FR2763500A1 - Stopper for diaphysis canal specially of hip prosthesis - Google Patents

Abstract

The stopper (1) is made from a biodegradable elastic material and comprises a cylindrical body (2) with a series of spaced radial collars (3) of identical shape and of greater diameter than that of the diaphysis canal. The surfaces (4, 5) of the stopper collars, facing respectively towards the distal and proximal ends of the body, are convex and concave in shape and converge towards one another so they meet at the edges of the collars. The stopper is made from 40 - 60 per cent gelatine, 20 - 40 per cent glycerol and 5 - 20 per cent water. The collars have a diameter of between 1.5 and 2.5 : 1 relative to the diameter of the cylindrical body. Prevent cement leaks while implanting a prosthesis. Easy to fit and stable in operation.

Description

The invention relates to a diaphyseal obturator usable in surgery

  orthopedic to limit the flow of cements during

implantation of prostheses.

  A very common method for implanting prostheses, and in particular hip prostheses, consists in cementing the prosthesis to the bone. To do this, a cement, generally poly (methyl methacrylate), is introduced into a cavity in the long bone. Before the cement hardens, the prosthesis is placed in the cavity so that it is immediately coated with cement, while avoiding the formation of empty cement interstices.

o0 between the bone and the prosthesis.

  The force applied to the cement during the placement of the prosthesis often causes the cement to the bottom of the intramedullary canal, far from the site of fixation of the prosthesis. In this way, voids are formed in the cement sheath at which concentrations of stress appear, then break points. We can avoid the flow of cement at the bottom of the intramedullary canal by having a diaphyseal obturator or obturator plug at the bottom of the canal. Such diaphyseal plugs have been described in the art, for example in US 4,254,359, US 4,293,982, US 4

  302,855, US 4,344,190, US 4,447,915, US 4,897,584 and US 5,092,891.

  The closure plug of the invention is particularly advantageous from the point of view of the ease of installation and of the seal to which it leads. Its particular structure and composition help to give it remarkable stability. In addition, its absorbable nature makes it particularly suitable for surgical recovery procedures, when it becomes necessary to replace a prosthesis initially implanted with a

second prosthesis.

  More specifically, the invention relates to a plug for a diaphyseal channel made of elastic biodegradable material, characterized in that it comprises a cylindrical body provided with spaced radial flanges, of identical geometry, and having a diameter greater than the diameter of the diaphyseal channel, the surfaces of each collar, facing respectively the distal end and the proximal end of the body converging towards each other in a peripheral zone of the collar, the surface facing the distal end having a convex profile while the opposite surface

  is flat or turns its concavity towards the proximal end.

  According to the invention, the shape of the diaphyseal plug and the nature of the material constituting it are essential since they give it the desired flexibility and resorbability. The advantages of the closure plug of the invention, and in particular its ease of installation, its stability and the desired tightness,

  result from the increased flexibility of the material.

  The blanking plug consists of an elongated cylindrical body

  provided with at least two radial flanges.

  The term "radial flange" means flanges arranged in

  planes perpendicular to the axis of revolution of the cylindrical body.

  According to a preferred embodiment of the invention, the cylindrical body has such a collar at its distal end. It should be understood that in the context of the invention the distal end of the cylindrical body designates the end introduced first into the diaphyseal canal while the proximal end designates the end introduced last

in the diaphyseal canal.

  According to the invention, the diameter of the cylindrical body is less than the

  diameter of the diaphyseal channel while the diameter of the flanges is greater than the diameter of the diaphyseal channel.

  The flanges have a particular geometry: they have the shape of discs of a given thickness whose surface facing the distal end has a convex profile, while the opposite surface of the disc is planar, that is to say perpendicular to the axis of revolution of the cylindrical body or else has a concave profile, it being understood that in this case its concavity is

  facing the proximal end.

  Another feature of these flanges is that their two surfaces respectively facing the distal and proximal ends of the cylindrical body converge towards each other in a peripheral zone of the flange. Thus, in said peripheral zone, the thickness of the disc forming

  collar is gradually decreasing.

  The exact profile of the flanges in the peripheral zone and more precisely the convexity of the surface facing the distal end and the shape of the surface facing the proximal end (its concavity or flatness), is adjusted by the man of the loom so as to ensure the deformability of this peripheral zone under the effect of a force parallel to the axis of revolution of the cylindrical body acting in the direction of introduction of the plug into the diaphyseal channel at the peripheral zone . In fact, when it is introduced into the dipahyseal canal, the zone situated on the periphery of the flanges must be able to be flexible enough to curl slightly towards the proximal end of the cylindrical body, insofar as the diameter of the flanges

  is greater than the diameter of the diaphyseal canal.

  The term “flange diameter” means the maximum diameter of the flanges in a plane perpendicular to the axis of revolution of the cylindrical body. The obturator plug can include any number of flanges. Those skilled in the art will determine the optimal number of flanges according to the nature of the material constituting said flanges and their exact geometry. An insufficient number of flanges affects the stability of the plug. It is preferred in all cases that the flanges are equidistant. According to a particularly preferred embodiment, the diaphyseal obturator comprises three flanges, one of which is located at the distal end

of the cylindrical body.

  More preferably, the diaphyseal plug of the invention has, at the proximal end of the cylindrical body, a cylindrical end-piece whose diameter substantially corresponds to the diameter of the medullary canal. In this case, the cylindrical end piece and the cylindrical body are concentric. The term "substantially" as used in the invention intends to cover variations in

  from 0 to 20%, preferably from 0 to 15%, better still from 0 to 10%.

  The cylindrical tip placed at the proximal end of the body

  cylindrical is intended to facilitate the positioning and guiding of the plug.

  Preferably, the end carrying the cylindrical end piece and, in the absence of a cylindrical end piece, the proximal end of the cylindrical body, has a central cavity suitable for receiving means for inserting the plug, for example a door shutter. According to the invention, the term central cavity means a cavity

  formed along part of the axis of revolution of the cylindrical body.

  When a tip is present at the proximal end, this cavity can only be provided in the cylindrical tip. It is preferable

  however, the cavity extends into a part of the cylindrical body.

  In the case of a plug with three equidistant flanges, the cavity preferably extends to the level of the

  collar immediately following the cylindrical end piece.

  The shutter holder is used for the fitting of the shutter plug of the invention. The shape of the cavity is arbitrary. According to the invention, a cylindrical cavity is preferred because of the most

  often cylindrical of the inserter and the shutter holder.

  According to a preferred embodiment of the invention, the elongated cylindrical body forming the obturator plug is traversed right through, along its axis of revolution, by a passage, in the form of a channel suitable for allowing the free evacuation of the in the diaphyseal canal at the time of

  fitting of the blanking plug.

  The dimensions of this passage are calculated so as to prevent a flow of the cement necessary for fixing the prosthesis through the obturator plug. Thus, advantageously, the shutter plug is traversed right through by a cylindrical channel with a diameter between 0.1

  and 0.7 mm, preferably between 0.3 and 0.6 mm, better still 0.45 and 0.55 mm.

  When the blanking plug has a cavity at its

  proximal end, the cylindrical channel opens into this cavity.

  This preferred embodiment makes it possible to minimize the risks of overpressure during the fitting of the obturator plug within

of the diaphyseal canal.

  The material from which the stopper is made is preferably biodegradable so that the stopper is gradually absorbed over time by the body and finally disappears completely. The bioresorbable nature is particularly useful for the application envisaged since the plug is essential only until the cement has solidified. The elasticity of the material is one of the essential characteristics of the stopper of the invention. In order to ensure sealing, the stopper has been shaped in the form of an elongated body consisting of a cylindrical body provided with

  flanges whose diameter is greater than the diameter of the diaphyseal canal.

  Thus, if one wants to be able to introduce the plug into the medullary canal, it is clear that the material constituting the plug must have a certain flexibility. Due to the particular shape of the flanges, the elasticity of the material may not be very high. A person skilled in the art will easily adjust the geometry of the flanges according to the bioresorbable material available to him or vice versa. The elasticity of the material can be characterized in a simple way by measuring the relative deformation under a force of 50 N. More precisely, the relative deformation "e" is given by the following equation: h - ho e = ho o ho est the length of a test piece subjected to a force of 50 N in the longitudinal direction, and h the measurement of this same length after release

  of coercion. The higher "e", the greater the elasticity.

  According to a preferred embodiment of the invention, e varies between

0.05 and 0.70.

  As an indication, any material having a Young's modulus of between 0.85 Mpa and 32 Mpa may be suitable for the preparation of the obturator plug of the invention. With the help of his general knowledge of the technique, a person skilled in the art can easily prepare an absorbable material having the desired elasticity as well as a Young's modulus of between 0.85 MPa and 32

  Mpa, for example, from a mixture of gelatin, water and glycerol.

  Advantageously, the absorbable material comprises, as essential constituents, from 40 to 60% of gelatin, from 20 to 40% of glycerol and

5 to 20% water.

  It goes without saying that to this basic composition can be added

  from 0 to 10% of various additives such as colorants or preservatives.

  Those skilled in the art will advantageously select biocompatible dyes and preservatives known in the art. An example of a suitable preservative is methyl parahydroxybenzoate. As a rule, small amounts of preservatives are sufficient, for example 0.001

at 0.01%, on a weight basis.

  When the material constituting the diaphyseal plug essentially comprises 40 to 60% of gelatin, 20 to 40% of glycerol and 5 to 20% of water, the preferred configuration of the plug is such that the ratio of the diameter of each flange to the corresponding diameter of the cylindrical body is included

between 1.5 and 2.5.

  For clarity, the invention will now be defined in

reference to figures.

  Figure 1 is a sectional view of a diaphyseal plug 1 according to the invention. This plug represents one of the preferred embodiments of the invention. Figure 2 is a sectional view of an alternative embodiment of the diaphyseal plug 1 according to Figure 1 having a passage for the free

air circulation.

  FIG. 3 is a side view of the plugs of FIGS. 1 and 2.

  The diaphyseal plug 1 of FIG. 1 comprises a cylindrical body 2 provided with three radial flanges 3. The surfaces 4 and 5 of each flange 3, facing respectively towards the distal end and towards the proximal end of the cylindrical body, converge the towards each other in a peripheral zone. The surface 4 has a convex profile while the surface 5 turns its concavity towards the proximal end 6 of the cylindrical body. At its distal end 7, the diaphyseal plug 1 carries a flange 3. At the opposite end 6, the diaphyseal plug 1 carries a cylindrical tip 8. Inside the cylindrical tip is formed a central cavity 9, which is extends into the cylindrical body 2 up to the level of the flange 3 closest to the cylindrical end piece 8. The diaphyseal plug 1 is introduced into the diaphyseal channel in the direction of the arrow, so that the flange 3 disposed at the end

  7 of the cylindrical body 2 enters the first in the diaphyseal channel.

  To introduce the diaphyseal plug 1 into the diaphyseal channel, a shutter holder, not shown in FIG. 1, is embedded

in the cavity 9.

  The plug is placed in position inside the diaphyseal canal

  then the shutter holder is removed from the cavity 9.

  According to a preferred embodiment of the invention, the collars of the diaphyseal plug came in one piece with the elongated cylindrical body, just as the cylindrical end piece preferably came in one piece

with the cylindrical body.

  Thus, a method of preparing the shutters of the invention comprises the steps consisting in: 1 - mixing the various constituents forming the material of the diaphyseal plug in a melter at a temperature sufficient to cause the melting of said constituents; 2 - pour the resulting mixture into a multi-cavity mold; 3 - cool the assembly to cause the solidification of the mixture;

  4 - unmold the solidified product.

  FIG. 2 illustrates a shutter plug 1 at all points identical to that of FIG. 1, except that it has, along its axis of revolution 10 a cylindrical passage 11 in the form of a channel originating at the end

  distal 7 of the cylindrical body 2 and opening into the cavity 9.

  Before use, it is recommended to sterilize the diaphyseal plug. This is perfectly suited for filling diaphyseal cavities with a diameter between 5 and 30 mm, preferably

between 10 and 22 mm.

  The following examples further illustrate the invention.

EXAMPLES 1 to 7

  In a melter maintained at 60 ° C., 50% of gelatin,% of glycerol, 20% of water and 0.2% of methyl parahydroxybenzoate are mixed. The resulting mixture is poured into multi-cavity molds A to G. Each mold is then kept for 20 minutes at -30 C. Once the mixtures have solidified, each of the obturator plugs is demolded. The

  molds A to G differ from each other in their dimensions.

  The characteristic dimensions of a diaphyseal plug are shown in Figure 3. The following table indicates in the case of each mold the

dimensions of the resulting plug.

BOARD

  Example I1 2 3 4 5 6 7 Mold ABCDEFGD (mm) 18 12 14 16 18 20 22 B (mm) 8 10 12 14 16 18 20 H (mm) 15 18 21 24 27 30 33 A (mm) 3.75 4 , 50 5.25 6.00 6.75 7.50 8.25 a (mm) 0.50 0.60 0.70 0.80 0.90 1.00 1.10

Claims (12)

  1. obturator plug (1) for diaphyseal channel made of elastic biodegradable material, characterized in that it comprises a cylindrical body (2) provided with spaced radial flanges (3), of identical geometry, and having a diameter greater than the diameter of the channel diaphyseal, the surfaces (4,5) of each flange, facing respectively towards the distal end and towards the proximal end of the body converging towards each other in a peripheral zone of the flange, the surface facing towards distal end (4) having a convex profile while the opposite surface (5) is flat or   turns its concavity towards the proximal end (6).   2. Stopper (1) according to claim 1, characterized in that   said flanges (3) are equidistant.   3. Plug (1) according to any one of claims   previous, characterized in that the cylindrical body (2) has at its   distal end (7) a collar (3).   4. Stopper (1) according to any one of claims   previous, characterized in that said flanges (3) came from   material with the cylindrical body (2).   5. Stopper (1) according to any one of claims   above, characterized in that the cylindrical body (2) has at its proximal end (6) a cylindrical tip (8) whose diameter corresponds substantially to the diameter of the diaphyseal channel, said cylindrical tip (8) and   2 5 the cylindrical body (2) being concentric.   6. Stopper (1) according to claim 5, characterized in that   the cylindrical end piece (8) came integrally with the cylindrical body (2).   7. Stopper (1) according to any one of claims   above, characterized in that it has at its proximal end (6) a cavity (9) formed along a part of the axis of revolution of the cylindrical body (2), said cavity being intended to facilitate guiding and the   positioning of the plug (1) in the diaphyseal channel.   8. Stopper (1) according to any one of claims   previous characterized in that said cylindrical body (2) is traversed right through, along its axis of revolution, by a passage (11) in the form of a cylindrical channel, the dimensions of said channel being suitable for preventing a   flow of prosthetic cements through said channel.   9. Stopper (1) according to claim 8 characterized in that the diameter of said cylindrical channel (11) is between 0.3 and 0.6 mm, of preferably between 0.45 and 0.55 mm.   10. Plug (1) according to any one of the preceding claims, characterized in that said material has a percentage   of elasticity e between 0.05 and 0.70, e being defined by the relation: h - ho e = ho o ho is the length of a test piece made of said material subjected to a force of 50 N in the direction of the length and h is the length of this same   test tube after release of the stress.   11. obturator plug (1) according to any one of   previous claims, characterized in that said material comprises   60% gelatin, 20-40% glycerol and 5-20% water.   12. Plug (1) according to claim 11, characterized in that the ratio of the diameter of each flange (3) to the corresponding diameter of   cylindrical body (2) varies between 1.5 and 2.5.