DE3311326A1 - IMPLANTABLE JOINT PROSTHESIS - Google Patents

Description

Dipl.-Ing. A. Wasmeier c Dipl.-lttgrH. Gfar "

Admitted to the European Patent Office · Professional Representatives before the European Patent Office Patent Attorneys P.O. Box 382 8400 Regensburg 1

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Applicant: VITEK, INC., 3143 Yellowstone Road, Houston, Texas 77054 _t USA

Title: "Implantable articulated joint prosthesis" Priority: USA - SN Ο6 / 369 731 dated April 19, 1982 Inventor: Charles Albert Homsy - engineer

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"Implantable joint joint prostheses"

The invention relates to orthopedic implantation of articulated joint prostheses in the form of intsamedullary prostheses or endoprostheses, especially intramedullary hip prostheses.

For many years surgeons have been able to replace the ball of the hip joint with a metal ball. This has happened in such a way that the ball and part of the neck have been removed from the upper bath of the femur. It was then a metal prosthetic implant with ball, neck and stem in inserted into the medullary canal of the femur. Before this onset, the one more centered became 'selegene'. softer, spongy bones of the medullary canal rasped to form a bone cavity or a pedicle cavity or pedicle socket so that the pedicle of the prosthesis can be accommodated therein could.

The graters that were used to form the pedicle cavity were variable in their shape and were not exactly tailored to the shape of the desired prosthesis. The cross-sectional dimensions of the stem were in most places much smaller in its longitudinal direction than the corresponding cross-sectional dimensions the prepared stem cavity. Thus, the stalks were usually picked up loosely within their burrows. Many patients who received such a prosthesis were due to severe pain and / or the limited area of the outline of the joint that received the prosthesis in its range of motion very disadvantaged.

In order to better stabilize such stalks, they were made first provided with transverse holes, and many years later with pores on their outer surfaces. The bone should go into the holes and / or grow into pores of the stems. It was hoped that the tissue ingrowth would increase the stability of the stems

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would improve their caves significantly.

Since the shapes of the stems with pores were modeled on the shapes of the stems with holes, the cross-sectional dimensions were the stems with pores also in many places - along their longitudinal extent, compared to the corresponding cross-sectional dimensions of their stem cavities, significantly undersized. Man was of the opinion that such undersizing was the Stalk was required so as not to obstruct the femur during insertion of the stalk into the prepared stalk cavity break. Due to such a deliberate dimensioning of the handle shape, the known handles lacked the necessary stability when inserting into their sockets, and they. could therefore not place loads on the bones surrounding the stalks in the the way you want.

Certain types of articulated joints hold high mechanical levels in use Loads from, e.g. hip joints, whereby loads occur in the bone that surrounds and defines the medullary canal. Because of the poor fixation of the stalk within the medullary canals, many patients have such undimensioned Stems inserted have received limited range of motion due to the pain in movement Have to buy.

Efforts to achieve improved stability for such undersized stems lead to the injection a bone cement paste into the prepared pedicle cavity »The Cement mass fills the laerrauia between the outer surface of the undersized stem and the adjacent tissue and hardens in it. Bone cement was used in significant quantities is used and is generally accepted as a way to fix a stem within its cavity.

Bone cement typically comprises an acrylic polymer powder mixed with a compatible, liquid acrylic monomer system is premixed to obtain a dough-like paste. Of the

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The stem is quickly inserted into the cement paste, which is then inserted into hard cement hardens or polymerizes between the stem and the bone. The hard cement is supposed to hold the stem in the Anchor the pedicle cavity. When using a cement paste, variations in the implantation process can be made, e.g. as follows: .

a) .Change in the manner and manner in which the cement mass is incorporated into the prepared Pedicel cavity was injected;

b) Reduction of the viscosity of the · .cement mass to the connection between the cement pavement and the porous, spongy bone.

c) extension of the stem,

• d) Enlargement of the center-lateral dimensions of the stem, and e) Elimination of the flange on the neck of the prosthesis, so that only one. small part of the central and / or lateral outer surface. ' ^1st of the stem in any longitudinal view strikes against the adjacent dense cortical bone during the insertion of the prosthesis by hand. The dimensions of the other cross-sections of the stem, in length above and below such a view, were still much smaller than. the corresponding dimensions of the cross-sections of the stem-right cavity. This undersizing of the stem made it easier to insert the stem and prevented the dense femoral cortical bone from breaking.

Cement paste allows the surgeon only a very short period of time, on the order of five minutes, in which to fix the stem in the cavity. If then <> the cement mass "polymerizes and hardens, it can sciiru-nr '-' ■ '■■' . !: / or DER ■ '> - • nientmasse and subsequent tissue on the other hand leads, ^ erartige vacancies affect the capability of the cured · hard cement for uniform transmission of load stresses between the stem and de ^r n surrounding crawled r_a-.. : '- part.

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If the cement mass is such load stress 8n non-uniform it can result in bone loss that begins and ends at the top of the thighbone a gradual decline in the useful life of the implanted prosthesis. In addition, the hard cement can break on its own, even three to five years after the Surgery. In extreme cases, this leads to the breaking of the cement mass also · to a breaking of the stem. If the cement paste and / or the stem breaks, the patient is in great pain, unable to walk and needs a new implantation.

A re-implantation of a new prosthesis requires that the old prosthesis remove the hard cement mass is drilled out and the medullary canal is rubbed out again, which leads to injuries and dangerous side effects in the patient's body.

The possible migration of unreacted monomer from the bone cement mass into the tissue and the need for the bone cement mass to enter into an exothermic polymerization, can result in serious damage to the tissue surrounding the prosthesis. Such damaged tissue leads to a loosening of the stem within the cavity.

Attempts to achieve a cementless stem fixation concluded the use of pores on the stem surface, or the addition of a porous outer coating made of a ceramic, a polymer or a composition of polymer, ■ glass and / or ceramic is made around the stem. The one with over ^ The handle provided with the handle was inserted into the handle cavity without the cement compound (see US Patents 3,938,198, 3-986.212, 4,164,794 and 4-.307.4-72).

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A known type of porous composite coating that has the ability to grow tissue into the pores, is in the article "Porous Implant Systems for Prosthesis Stabilization "by CA. Homsy, et al., Clinical Orthopedics, No. 89, November / December 1972, pages 220-235 and in U.S. Patent 5,992,725 explained. This "known coating" was with the stems of conventionally shaped and dimensioned prostheses tied together. .

The use of conventionally shaped prostheses has been responsible for many clinical failures. It was determined, that the void in the pedicel cavity was essentially surrounded by relatively soft, spongy bones, who could not withstand the mechanical stresses acting on him. The advantages of this well-known, compound Coating had therefore not been fully utilized until the present invention was completed.

The success of an implant is typically measured according to how he is able to assume the natural functions of the joint in which the implant is placed and execute. An implant must therefore be able to withstand the required compression and bending loads, that are given to him during normal joint movements.

Before the present invention, known medullary prostheses were especially hip joint prostheses, often not in the-. Able to perform normal body functions mainly because of the crucial importance of the cross-sectional dimensions of the stem were not fully recognized.

The present invention resides in the recognition of the importance and critical importance of the cross-sectional dimensions of the Stalk in the longitudinal direction of its length in relation to the corresponding cross-sectional dimensions of the medullary canal, as it is through the surrounding, dense cortical bone., which as Cortex is known to have been set.

The object of the invention is to provide an improved implantation technique using an intramedullary prosthesis that is characterized by (1) good initial stabilization within the stem cavity, (2) a permanent subsequent stem stabilization, (3) a distributed, longitudinal Stress transfer, (4) improved stress transfer between the stem and surrounding dam hard, spongy bones and sinus bones »and (5) decreased, localized stress zones in the bone opposite to the entire stem and facing this.

The technology of. surgical, orthopedic implantation the invention resides in the selection of a prosthesis having a stem portion which is shaped and dimensioned to substantially the geometry of the medullary canal in the patient's bone corresponds to, as it is defined by the cortical bone or the cortex, and on a subsequent formation of a complementary Pedicle cavity in the canal that houses the selected prosthesis.

One device for performing this technique provides a prosthesis with a handle made of a base material, preferably metal, with which a thin, flexible, compressible, porous coating is connected. The covered stem is the full length with respect to the empty space oversized in the sculpted cave. This results in, that the handle is inserted into the cave under the action of force must become. Such an introduction under the action of force compresses the coating somewhat in relation to the adjacent one hard bone that surrounds and defines the medullary canal. The compressed cover provides a compression fit without significant weakening of the porosity of the coating. This compression seat extends essentially over the entire length of the stem. The compression seat immediately stabilizes the stem within its cavity and enables it then that the tissue grows into the pores of the coating. The initial compression fit and the subsequent one

Tissue ingrowth "both ensure long-term stability of the stem and [rod load transfer properties of the stem.

The improved intramedullary prosthesis according to the invention has a stem part , the cross-sectional dimensions of which correspond essentially to the cross-sectional dimensions of the medullary canal as defined by the cortical bone or cortex into which it is to be inserted.

In a preferred embodiment of the invention, the base material for the handle is a metal, the cross-sectional dimensions of which are only slightly undersized over the entire length compared to the cross-sectional dimensions of the prepared handle cavity. The base material of the handle is completely covered with a thin coating. The cross-sections of the stem part provided with cover are in comparison to the. corresponding sections of the prepared cave are oversized by a fourth between 0.2% and 7 %.

By shaping the stem part of the prosthesis in such a way that it essentially corresponds to the geometric shape of the medullary canal, which is defined by the dense cortical bone of the femur, and by connecting a compressible, porous, flexible coating to the stem, it is now possible to achieve an approximately uniform interference fit between the stem cover and the surrounding hard, spongy bone and hind bone during implantation. Such a press fit enables the stem to distribute mechanical "loads" on the cortical bones, especially in the dkphysial area, as well as on the relatively hard, spongy bone and on the cortical bones in the metaphysial and epiphysial areas the long-lasting, post-operative results of the implantation are improved.

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One applies the procedure of selecting the shape and size of the prosthesis and creating the pedicle cavity according to the present Inventions that can make decisive improvements in the Achieve stalk irstabilization and fixation in the case, even if uncovered stems are used which are to be implanted with the aid of bone cement.

After the correct prosthesis has been selected, the medullary canal in the femur is rubbed or widened and filed, so that a stem cavity is formed which has a predetermined shape and length so that either the oversized, Covered stem alone or the slightly undersized stem without cover together picked up with a thin layer of cement.

In the case of the covered stem, after the cavity has been formed, the stem is properly attached to the The mouth of the cave is oriented and gradually inserted into the cave with sufficient force, whereby the resilient, porous coating is slightly compressed. At the metaphysial and epiphysial levels of the medullary canal the coating is compressed uniformly, while at the diaphysial level of the canal the medial and lateral Surfaces of the coating are predominantly compressed. These compressions, however, are such that the porosity part of the coating is only slightly reduced. The bone tissue is then in intimate contact with the Pores of the compressed coating to enable rapid tissue ingrowth.

The invention is explained below in conjunction with the drawing on the basis of exemplary embodiments. It wins:

1 shows a side view of a hip joint prosthesis according to FIG Invention,

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Pig. Figure 2 is a right side view of the prosthesis along the line 2-2 in Fig. 1, with the flange, neck and ball removed,

Fig. 5 is a sectional view of the stem taken along line 3-3 in Fig. 1 with the flange visible;

Fig. 4 is a sectional view of the stem taken along line 4-4 in Fig. 1,

FIG. 5 is a side view of a preferred embodiment of FIG Invention, wherein the prosthesis corresponds essentially to that of FIG. 1, but a flexible, porous, has a coating that promotes tissue ingrowth,

6 shows a view of the hip joint prosthesis according to FIG. 5 installed in the upper end of a femur, the. .Stalk ¹ extends completely into the medullary canal of the femur.

The prosthesis 10 has a stem 18 which extends into the medullary canal 28 (Fig. 6) of a femur 27 can be used. The prosthesis 10 is designed as a hip joint prosthesis or Femoral prosthesis shown. The part of the description which relates to the stem 18 and the interrelationship of the stem with and its fixation within the medullary canal 28 but is equally applicable to other articulated joints.

In connection with FIGS. 1 to 4, the prosthesis has a ball 12, a flange 16 and a neck 14 provided between the ball and the surface. A handle 18 has a shaft part which extends from the opposite side of the flange 16 substantially at right angles thereto. In side view 1, the stem 18 is curved at its proximal end and tapers at the distal end down to an annular flange 20.

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The flange 20 is formed so that it has a circular cross-section and slightly, e.g. extends beyond the body of the stem 18 by a little less than 2 mm. The near end of the stem 18 is relatively flat and has an inner surface 22 that is rounded and an outer surface 24 that is flat but rounded Has edges, as shown in FIGS. 3 »4 · instead of a circular section, the flange 20 can have an oval cross-section.

The improved handle 18 of the present invention is intended to be manufactured in at least three separate forms, each Shape has a set of different dimensions, shown in Figures 1, 3 and 4- with the letters a to g are. It has been found that with three different shapes for a femoral prosthesis in practice most shapes of Femur bones 27, which occur in normal human skeletal structures, can be detected. These three separate Molds for an implant 10 can therefore be prepared in advance and provided to the surgeon along with instructions who specialize in the manufacture of the appropriate Stielhg & XeQ as described below.

Below are dimensions in mm for such a shape of a typical small stem prosthesis «? specified ':

a = 139.7 mm - e «10.0 mm

. b = 8.2 mm f = 32.0 mm

c = 8.1 mm g = 8.0 mm

d = 12.0 mm ■

In a preferred embodiment, as in the figures 5 and 6, a coating 26 made of a resilient, porous, the tissue ingrowth promoting material with the Handle 18 and connected around this, so that the handle is completely provided with a coating. However, it is on the flange 20 no coating provided.

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The cross sections of the stem 18 represent at least 7056 the corresponding cross section of the medullary canal 28, which is defined by the endosteal or inner contour of the dense, hard cortical bone for metaphysial and epiphysial segments of a typical long bone of the skeleton, and at least 90 % of the corresponding cross-sections of the diaphysial segment. ^r;

Esfeann any resilient, resilient tissue ingrowth promoting, porous coating 26 can be used as long as it is compatible with the body system of the patient and bonds sufficiently with the base material of the stem. This material is typically a metal such as an ASTM F-75 orthopedic chromium-cobalt-molybdenum alloy.

One such preferred coating composition is described in d & f US Pat. No. 5,992,725 and is manufactured and sold by Vitek, Inc., Houston, Texas under the designation PROPLAST.

In its preferred embodiment, this material has a flexible, fibrous, porous structure made of carbon or Graphite fibers is composed, where it is optionally used together with a proportion of polytetrafluoroethylene fibers is bonded together with the help of a sintered polytetrafluoroethylene resin are connected.

The porous coating should be at least substantially throughout Be connected to the surface of the prosthesis, which is normally intended for the fixation. For example, the stem a femural prosthesis completely covered with a coating. .

Preferably, this coating 26 has a thickness of 2 mm, which is a compromise between the various ones indicated below Factors means: Desired handle strength, coating compression, ingrowth of the tissue into the coating, size of the Medullary canal of the patient, a higher coating compression

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leads to a further reduction in porosity «,

Before an implantation, a pedicle cavity or pedicle socket 25 must be in the femur 2? be formed "Dia-sectional dimensions of the empty space in the cavity 25 are designed so that at least 1% and preferably from 10% compression of the coating 26 are obtained after the stem 18 in its final seat © _A. position in the cavity 25 has been pressed, as in 3Ig ,. 6 shown.

The coating 26 is sufficiently porous and sufficiently resilient, so 'that the porosity properties and the ability to grow into the tissue only marginally "impacted" if during force insertion of the stem 18 is partially compressed into the preformed stem cavity 25. The cover 26 is also able to accommodate 9 & evenly £ örmigk @ it © n at least in the upper part of the cavity and substantially uniform compression fit or interference fit with the adjacent hard bone, usually the cortes.

A correct preparation of the cave 25 uses the form 4er Prosthesis 10 in full. for example, the outer surface 2 * 1 * is not covered by the flange 16 and extends substantially perpendicularly away from the flange 16 · The surface 24- curves sharply and then runs in an approximately straight S & nie to the Bottom flange 20.

With such a geometric configuration of the prosthesis 10 becomes when the lower Snd © of the handle IS. is chosen so that ss J the prepared cave 25 fits, the overmg 26 through the surrounding one Bone compressed for substantially the entire length of the stem.

The surgeon uses a combination of ύοώ. Special surgical tools are used to make the cavity 25 on the receptacle of the droi molds for the femural prosthesis 10 that is at his disposal.

In general, the cavity 25 is rubbed into the correct shape and rasped so as to force the oversized, coated stem 18 onto the implant IO can be used. The tissue around the empty space of the cavity is thereby completely enclosed and results in an intimate atmosphere Pressure substantially with the coating 26 of the stem over its entire length.

In particular, the correct shape of the prosthesis can be determined in advance with an appropriate radiograph. The instru-; Ments that are then used to form the cavity 25 are then checked to determine whether the correct shape for. the prosthesis 10 has been predetermined by the radiograph . "'''"' ■ '■ "''"' ■■■■■■■■■.

Conventional surgical methods used. The chosen method should allow access to the femur near the body in the direction of the longitudinal axis. When the hip joint is exposed, a displacement of the femoral head from the acetabulum can either be achieved or can be achieved without a trochanteric osteotomy. ·

In the following description, the trochanteric osteotomy will be longitudinal 6, and the trochanter is pivoted away from the neck and ball of the femur.

The femoral neck osteotomy is performed using a guiding device ' performed. The mean level of the osteotomy should be as high as possible above the uppermost limit of the lower trochanter.

Bone forceps are used at the vertex of the two osteotomies to create an entry cavity for a hand reamer about 8 mm 'diameter. If the trochanter doesn't has been released, a small boring iron is used to create the entry lumen for the hand reamer. the

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Reamer is the femur gerieht along the longitudinal axis 27 © t _t allow access to Medullärkanal 28 through the metaphyseal bone is reached. A guide is expediently used to control the position of the tip of the hand reamer or the drill bit.

Following this, a guide rod is a power-driven flexible reamer down the longitudinal axis of the femur 27 Following the cavity, which is created by the Handreibaal® or the Drilling iron produces ■. will.

The flexible reamer is used in increments of 0.5 mm to the distal end of the cavity 25 in the diaphysial segment of the To produce Medullärkaüales. The guide rod previously used in the channel has been inserted acts as a guide for remotely the cannula-shaped cutting heads of the reamer. The reamer cutting heads are enlarged in their dimensions until the endostial cortical bone is in the diaphysial part of the medullary canal is touched. The size dimension of this reamer gives and fixes the dimension of the last reamer used to create the cavity 25 in the direction of the longitudinal axis of the femur 27 This dimension of the last reamer corresponds to a special, prefabricated shape for the implant 10, e.g. a small prosthesis 10 with the dimensions a - g according to Figures 1, 3 and 4 »

As mentioned above, the implant 10 consists of three different ones Shapes to accommodate most of the shapes of the femur that are normally used when performing femural implants occur, can be taken into account.

Using a ¹ Trans-lationsbewegung in the direction of the longitudinal axis of the femur a Handraspelung the stem cavity is created with. If the stem cavity 25 is correctly sized and shaped, the stem 18 is inserted into the cavity under pressure. Because the coated stem 18 by a value between 0.2% and 7% in the cross-sections compared to the corresponding cross-sections

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of the cave 25 produced is oversized, he cannot be pressed down by hand and must be gently driven in with a surgical mallet. The flange 20 is used for Protection of the leading edge of the cover 26 from abrasion during the forcible introduction of the cover Stem 18 into its cavity 25.

After the preceding steps, the prosthesis 10 according to the invention is implanted with positive results, the implant immediate stability in the cave 25 results. Tissue begins ratchet in the. Wax in the coating 26, so that a perfect permanent fixation of the erothesis is guaranteed.

The soft, porous coating 26 provides an intimate physical one Contact with the surrounding bone and prevents abrasion of the cortex bone or hard spongy bone during physical movements of the body following an implantation. Due to the resilience of the coating 26 is on the Covering built up an impact gradient that supports the distribution of pressure loads along the length of the implanted stem 18 and increases results in a longer-lasting and more comfortable implant for the patient.

Patients who have received such implants 10 are in usually been able to comfortably support normal weight as early as 5 to 6 weeks after surgery.

Although this is less desirable, a similar technique for implanting a prosthesis 10 having the form of the invention can be used can be used which, however, do not have a resilient, porous, tissue-ingrowth-promoting coating on the base material of the stem 18 has.

The stem 18 without a coating must be made using a bone cement be implanted to create a cement coating around the stem. 18 is formed. The improved load transfer to the cement pavement and the hard, spongy bone and the covering

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The support provided by the hard bark ceases Link against premature breaking of the cement

a stem 18 without tJberssug is the bottom flange 20 either eliminated or its outer surface grooved in a vertical sighting, so that the cement the end of the stem at the time of implantation can enclose. The grooved flange 20 also contributes to Centralization of the stem in relation to the surrounding cement pavement.

A cement or plastic wad is usually placed away from the end of the stem to provide back pressure in the cement during the insertion of the prosthesis.

While the prosthesis 10 according to the present invention in connection has been illustrated and described with a hip joint prosthesis, it is also applicable to other joint joint prostheses applicable in which the load transmitted by the joint from the implant to the skeleton ax using a Stem or an extension is directed or, di # into a prepared cavity or cavity in the hedullary canal part of the skeletal element in the patient's body fits.

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Claims (1)

P 33 11 3 ^ 5.2 ~ X ~ 10.6.1983 W / He New patent claims: l'J intramedullary Ριό thesis with a stem part for insertion into a stem cavity, which is formed in the medullary canal of a patient's bone, as defined by the cortex of the bone, characterized in that the stem part (18) cross-section 3-dimensions which essentially correspond to the geometry of the medullary canal (28). 2. A prosthesis according to claim 1, characterized in that the \ stem part (18) has a base whose cross-sectional dimensions \, are dimensioned in the direction of the entire length slightly relative to the cross-J sectional dimensions of the stem height (25). ! 3. Prosthesis according to claim 2, characterized in that a thin, resilient, tissue ingrowth promoting, porous coating (26) covering substantially all of the outer surface of the base, with the cross-sectional dimensions of the Covered handle part (18) is slightly oversized with respect to the corresponding cross-sectional dimensions of the handle (18) are. 4. Prosthesis according to Claim 3 »that with - provided \ coating shaft (18) j ^v oversized in its cross-sectional dimensions' in comparison to the corresponding Qifrschnittsdimensionen the cavity (25) to a value between 0.2% and 7% is. 5 * Prosthesis according to claim 3 * characterized in that the cross section of the stem part (18) is at least 70% the cross section of the medullary canal (28) for the metaphysial and epiphysial | len segments of the bone, and at least 90% of the cross section \ of the medullary canal (28) for the diaphysial segment of the bone * jj. BATH ORIGINAL 6. Prosthesis according to one of claims 1-5 »characterized in that that the prosthesis (10) has a head part with a flange (16), a neck (14-) extending from one side of the flange (16) and a ball (12) at the end of the neck (14), that the stem part (18) has a near.End that from the opposite side of the Flange (16) extends approximately at an angle of 90 °, and a distal end that extends from the near Eade at an angle approximately equal to that Angle of the cavity (25) into which the stem part (18) is to be inserted up to the neck and on the ball (12) starts. '7 · Prosthesis according to claim 6, characterized in that the Tip of the distal end of the stem (18) has a curved ϊ has flange (20) which is radially outward extends and its largest dimension is slightly smaller than the corresponding dimension of the handle cavity (25) at the level of the ¹ curved flange. 8. Prosthesis according to one of claims 3-5, characterized in that the coating (26) has a thickness of about 2 mm. 9. Prosthesis according to one of claims 3-5 and 8, characterized in that that the resilience of the coating (26) is such that when the handle part (18) in its handle cavity (25) is inserted, the coating (26) is compressed by an amount which is between 1% and 10% of the original thickness. 10. Prosthesis according to one of claims 3-5 and 8, 9, characterized in that the. Porous coating material (26) is a resilient, has a porous structure made of carbon or graphite fibers, which optionally contain a proportion of polytetrafluoroethylene. fibers is mixed in and with a sintered polytetrafluoroethylene resin are connected. BADORIQINAL
^ COPY P 33 11 326.2 - 3 - 10.6.1983 W / fce 11. Prosthesis according to one of claims 1-10, characterized in that in the plane (25) bone cement is provided ± s € and that by pressing the stem (18) into the cavity (25) a thin cement coating surrounds the outer surface of the stem , 12. Prosthesis according to one of claims 1-10, characterized in that that the stem part (18) has an elastically resilient, porous coating (26) which promotes the ingrowth of the tissue having, the covered handle (18) being slightly oversized compared to the Leerraum.der cavity (25) and that the stem part (18) is inserted into the cavity under the action of force, the coating (26) by a value between 1% and 10% the original thickness is compressed. 13. Prosthesis according to one of Claims 1 to 10, characterized in that the stem part (18) has a base material that a thin, elastically flexible, compressible, porous coating (26) which promotes tissue ingrowth blends with the base material The stem part is overdimensioned in its cross-section compared to the corresponding cross-sections of the stem cavity (25) provided with bad tension by a value between 0.2 $ u >> 4 7% , and that the one provided with the cover enters the cavity is inserted under the action of force, the coating being slightly compressed against the cortex. 14-. Prosthesis according to Claim 13, characterized in that the Porosity of the coating (26) is only slightly reduced by the insertion of the stem part (18) in the cavity (25). 15. Device for the surgical, orthopedic implantation of an intramedullary prosthesis into the medullary canal, as defined by the cortex of a patient's femur, characterized by a hand reamer, for which an entry cavity is created along the long axis of the Fsaur to create a pedicle cavity in the medullary canal train, and in order to achieve © inen ^ to the medullary canal through the metaphysial bone ⁰ * ft / COMPLETE ^COPY BAD ORIGINAL a, guide rod of a power-driven, flexible reaming tool, the one in the lengthwise axis of the femur that through the reaming tool generated cavity is used following, and as Guide used for the cutting head of a flexible reaming tool the use of progressively enlarged dimensions. de »cutting head of the reaming tool until the endostial cortex bone is touched in the diaphysial part of the medullary canal, where the final dimension used for the cutting head is the final size dimension of the stem cavity formed, and a correspondingly dimensioned rasp for working up the pedicle cavity formed in this way. COPY