    
     FIG. 2 c  shows a top view of the element according to FIG. 2 a;    
     FIG. 3 shows a kit comprising a fitting instrument, a centering and/or sealing element, a spacer element and a shaft; 
     FIG. 4 shows a shaft which has been inserted with a fitting instrument according to FIG. 3; 
     FIG. 5 shows a cross section through a further illustrative embodiment of a centering and/or sealing element; 
     FIG. 6 shows a further kit comprising a fitting instrument, a centering and/or sealing element and a shaft; 
     FIG. 7 shows a further kit comprising a fitting instrument, a centering and/or sealing element and a shaft. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 3 shows an illustrative embodiment of a kit according to the invention, comprising an endoprosthesis shaft  4  which is designed as a straight shaft, the actual shaft  4   f  having an essentially rectangular cross section with two narrow-side surfaces  4   c,    4   d  and two broad-side surfaces  4   e.  At the proximal end, the shaft  4   f  has an internal thread  4   a  and a cone  4   b  for a joint head. The kit further comprises a fitting instrument  3  which has a connection rod  3   d  on which a stamp  3   c  is secured which opens into an adapter piece  3   b  and an external thread  3   a.  The kit further comprises a spacer element  2  which is designed as a sleeve-shaped, rectangular body  2   d,  with two side wings  2   a  which form an upper limit stop surface  2   b  and a lower limit stop surface  2   c.  The kit also comprises a proximal centering and/or sealing element  1 . The spacer element  2  is designed in such a way that it lies with its upper limit stop surface  2   b  on the stamp  3   c.  Upon insertion of the endoprosthesis shaft  4 , the lower limit stop surface  2   c  comes to lie at some time on the reference surface  1   m,    1   n  of the proximal centering and/or sealing element  1  and thereby limits, in the direction of extension of the shaft, the mutual positioning of endoprosthesis shaft  4  and centering and/or sealing element  1 . Since the centering and/or sealing element  1  lies with its surface  1   m,    1   n  preferably flush with the resected surface of the femur during implantation, the depth of fitting of the shaft  4   f  is determined by the spacer element  2 . A selection of spacer elements  2  are available to the operating surgeon, said spacer elements  2  being designed with different lengths in the proximal-distal direction C. The spacer element  2  represented in FIGS. 3 and 4 is to be regarded as only one illustrative embodiment from a large number of possible designs. The object of the spacer element  2  is to provide an upper and a lower limit stop  2   b,    2   c  in order to ensure a defined depth of fitting of the shaft  4  with respect to the proximal centering and/or sealing element  1  or its reference surface  1   m,    1   n.  This function can be satisfied by spacer elements  2  of widely different designs. 
     FIG. 4 shows an endoprosthesis shaft  4  in the inserted position, the femur not being represented. After inserting a manipulating shaft into the medullary cavity, the operating surgeon determines the depth of insertion of the shaft with respect to the resection plane. From the plurality of spacer elements, the operating surgeon selects the one which ensures the intended depth of insertion. This selected spacer element  2  is secured on the stamp  3   c  of the fitting instrument  3 , and the endoprosthesis shaft  4  is then screwed onto the external thread  3   a  via the internal thread  4   a.  The centering and/or sealing element  1  is then pushed onto the shaft  4   f  from the distal direction. The endoprosthesis shaft  4  together with the centering and/or sealing element  1 , as is represented in FIG. 4, is then inserted into the medullary cavity until the spacer element  2  abuts the proximal centering and/or sealing element  1  and as far as the resection plane which forms a reference plane. The bone cement located in the medullary cavity is thereby compressed and forced out from the medullary cavity toward the centering and/or sealing element  1 . At least the inner side surfaces  1   b,    1   c,    1   d  lie on the endoprosthesis shaft  4  and exert a sealing action. As long as the endoprosthesis shaft  4  does not lie with its side surface  4   d  on the inner side surface  1   e,  a gap  1   p  is formed between these surfaces, through which gap the bone cement can escape. An operating surgeon can cover this gap  1   p,  for example with his finger, and can thus control the escape of the bone cement relatively precisely by pressing his finger against the gap  1   p  or uncovering said gap. The inner side surface  1   e  can also be arranged with respect to the side surface  4   d,  or the shaft  4  can be pushed deep into the centering and/or sealing element  1 , in such a way that a sealing effect is achieved between these two surfaces  1   e,    4   d,  so that the element  1  acts simultaneously as centering and sealing element. In a preferred embodiment, the centering and/or sealing element  1  is designed, and the bone cement selected, in such a way that said bone cement flows all round the proximal centering and/or sealing element, the bone cement being forced out between the inner side surfaces  1   b,    1   c,    1   d,    1   e  and the shaft  4   a  and also between the outer surface of the centering and/or sealing element  1  and the femur. 
     An illustrative embodiment of the centering and/or sealing element is described with reference to FIGS. 2 a  through  2   c.  The centering and/or sealing element consists of a sleeve-shaped body extending in a proximal-distal direction C, said body having two broad-side boundaries  1   q,    1   r  and two narrow-side boundaries  1   f,    1   g  which, as can be seen from the view according to FIG. 2 c,  enclose an essentially rectangular inner space  1   a.  The inner side surfaces  1   b,    1   c  of the broad-side boundaries  1   q,    1   r  are designed extending essentially parallel to the proximal-distal direction C and also parallel to the lateral-medial direction A. In the illustrative embodiment shown, as can be seen from FIG. 2 c,  the inner side surface  1   d  of the narrow-side boundary  1   g  extends parallel to the proximal-distal direction C. The broad-side inner side surfaces  1   b,    1   c  could also be designed extending parallel to the proximal-distal direction C, but in the illustrative embodiment shown they converge slightly in the distal direction, this having the advantage of affording an improved sealing effect between endoprosthesis shaft  4  and inner side surface  1   b,    1   c.  The second narrow-side boundary  1   f  has an inner side surface  1   e  extending at an inclination to the inner side surface  1   d.    
     In the illustrative embodiment shown, all the boundaries  1   q,    1   r,    1   f,    1   g  have a part section  1   l  which extends in the proximal-distal direction C and which forms, adjacent to the part section  1   k,  a wall thickness tapering in the distal direction, as can be seen in particular from the cross section shown in FIG. 2 b.  In the proximal direction, the broad-side boundaries  1   q ,  1   r  end in a reference surface  1   m ,  1   n . This reference surface  1   m ,  1   n , extending in the medial-lateral direction A, has, as can be seen from FIGS. 2 a  and  2   b , a course which is bent so as to follow the course of the broad-side boundary  1   r.    
     In contrast to the illustrative embodiment according to FIGS. 2 a  through  2   c,  the otherwise identically designed body  1  shown in FIG. 5 has two broad-side boundaries  1   r ,  1   q  which are rectilinear, i.e. they have no bend point. 
     In contrast to the illustrative embodiment according to FIGS. 2 a  through  2   c,  the body  1  shown in FIG. 1 has a narrow-side boundary  1   g  which is designed wider in the medial-lateral direction A and which additionally has in the center a continuous gap  10  extending in the proximal-distal direction C. 
     The endoprosthesis is implanted, for example, as follows: 
     The femoral neck is resected. The medullary cavity is then widened using a bone rasp. The outer shape of the centering element, i.e. the outer surfaces  1   r ,  1   k , preferably corresponds to the outer shape of the bone rasp. A manipulating shaft is then inserted into the widened medullary cavity and a joint head is fitted onto this manipulating shaft. The bone rasp can if necessary also be designed to receive a joint head or can comprise a joint head and can therefore be left for the time being in the medullary cavity. The position of the joint head is then checked and the leg manipulated, for example in order to examine the leg length, and the depth of fitting of the manipulating shaft or bone rasp can be adjusted in particular in the proximal-distal direction C until an optimum position has been found for the leg. The depth of fitting of the manipulating shaft or bone rasp is then read off. The manipulating shaft or bone rasp is then removed from the medullary cavity, whereupon the bone cement is filled into the medullary cavity. Then, as is represented in FIG. 6, the centering and/or sealing element  1  is pushed over the tip of the shaft  4   f,  the shaft is secured on the fitting instrument  3 , if appropriate using spacer elements  2  determining the depth of fitting, as shown in FIG. 3 or FIG. 4, whereupon the shaft is inserted into the medullary cavity. The centering and/or sealing element  1  is likewise introduced into the medullary cavity. The tapering part section  1   l  facilitates reliable and centered insertion of the centering and/or sealing element  1  into the medullary cavity. The centering and/or sealing element  1  is pressed in so that the end faces  1   m , in preferably are flush with the resected surface, whereupon the shaft is inserted further until the predetermined depth of fitting is reached. The fitting instrument  3  and the optionally used spacer element  2  are then removed. 
     In the illustrative embodiment shown, as can be seen from FIG. 2 c,  the narrow-side inner side surface  1   d  is designed extending in the proximal-distal direction C, the advantage of which is that this surface serves as a bearing and reference surface during insertion of the shaft  4   f , said surface  1   d  causing no displacement of the shaft  4   f  in the medial-lateral direction A. 
     A distal centering element can also be arranged on the shaft tip  4   g.    
     To achieve a sealing effect, it is necessary that the inner side surfaces  1   b ,  1   c ,  1   d ,  1   e  of the centering and/or sealing element  1  are designed to match the geometry of the shaft  4   f,  so as to achieve a sealing effect. For this reason, these inner side surfaces  1   b ,  1   c ,  1   d ,  1   e , predetermined by the shape of the corresponding shaft  4   f , can be designed in very different configurations in such a way that a sealing effect between shaft  4   f  and centering and/or sealing element  1  is achieved with at the same time mutual displaceability in the proximal-distal direction C. 
     FIG. 6 shows an illustrative embodiment of a kit which comprises an endoprosthesis shaft  4 , a distal centering and/or sealing element  1  and a fitting instrument  3 . Markings  6  are arranged on the shaft  4  in order to indicate the depth of fitting with numbers “0”, “5” and “10”. The fitting instrument  3  also has markings  6  with the same numbers. During implantation, the optimum depth of fitting is determined with a manipulating instrument, markings and numbers being arranged on the manipulating instrument. The marking lying at the resected surface is read off. The centering and/or sealing element is then anchored with its upper edge  1   m ,  1   n  flush with the resected surface in the medullary cavity and the bone cement is inserted into the medullary cavity. The shaft  4  is then secured on the fitting instrument  3  and introduced into the medullary cavity. During insertion, the operating surgeon can use the markings  6  to accurately determine the depth of insertion of the shaft  4  with respect to the upper edge  1   m ,  1   n  of the centering and/or sealing element. 
     FIG. 7 shows a further illustrative embodiment of a kit which comprises an endoprosthesis shaft  4 , a distal centering and/or sealing element  1  and a fitting instrument  3 . The stamp  3   c  comprises a securely connected limit stop part  3   e  which has a limit stop surface  2   c  for abutting the centering and spacer element  1 . Stamps  3   c  with limit stop parts  3   e  of different lengths in direction C can be provided, so that the mutual position of centering and/or sealing element  1  and shaft  4  can be set by appropriate choice of stamp  3   c.