DE10221965A1 - Femoral - Google Patents

Abstract

An endoprosthesis lying in the femoral neck is presented, which, through the combination of a wide support collar with incoming ribs, has a rotationally and flexurally stable proximal anchoring directly on the osteotomy level, so that maximum stability is achieved in the important proximal area directly on the osteotomy level. In addition, the stability during the healing phase can optionally be increased by tightening the endoprosthesis against the bone using an anchoring element introduced from the proximal end.

Description

The invention relates to an endoprosthesis for anchoring in the femoral neck Femur.

The long-term stable anchoring of artificial joints (endoprostheses) in the Bones pose one of the major challenges in orthopedics and Trauma surgery. As always, all endoprostheses anchored in the bone loosen up one day, the question arises as far as possible to anchor proximally Endoprostheses, because of the proximal loading of the bone Bone growth stimulated in this area and a bone atrophy in the sense the so-called "stress shielding" is avoided. If there is a loosening then in the proximal area of the femur i. a. still sufficient Bone mass available, so the prerequisites for a Exchange operations are cheaper. The most proximal and only in the femoral neck lying prostheses (the so-called "femoral neck prostheses") are the Conditions with a change operation even very favorable, because the Loosening of such small implants is usually only a small one Cause bone loss.

As early as 1952 Thomson presented such an endoprosthesis in the proximal femur, which uses the principle of the then known lamellar nail to stabilize the femoral neck (Thomson JEM ( 1952 ) A prosthesis for the femoral head.The Journal of bone and joint surgery 34-A No 1 : 175-182)

In 1977, a femoral neck prosthesis was presented (DE 27 24 234 C2), which is supported on the femoral neck with the help of a "thrust washer" on the osteotomy level (see also Huggler AH, Jacob HAC ( 1980 ) A new approach towards hip prosthesis design. Arch Orthop Traumat Surg 97 : 141-144). This so-called "pressure disc endoprosthesis" represents the most common endoprosthesis of this type today.

Other so-called "femoral neck prostheses" have also been developed so z. B. the so-called "cigar prosthesis" (DE 196 01 340 C1) and her Successor, the so-called "cut prosthesis" (DE 197 20 493 C1 and DE 299 21 577 U1).

Also of great interest are the efforts of Munting und Verhelpen (Munting E, Verhelpen M ( 1995 ) Fixation and effect on bone strain pattern of a femoral stemless hip prosthesis. Journal of biomechanics Vol 28 No 8 : 949-961), the problem of complex force introduction into the calcar femoris.

DE 837 294 also describes a femoral neck prosthesis with smaller lamellae and Spikes on the osteotomy surface described.

DE 38 39 704 A1 and DE 198 42 554 A1 also describe femoral neck prostheses described the problem of distributed load introduction through a support realized via a series of rods protruding into the bones of the femoral neck.

Despite the diverse efforts, those known from the prior art are endoprostheses anchored in the femoral neck with a number of disadvantages afflicted with all previously known and implanted endoprostheses high loosening rates and poor clinical results or to others Have caused problems.

Disadvantageous with the quite common pressure disc endoprosthesis (DE 27 24 234 C2) is that a so-called "tab" is attached below the trochanter major in order to avoid the so-called To clamp "thrust washer". Because the support surface of the thrust washer is not is suitable, substantial rotational and bending loads around the longitudinal axis of the Introducing the endoprosthesis into the bone is the tension in the phase of Bone healing inevitable with the pressure disc prosthesis. The one for that However, the "tab" required does not only mean an additional operative Measure, but often for the patient also pain directly under the Muscle lying tab area. Another disadvantage is the high Loosening rate of the pressure disc endoprostheses. Especially not exactly positioned endoprostheses (especially varus deformities) Overloading of the bone bed on the calcar femoris and causing a migration of the Endoprosthesis in another varus position and ultimately to loosen it of the implant. Reason for overloading the bone bed on the calcar femoris is likely the already mentioned small contact surface in the absence of rotation and Bending stability around the longitudinal axis of the pressure disc endoprosthesis.

The so-called "cigar prosthesis" has already disappeared from the market: Lack of rotation stability and insufficient anchorage areas on the calcar femoris caused rapid implant failure with early loosening. Also about that Successor model, the so-called "cut prosthesis" are very different Results with sometimes high implant failure reported (congress reports). Here, too, the rotational and bending stability is obviously not sufficient to to ensure sufficient long-term stability in the bone bed.

The endoprosthesis presented by Munting and Verhelpen appears problematic that with this concept one of the pressure disc endoprosthesis Similar force application directly and largely only on the osteotomy surface should and also a similar to the pressure disc endoprosthesis Screw tension via the outside of the thigh bone screwed tab and another lag screw should be what intraoperatively a lot of effort and corresponding detachment of the muscles means. Whether the planned anchorage areas are sufficient in the long term Rotation and bending stability with decreasing screw tension in the Ensuring bones has to be waited for.

Unfortunately, with the prosthesis presented by Thomson, the problem of Contact surface in the calcar femoris and in particular the rotational stability despite the the lamellae used in the distal section of the endoprosthesis were under-considered and - from today's perspective - the material with plastics and smooth metal surfaces wrongly chosen. In particular the small dimensions of the ribs (= lamellae), which is no longer effective proximally at the significant load introduction area are not a load-supporting effect of the ribs in this area. Also, the small dimensioning of the ribs and the lack of them in the proximal area no significant rotation and bending stability around the Expect the longitudinal axis of the endoprosthesis. It can be assumed that the essential The purpose of the slats - as was common at the time - was the possibility of axial sliding of the Endoprosthesis was seen. Overall, the endoprosthesis failed preprogrammed.

This also applies to DE 837 294: here too, the slats are not in the Support collar integrated and therefore not at the location of the maximum load transfer and high bone density effective.

A disadvantage of those described in DE 38 39 704 A1 and DE 198 42 554 A1 Systems is the intraoperative anchoring of the endoprosthesis as well the unclear blood supply to the remaining bone after cutting the Thread, since the bone is severely cut open from the inside and is damaged accordingly.

It is therefore the object of the invention, one in the femoral neck Thigh bone endoprosthesis safely and biologically useful largely maintain the bony blood supply in the bone storage anchor. The fixation in the bone should be easy to handle intraoperatively. Load transfer in the area of the calcar femoris (at the site of the greatest load transfer and greatest bone density) as well as a high rotational and bending stability around the longitudinal axis of the endoprosthesis must be ensured. Stress shielding by introducing loads distal to the calcar femoris must be avoided become.

This object is achieved according to the invention by claims 1 and 5. Through the Combination of a wide support collar with in Longitudinal direction of the endoprosthesis extending ribs provides maximum stability achieved in terms of bending and rotation stability and thus load initiation in the proximal bone bearing induced, causing bone atrophy as a result of stress shieldings in this area can be prevented.

At least two ribs - in a preferred embodiment of the invention four ribs ( 1 ) circular - are arranged around the longitudinal axis of the endoprosthesis. The outer boundary of the ribs is adapted to the oval cross section and possibly also the proximal expansion of the femoral neck. In the distal direction, the ribs can also lose depth or leak completely. The cross section of the endoprosthesis increases in the proximal area and forms a wide support collar ( 2 ) interrupted by the ribs for the proximal load introduction into the femur. In order for the load to be distributed in the direction of the trabecular structures of the bone, it is advantageous if, at the level of the osteotomy plane, the angle ( 6 ) in the sectional plane ( 4 ) extending through the longitudinal axis of the endoprosthesis between the support collar and the osteotomy plane is greater than 40 °. It is also advantageous if the support collar formed in this way opens into an additional end plate ( 3 ). It is advantageous if the depth of each rib ( 7 ) at least at one point is> 10% of the endoprosthesis diameter ( 5 ) measured at the osteotomy level. With a typical femoral neck diameter of 30 mm at this point, the depth of each rib should be at least 3 mm at one point.

It is also particularly advantageous if the proximal area of the endoprosthesis has a special microstructuring or coating which promotes the growth of the bone in this area and prevents it in the distal area. This leads to increased load introduction in the proximal area and axial sliding of the endoprosthesis in the distal area, so that the effect of stress shielding with the dreaded bone atrophy in the proximal area is prevented. The coated or microstructured proximal area should not extend deeper than 40 mm into the neck of the femur. In order to support this effect of the proximal load introduction, it can be useful in a preferred embodiment of the endoprosthesis to provide a recess ( 10 ) at the lateral end (ie the distal end of the prosthesis), e.g. B. in the sense of a hole, so that here no growth of the bone and thus no load transfer can take place.

Advantageous materials for the endoprosthesis are titanium or those for endoprostheses provided titanium alloys, in particular TiAlV, TiAlFe or TiAlNi- Alloys. Other metals intended for endoprostheses, e.g. B. also on Co-based, are suitable.

In a further embodiment of the invention, distal fixation can also be used to brace the endoprosthesis. It when the fixation z. B. is carried out in the sense of screw anchoring from proximal to distal (in the sense of an "anterograde" bracing of the endoprosthesis in the bone, see arrow ( 9 )), so that the femur on the greater trochanter area does not move laterally to accommodate a flap o. Ä. must be prepared. For this purpose, in a preferred embodiment of the invention, a screw ( 8 ) is screwed into the femoral neck from proximal to distal. This screw can also perforate the lateral cortex for better anchorage in the bone. The endoprosthesis is then pushed over the proximal end of the screw and, with the help of a further screw, which is pushed through a central hole in the endoprosthesis in direction ( 9 ), is screwed into the screw located in the bone, which has a thread in this area , It is advantageous if the thread cutting into the bone and the thread in this screw for receiving the second screw are designed in opposite directions. It can also be advantageous if at least one of the two screws is made of a resorbable material, so that the endoprosthesis is only braced during the critical bone healing phase. In addition to screw connections, other connections such as dowels are of course also conceivable, in particular for anchoring in the bone.

It can also be advantageous if the endoprosthesis is slightly curved is performed to better, especially in larger patients to ensure geometric adaptation to the femoral neck geometry.

The invention and the environment of the endoprosthesis as well as the introduction Additional screw fixation from proximal to distal is shown in the drawings explained in more detail using some preferred exemplary embodiments.

The Fig 1 2 from lateral distal. 3 shows a side view of a preferred embodiment of the endoprosthesis having 4 ribs and representation of the reference plane, Fig. An oblique view of the same preferred embodiment of the endoprosthesis having 4 ribs and Fig., A further embodiment with the clamping element for anterograde strain the endoprosthesis in the bone. Specifically, the shows:

Fig. 1 shows a preferred embodiment of the endoprosthesis anchored in the femoral neck with 4 ribs. The depth ( 7 ) of the ribs ( 1 ) should be at least 10% of the diameter ( 5 ) of the endoprosthesis measured at the osteotomy level. The diameter of the endoprosthesis increases in the proximal direction and forms a wide support collar ( 2 ). The angle ( 6 ) of the support collar on the osteotomy plane - measured in the sectional plane passing through the longitudinal axis of the endoprosthesis - should be greater than 20 °. To improve the support of the support collar on the bone at the osteotomy level, the support collar opens into an end plate ( 3 ).

Fig. 2 shows the preferred embodiment shown in Fig. 1 of the femoral anchoring endoprosthesis with 4 ribs in a lateral distal view. This view also clearly shows the recess ( 10 ) located laterally in the bone to reduce the distal load introduction into the bone.

Fig. 3, shown in FIG. 1 preferred embodiment of the anchoring in the femoral neck endoprosthesis with 4 ribs in the lateral view distally with distal fixation element. In this case, the fixation element is designed as a screw anchor with the help of an interrupted thread for better bony integration. A second screw, not shown, which is inserted through a central bore in the endoprosthesis in the direction ( 9 ), can be screwed into a thread in the screw ( 8 ) and thus the endoprosthesis can be clamped in the direction ( 9 ), so that support collars ( 2 ) and end plate ( 3 ) are pressed against the bone.

Claims (9)

1. Endoprosthesis for cementless bone anchoring in the femoral neck of the femur, characterized in that the endoprosthesis has at least two ribs running in the longitudinal direction of the endoprosthesis, which reach the osteotomy plane, and the cross section of the endoprosthesis rises proximally and thus forms a support collar, so that at the osteotomy plane the angle in any (but not through the ribs) cutting plane through the longitudinal axis of the endoprosthesis between the surface of the endoprosthesis at the osteotomy plane and the longitudinal axis of the endoprosthesis at the osteotomy plane is greater than 20 °. 2. Endoprosthesis for cementless anchoring in the femoral neck of femur according to claim 1, characterized in that the proximally increasing cross section in one of the osteotomy surfaces overlying and adapted to the bony cross-sectional shape End plate ends. 3. Endoprosthesis for cementless anchoring in the femoral neck femur according to any one of the preceding claims, characterized in that the distal section of the endoprosthesis has a central recess, which is the growth of bone in this area of the endoprosthesis prevented. 4. Endoprosthesis for cementless anchoring in the femoral neck femur according to any one of the preceding claims, characterized in that the proximal section of the endoprosthesis is microstructured and / or with osteoinductive substances is coated, but smooth in the distal area is performed so that the bony integration in the proximal area is improved and is made more difficult in the distal area. 5. Endoprosthesis for cementless anchoring in the femoral neck of femur, characterized in that the endoprosthesis has an anchoring element at the distal end, the can be connected to the bone from the proximal side and with which the endoprosthesis is pulled distally and thus against the Bone bed can be pressed. 6. Endoprosthesis for cementless anchoring in the femoral neck femur according to any one of the preceding claims, characterized in that the anchoring element for better anchoring in the bone with a further anchoring element lying against the outside of the bone is connected. 7. Endoprosthesis for cementless anchoring in the femoral neck femur according to any one of the preceding claims, characterized in that the anchoring element is made of non-resorbable materials. 8. Endoprosthesis for cementless anchoring in the femoral neck femur according to any one of the preceding claims, characterized in that the at least part of the anchoring element made of absorbable Materials is made. 9. Endoprosthesis for cementless anchoring in the femoral neck femur according to any one of the preceding claims, characterized in that the endoprosthesis in the longitudinal direction from proximal to distal one of the Femoral neck geometry has adapted curvature.