GB1603453A

GB1603453A - Osteosynthesis devices

Info

Publication number: GB1603453A
Application number: GB1993878A
Authority: GB
Original assignee: MEDICINSKA AKADEMIA
Current assignee: MEDICINSKA AKADEMIA
Priority date: 1978-05-16
Filing date: 1978-05-16
Publication date: 1981-11-25

Description

(54) OSTEOSYNTHESIS DEVICES (71) We, MEDICINSKA AKADEMIA, of 1, Georgi Sofiiski Street, Sofia, Bulgaria, an Academy of Medical Science organised under the Laws of Bulgaria, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement :- This invention relates to surgical devices for use in traumatological and orthopaedic practice.

Hitherto, two basic methods have been employed in traumatological and orthopaedic practice for achieving the connecting together of broken bone parts.

Firstly there has been employed osteosynthesis, that is the surgical fastening of the ends of a fractured bone by sutures, rings, plates or other mechanical means which include for example plates with screws and other fixing means employed both internally and externally. A general feature of all the osteosynthetic means employed hitherto has been that they have been made of electrically conductive material. As an alternative to osteosynthesis, there has been the traditional method of treatment in which bone knitting is achieved by immobilisation of the bone parts in plaster of Paris.

Three types of electrical phenomena are known to take place in bones. Firstly, bioelectrical potential is set up in accordance with the stressed bone; this is alternatively termed piezo-electrical potential and also originates in the tendons and cartilage. secondly there is bioelectrical potential caused by muscle contractions and nervous stimulation lasting for periods of the order of milliseconds. Finally, there is the bioelectric potential which results from the voltage difference which exits in all living tissue. This potential is almost constant and does not depend upon muscle contractions and stresses, but only upon the basic tissues concerned.

It has been observed that in the long hollow bones, the constant potential is manifested as a voltage difference along the length of the bone, always being electronegative in the epiphysis, while being mainly electropositive in the diaphysis. The maximum negative values are achieved under the epiphysical line of the metaphyses, where in fact the growth of bones takes place and where increased metabolism is observable.

It has also been observed that when bone fracture occurs, the normal biopotential pattern is abruptly changed. A second negative extrenum or peak appears at the place of fracture and this is considerably higher than the extrenum at the bone ends.

The second negative extrenum is preserved during the process of bone knitting, decreasing gradually in the course of time as that when the bone mending process is completed, the bioelectrical potential pattern has returned to its normal state. The presence of a negative bioelectric potential at the site of a bone break is obviously an obligatory condition since it is in fact closely connected with the increased metabolism which is required at such a position and which is generally associated with bone growth and the development of bones.

When employing metal osteosynthesis means, the electroconductive metal provides a short circuit and balances the negative electric potential in the region of the fractures which otherwise appear naturally. As a result, the negative extrenum necessary for the increase in metabolism at the place of the fracture is reduced substantially. Hence when employing metal osteosynthesis means, the required natural condition for normal regeneration of the bone are disturbed and this leads to a delay in the knitting of the bone and even possibly to dis-union. This observation is confirmed by the fact that when the traditional method of plaster immobilisation is effected, this method allowing the natural allocation of the biopotential in the bone to be preserved, the percentage of non-unions achieved is less than that when surgical treatment is employed. However, a disadvantage of this traditional method is the length of time it takes to carry out, including a long recovery period after bone knitting has been achieved.

According to the present invention, there is provided surgical fastening means for use in osteosynthesis, which means is formed of electrically nonconductive material or of electrically conductive material which is such that the distributions of biopotentials in bone undergoing fastening corresponds to the natural distribution of biopotentials in the bone in the absence of any break therein.

In practising this invention both load bearing elements for use in osteosynthesis, that is plates and internal and external fixing means, and elements for connecting them to bone, for example screws and Kirschner needles should be formed of electrically nonconductive material or electrically conductive material completely covered in electrically non-conductive material. As a result of the surgical fastening means for osteosynthesis being formed of dielectric material, there is no longer any cancelling or increase in the required negative bioelectrically extrenum at the fracture site.

The electrically non-conductive, or dielectric, osteosynthesis means does not interfere with the natural allocation of bioelectric potential lengthwise of the injured bone and hence does not interfere with the normal regeneration of bone tissue, nevertheless providing the required mechanical stability for osteosynthesis and maintaining a high level of negative bioelectric potential at the site of fracture.

More specifically, surgical fastening means according to this invention allow normal conditions for accelerated metabolism to take place in the bone and for the transportation of positive mineral ions to the site of the break, this being in contrast to the situation which obtains when metal surgical fastenings are used in osteosynthesis. Moreover, an electrically nonconductive surgical fastening is devised to provide more favorable conditions for healing of adjacent soft tissues damaged simultaneously with the break in the bone or in a surgical operation for installing surgical fastening means for osteosynthesis.

Moreover, provision of an electrically nonconductive surgical fastening means enables a more positive effect to be achieved when applying electrical stimulation to enhance bone knitting.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying Figures, wherein : Figures la and lb show respectively the natural allocation of bioelectrical potential in an intact and a fractured human tibia; Figures 2a and 2b show respectively the allocation of the bioelectrical potentials on application of a metal and an electrically nonconductive surgical fastening plate for use in osteosynthesis to a fractured human tibia; and Figure 3 is an X-ray showing bone knitting one month after osteotomy of bones of a test rabbit, the lefthand bone having undergone osteosynthesis with a metal plate and the right-hand bone having undergone osteosynthesis with a plate formed of electrically non-conductive material.

The surgical technique to be employed when establishing osteosynthesis of a fractured hollow bone or a bone which has undergone osteotomy is the same as that carried out hitherto when employing metal osteosynthesis means. The only difference is that the surgical fastening means known for the osteosynthesis is of electrically nonconductive type.

Insofar as surgical fastening devices such as plates may be formed of metal and provided with electrically non-conductive coatings according to this invention, such coatings may be provided by: a) coating of the metal devices with biologically acceptable thermoplastic plastics material, for example polyamides applied in powder form inter alia for anticorrosive coatings of metal parts, preferred such polyamides having the general formula N (HN- (CH,),.-CO), OH ; and b) coating of metal surgical fastening means with biologically acceptable glass and non-electrically non-conductive ceramic material, the latter material being applied electrophoretically to an intermediate glass layer.

A suitable material for use when the entire surgical fastening means is to be formed of electrically non-conductive material is polycarbonate plastics material.

Testing of the applicability of the principe of this invention has been carried out in vivo using rabbits. The tests show that when an electrically non-conductive plate according to this invention was placed on an osteotomed rabbit bone, the plate allowed accelerated regeneration of bone tissue to take place in comparison with the regeneration which was obtained in a comparative experiment carried out employing a metal plate placed on the symmetrical bone of the same animal. Five weeks after the operation, a thicker and almost complete filling of inter-fragmental space with callus was observable both microscopically amd by means of X-ray without any periostal formation, when employing a plate formed of electrically non-conductive material. In contrast, the symmetrical leg of the rabbit, which bone was a leg bone and to which a metal plate had been applied, showed an osteoid periostal callus without strongly pronounced endostal callus formation and filling of the inter-fragmental space. It is Xrays of these leg bones which are shown in Figure 3 of the accompanying figures.

Although the present invention has been described herein primarily with reference to the mending of fractures, it will be appreciated that this invention is also applicable to any operation in which osteosynthesis is required, including, in cases of severe arthritis, joint replacement.

The experimental results referred to herein have been confirmed clinically in cases of severe pseudarthrosis.

Claims

WHAT WE CLAIM IS :-

1. Surgical fastening means for use in osteosynthesis, which means is formed of electrically nonconductive material or of electrically conductive material which is such that the distribution of biopotentials in bone undergoing fastening corresponds to the natural distribution of biopotentials in the bone in the absence of any break therein.

2. Surgical fastening means as claimed in claim 1, which is made of metal completely coated with a biologically acceptable synthetic plastics material.

3. Surgical fastening means as claimed in claim 2, wherein said plastics material is a polyamide.

4. Surgical fastening means as claimed in claim 3, wherein said polyamide has the formula H (HN- (CH,),.-CO), OH.

5. Surgical fastening means as claimed in claim 1, which is formed of metal having a coating of biologically acceptable glass having a coating of ceramic material thereon.

6. Surgical fastening means as claimed in claim 1, which is formed of biologically acceptable thermoplastic plastics material.

7. Surgical fastening means as claimed in claim 6, which is formed of polycarbonate.

8. Surgical fastening means as claimed in any one of the preceding claims, which is a fixing plate, an internal or external fixing means, a screw or a Kirschner needle.