DE102011055106B3 - Hip prosthesis for total hip replacement applications during e.g. orthopedics, has shank with anchorage element transferred from inactive position into active position, where element is formed as cam rotatably supported in recess of shank - Google Patents

Abstract

The prosthesis has a shank (3) inserted into a cavity of a thigh bone (2), and including a proximal end (4) connected with a joint head (7) over a neck part (5). The shank includes an anchorage element adjustable by an adjusting unit (15) actuatable from outside. The element is transferred from an inactive position into an active position, where the insertion of the shank into the cavity is not hindered in the inactive position. The element is protruded over adjacent areas of shank surfaces in the active position, and formed as a cam (14) that is rotatably supported in a recess of the shank.

Description

The invention relates to a hip prosthesis with a usable in a cavity of the thigh and anchored in the cavity shaft, which is connected at its proximal end via a neck portion with a condyle.

Hip prostheses of this type are used in total hip arthroplasty, with the ball at the proximal end of the shaft cooperating with a socket prosthesis implanted in a suitably prepared natural acetabulum. They are used in joint replacement orthopedics and trauma surgery.

The bone of the femur is prepared so that a cavity is formed in the bone to receive the stem as an implant. To produce the cavity, it is known to use rasps, which are similar in shape to the shaft to be inserted, to make it possible to make the cavity so that the inserted shaft as far as possible exactly abuts the wall of the cavity and thus safely in the Bone is anchored. In this known as "fit and fill" method, the secure fit of the cementless prosthesis used depends significantly on the dimensional accuracy with which the cavity could be shredded in the femur. However, the difficulty of rasping lies in the fact that during the preparation of the femoral shaft, the rasp is guided further distally in the femoral shaft. As a result, the rasp can not simultaneously rest in conformity in the medullary cavity in the femoral shaft and in the region of the femoral neck. In practice, this means that occasionally a great deal of Substantia spongiosa, or spongiosa, is first removed in places where it is then missing for the final correct fit of the prosthesis used.

For example, from the EP 1 438 933 B1 and the EP 1 643 940 B1 For example, hip prostheses are known in which the shaft is provided with grooves and / or ribs which extend substantially in the longitudinal direction of the shaft and are provided starting from its proximal end adjacent to the condyle and / or the distal end opposite thereto To achieve stability and better anchoring of the inserted into the prepared cavity hip prosthesis stem. In practice, it has been found that after inserting a grooved and / or ribbed hip prosthesis stem into the lumen of the femur, it is difficult and often impossible to re-correct the position of the stem or change its orientation. For this purpose, the hip prosthesis stem must be taken out of the cavity again and repositioned, which increases the risk of bone damage. In addition, an alignment device is often needed to reposition such a hip prosthesis stem with grooves and / or ribs. This can lead to prolonged surgery times and associated risks, such as increased blood loss, etc.

In the more or less strongly tapered to the distal end, provided with grooves and / or ribs Hüftprothesenschäften occurs when inserting the shaft into the cavity of the femur, a local displacement of spongious bone tissue in the axial and radial directions, in this so-called "Press-Fit "Anchoring the shaft can lead to an unpredictable local force development with the risk of bursting of the femur in the shaft area. In addition, there is a risk that in an intraoperative correction of the hip prosthesis stem to be introduced as a primary implant, the cancellous bone is displaced not only in the first process, but that in the re-introduction of the shaft cancellous bone is displaced so that the grooves and / or ribs of the shaft their Can no longer fulfill the purpose. In the case of revision, this press-fit anchoring must be resolved by a higher force, which in turn is associated with the risk of injury to the remaining bone and a loss of cancellous bone material.

In addition to such hip prostheses whose shanks are provided with ribs and / or grooves, hip prostheses are also known, the different contours having shanks without ribs and / or grooves are formed, as for example in one of the EP 0 622 061 B1 known hip prosthesis is the case.

In these Hüftprothesenschäften but the preparation of the femur with several successively handled rasps is not tolerances possible, because the introduction of the rasps in ascending order can lead to different displacement of the bone tissue. The ruffled cavity thereby enlarges and then no longer fits exactly to the respectively following (larger sized) rasp and finally to the hip prosthesis socket to be implanted. There is a risk of improper anchoring of a hip-fit socket inserted in the press-fit with insufficient primary anchoring. The press-fit anchoring of the introduced hip prosthesis shaft is namely at unpredictable bone points or bone surfaces with the risk of Nachsinkens and loosening of the prosthesis stem over time.

Besides that is from the WO 2007/124607 A1 a shaft of a joint prosthesis is known which has a longitudinal bore with internal thread and continuous, the longitudinal bore traversing transverse bores to which, on both sides of the longitudinal bore, designated as retention elements anchoring elements are arranged, which are spreadable by a guided in the longitudinal bore threaded rod. The Retensionselemente are in the form of rounded end, two-piece bolts, which are separated by a groove, which represents a predetermined breaking point, which strikes when screwing the threaded rod, the tip of the threaded rod, so that upon further insertion of the threaded rod there breakage and thus the spreading the Retensionselement parts into the bone takes place. Apart from the fact that the breaking of such a retentive element is associated with a certain mechanical uncertainty, a revision is not possible because the retainer elements can not be returned to the shaft. With in radial transverse bores of the shaft of the prosthesis radially adjustable anchoring elements in the form of pins or screws also works from the US-A 6,126,691 A known prosthesis fixation device, in which oppositely arranged pins are spreadable by an inserted into a longitudinal bore of the shank Spreizstab so that they penetrate with their respective tip in the bone. When using anchoring elements in the form of screws here the cross holes are formed as threaded holes, while the end-pointed bolts carry a self-tapping thread, with which they can cut into the bone tissue surrounding the shaft. The advance of the screws in the radial direction takes place in each case via a bevel gear with a arranged in the longitudinal bore of the shaft, accessible from the outside actuating shaft. The sharpened pins or screws which penetrate into the bone tissue necessarily provide only a limited support surface for acting in the longitudinal direction of the shaft loading forces; Also, the associated with spring-loaded radially movable pins or trained as parts of bevel gears self-tapping screws and their actuator drive is relatively large and complicated.

Based on this prior art, the present invention seeks to provide a hip prosthesis of the type mentioned above, which is characterized by an improved primary and secondary anchoring in the femur and easy to implant.

To solve this problem, the hip prosthesis according to the invention, the features of claim 1.

In the new hip prosthesis, the hip prosthesis stem has at least one adjustable anchoring element which can be transferred from an inactive position which does not obstruct the insertion of the stem into the cavity of the femur into an active position in which it protrudes beyond adjacent regions of the stem surface.

The at least one anchoring element can be locked at least in the active position relative to the shaft in order to prevent, for example, too deep penetration into the cancellous bone. There are provided externally operable actuating means by which the anchoring element from an inactive position can be converted to its active position, so as to facilitate handling.

The at least one anchoring element is designed as a cam, which is rotatably mounted in a recess of the shaft. Particularly simple conditions arise when the adjusting means have a shaft coupled to the cam, which is rotatably mounted in the shaft and accessible from the shaft outer side, preferably from the proximal end of the shaft forth.

Embodiments are conceivable in which only one adjustable cam is provided in the prosthesis shaft, but the new hip prosthesis is generally equipped with a plurality of cams arranged distributed over the shaft length and / or shaft width. The hip prosthesis can have a plurality of cams arranged coaxially with one another, which protrude in the active position in each case the same or different distances beyond the respectively adjacent surface regions of the shaft.

The new hip prosthesis allows a particularly simple implantation in the femur, because the introduction of the hip prosthesis shaft in the cavity of the bone in standing in the inactive position at least one cam, done. Thus, the obstacle-free surface having a trained and usually without grooves or ribs shank can be relatively easily introduced into the cavity and positioned there. After implantation, the at least one adjustable cam is translated to its active position projecting beyond adjacent portions of the shaft surface thereby increasing the effective volume and surface area of the shaft, promoting rapid adhesive bonding between the hip prosthesis shaft surface and the bone tissue. At the same time, a positive bond with the cancellous bone tissue is achieved, which ensures improved primary and secondary anchoring of the shaft in the femur. In addition, an improvement of the "fit and fill" principle by the mentioned surface and Increased volume of the hip prosthesis shaft achieved, with an optimization can be achieved by the geometric design and the arrangement of the cams.

Likewise, with a possible revision, i. H. necessary distances of the shaft, the at least one cam are returned to its inactive position, whereby the size of the effective shaft surface is reduced and the barrier formed by the at least one cam against loosening removed, so that the hip prosthesis stem can be relatively easily removed from the femur.

By the transfer of the at least one cam in the active position after the positioning of the hip prosthesis shaft in the cavity of the femur, a displacement of the cancellous bone tissue in the radial and axial direction takes place. If a plurality of mutually spaced apart cams arranged coaxially with one another exist, an axial compression of the cancellous bone tissue takes place between the individual cams. This results in improved support with additional radial anchoring of the hip prosthesis stem. The risk of Nachsinkens the hip prosthesis stem is thereby avoided. At the same time, the tilting moment originating from the body weight acting on the joint ball during walking and acting on the hip prosthesis shaft via the neck part is reduced because the force lever is reduced. Each of the active cams provides an increase in the effective surface area of the hip prosthesis stem, thereby also allowing for improved osteointegration over time and thus improved secondary anchoring.

The described enlargement of the effective surface and the effective volume of the hip prosthesis shaft and resulting shaft cross-section, also provides an increased rotational stability of the prosthesis, which may optionally be further supported by the fact that the shaft has at its distal end at least one axially projecting part, which at The shaft of the femur inserted shaft is anchored in the cancellous bone. This projecting part may advantageously be formed by the edge of a depression formed at the distal end of the shaft.

The prepared for the implantation of the prosthesis bone cavity must be dimensioned in the new hip prosthesis only slightly below the level of definitively introduced hip prosthesis stem, because the final dimension and the positive anchoring is achieved by the transfer of the at least one cam in its active position. The risk of inaccurate rasping of the bone cavity existing in all hip prostheses can be additionally compensated by transferring the at least one cam into its active position.

As already mentioned, by a specially shaped distal hip prosthesis stem end, z. B. with a depression formed at the distal end of the shaft, an additional spongious compression of the bone tissue can be achieved at the shaft end. When loading the leg and the resulting force introduction, the distal lateral support of the shaft shifts to the shaft end on the medial side. By a plurality of axially spaced apart and each in its active position standing cam results in a significant improvement in the introduction of force into the bone, in particular, the tilting moment is reduced because of a reduction of the power arm. This is aided by the specially shaped shank end, which helps to further reduce the risk of sinking the hip prosthesis stem and prevent shaft tilt while increasing rotational stability.

Further advantageous features and modifications of the new hip prosthesis are the subject of dependent claims.

In the drawing an embodiment of the object of the invention is shown, showing:

1 a hip prosthesis according to the invention in a side view, inserted into a thigh bone shown in section, with cams standing in the inactive position,

2 the hip prosthesis after 1 in a 90 ° side view from the back,

3 the hip prosthesis after 1 with cams in the inactive position in a plan view,

4 the hip prosthesis after 1 with active in standing cam in a plan view accordingly 3 .

5 the hip prosthesis after 1 partly in axial section in a side view and in an exploded view with the cam removed, the camshaft taken out and the fixing screw removed,

6 the hip prosthesis after 5 cut along the line VI-VI of 5 in a Side view without camshaft, fixing screw and without cam,

7 the cams of the hip prosthesis after 5 , in a sectional view accordingly 5 .

8th the hip prosthesis after 1 in a partial view, illustrating the fixing screw shown in axial section in a side view and on a different scale,

9 the shaft of the hip prosthesis after 1 , taken along the line IX-IX of 1 in plan view with inserted camshaft,

10 a detail at "A" of the hip prosthesis after 1 in axial section, in a side view and on a different scale,

11 the shaft of the hip prosthesis after 1 , taken along the line XI-XI the 1 in a plan view and in a detail showing the cam adjacent to the proximal end of the stem of the hip prosthesis in the inactive position,

11a the arrangement after 11 , in a side view in the direction of the arrow "X" of the 11 in the neckline,

12 the sectional view after 11 , showing the cam in the active position in a corresponding representation,

12a the arrangement after 12 in a view in the direction of the arrow "X" the 12 in one of the 11a appropriate representation,

13 after the cam 11 . 12 in a plan view and on a different scale,

14 . 14a after the cam 13 , taken along the line XIV or XIVa of 13 each, in a side view,

15 the cam of the sectional view of the 17 . 18 , in a plan view accordingly 13 .

16 . 16a after the cam 15 , in each case taken along the line XVI-XVI or XVIa-XVIa of 15 and in each case in a side view according to the representation of the 14 . 14a .

17 the shaft of the hip prosthesis after 1 , taken along the line XVII-XVII of 1 in a plan view, showing the cam in the inactive position,

17a the arrangement after 17 , in a side view in the direction of the arrow "X" of the 17 in the neckline,

18 the sectional view after 17 , showing the cam in the active position, in a corresponding representation,

18a the arrangement after 18 in a view in the direction of the arrow "X" the 18 , in one of 17a appropriate representation,

19 the shaft of the hip prosthesis after 1 , taken along the line XIX-XIX the 1 in a plan view and in a detail, showing the cam in the inactive position,

19a the arrangement after 19 in a view along the arrow "X" the 19 , in clipping,

20 the sectional view after 19 , showing the cam in the active position, in a corresponding representation,

20a the arrangement after 20 in a view in the direction of the arrow "X" the 20 , in one of 19a appropriate representation,

21 after the cam 19 . 20 in a plan view,

22 . 23 after the cam 21 , each cut along the line XXII-XXII and XXIII-XXIII of 21 and in each case in a side view,

24 . 25 a detail at "B" of the hip prosthesis after 5 , Illustrating the force introduction conditions into the cancellous bone at two different depths of penetration of the shaft end into the cancellous bone, respectively in a corresponding sectional view and on a different scale and

26 the arrangement after 8th , Illustrating a screwed into the shaft ejector in a corresponding sectional view.

The particular in 1 to 5 The hip prosthesis depicted is the femoral component for use in total hip arthroplasty. It points you into a cavity 1 one at 2 in 1 schematically indicated thigh bone to be inserted shaft 3 on, at a proximal end 4 with a cylindrical neck part 5 is formed in a recording cone 6 for one at 7 indicated joint ball passes. The shaft 3 points, in particular the 2 . 6 and 9 to take a substantially rectangular cross-sectional shape, wherein he laterally at 8th . 9 is bounded by substantially flat surfaces and on its narrow sides from the proximal end 4 to the distal shaft end 10 wedge-shaped tapers. The thus essentially plate-shaped shaft 3 is narrow side of the shape of the cavity 1 in the thighbone 2 adapted, like this 1 can be seen.

In the shaft 3 are between the two lateral side surfaces 8th . 9 continuous recesses in the form of parallelflankig limited slots 11 . 11a . 11b and 11c educated ( 5 and 6 ), which are parallel to each other and perpendicular to one 12 Designated shaft longitudinal axis are arranged to extend. The particular of a proximal shaft end 4 adjacently disposed portion of the shaft 3 starting slots arranged 11 to 11c , are of a trained as a blind hole 13 passes through, at the proximal end 4 in a coaxial threaded hole 140 flows, leading to the proximal end 4 opens.

The shaft longitudinal axis 12 is defined as the intersection of two in 3 With 12a respectively. 12b denoted at right angles to each other extending reference planes, which in the illustrated embodiment, each centered to a proximal flat end face 3a of the shaft 3 are arranged, wherein the reference plane 12b centrally between the two lateral side surfaces 8th . 9 of the shaft 3 extends. The shaft longitudinal axis 12 can also be laterally displaced or inclined relative to the conditions shown in other embodiments.

In each of the slots 11 to 11c is an anchoring element in the form of a cam 14 to 14c used, which has a substantially disc-shaped, limited on its broad sides by parallel planes shape and with a continuous hexagonal hole 150 is provided, as for example from the 7 . 13 . 15 can be seen. The slots 11 to 11c and the cams 14 to 14c are dimensioned such that with cams inserted into the slots, the cams in the inactive position are flush or minimally recessed with the shaft side surfaces 8th . 9 complete and through the walls of the slots 11 to 11c are guided laterally. In the slots 11 to 11c inserted cam 14 to 14c , are their hexagonal holes 150 coaxial with each other and with the axis of the bore 13 aligned with the shaft longitudinal axis 12 coincides.

Into the hole 13 is an adjusting means forming camshaft 15 used, which is designed as a hexagonal shaft and in the inserted state through the hexagonal holes 150 the cam 14 to 14c runs with which it is positively coupled rotatably. The camshaft 15 can in the off 10 apparent way to the distal stop at the bottom of the hole 13 be advanced and then together with the threaded cams 14 to 14c through one into the threaded hole 140 screwed fixing screw 16 be fixed. The fixing screw 16 carries a hexagon socket used for the key approach 17 and presses in the screwed state axially on the camshaft 15 as well as this 8th can be seen.

The essentially disc-shaped cams 14 to 14c wise, like that 13 . 15 and 21 to take a basically similar contour. They each have the same thickness in the illustrated embodiment and are by appropriate operation of the camshaft 15 common between an inactive position after the 11 . 17 and 19 and an active position according to the 12 . 18 and 20 rotatable. In the inactive position are the cams 14 to 14c completely in the respectively assigned slot 11 to 11c taken in the way that they are laterally with their sidewalls 18 . 19 flush with the adjacent surface areas of the sides 8th . 9 extend the shaft or are set against these and thus the unimpeded insertion of the shaft into the cavity 1 of the femur 2 allow. In contrast, by a predetermined angle 26 ( 12 ) twisted active position, protrude the cams 14 to 14c each with two substantially triangular areas 20 over the adjacent surface areas laterally, like this 12 . 18 and 20 is apparent. In that area 20 are the cams 14 to 14c each with a narrower edge rounded rib 21 (See, for example 14 ), which displaces the adjacent cancellous bone tissue. The the 11 . 12 . 17 . 18 and 19 . 20 attached sectional views of the figures 11a . 12a . 17a . 18a and 19a . 20a of the cavity 1 in the area of the respective cam 14 to 14b , c show conspicuously the operation of the cams 14 to 14c : In the inactive cam position after the 11 . 17 and 19 finds no suppression of 210 indicated by dotted, the cavity 1 spongious bone tissue, whereas in active position cams spongious bone tissue 210 through the rib-shaped areas 20 the cam is radially displaced locally. In this cam position, the shaft 3 take an axial force F _{ax of} considerable magnitude exerted on it and safely into the adjacent areas of the cancellous tissue 210 initiate, by the cam sections 20 Radial forces F _rad (cf., for example. 12a ) are used to secure anchoring the shaft 3 in the cavity 1 contribute significantly.

The disc-shaped cams 14 to 14c Show how 7 to take, according to the shape of the shaft 3 in the area of the respective slot 11 to 11c different sizes (lengths). While in the illustrated embodiment, the cams 14b . 14c are the same size and the proximal side 4 towards subsequent cams 14a and 14 each larger, could according to the design of the shank 3 also be selected a different cam formation and distribution in the shaft. The cams are each double-lobed, ie with two sides of the hole 150 lying wings formed at the cams 14a to 14c are the same length, while they are at the cam 14 have a different length, like this 7 (and 13 ) shows. In the illustrated embodiment, the cams protrude 14 to 14c in the active position in each case over the lateral side surfaces 8th . 9 of the shaft 3 in front. However, embodiments are also conceivable in which the cams are formed and arranged completely or partially or even exclusively over the narrow sides of the shank in the active position.

In the illustrated embodiment, the cams 14 to 14c each equipped with an angle of rotation limitation. This rotation angle limitation is briefly based on the 11 . 13 at the cam 14 exemplified:
On its opposite side walls 22 . 23 of the slot 11 facing end faces, the cam has two cylindrical surfaces 24 . 25 whose radius with r2 or r3 in 13 is designated and from the center of the hexagonal hole 150 goes out, by the mounted state, as drawn, the shaft longitudinal axis 12 runs. An axis of symmetry 00, which in the shaft 3 inserted and in the inactive position cams in the reference plane 12b lies, runs through the middle of the hexagonal hole 150 and is to the two flat side surfaces 18 . 19 parallel, of which it is equally spaced. In the area of the symmetry axis 00, the two cylindrical surfaces go 24 . 25 each tangential to a first flat surface 24a respectively. 25a over, with the two flat surfaces 24a . 25a as 13 shows lie on opposite sides of the axis of symmetry 00. Starting from the symmetry axis 00, the cylindrical surfaces extend 24 . 25 each over an angular range, the angle of rotation 26 between the inactive and active position of the cam corresponds. At the outer boundary of this angular range, the cylindrical surfaces go 24 . 25 each tangent to a second flat surface 24b respectively. 25b over that the side surface 19 respectively. 18 cuts. The two flat surfaces 24b . 25b lie as well as the first two flat surfaces 24a . 24b each in parallel planes.

The operation of the thus designed cam 14 is as follows:
In the inactive position after 11 in which the cam 14 completely in the shaft 3 is recorded are the first two flat surfaces 24a . 25a at the slot side walls parallel to them 22 respectively. 23 and thus form a rotation of the cam against rotation in a counterclockwise direction, based on 11 ,

Based on this inactive cam position allow the two cylindrical surfaces 24 . 25 whose radii r2, r3 are matched to the slot width, the cam by the angle 26 in the active position 12 to turn clockwise. This twisting movement in a clockwise direction is limited by the fact that after the rotation by the angle 26 the diametrically opposite second planar surface areas 24b . 25b at the slot side wall 22 respectively. 23 come to the plant and thus prevent further rotation of the cam, like this 12 is apparent.

The cam 14 is thus behind in both its inactive position 11 as noted, locked against rotation in a counterclockwise direction while turning around the angle after twisting 26 in the active position 12 is locked against further rotation in a clockwise direction. In this way it is ensured that the cam 14 is defined exactly by a positive stop both in its inactive position and in its active position. As a result, the handling is much easier, while at the same time avoiding that the cam, for example, in its active position, is pressed too far into the cancellous bone tissue by improper handling and thus endangered the bone. Both in the active and in the inactive position, the cam is 14 , together with the other cams 14a - 14c , through the fixing screw 16 held in position, from which he only after loosening and removing the fixing screw 16 can be moved out.

In that as a rib 21 trained area 20 is the cam side surface in the on the side surface 18 subsequent section 18a formed with a relatively large radius R rounded, from one to one through the center of the hexagonal hole 150 extending transverse axis 00 'lying point M emanates. The section 18a goes, how 13 shows, on the adjacent cam end face via a rounded corner in a second section 18b about, which is also rounded, with its radius designated r ( 13 ). The radius r starts from a center m, which is on a to the symmetry axis 00 parallel line lies at the distance of the length of the flat surface 24a from the axis of symmetry 00 runs.

The side surface 18 opposite side surface 19 is in a similar way with rounded sections 19a . 19b formed, their radii in 13 are denoted by R1 and r1 and emanate from a center M1 or m1.

Through this to the respective corner of the area 20 down sloping design of the surface sections 18a . 18b respectively. 19a . 19b result in more favorable leverage when penetrating the rib-like area 20 into the cancellous bone during the transfer of the cam 14 from the inactive to the active position.

On the hole 150 facing inside are the rib-shaped areas 20 each through a straight surface 20a bounded parallel to one through the diagonally opposite endpoints of the cylindrical surfaces 24 . 25 walking line 240 run, with the 20b designated distance of the two surfaces 20a in the selected embodiment equal to the distance between the two cam side surfaces 18 . 19 is. Both surfaces 20a have the same distance 20c to the line 240 on.

The described rotation angle limitation applies to the same extent for the cams 14a to 14c in which the radii r2, r3 of the opposite cylindrical areas 24 . 25 because of the symmetry of the cams is the same size ( 15 ). With the cam 14 to 11 to 13 the same or similar parts are provided with corresponding reference numerals and not explained again.

The implantation of the described hip prosthesis takes place in the following way:
The hip prosthesis is made by the manufacturer with the cams 14 - 14c and the camshaft 15 as well as with inserted fixing screw 16 delivered pre-assembled. The cams 14 to 14c stand in the inactive position in which they are completely in the slots 11 to 11c are included. Because the fixing screw 16 into the threaded hole 140 screwed in, are the cams 14 to 14c over the camshaft 15 fixed in rotation in its inactive position.

After the preparation of the cavity 1 becomes the shaft 3 in the cavity 1 used with Press Fit and positioned properly. Subsequently, the fixing screw 16 removed, and the cams 14 to 14c are brought to their final desired position. For this purpose, the camshaft is with a hexagon wrench 15 with the cams 14 to 14c clockwise, for example, based on 11 turned to the stop ( 12 ). Afterwards, the camshaft is secured again 15 with the cams 14 to 14c through the into the threaded hole 140 screwed fixing screw 16 ,

At the distal end of the shaft 3 is a cup-shaped depression 260 formed, whose boundary a circular closed rounded projection 27 forms. When inserting the shaft 3 in the prepared cavity 1 spongy bone tissue 210 the shaft is advanced with a force F1 _ax until it is about a line YY of 24 reached at, as at 28 schematically indicated cancellous bone tissue at its proximal end 10 The transition is, of course, fluent and in nature is not represented by a straight line. In this position, the shaft is lateral to the cancellous bone tissue 210 against which it is laterally supported, as indicated by arrows 29 in 24 is indicated, wherein the effective radial force is denoted by F1 _rad .

Starting from this axial position of the shaft 3 it allows the recess 260 axially _advancing the shaft with an increased axial force F2 _ax , so that the recess 26 surrounding annular edge region, which has a substantially wedge-shaped cross section, into the cancellous bone tissue 210 penetrates and compresses and shifts it until it has reached its final position on the line Y'-Y 'in which an increased radial force F2 _rad acts. As in 25 through arrows 30 is indicated by the crossing of the line YY to an additional compression of cancellous bone tissue both in that of the depression 260 enclosed cavity as well as in the outer environment of the distal end of the shaft 10 , F2 _ax > F1 _ax and F2 _rad > F1 _rad .

The force is introduced into the implanted hip prosthesis via the center of the mounted ball joint 7 ( 1 ) in one to the shaft axis 12 approximately parallel direction. This introduction of force causes a support of the shaft 3 in the area of the proximal medial neck 31 ( 1 ) and at the distal lateral shaft region and at the distal shaft end 10 , Because of the neck part 5 and the adjoining shaft portion Krafthebelarms, a tilting moment is exerted on the shaft, which, based on 1 , strives to the shaft 3 around a pivot point in the medial neck arm part 31 to turn clockwise. This tilting moment can especially with a short shaft 3 the risk of loosening the shaft 3 in the cavity 1 and the Nachsinkens the hip prosthesis stem in itself. The acts in the 25 shown additional radial support of the distal end of the shaft 10 if necessary. The lateral support of the Schaftendbereichs is of laterally displaced medially with which the power arm lever shortens and additionally improves the rotational stability of the implanted shaft 3 be achieved. In addition, this results in further advancement of the shaft 3 from the line YY the 24 up to the line Y'-Y 'of 25 ie, to the final position, further densification of cancellous bone tissue on the shaft outside, from the distal shaft end 10 proceeding to the proximal shaft end 4 out.

The surface of the shaft 3 may as well as at least coming into contact with the cancellous bone tissue areas of the cam 14 to 14c , coated with an osteointegrative material or prepared accordingly, for example, be roughened.

In case of revision, the shaft 3 relatively easy and, above all, very gently from the cavity 1 of the femur are removed. For this purpose, first the fixing screw 16 loosened and out of the threaded hole 140 unscrewed. Then the now from the proximal end 4 of the shaft 3 accessible camshaft 15 by means of an attached hex wrench, for example based on 12 , counterclockwise so far twisted until the rotation with the camshaft 15 coupled cam 14 to 14c in the inactive position after the 11 . 17 and 19 turned back to the stop. In this position, the camshaft 15 by means of the fixing screw 16 or the ejector or extractor described below 310 fixed so that the cams 14 - 14c are fixed. This allows the shaft 3 relatively easily either by means of extractor or by means of a universal applicator attached to the cone of the femur and released from the cavity 1 be pulled out.

This loosening and pulling out of the shaft 3 from the cavity 1 is achieved by the use of an optional ejector or extractor 310 relieved, in 26 is shown. The extractor 310 has a screw part 32 on that in 26 is shown only in part and designed appropriately, for example. With a handle or a tool attachment, etc. may be formed and to which a coaxial cylindrical threaded extension 33 followed. The thread extension 33 carries an external thread 34 with he in the tapped hole 140 of the shaft 3 can be screwed. Starting from his free face 35 is the thread extension 33 with a coaxial blind hole 36 provided whose diameter is greater than the largest diameter of the camshaft 15 , such that between the camshaft 15 and the inner wall of the blind bore 36 a radial game 37 remains.

After the cams 14 to 14c in the above-described manner have been returned to their inactive position, the extractor 31 with its threaded extension 33 into the threaded hole 140 as if by an arrow 38 indicated, screwed in, because of the radial play 37 the camshaft 15 not rotated. The thread extension 33 it is screwed in until it reaches the bottom of its blind hole 36 on the face of the camshaft 15 and the extractor 310 with the camshaft 15 is firmly clamped. In this way, the camshaft 15 and the cams 14 to 14c rotationally fixed in its inactive position in the shaft 3 fixed.

The hip prosthesis stem 3 can now by means of the easily accessible extractor 310 that with the shaft 3 is rigidly connected, out of the cavity 1 be removed. To facilitate the loosening of the shaft 3 can the extractor 310 in his part 32 in 26 not shown auxiliary equipment, such as having an anvil surface, which allows to carry the dissolution process by light hammer blows.

The described embodiment of the new hip prosthesis is not restrictive. Both the number and the size of the cams 14 to 14c can, as well as their distribution and mutual spacing in the shaft 3 be appropriately selected according to the respective anatomical requirements. The camshaft 15 also does not need coaxial with the shaft longitudinal axis 12 but can with this if necessary include an angle, so that the cams 14 to 14c lie in a corresponding inclination. The shaft 3 even here is with a in 9 illustrated, formed substantially rectangular cross-sectional shape in the manner of a disc. But it is also conceivable to execute the shaft with a, at least partially, round or oval or otherwise designed outline. Finally, as already mentioned, the here through the cams 14 to 14c formed anchoring elements also be designed differently. In the described embodiment, all cams 14 to 14c jointly adjustable. Embodiments are also conceivable in which individual cams are individually adjustable. The rotation angle limitation of the cams can be structurally different. Finally, the rib-like areas 20 the cam 14 to 14c be designed in another way as shown in the description; they can z. B. obliquely or be formed on the type of parts of threads.

A hip prosthesis in the form of the femoral component for use in total hip arthroplasty has a shaft insertable into a lumen of the femur and anchored in the lumen 3 on, at its proximal end 4 over a neck part 5 with a condyle 7 connected is. The shaft 3 has at least one adjustable anchoring element 14 which can be transferred from an insertion position of the shaft into the cavity which does not obstruct the inactive position into an active position in which it projects beyond adjacent areas of the shaft surface.

LIST OF REFERENCE NUMBERS

1

cavity

2

thighbone

3

shaft

3a

Face of the shaft

4

proximal end of the shaft

5

cylindrical neck part

6

receiving cone

7

joint ball

8, 9

lateral side surfaces of the shaft

10

distal shaft end

11, 11a, 11b, 11c

slots

12

long shaft axis

12a, 12b

reference planes

13

drilling

14, 14a,

14b, 14c

cam

15

camshaft

150

Hexagonal hole

16

fixing screw

17

Allen

18, 19

Side walls of a cam

18a, 18b

Side surface sections of a cam

19a, 19b

rounded side surface portions of a cam

20

triangular area of a cam

20a

level even surface of a cam

20b, c

distance

21

rib

210

cancellous bone tissue

22, 23

Side walls of a slot

24, 25

Cylindrical surfaces of a slot

24a, 25a

first flat surface of a slot

24b, 25b

second flat surface of a slot

240

line

26

angle of rotation

260

deepening

27

head Start

28

Transition to cancellous bone tissue

29

arrows

30

arrows

31

proximal medial neck of the thighbone

310

extractor

32

screw

33

Threaded extension

34

external thread

35

free end face

36

blind hole

37

radial play

38

arrow

140

threaded hole

00, 00 '

Symmetry axes of a cam

Claims (19)

Hip prosthesis with one in a cavity ( 1 ) of the femur ( 2 ) and to be anchored in the cavity shaft ( 3 ), which at its proximal end ( 4 ) over a neck part ( 5 ) with a condyle ( 7 ), wherein the shaft ( 3 ) at least one actuatable by externally actuating means ( 15 ) adjustable anchoring element, which consists of a the insertion of the shaft into the cavity ( 1 ) can be moved to an active position in which it has adjacent areas of the shaft surface ( 8th . 9 ), and that as a cam ( 14 ) formed in a recess of the shaft ( 3 ) is rotatably mounted. Hip prosthesis according to claim 1, characterized in that the cam ( 14 ) at least in the active position relative to the shaft ( 3 ) is lockable. Hip prosthesis according to claim 1, characterized in that the cam ( 14 ) is at least partially disc-shaped and the recess receiving it in the manner of a slot ( 11 ) is designed. Hip prosthesis according to claim 2, characterized in that the adjusting means one with the cam ( 14 ) coupled camshaft ( 15 ), which in the shaft ( 3 ) is rotatably mounted and accessible from the shaft outside. Hip prosthesis according to claim 4, characterized in that the camshaft ( 15 ) from the proximal end ( 4 ) of the shaft ( 3 ) is accessible. Hip prosthesis according to claim 5, characterized in that the camshaft ( 15 ) is assigned a non-rotatably fixing the camshaft fixing. Hüftprothese according to claim 6, characterized in that the fixing means into a threaded bore ( 140 ) of the shaft ( 3 ) releasably inserted fixing screw ( 16 ). Hip prosthesis according to claims 2 and 3, characterized in that the cam ( 14 ) at least one peripheral area ( 24b . 25b ) in which it is in the active position under rotationally fixed limitation of its rotation against the shaft ( 3 ) on a wall ( 22 . 23 ) of the recess ( 11 ) is present. Hip prosthesis according to claim 8, characterized in that the cam ( 14 ) at least one peripheral area ( 24a . 25a ) in which it is in the inactive position under rotationally fixed limitation of its rotation against the shaft ( 3 ) on a wall ( 22 . 23 ) of the recess ( 11 ) is present. Hip prosthesis according to claim 8 or 9, characterized in that the cam ( 14 ) on at least one side a first cylindrical surface ( 24 ; 25 ), to which on at least one side a flat surface ( 24a . 24b ; 25a . 25b ), in cooperation with an associated side wall ( 22 ; 23 ) of the recess ( 11 ) the rotation limit of the cam is formed. A hip prosthesis according to claim 1, characterized in that the cam on at least one in the active position on adjacent areas of the shaft surface projecting side a rib-like area ( 20 ) has reduced thickness. Hip prosthesis according to claim 11, characterized in that the rib-like area ( 20 ) is rounded at its periphery against a corner of the cam sloping. Hip prosthesis according to claim 1, characterized in that it comprises a plurality of coaxial cams (FIG. 14 to 14c ) in the active position in each case the same or different distances over their respective adjacent surface areas of the shaft ( 3 ) protrude. Hip prosthesis according to claim 13, characterized in that at one of the proximal end ( 4 ) to the distal end ( 10 ) tapered shaft, the cams ( 14 to 14c ) have a decreasing length toward the distal end. Hip prosthesis according to claim 1, characterized in that the shaft ( 3 ) at its distal end ( 10 ) has at least one axially projecting part which in when in the cavity ( 1 ) of the femur ( 2 ) inserted shaft ( 3 ) in cancellous bone ( 210 ) is anchored. Hip prosthesis according to claim 15, characterized in that the projecting part is defined by the edge ( 28 ) one in the distal end ( 10 ) of the shaft ( 3 ) formed recess ( 260 ) is formed. Hip prosthesis according to claim 1, characterized in that the shaft ( 3 ) and / or the at least one anchoring element is osteointegrated or coated. Hip prosthesis according to claim 7, characterized in that the shaft ( 3 ) Facilities for connection to an extractor ( 310 ), which the threaded hole ( 140 ) of the fixing screw included. Hip prosthesis according to claim 18, characterized in that the cam ( 14 ) through the extractor ( 310 ) in its inactive position relative to the shaft ( 3 ) is lockable.

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