FR2543820A1 - SEALING ANCHOR FOR SEALING A CAVITY OF THE BONE MARROW - Google Patents

Abstract

SEALING ANCHOR FOR SEALING A CAVITY OF THE BONE MARROW; IT IS USED IN ORTHOPEDIC SURGERY TO SEAL A CAVITY OF THE BONE MARROW OF A FEMUR WHEN THE STEM OF A HIP PROSTHESIS IS INSERTED INTO THE CAVITY OF THE BONE MARROW TO FIX IT; THE SEALING PLUG IS MADE OF A CALCIUM PHOSPHATE COMPOUND AND HAS A COMPRESSION RESISTANCE OF AT LEAST 490 BARS.

Description

The present invention relates to a sealing plug for sealing a

  Bone marrow cavity More particularly, the invention relates to a sealing pin made of a calcium phosphate compound intended to be implanted in a

  bone marrow cavity to seal it.

  In orthopedics, when it is necessary to replace the joint between the femur and the pelvis, a hip prosthesis is implanted with a rod which is an integral part of it, the rod being inserted in the

  cavity of the bone marrow of the femur to be fixed there.

  Generally, we use a bone cement to fix the rod in the davit of the bone marrow It is

  of course desirable that the hip prosthesis be im-

  planted sustainably for use for an extended period It is also preferred to apply the bone cement to the peripheral surface of the stem under sufficient pressure to fill the recessed portions such as the notches, grooves or indentations disposed on the peripheral surface of the rod and so that it adheres intimately between the hollow portions and on the surface of the living bone tissue so as not to leave any gap or void between the interior surface of the cavity of the bone marrow and the filling bone cement to prevent moods from entering

in these intervals or voids.

  However, in the standard operating method

  sic in which the bone marrow cavity is initially filled with bone cement and then the rod of a hip prosthesis is inserted into the cavity filled with bone cement, a significant amount of bone cement is driven out by the inserted rod, which causes a

  insufficient adhesion necessary for fixing.

  D. on the other hand, although it is possible to fill completely-

  the bone marrow cavity of the bone cement in order to obtain a satisfactory fixation by adhesion, the quantity of bone cement necessary for this complete filling is extremely increased This is ineconomic and, moreover, the introduction of an extremely large quantity of cement bone in the marrow cavity

  bone which is one of the important constituents of gold-

  living organism is dangerous for living tissue because bone cement is a foreign material for

living tissue.

  Otherwise, it has been proposed to cut bone spon-

  large in the dimensions required in the femoral head

  and insert the cancellous bone thus obtained into the

  bone marrow cavity as an anchor.

  However, as the excision of the cancellous bone must be carried out during the operation, the patient is subjected to additional fatigue because the duration of the operation is increased.Moreover, in many cases, the amount of cancellous bone contained in the head of the patient's resected femur during the operation is too weak to allow insertion and a resection should be resected

  greater amount of cancellous bone.

  The Applicant has endeavored to eliminate the disadvantages of conventional orthopedic techniques

  and the invention results from these efforts.

  The main object of the invention is to provide a sealing pin intended to be inserted into a bone marrow cavity during an orthopedic operation in which a hip prosthesis is implanted, in order to close the bone marrow cavity and facilitate the intimate adhesion between the stem of the hip prosthesis and the bone cement and between the bone cement and the inner peripheral wall of the bone marrow cavity and thus ensuring a solid fixation

of the stem.

  The invention also aims to provide

  a sealing plug having excellent adaptability

  bility or compatibility with living tissue does not

  as for no appreciable inflammation, even when implanted in a cavity of the bone marrow of a

  organism living for an extended period.

  The invention provides a sealing plug intended to be inserted into a cavity of the bone marrow to fill the cavity, this plug being made of a calcium phosphate type compound and having a compression resistance which is not not

less than 490 bars.

  The invention will now be described from

in detail.

  Although various materials, including metals, organic substances and alumina, have been studied as materials of a sealing pin intended to be inserted into a cavity of the bone marrow, calcium phosphate compounds have found to be the most favorable for this purpose, since they have excellent adaptability or compatibility with living tissue when implanted in the bone marrow cavity for an extended period. The calcium phosphate compounds which can be used in the present invention include tricalcium phosphate (Ca 3 (P 04) 2),

  hydroxyapatite (Ca 5 (PO 4) 30 H), phosphate t 9 tra-

  calcium (Ca 40 (P 04) 2), oxy-apatite, calcium pyrophosphate (Ca 2 P 207), fluoro-apatite, derivatives of hydroxy-apatite each having one or more hydroxy groups replaced by fluorine or oxygen ions and their mixtures We prefer to use phosphate

  tricalcium, hydroxyapatite, tetra phosphate

  calcium, oxy-apatite, fluoro-apatite or their mixtures because they do not cause inflammation

  and have excellent compatibility with living tissue.

  The anchor according to the invention is fixed in place in the cavity of the bone marrow slightly deeper than the length of the stem of a hip prosthesis so as to close the cavity of the bone marrow so that the bone cement of which

  we fill the cavity, cannot penetrate deeper-

  In the cavity when the stem of the hip prosthesis is inserted therein Consequently, the insertion of the stem causes in the cavity an increase in pressure, so that the bone filling cement is applied to the stem and to the internal wall of the cavity under increased pressure to adhere intimately to the surface of the rod and the internal surface of the cavity in order to ensure a robust fixing of the rod after its solidification For this, the anchor of the invention must be able to be inserted into the bone marrow cavity and must be able to withstand the pressure created by the fitting of the hip prosthesis Consequently, the ankle must have a compressive strength at least equal to 490 bars, preferably at least equal to 784 bars and better at least equal to 1,176 bars If the compressive strength of the anchor is less than 490 bars, it tends to break during insertion or it cannot resist the pressure created by insertion

of the stem.

  The anchor of the invention must have a shape and dimensions such that it can be fixed in the cavity of the bone marrow in a position slightly deeper than the length of the stem of the hip prosthesis and that it , can withstand the pressure created by the insertion of the rod which must be held firmly in the implantation position Preferably, the anchor has the shape of a truncated cone or a combination of a truncated cone and a cylinder The frusto-conical dowel, for example, is pushed into the cavity of the bone marrow with its base surface, i.e. the largest face looking upwards and in contact with a suitable pushing device, for example a stainless steel tube To facilitate the insertion operation, the base or upper surface of the pin may be provided with a cylindrical projection ensuring a solid grip with the end of the tube. Otherwise, the base or upper surface ankle may have a central recess to receive the end of a pushing device in the form of a solid rod When implanting in a cavity of the bone marrow a hip prosthesis having a relatively short rod and that the cavity should not be cut in the form of a cylinder, one can prepare a dowel having a shape closely matching that of the cavity of the

  bone marrow and fix it in the desired position.

  Primarily, the shape of the anchor does not matter as long as the ankle can withstand the pressure created by the insertion of the stem of a hip prosthesis to be held in a position

determined.

  The sealing plug of the invention can be prepared by sintering a calcium phosphate compound to obtain a sintered mass which is then machined to form a plug having the desired shape and dimensions. Otherwise, it can be molded by

  compression of calcium phosphate powders in use

  sant a rubber press or, after sintering, to machine it

  with a lathe in the desired shape and dimensions.

  Other characteristics and advantages of the invention will be better understood on reading the

  description which follows of several examples of

production.

Example 1

  One pushes in holes each having a diameter of 9 mm drilled in the femurs of killed sample cats each having a frustoconical shape (diameter of the base 10 mm, diameter of the small surface 8 mm, height 5 mm) made of hydroxy- apatite, tricalcium phosphate and fluoroapatite having various compressive strengths as indicated in the following table The number of broken pegs in each sample is determined and the pegs which have been pushed without breaking in the opposite direction of the push are exerted 49 bar effort to determine the number of plugs removed from the holes The compressive strength is determined using a test tube 5 mm in diameter and 5 mm in length with a testing machine

  universal (produced by Instron Engineering Corp).

  The results are shown in the following table.

BOARD

  Material Peg resistance no Number of cuffs

  the compression broken cities remaining

  (bars) Plug inserted after the app

  pressure cation ankles not broken Hydroxy-apatite 392 415 0/4

490 5/5 3/5

784 5/5 4/5

1420 5/5 5/5

8036 5/5 5/5

294 3/5 0/3

  Phosphate 490 5/5 3/5 tricalcium 990 5/5 4/5

1176 5/5 5/5

7477 5/5 5/5

Fluoroapatite 343 4/5 0/4

490 5/5 3/5

1176 5/5 5/5

9065 5/5 5/5

Example 2

  The head of the femur is excised near the end of the femur of a killed dog, the femur being frozen immediately after death, and the bone marrow cavity thus exposed is filled with bone cement in which a rod of stainless steel, having a diameter of 5-mm and a length of 20 mm, the surface of which

  has been made as rough as that of a file, has been inserted

  4 cm height A similar femur of a killed dog is drilled to eliminate the bone marrow and to form a hole 5 mm in diameter extending over the length of the bone marrow. In the hole thus formed, a sample of hydroxyapatite peg having a base diameter of 5.5 mm, a small area diameter of 4.5 mm and a height of 3 mm, the compressive strength of the peg being 1,176 bar, then the cavity closed by the implanted ankle is filled with the same bone cement. 4 cm is inserted into the

  bone cement a stainless steel rod having a diameter

  meter of 5 mm and a length of 20 cm whose surface

  was roughened like a lime -

  The free end, i.e. the end, which has not been inserted into the bone marrow cavity, is clamped with the mandrel of a universal testing machine (produced by Instron Engineering Corp.) of the femur, from each of the stainless steel rods, and the femur is clamped with the other mandrel of the testing machine to test each sample

  The results of the tensile tests

  show that the sample implanted without the hydroxyapatite peg is torn off at the interface between the bone and the bone cement when the tensile force reaches 29.4 bars, while the union surface of the sample implanted with the hydroxyapatite ankle does not separate, even when the tensile force reaches

58.8 bars.

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Example 3

  In the bone marrow of a femur of a living dog, we implant pins measuring

  3 mm x 3 mm x 3 mm each made of tricalcium phosphate-

  (compressive strength: 1,176 bar) hydroxyapatite (compressive strength: 1,420 bar), tricalcium phosphate (compressive strength: 1,088 bar), fluoro-apatite (compressive strength:

  1,176 bars) and a mixture of hydroxyapatite and oxy-

  apatite (compressive strength: 2,480 bars) The tissue is examined in the vicinity of each of the implanted ankles after 6 months and there is no inflammation in the tissue around the implanted ankle. This result shows that all the ankles according to the invention studied have adaptability or

  satisfactory compatibilities with the living organism.

  Of course, various modifications can be made by those skilled in the art to the devices or methods which have just been described solely by way of nonlimiting examples without departing from the

part of the invention.

Claims (9)

  1 Sealing plug intended to be inserted into a cavity of the bone marrow to seal this cavity, characterized in that it is made of a compound of calcium phosphate type and in that it   has a compressive strength of at least 490 bars.   2 Sealing plug according to claim 1, characterized in that said calcium phosphate type compound is chosen from the group consisting of tricalcium phosphate, hydroxyapatite, tetracalcium phosphate, oxyapatite, pyrophosphate calcium, fluoroapatite, hydroxyapatite derivatives each having one or more hydroxy groups replaced by   fluorine or oxygen ions and their mixtures.   3 Sealing plug according to claim 1, characterized in that it has resistance to   compression at least equal to 784 bars.   4 Sealing plug according to claim 3, characterized in that it has resistance to compression of at least 1,176 bars.   Sealing plug according to claim 1, characterized in that it has the general shape of a truncated cone.   6 Sealing plug according to the claim   cation 1, characterized in that it comprises a first segment having the general shape of a truncated cone and a second segment contiguous to the first and having the shape general of a cylinder.   7 Sealing plug according to the claim   cation 1, characterized in that it comprises a device engaging with an external device for pushing   said ankle in the cavity of the bone marrow.   8 Sealing plug according to the claim   cation 7, characterized in that said external device is a tube and said engagement device is a cylindrical projection disposed on the upper surface of said pin.   9 Sealing plug according to the claim   cation 7, characterized in that said external device is a solid rod and said engagement device is a concave recess formed on the upper surface of said pin.   Sealing plug according to the claim   cation 7, characterized in that said external device is a solid rod and said engagement device is a blunt end tube mounted on the upper surface of said pin to receive the end front of said full rod.   11 Sealing plug according to the claim   cation 1, characterized in that it has a general form   rale closely following that of the spinal cavity bone.