FR2585945A1 - Method of implanting a resection prosthesis in the diaphysis of a long bone and prosthesis allowing implementation of this method. - Google Patents

Abstract

This resection prosthesis comprises an elongate rod 1 which comprises a main frustoconical body of revolution 10, with small conicity alpha , and its wall is free from any shoulder or any other sharp discontinuity in diameter. Only the distal end 11-10d of the rod is fixed in the medullary canal of the diaphysis using a cement, the irregularities 2 of the proximal part 10b of this rod, free from cement, promoting regrowth of the bone and producing secondary anchoring of the prosthesis in the diaphysis at this level. This conical shape allows adaptation to various resection lengths in spite of a reduced number of rods; it allows the sleeve-coupling of the rod 1 by large homografts.

Description

The present invention relates to a method of implanting a resection prosthesis in the diaphysis of a long bone, as well as the prosthesis which makes it possible to implement this method.
In certain cases of tumors localized in the epiphysis or the metaphysis of a long human bone, for example of a femur, a tibia or a humerus, it is necessary to resort to the excision of the whole of the diseased part, by resection of the bone at the level of its diaphysis.

The prostheses - resection - that lion puts in place after this kind of extensive resection, are generally rigid metal prostheses, for example in Stellite which include three main parts:
- an articular piece
- a cylindrical body whose diameter is close to that of the diaphysis or slightly smaller than this, this body being connected to the articular part
- a centro-medulla rod; re having a cylindrical part of reduced diameter, close to that of the medullary canal, and a conical end advantageously provided with anti-rotation grooves.

 Due to the abrupt discontinuity between the diameters of the body and the head of the prosthesis, the connection zone of these two parts has a shoulder (or plate) whose annular surface is perpendicular to the axial direction of the prosthesis.

 To implant this traditional prosthesis in the resected bone, the medullary canal is bored to a diameter corresponding to that of the cylindrical portion of the centro-tredullary rod; is coated with a cement, usually methyl methacrylate, the medullary cavity thus prepared, and the prosthesis is placed there in such a way that the shoulder of its main body comes to bear against the slice of resected section of the bone.

 Unfortunately, it has been found that this type of prosthesis has certain drawbacks.

Due to the high rigidity of the prosthesis,
Observe at the section level a bone resorption due to a negative local physiological reaction, usually designated by the English expression "stress-shielding n with loss of permanent support of the plate against the resection section. This phenomenon may extend in causing the loosening in the medium or long term of the prosthesis.

 Furthermore, the materials used, with a high modulus of elasticity such as Stellite, generally have poor resistance to fatigue; in addition, the solution of continuity between the body and the stem of the prosthesis constitutes a zone of concentration of stresses at this level which weakens the mechanical resistance of the prosthesis. This is why fractures of known prostheses of the type mentioned occur quite frequently, these fractures requiring a new intervention and causing significant complications in the treatment of the patient. This problem of insufficient longevity of the material becomes all the more worrying. on the contrary, thanks to recent advances in surgical, radio - and chemotherapy treatments, the life prognosis of patients subject to this type of tumor is often very prolonged.

 Another problem encountered during the implantation of known prostheses is that it is necessary to provide a wide range of prostheses of different shapes and sizes, in order to be able to cope with all the therapeutic conditions encountered. It is necessary in particular to have at its disposal a series of prostheses (the main bodies of which exit the articulation piece) have different lengths and staggered because the location of the resection section - against which the main body of the prosthesis must come to rest - naturally depends on the case being treated.

 Also known are common prostheses for osteoarthritis of the hip, the upper part of which has the shape of a wedge intended to be implanted in the epiphyso-metaphyseal part of the femur. However, due to the elliptical (not circular) section of the metaphysis and its DS-shaped configuration in the frontal plane, this type of prosthesis has the shape of a flat blade which does not achieve the wedge effect in the sagittal plane.

 This is a category of prosthesis quite different from that which is the subject of the present invention both because of its shape and of its location; moreover, the distribution of the mechanical stresses from the prosthesis to the bone, and correspondingly the loosening problems encountered are absolutely not comparable in the two cases.

 The object of the invention is to eliminate the drawbacks due to known resection prostheses, by proposing a method for implanting a resection prosthesis in the diaphysis of a long bone which achieves a secure and lasting connection of the prosthesis with the diaphysis, the positioning of this prosthesis can also be done easily and with the desired precision without having to have a large number of prostheses of different dimensions.

 The invention also provides a prosthesis, resection which allows to implement this. process while being easy to manufacture, which has high mechanical strength and has a long service life.

This result is obtained, in accordance with the invention, by the fact that the implantation of the prosthesis in the diaphysis is carried out in the following manner:
at. The medullary canal of the resected bone is axially bored to form a frustoconical cavity of revolution of small conicity, the apex of which is directed on the side opposite to the resection section;
b. A prosthesis is placed therein which comprises an elongated conical rod whose conicity corresponds to that of the reamed cavity, so that this rod is applied intimately against the bone tissue constituting the wall of said cavity, said rod having a certain elasticity to bending;
c. The end zone of the prosthesis is fixed to the surrounding bone tissue using cement, while leaving free of cement the part of its stem which is located in the zone adjacent to the resection section.

 In addition, preferably, means are provided on the surface of the rod portion located in the vicinity of the resection section, inside the diaphysis, capable of promoting regrowth and anchoring of the bone tissue to this. level.

 Furthermore, it is advantageous to surround the part of the stem which corresponds to the resection zone, outside the diaphysis, with a massive homo-graft, possibly surrounding the latter with a few self-grafts intended for favor the taking.

 The resection prosthesis which is the subject of the present invention, and which makes it possible to implement this method, is characterized in that it comprises an elongated rod which comprises a frustoconical main part of revolution, of low conicity, and that its wall is devoid of any shoulder or other abrupt discontinuity of diameter.

 This taper is preferably between 1.5 and 4 degrees; it is advantageously about 2.5 degrees.

 According to an additional particularly advantageous characteristic of the invention, the part of its stem which is intended to be placed in the vicinity of the resection section of the diaphysis has surface irregularities capable of promoting invasion and anchoring by the tissue. peripheral bone.

 These irregularities advantageously consist of the meshes of a metal mesh, for example made of titanium, attached to the prosthesis rod in the vicinity of the resection section.

 In a preferred embodiment of the invention, the frusto-conical rod is extended by an advantageously cylindrical or conical shape.

 According to another additional characteristic of the invention, the prosthesis is equipped with a sleeve which is adapted to be attached to the part of the rod intended not to penetrate inside the diaphysis, and to come into contact with the resection section after implantation of the prosthesis in the diaphysis.

 This sleeve is made for example of plastic (such as polyethylene), and has orifices intended to receive muscle reinsertions.

 The sleeve can be eyal entent constituted by a massive homo-graft, shaped by machining to the required shape. This sleeve can finally n: be a simple metal ring.

 Other characteristics and advantages of the invention will appear from the description and the appended drawings which show a preferred embodiment thereof.

In these drawings,
Figure 1 shows a resection prosthesis according to the in # ention after its placement at the extremity ~ proximal mite of a resected femur shown in section)
- Figure 2 shows the diaphyseal and proximal parts of the diseased femur, before resection
- Figure 3 shows on a larger scale, in section, the proximal part of the resected diaphysis, after reaming of the medullary cavity;
- Figure 4 shows the frustoconical stem of the prosthesis after its implantation in the medullary cavity;
- Figures 5 and 6 are views similar to Figure 1, on a slightly reduced scale showing two different implantations of the same prosthesis stem
- Figures 7, 8 and 9 show three variants of sleeves which can be adapted on the proximal part of the prosthesis stem.

 FIG. 2 represents the proximal part of a human femur, comprising the substantially cylindrical diaphysis D, the metaphysis M, and the epiphysis E, this constituting the ball joint of the hip.

 It is a diseased bone, subject to a tumor T which justifies the excision of the whole of the proximal part constituted by the epiphysis and the metaphysis; the resection plane has been designated by the reference R in FIG. 2.

 In Figure 1 there is shown a reconstruction prosthesis after upper epiphyso-diaphyseal resection of this femur, a prosthesis which will subsequently be called more simply resection prosthesis; this prosthesis is represented after its implantation in the resected diaphysis D. The section of resected section, which will be called more simply resection section, has been designated by the reference S in the drawings.

This prosthesis, designated by the reference 1, comprises an elongated main part 10, in the form of a cone of revolution cone, the apex of which is directed towards the distal part of the femur. The angle at the top (or taper)
<of this cone trunk is weak; e is between 1.5 and 4 degrees; is for example of the order of 2 to 2.5 degrees. At its lower (distal) part, the rod 1 comprises an appendage, or cylindrical tail 11, preferably grooved longitudinally; these grooves 12 are for example three in number, regularly distributed at 120 degrees on the periphery of the rod 1; part of these grooves can encroach on the frustoconical area 10. The diameter of the cylindrical appendage is equal to that of the small base of the truncated cone 10, so that these two sections 10, 11 of the prosthesis stem, connect to each other without any continuity solution.

 This distal appendage 11 could possibly, for certain prosthesis dimensions, have a conical shape.

 At its upper part, the rod 1 comprises a nesting cone 13, which is used for fixing, in a known manner, a neck 3 provided with a conical hole for complementary fitting 30. This neck 3 is integral with a joint ball 4, which can either be attached to the neck 3 or, on the contrary, form an integral part thereof. The ball joint 4 is intended to cooperate with a cup attached to the iliac bone so as to constitute the hip joint.

 Around the middle part of the portion of frustoconical rod 10, is wound and fixed a wire mesh 2, for example made of titanium. The part of the rod 10 covered with this trellis has been designated by the reference 10b, while the upper part of this rod, situated above this trellis 2, has been designated by the reference 10a.

 We will now describe the implantation process of the prosthesis which has just been described, with reference to both Figures 1 and 3.

 In FIG. 3, the medullary canal of the diaphysis D, as well as the external wall of the latter, have been represented as two perfect cylinders of revolution, co-axial. This simplification of the forms is close to reality and we are dealing with a mechanical design totally different from that encountered for the usual prostheses for osteoarthritis of the hip.

 Indeed, the section of the upper part of the femur is approximately elliptical and the wedge effect due to the taper of this type of prosthesis can only be obtained in the frontal plane.

 The wall of the cylindrical medullary canal has been designated by the reference C. To prepare this medullary canal, in accordance with the invention, the latter is bored, using a cutter not shown, the shape of which corresponds to that of the tapered rod portion 10 of the prosthesis. The wall of the medullary cavity after reaming shows the thin dashed line representing the outline of the medullary canal before this operation.

 As will be seen later, the depth at which the bur is penetrated into the diaphysis, to form the required cavity there, depends on the implantation depth which it is desired to give to the prosthesis stem; the dashed line A 'denotes a possibility of preparing a medullary cavity deeper than the cavity A, the depth of penetration of the cutter being, in this case, greater.

 To place this prosthesis in the shaft of the femur, the surgeon begins by injecting a cement, for example methyl methacrylate, possibly supplemented with antibiotics, inside the medullary cavity which he has just prepared. He then pushes the prosthesis rod 1 into this cavity, using an appropriate impactor, so that the conical part 10 comes to bear intimately against the frustoconical wall A of the cavity. The cement previously injected, designated by the reference 5, surrounds the cylindrical appendage 111 by being housed in the grooves 12, and partially rises around the frustoconical section 10; however, this ascent of the cement is limited due to the complementary frustoconical shape of this part 10 and of the bore A.We have designated by the references 10d and 10c the parts of the rod 10 which are respectively filled and not filled with cement . The insertion is determined in such a way that the titanium mesh 2 comes to be placed in the vicinity of the resection section S. An implantation of the rod 1 has therefore been carried out in the diaphysis of the femur, according to which only the cylindrical appendage 11 and the lower part (distal 10d of the tapered rod section 10 are fixed to the bone on the contrary, the middle parts 10c and 10d are free.

The rod 1 is made of a metal or another material which has a modulus of elasticity substantially lower than that of Stellite; it is for example made of titanium alloy (such as Ti A16 V4). It has a considerable flexibility, closer to that of bone tissue than that of Stellite. This characteristic is excessively important because it will make it possible to gradually obtain a secondary anchoring of the prosthesis stem in the diaphysis, in the region close to the section. resection S. To understand the mechanism of this secondary fixation of the prosthesis, generated by the organism itself, it is necessary to refer to FIG. 4; in this figure we have designated by the arrows F and M the stresses due to the axial compression forces and, respectively, at the bending moments received by the prosthesis f these stresses can be considerable, even simply during normal physical activities of the patient.

 The axial compressive force F will generate, by wedge effect, due to the conical shape of the rod 10, on the internal wall of the diaphysis, a distribution of radial forces designated by f.

 The prosthesis stem 1 constitutes a beam, of considerable flexibility, which is embedded only at its end 10d - 11 (cemented end) under the action of the bending moment M, the stem will therefore deform slightly and stress, also radially outwards, a region of the internal wall of the diaphysis: these stresses generated by the moment M have been represented by the arrows m. The orientation of these arrows will naturally depend on the direction of the moment M.

The radial secondary forces f and m which will constantly develop in the bone tissue surrounding the prosthesis in the vicinity of the resection zone, will cause a reaction of the bone tissue, which will tend to push back, so as to better resist these solicitations; by pushing back, the tissue will penetrate between the meshes of the titanium mesh 2, causing at this level a natural secondary anchoring of lfos with the prosthesis; ultimately, in the medium term, the prosthesis will therefore be completely integral with the diaphysis
- at its distal part by the cement injected at the time of its implantation
- at its proximal part by the bone tissue gradually regenerated in the titanium lattice.

 Or. Thus obtains a perfect and lasting anchoring of the prosthesis in the diaphysis.

 FIGS. 5 and 6 represent prostheses which have been implanted in femurs whose diaphyseal resections are offset, the resection section S 'of FIG. 6 being distally more distant than the resection section S of FIG. 5.

 These two figures show that it is however possible, for these two offset resections, to use the same prosthesis stem 1 according to the invention; for this purpose, in the case of FIG. 6, an intermediate cylindrical part 6 was used, connecting the prosthesis rod 1 to the neck 3 carrying the articulation ball 4; this cylindrical part 6 is provided with a frustoconical hole capable of receiving the cone 13 of the prosthesis it also has a cone 60 capable of being fitted into the frustoconical hole 30 of the neck 3.

 To obtain correct positioning of the patella 4 with respect to the resection section S or S ′, it is therefore possible to act both on the depth of penetration of the frustoconical cutter during the preparation of the medullary cavity, and on the intercalation of one or more intermediate pieces 6, so that it is possible to deal with all the therapeutic cases encountered, without having to have a high number of prosthesis rods 1.

 FIG. 7 shows how it is possible to consolidate the connection between the prosthesis and the diaphysis, above the resection section, by means of an attached sleeve 7; the latter can be made of molded plastic, for example polyethylene.

 This sleeve 7 has an internal bore 71, of frustoconical shape complementary to the upper part 10a of the prosthesis stem; it is placed on the prosthesis stem, from bottom to top, before implantation of this stem in the bone. Its external diameter advantageously corresponds approximately to the external diameter of the diaphysis, so that a certain continuity is obtained between the external contours of the resected bone and of the prosthesis equipped with the sleeve 7; this sleeve mechanically consolidates the prosthesis; in addition, there are provided in the proximal upper part of the sleeve orifices 70 which are adapted to receive muscle reinsertions, so as to assist in the reconstruction of the surrounding muscle mass.

 The prosthesis, shown in Figure 8, is also equipped with a sleeve 8 attached to its rod end 10a t this time it is a homo-graft, that is to say a bone graft coming from another individual, this graft having been cut by milling to the desired dimensions and shape; the homo-graft is advantageously surrounded by a few grafts from the patient himself (auto-grafts), so that the mutual taking of the bone tissue of the diaphysis D and of the homo-graft sleeve 8 is favored.

 In Figure 9, there is shown a sleeve which consists of a ring made of the same material as the rod 1 - for example made of titanium alloy - fitted on the conical part 10a (and blocked on the latter due to this self-locking form).

 The total length of the prosthesis rod 1 is advantageously between 100 and 300 mm; the length of its centromedullary rod is advantageously of the order of 120 to 180 mm and the height of the intermediate pieces 6 is from 20 to 100 mm.

 The diameters of the large and small bases of the truncated cone 10 are advantageously respectively of the order of 15 to 19 mm, and of 9.5 to 14.5 mm.

 These dimensional values are given for information only, but in no way limit the scope of the present invention.

 It is possible to provide a set of five rods whose nominal diameters - that is to say the diameters corresponding to the resection plane R - are as follows 10 mm; 12 mm; 14 min; 16 mm and 18 mm.

 These dimensions have been verified to be suitable to cover all of the resections of the upper and lower extremities of the femur, the upper end of the tibia and the upper end of the humerus in adults and children .

 It goes without saying that for the stems of prostheses intended for locations other than the upper part of the femur (described above), articular or assembly parts different from the articulation ball joint can be provided to adapt to these rods.

Claims (9)

-REVENDIcATIONS  1. Resection prosthesis intended to be implanted in the diaphysis (D) of a long bone, characterized in that it comprises an elongated rod (1) which comprises a main frustoconical part of revolution (10), of low conicity ( oc), and that its wall is devoid of any shoulder or other abrupt discontinuity of diameter.  2. Prosthesis according to claim 1, characterized in that the taper () of the frustoconical part (10) is between 1.5 and 4 degrees, and that it is advantageously of the order of 2.5 degrees.  3. Prosthesis according to one of claims 1 or 2, characterized in that the part (lob) of its rod (10) intended to be placed in the vicinity of the resection section (S) of the diaphysis (D) has surface irregularities capable of favoring invasion and anchoring by the peripheral bone tissue.  4. Prosthesis according to claim 3, characterized in that the surface irregularities of the rod part (lob) consist of a titanium lattice (2) attached thereto.  5. prosthesis according to one of claimsq to a, characterized in that it comprises a sleeve (7, 8, 9) which is adapted to be attached to the part t1OaJ of the rod (1) intended not to penetrate the inside the diaphysis (D), and to come into contact with the resection section (S) after implantation of the prosthesis in the diaphysis.  6. Prosthesis according to claim 5, characterized in that the sleeve (8) is a massive homo-graft.  7. Prosthesis according to claim 5, characterized in that the attached sleeve (7) is a plastic sleeve which has orifices (TO) intended to receive muscle reinsertions.  8. Prosthesis according to claim 5, characterized in that the sleeve (9) is a metal ring.  9. Prosthesis according to one of claims t to 8, characterized in that it comprises an articular piece (4) which is fixed to the elongated rod (1), optionally by means of a cylindrical intermediate piece (6 ).