DE3921030C2 - Endoprosthesis for partial replacement of bones, especially hip joint endoprosthesis - Google Patents

Description

The invention relates to an endoprosthesis for par tial replacement of bone, the endoprosthesis at least least on one of their two sides with a shaft in engages a bone fragment. Such endo-, that is implantable prostheses are used wherever parts are irretrievably lost from bones. With heavy debris fractures on the long limb bones or on the lower pine, as observed in particular on accident victims are, such an endoprosthesis Bone restored to the correct length the one of which there are only two sufficiently long ends while a middle area must be removed. In favorable cases, a spon giosaplastik are performed and after the together grow the bone ends by means of the implanted Bone material the endoprosthesis are removed; however, the cases where the endoprosthesis predominate for the rest of the patient's lifetime in his Body should remain.

In any case, the endoprosthesis must be used for a long time remain in the body, which so far has problems with Durability of the connection between the endoprosthesis and caused the bone fragments. The verb dung tend to loosen up gradually. It is attempts have already been made to solve this problem by or barb-like surface structure of the Endopro to solve this. Even if this only loosens it up delay occurs, the loosening is not prevented.

Based on this problem, the task arises Endoprosthesis so that the connection to bone fragments is permanent, so the connection is not loosens.

A particularly important special case of endoprostheses for partial replacement of bones are the hip joint endopro theses. They consist of one in the resected waiter femur shaft, a neck and a Inner joint member, which in a joint socket with connected to the hip bone. Here there are therefore only one joint between the bone and the prosthesis two, which has no influence on the problem, that namely, hip joint endoprostheses often with of time.

DE 33 01 415 A1 is an attempt to suppress the Loosening tendency became known where the shaft at its Upper side depressions with ribs in between has, the bone in this substantially radial inward depressions and the resultant Form-fit to such a stiffening of the shaft- Remaining bones should lead to the fact that the load conditions of the Bones mainly on the medial side of those in the healthy Get close to the femur.

Hip joint endoprostheses are particularly common in elderly patients used for pathological care changes in the hip or thigh neck breaks. Despite the size of the implan, they enable tations operation a rapid mobilization and stress availability of the hip joint. The other supply options options for fractures of the femur are all included prolonged resilience associated with this time range due to reduced growth in elderly patients on the one hand, it is particularly long and on the other hand, it is included degraded physical strength is particularly difficult to recover long, it is sometimes to be feared that the Patient can never raise again without walking aids and in General condition becomes ailing and depressed.

To take advantage of hip joint prostheses in larger To be able to take advantage of scope, the task is that Loosen the prosthesis in the resected femur at least this way to delay far that in the remaining life patient did not experience any complaints or the reattachment of a loosened hip joint prosthesis to radically simplify the operation  lasts only a few minutes and under local anesthesia can be performed.

The loosening of the connection between a bone fragment that is not a femur and an endoprosthesis is prevented according to the invention in that the in a prosthesis shaft engaging a fragment of a bone End of the shaft, which on one Bone fragment boundary or fracture line or resection a ring-shaped recess that surrounds the prosthesis neck has, whereby this end of the shaft increased to a collar elastic deformability is reduced. This recess could also be referred to as a throat become. The collar to which the bone fragment border or fracture line or resection site lying shaft end is reduced according to the invention elastic deformation a certain mobility opposite the prosthesis neck. Crucial is that the transverse stiffness at the end of the shaft, that is on a bone fragment boundary through which thin-walled and collar-like design so far ver is reduced by a bending load called pressure course over the towards the bone fragment length positively counted prosthesis length on the Bone fragment limit does not rise, i.e. at most con is constant, preferably something falls.

Where none due to lack of space or for reasons of strength sufficiently deep throat is possible or where with back not sufficiently thin in view of the dent resistance Wall thickness is possible to avoid the increasing pressure To achieve progress, there should be the prosthetic socket Have slits in the collar. The collar then shows no longer the deformation behavior of a cantilever pipe but several cantilevers, is therefore even more compliant.

The loosening of a hip joint endoprosthesis according to the preamble of claim 2 in the resected According to the invention, the femur is at least considerably delayed in that the prosthetic socket at its upper end an annular Has a recess surrounding the prosthesis neck, making this end of the shaft into a collar of increased elastic deformability is reduced.  

With static load by the weight of the stand the connection point between Pro thesis and the rest of the femur not only in the direction of the longitudinal axis of the tubular thigh of the bone, but also due to bending as a result the offset of the Prosthesis neck from the longitudinal axis of the resected Fe murs out. This leads to the top of the connection for pressing on the proximal and lower ends of the Connection to pressure on the distal side of the femur.

The invention is based on the knowledge that until long the pressure distribution generated by bending the gradual loosening causes. While so far care was taken to ensure that the one produced by bending Maximum pressure at the top of the remaining bones tube becomes as small as possible, the invention aims at one decreased slope of the pressure above that positively counted shaft length at the point where the Femur is resected. For the diminished at this point Incline will even increase the maximum pressure accepted.

In the case of hip joint endoprostheses according to the state of the art nik shows the pressing process in the immediate vicinity the resection site not only its maximum but also its highest slope. Through the application the invention becomes the point of highest pressure gradient moved away from the resection site to the knee. Where sufficient material strength and not too large The patient's physical strength should allow it Saving be dimensioned so large that the compression stone not only reduce the area around the resection site compared to a knee that is shifted to the knee maximum but rather zero or slightly less is as zero.  

The biological control loop of local bone growth, this is the hypothesis on which the invention is based to increased stress not only with increased kno growth, but as a further effect together menhang also that the bone growth by strong local load increase is reduced. Both active relationships are in competition with each other.

A confirmation for the other, so far at the Pro thesis design at least not considered, true connection apparently not recognized at all, namely bone growth depending on the first derivative the burden decreases according to the location, provides the fact (which has long been known) that a bone is its optimal Shape out even after initially crooked or offset healed fractures almost reached again. - Especially with misalignment occurs at the offset point high lines of force due to the sharp force deflection concentration. With the Zu, which has so far been adopted alone context that bone growth is dependent increased by the load, only the magnification The build-up in both inner grooves is offset be explained, but not the dismantling in the External fillets of the offset point. The previous one trying to explain that nature just about Eliminate what has become liquid over time applies here too short especially because the outer throats an offset point not only superfluous, but are also harmful; the outer throats are wearing help in drawing the lines of force on the outer fibers to focus the offset point. Even if it is on The first glance may seem paradoxical, the targeted Removal of bone material from the outer throats of one Offset increases the strength of the bone.

The proposed solution is based on the knowledge that at Shaping the prosthesis not just the load - well essentially the pressure between the prosthesis and Bones - but also the first derivative of this Be load according to the location, especially the length of the shaft,  must be observed. By reducing the slope, that is, the first derivative of the pressure will be Bone growth less inhibited and bone growth increasing effect of the pressure itself (i.e. the zero Derivative) wins the upper hand. Hereby the of loosening of the prosthesis at the resection site bound.

To the caused by the recess according to the invention To keep the drop in strength low, are preferably pro thesis and prosthesis neck in one piece bound.

For additional "softening" of the prosthesis area, the touches the resection site of the femur, i.e. of the collar trained upper end of the shaft, which by means of a ring shaped recess opposite the prosthesis neck slots can be provided in this prosthesis area his. To avoid excessive stress concentrations these slots should be at their roots with a radius ver or slightly larger than half the slot width be rounded.

To avoid cracks from the surface are in the surface - especially in the area of Recess - according to a preferred further education of the Er pressure residual stresses are generated. If the Endopro These are made of steel, can cause residual compressive stresses a volume-increasing hardening process, in particular one with carburizing, or by sandblasting. It is understood that the material has a significant notch must have impact strength. Therefore, it is recommended possible hardening a tempering for remuneration.  

Where the strength of the prosthesis material and the height of the belas can allow the adjustment of the prosthetic socket to the rest of the femur and adapting the Cranking or of the inner joint to the individual anatomical conditions of the patient thereby facilitated be that the prosthesis socket and the prosthesis neck loosen are connected to one another in cash. Using the same Fit in the connection point can be different Sizes of prosthetic stems and prosthetic necks or joints inner links can be combined with each other, so that already with a small number of different prosthesis parts there is a wide variety of possible combinations.

Furthermore, the detachable connection enables a fine ju the thigh length and the offset level. The Fabrication of the recess that the exemption between The prosthesis neck and prosthesis socket is caused by the releasable connection facilitated.

The prosthesis points to the realization of the detachable connection neck expediently pointing towards the knee joint Extension that engages in the hollow prosthesis socket.

If the detachable connection is strengthened solely by friction continuous adjustment is possible. The to press solution required expansion is preferably by a causes inner cone movable in the longitudinal direction of the shaft. The organ on which the position is preferably located of the inner cone and thus the friction force is set - preferably an Allen screw head - easily accessible at the top edge of the crank. This is even a later readjustment possible with only a minor skin incision. Also may be worn or to the hip or too a renewed artificial socket no longer fit of the inner joint member without renewed intervention on the femur be exchanged.  

As another solution to alleviate the easing problem, It is proposed to insert the prosthesis socket after implantation expand the resected femur, taking the degree of expansion on the prosthesis neck - preferably with an analog mechanism must be set as described in the previous section. As a result, the reattachment is possible after loosening simplified. This alternative solution is the subject of Claim 7.

Without prejudice to the independence of claims 1 and 7 the combination of these two claims creates a synergetic Effect on pressure distribution. Through the overlay the pressure caused by the expansion with the by Bending moments caused at least in the most surface areas can be achieved by at during a load cycle (e.g. a walking step) Alternating load is replaced by a threshold load, whereby game development and movements of the endoprosthesis in the Femur are at least largely prevented.

The invention is described below with the aid of four figures explained in more detail. It shows:

Fig. 1 is a hip joint endoprosthesis with an integral connection between the prosthesis neck and shaft,

Fig. 2 is a hip joint endoprosthesis with releasable Verbin connection between the prosthesis neck and shaft,

Fig. 3 different pressure profiles of conventional and inventive endoprostheses and

Fig. 4 end a bone nail with two shaft designed according to the invention, lying on the bone edge.

The endoprosthesis 1 shown in FIGS. 1 and 2 is divided into a shaft 2 , a neck 3 and an inner joint member 4 . In Fig. 1, the resected femur 5 , the socket 6 , the relevant part of the hip bone 11 and the body outline line 12 is shown in dashed line. The prosthesis socket 2 is free at its upper end 7 relative to the prosthesis neck 3 by means of an annular recess 8 , that is to say it ends up in a collar 25 . The recess 8 has a depth of about 4 cm in this example and acts together with the small, upwards ver tapering wall thickness of the collar 25 a small pressure drop at the resection point 22 when looking at the pressure profile over the shaft length 1 , from the lower Shaft end 13 is counted up positive.

The highest stress occurs on the surface 9 of the recess 8 , in particular basically 21 of the recess 8 . In order to prevent cracks from propagating from here, compressive residual stresses are preferably generated in these areas. In order to achieve a favorable fiber course, the recess 8 should at least be shaped without cutting.

The highest prosthesis strength is achieved with the one-piece form of the endoprosthesis shown in FIG. 1. In younger patients, where higher loads are to be expected, this embodiment should be recommended, while the two-part form shown in FIG. 2 should be recommended where a particularly precise adjustment is necessary or the adjustment is agile.

In the embodiment shown in FIG. 2, as in FIG. 1, the prosthesis neck 3 and the collar 25 , in which the prosthesis socket 2 runs upwards, are released from one another by an annular recess 8 , but the prosthesis neck 3 engages egg nem in the direction of the knee extension 10 in the tubular prosthesis socket 2 . In this example, a releasable connection between the neck extension 10 and the prosthesis socket 2 is realized in such a way that the neck extension 10 fits practically without play with its outer cylindrical surface in the inner cylindrical upper surface of the prosthesis socket 2 and the neck extension 10 is expanded after the implantation. For this purpose, the neck extension 10 has a continuous, downwardly flared cavity 15 along the prosthesis axis 14 and a slot 26 at its lower end 23 . In the cavity 15 , a corresponding, upwardly tapering cone 19 with an internal thread was used before implantation and prevented from falling down by means of a clamping screw 17 , whose Allen key 18 is supported on a bulge 24 of the prosthesis neck 3 . The cone 19 has a narrow web 20 designed as a feather key, which engages in the slot 26 of the neck extension 10 and thereby prevents the cone 19 from rotating. After the prosthesis shaft 2 has been anchored in the femur 5 and the prosthesis neck 3 has been correctly adjusted, the clamping screw 17 is tightened, expands the neck extension 10 and thereby clamps it in relation to the prosthesis shaft 2 .

With a sufficiently small clamping force, such a releasable connection also fulfills an overload function; rather the neck extension 10 telescopes further into the shaft 2 than the prosthesis neck 3 or the femur 5 breaks.

The thinner the wall thickness of the prosthesis shaft 2 is, the more the expansion of the cervical extension 10 has the effect that the prosthesis shaft 2 is expanded in accordance with claim 7 and thereby improves the fit of the prosthesis shaft 2 with respect to the resectioned femur 5 , that is the durability of the anchorage is increased. The same effect can also be achieved on a partial endoprosthesis using the conical bore and inner cone.

The Fig. 3 schematically shows the course of the pressure p in the direction perpendicular to the walking direction, the longitudinal axis of femur plane containing namely
in dashed line I with an endoprosthesis according to the prior art,
in dash-dotted line II with an endoprosthesis according to the invention,
in a thin solid line III the pressure due to an expansion of the shaft according to FIG. 2 and
in thick solid line IV with an inventive endoprosthesis with shaft expansion.

The distal side is shown from the upper half of the diagram and the proximal side on the lower half. For the sake of clarity, the distal pressure is plotted upwards on the ordinate, the proximal pressure downwards. Is plotted on the abscissa as variable l, which runs from 0 to L, L being the length from the lower end 13 (see FIG. 1) of the prosthesis socket 2 to the resection site 22 of the femur 5 or to the upper end 7 of the prosthesis socket 2 , depending on which of the two lengths is the shorter. In the second case, the prosthesis socket 2 is "lowered" in the femur 5, so to speak, ie the upper end 22 of the resected femur 5 projects beyond the upper end 7 of the prosthesis socket. With this arrangement, the bone growth at the end 7 of the prosthesis socket 2 is further promoted in a synergetic effect.

In order not to affect the clarity of the diagrams are short-wave overlays, as provided by equipping the outside of the shaft with a "Rough" surfaces that improve anchorage structure can occur, not shown.

The most important thing that FIG. 3 wants to show is the avoidance, achieved with endoprostheses according to the invention, of maxima of the pressure gradient located at the edge 22 or 7 — that is, in the diagram at l = L. Here the edge slope is even reduced to negative values, so that the pressure maxima 28 _II and 28 _{IV occur} at L less than L. The location of the maximum slope of curves I, II and IV is designated 29 _I , 29 _II and 29 _IV , respectively.

In summary, the invention teaches according to claim 2 strengthening the prosthesis-femur connection due to reduced stiffness of the implant the prosthetic socket at the resected end of the thigh bone while accepting a weaker dimension the prosthesis itself.

As already expressed in claim 1, lets the invention analogously applies to all bones apply prostheses and develop theirs everywhere Advantage of more permanent connection to the bone where at the connection bending moments between bone and Prosthesis must be transferred.

In Fig. 4 a bridging nail is shown for the care of a debris fracture on the lower jaw bone in its offset lying in front of the - not shown - wisdom teeth. Instead of on one side with an inner joint member, the bone replacement shown here ends on both sides with a shaft 2 , the neck end 7 of which is "softened" by a recess 8 . As a result, the shaft ends 7 can deform in a free space without being hindered by direct contact with the neck 3 . Analogous to FIGS. 1 and 2, the bone remnants, which are shown hatched here, with the reference number 5 , the breaking edges with the reference number 22 .

The exemplary embodiments are not conclusive counting possible applications of the invention but just examples. Regardless of whether the endoprosthesis straight or cranked, one or more parts, one or multi-vaulted and whether small or large, the Grundge thanks to the invention is the "softening" of the shaft lying at the end of the bone through a ring shaped recess that the first derivative (slope) the transverse pressure according to the length of the prosthesis at the end of the bone no longer has a maximum.

A list of the reference symbols used is a component the description.

Reference list

1 endoprosthesis
2 shaft of 1
3 neck of 1
4 inner joint of the hip joint endoprosthesis
5 bone fragment or resected femur
6 acetabular cup of the hip joint endoprosthesis
7 the end of FIG. 2 , which lies on the bone fragment concerned; in the case of a hip joint endoprosthesis, the upper end of 2
8 annular recess with which 2 is "softened" in the range of 7 , ie is reduced in transverse rigidity.
9 surface of 8
10 extension of the prosthesis neck with detachable connection between 2 and 3
11 hip bones
12 body outline
13 the end of 2 opposite 7 ; in the case of a hip joint endoprosthesis, the lower end of 2
14 prostheses (longitudinal) axis
15 conical cavity in 2nd
16 slot in 2
17 clamping screw
18 Allen key from 17
19 cone to expand 10 or / and 2
20 bridge on 19 as anti-rotation
21 reason (lowest point) of 8
22 fracture line or resection site of the 5th
23 lower end of 10
24 bulge of 3 to support the head 18 of 17
25 collars on 2 in area 7 , whereby 3 and 25 are exempted from each other by 8
26 slot in 10
27 possible but not necessary depth stop on 7 to facilitate the surgical technique and / or improved longitudinal force transmission
28 maximum pressure
29 Maximum of the first derivative of the pressure according to the shaft length

Claims (9)

1. Endoprosthesis ( 1 ) for partial replacement of bone, the endoprosthesis ( 1 ) engaging at least on one of its two sides with a prosthesis shaft ( 2 ) in a bone fragment ( 5 ), characterized in that the one engages in a bone fragment ( 5 ) The prosthesis shaft ( 2 ) has at least at one end ( 7 ) of the shaft ( 2 ), which lies on a bone fragment boundary or fracture line or resection site ( 22 ), an annular recesses ( 8 ) surrounding the prosthesis neck ( 3 ), whereby this end ( 7 ) of the shaft ( 2 ) to a collar ( 25 ) of increased elastic deformability is reduced. 2. Hip joint endoprosthesis ( 1 ) consisting of a prosthesis shaft ( 2 ) to be inserted into a resected femur ( 5 ), a neck ( 3 ) and an inner joint member ( 4 ) which is connected to an acetabular cup ( 6 ) which is connected to the hip bone ( 11 ) engages, characterized in that the prosthesis socket ( 2 ) has at its upper end ( 7 ) an annular recess ( 8 ) enclosing the prosthesis neck ( 3 ), whereby this end ( 7 ) of the socket ( 2 ) forms a collar ( 25 ) increased elastic deformability is reduced. 3. Endoprosthesis ( 1 ) according to claim 1 or 2, characterized in that the prosthesis shaft ( 2 ) and the prosthesis neck ( 3 ) are integrally connected. 4. hip joint endoprosthesis ( 1 ) according to claim 2, characterized in that the prosthesis socket ( 2 ) and the prosthesis neck ( 3 ) are detachably connected to one another and the prosthesis neck ( 3 ) with an extension pointing towards the knee in the prosthesis socket ( 10 ) 2 ) intervenes. 5. hip joint endoprosthesis ( 1 ) according to claim 4, characterized in that it ( 1 ) on the distal side in the vicinity of the offset has a member for releasing the connection between the prosthesis neck ( 3 ) and prosthesis shaft ( 2 ). 6. Hip joint endoprosthesis according to claim 5, characterized in that the position between the prosthesis neck ( 3 ) and shaft ( 2 ) is adjustable without any intervention on the femur ( 5 ). 7. hip joint endoprosthesis according to the preamble of claim 2, characterized in that the prosthesis shaft after implantation in the resected ornamented femur ( 5 ) is to be expanded and the degree of expansion on the distal side of the prosthesis neck ( 3 ) is adjustable. 8. hip joint endoprosthesis according to claim 2 with the kenn characterizing features of claim 7.   9. Endoprosthesis ( 1 ) according to one of the preceding claims, characterized in that the prosthesis shaft ( 2 ) in the collar ( 25 ) to which it ( 2 ) is reduced at one end ( 7 ) has slots ( 16 ) for further Increasing elastic deformability.