GB2307179A

GB2307179A - Surgical fixator

Info

Publication number: GB2307179A
Application number: GB9623643A
Authority: GB
Inventors: Pertti Toermaelae; Markku Tamminmaeki
Original assignee: Biocon Oy
Current assignee: Biocon Oy
Priority date: 1995-11-17
Filing date: 1996-11-13
Publication date: 1997-05-21
Also published as: FR2741255A1; DE19647410A1; FI955547A; FI955547A0; GB9623643D0; FR2741255B1

Description

1 Surgical fixation instrument 2307179 The invention relates to a surgical

fixation instrument according to the preamble of the claim 1.

The present invention particularly relates to surgical instruments manufactured of biodecomposing, i.e., biodegradable, i.e., absorbent, i.e. under tissue conditions without any significant harmful irritation reactions disintegradable andlor soluble andlor metabolising material and used for joining (fixating) tissues and parts thereof to each other or for immobilizing these to each other or for fixation of implants, such as plates, synthetic ligaments, fascios etc. into tissues.

in surgery it is generally known to use macroscopic fixation instruments, such as screws or plates, spikes, nails, hooks, bolts etc. connected by screws for healing, fixation or immobilisation of osteotomies, ankylosed joints (arthrodesis), bone fractures, joint damages, cartilage damages, connective tissue damages, meniscus ruptures, damages of ligaments, tendons or corresponding musculoskeletal tissues that are released from the surface of the bone, said screws or the like being used for joining together the desired tissues or parts thereof or for fixation of surgical implants, such as sutures, plates, ligament prostheses, etc., to tissues.

Above mentioned macroscopic fixation instruments are manufactured typically of metals, ceramics, polymers or polymer alloys (cf. e.g. P. T6rm.11J et al. J. Biomed Mater. Res., Vol. 25, (1991), pp 1-22).

It is particularly advantageous to manufacture the above mentioned fixation instruments of tissue-adapting, biostable or biodecomposing, i.e. , biodegradable polymer materials and polymer alloys. Macroscopic fixation instruments of this type are described in numerous patent publications.

Biodegradable fixation instruments, such as rods, plates, screws, intramedullary nails, hooks or the like are disclosed e.g. in the following patent publications: US-4655203, US-4743257, US-4863472, US4968317, US-4873976, EP-390613, EP-389102. Patent publications 2 US-4570623 and US-4454875 disclose surgical hooks having flake like or corresponding projections for improving the tissue fixation of the hook.

Using screws as fixation instruments of bone tissue is complicated by the fact that in many cases it is necessary to drill a hole (drill canal) to the bone and to make a threading for a screw inside the hole by using special tools, only whereafter the screw can be driven in. When driven in, the screw is tightened to its place by means of friction forces and the final tightening is facilitated by pressing of the screw end when the screw is driven against the bone, wherein compression is attained in the tissue to be supported. Using nails and the like in fixation is complicated by the fact that tissues can glide on their surface in the direction of the longitudinal axis of the nail, wherein the fixation is slackened up.

To use biostable screws, such as metal screws, also includes the problem that the screw cannot be locked to be non-returnable, since the screw has to be able to be removed in a new operation after the fracture has healed, wherein the screw is removed by driving it to the opposite direction than when inserting it, wherein the screw rises upwards and is finally released. However, the screws may also slacken up in use conditions when external strains affect the tissue to be fixated, wherein the screw can begin to open and move away from the drill canal in the axial direction. The moving of the screw from the drill canal which takes place in form of axial directed threading will also deteriorate the fixation.

In surgery it is also known to use dual-part instruments which are made of biostable and biodecomposing polymers and consist of cylindrical, hollow and elongated means which is split at the end that penetrates the tissue, i.e., at the head part, and a thinner, elongated expanding means which is pushed therein. As the hollow means is pushed e.g. into a hole that is drilled to a bone and the expanding means is pushed inside the hollow means, the head part of the hollow means is expanded and the means is pressed by tension forces against the surrounding bone.

3 1 Publication GB-2084468 discloses a surgical instrument which is composed of a stem part and two base parts situated in the heel part of the stem. The stem part of the instrument has a drilling hole in the direction of its longitudinal axis and further a split in the longitudinal axis of the instrument.

The instrument according to publication GB-2084468 further comprises a taper pin which can be pushed into the hole that penetrates the stem part, wherein the split stem part is expanded and locked tightly in relation with the surrounding tissues.

An instrument (fixator) operating in a corresponding manner is disclosed in publication EP-504915. The instrument having expanding branch parts in its head part is implanted to a drill canal in a bone. The branch parts of the fixator are expanded by pulling a gliding rod placed inside the fixator and having a conical head part which has a greater diameter than the stem of the rod.

Fixation instruments expanding in the radial direction have several advantages compared to rod-like, tubular and screw-like fixation instruments. A drawback of fixation rods and tubular fixation instruments is that they can not bring about a good fixation effect in the longitudinal (axial) direction of the implant. When screws are used, it is possible to attain a good fixation effect in the direction of the longitudinal axis of the screw, but surgical use of the screw is difficult since it is often necessary to make in the tissue a pre-hole corresponding to the threaded profile of the screw by using special threading equipment, and, furthermore, the driving of the screw into the tissue is a time-consuming operation and also a difficult operation in cases where the tissues surrounding the tissue to be operated restrict the operating surgeon.

Instruments (bolts) according to publication GB-2084468 provide a better fixation effect than mere rods or tubular fixation instruments. However, the restriction of this instrument is that the base part of the instrument does not expand, because the split which is parallel with the longitudinal axis and situated in the stem part is short when compared to the total length of the stem part. Consequently, the instrument has to comprise a base part which is broader than the stem part, the base part 4 anchoring the instrument on the surface of the tissue to be fixated, whereas the head part of the stem part of the instrument is expanded by the influence of the taper pin, wherein the head part of the instrument is fixated to the tissue. The broad base part is the substantial element for the structure and operation of the instrument disclosed in publication G13-2084468. However, disadvantageous effects are caused by said base part when the instrument, particularly one made of biodegradable material, is applied for fixation of tissue damages and the like. When the base of the instrument remains above the surface of the bone (e.g. upon fixation of a bone fracture or a ligament which has come off), the base of the instrument causes mechanical stress on the tissues thereabove. This stress may release macroscopic clinical foreign body reactions which take the form of so-called fluid accumulation or sinus formation. These are typical complications when biodegradable fixation instruments, such as screws, with base parts are used (cf. e.g. E. Partio, Doctoral Thesis, Helsinki University, 1992). Particularly disadvanta geous would be to use a fixation instrument with a base part in fixation operations for tissues inside joints, because the base of the fixation instrument might easily damage the opposite joint surface if it remains on the joint surface.

In surgery, it is also known to use dual-part instruments without a base part, manufactured of biostable or biodegradable polymers, and composed of a cylindrical means with a hole, i.e., hollow and split at its lower end (head), as well as a thinner expander equipment (taper pin) to be pushed to the hole in the means. As the hollow means is pushed e.g. to a hole drilled in a bone and the expander equipment is pushed inside the hollow means, the split head part of the hollow means is expanded and pressed by means of friction forces against the surrounding bone. The drawback of such instrument is that because the cylindrical hollow means is split only at its head the fixation effect is attained only at the head part, whereas no particular fixation effect takes place in the stem part of the instrument (i.e., in the opposite end of the instrument in relation to the head part). Consequently, an instrument of this type is not capable of fixating bone fragments or other tissue pieces in the area of the stem part of the bolt against such powers which influence in the direction of the longitudinal axis of the instrument and detach tissue pieces.

The present invention surprisingly discloses that the problems relating to the state of art can be eliminated to a great extent by carrying out the surgical fixation instrument mainly in a manner described in the characterizing portion of claim 1. Thus, there is manufactured of biodegradable, polymer material or composite a bioabsorbable, expanding hollow means, which is placed into a hole or a drill canal made in a bone, cartilage, ligament or a corresponding tissue and expands by means of a taper pin at its entire length. By using a solution in accordance with the invention, it is possible, when inserting fixation instruments, to eliminate the above-mentioned difficulties and functional restrictions present in connection with screws, nails and partially split instruments.

The accompanying dependent claims describe some advantageous embodiments of the fixation instrument of the invention.

The invention is illustrated in the following specification with reference made to the accompanying drawings. In the drawings

Figs. lato 1d show a first embodiment and the use of the instrument in accordance with the invention, Figs. 2a to 2c show a perspective view of a second, third and forth embodiment of the instrument in accordance with the invention, Figs. 3a to 3e show schematically in phases the use of the instrument in fixation of a bone fracture, Figs 4a to 4b show, seen in the side, yet other form embodiments for splitting the hollow means in accordance with the invention, Fig. 5 shows, seen in the side, one embodiment of the hollow means of the instrument seen from the side, and 6 Fig. 6 shows a perspective view of a comparison instrument of the prior art used in Example 1.

A fixation instrument in accordance with the invention is formed according to Fig 1:

(a) (b) of an elongated, cylindrical means 1 having a hole; i.e., hollow, which means is split at both ends starting with at least one elongated split 2, 2 penetrating the wall material and extending to a part of the length of the hollow means 1, in a manner that these splits together extend in the wall la of the means to the length of the entire means 1, preferably passing each other, and an elongated taper pin 3 which can be pushed inside an inner hole 4 of the hollow means 1, and the diameter of which taper pin 3 has at least one cross section dimension which is greater than the greatest perpendicular cross section, i.e., usually a diameter, against the longitudinal direction of the inner hole 4 of the hollow means 1, wherein the taper pin 3 expands the hollow means 1 in the radial direction at its entire length when the taper pin 3 is pushed, starting at its sharpened head 3a, into the inner hole 4 of the means 1 at the entire length of the hollow means 1 (Fig. 1 b).

Fig. la shows schematically a perspective view of the hollow means 1 of the fixation instrument according to the invention, the means 1 having inside a longitudinal inner hole 4 and in its wall 1 a splits 2 and 2' in the direction of the longitudinal axis of the means 1. Fig. l a also illustrates a cylindrical taper pin 3. Fig. 1 b shows the taper pin pushed into the hole 4, wherein the diameter of the split means 1 is expanded. Fig. l c shows the means 1 seen in the direction of the arrow AS of Fig. 1 a before the taper pin 3 is installed, and Fig. l d shows the same after the taper pin 3 is installed. Thus, the splits 2 and 2' have expanded into grooves 2a present in the hollow means 1 and penetrating the wall l a.

7 In accordance with a particularly advantageous embodiment, there can be two or several splits 2, 2' in the wall of the hollow means 1 at both ends thereof, in a manner that they pass each other in the direction of the longitudinal axis of the hollow means 1, wherein due to penetration of the taper pin 3 the hollow means 1 is expanding evenly (preferably symmetrically) at the entire length of the hollow means 1. Fig. 2a shows a perspective view of the hollow means 1 having at their both ends two splits 5, 6 and E, 6' (angle distance 1800; 900 phase shift) and Fig. 2b shows the same with three splits 7, 8, 9 and T, 8', 9' (angle distance 1200; 600 phase shift). When the number of the splits is two or more at both ends of the hollow means 1, the compression tension caused by the extension of the means 1 is divided evenly to the surrounding tissues, wherein the risk of press necrosis or corresponding press complications is decreased and the attachment of the implant to the tissue is improved.

Fig. 2c shows further an application having, in accordance with Fig. 2a, two splits 5, 6, S, 6' at both ends of the hollow means 1 at angle distances of 1800. Furthermore, the splits 5, 6, S, 6' in this embodiment of Fig. 2c are shorter than those of Fig. 2a, wherein third splits 16 are arranged in the central part of the hollow means 1, e.g. in a manner that there is created a phase shift of 600 seen from the end of the hollow means 1. The central splits 16 are positioned in a manner that their heads extend, parallel with the longitudinal direction of the hollow means 1, to the splits 5, 6, S, 6' which begin at its ends. It is obvious that the number of the splits also in the embodiment in accordance with Fig. 2c can vary even to a great extent. Thus, the splits are divided into two groups beginning at the opposite ends of the hollow means. A supplementary group is formed by possible central splits.

Further, the embodiments of Fig. 4a and 4b show options in which the splits are made in an oblique angle in relation to the longitudinal direction of the hollow means 1 (4a) and curved in relation to the longitudinal direction (4b).

It can generally be noted that the splits are formed advantageously in a manner that their placing on the periphery of the wall 1 a, seen in a perpendicular direction against the longitudinal direction of the hollow 8 means 1, is in accordance with the formulae of the relation between the angle distance and the end where the splits are inserted K, = 3600/Nhl and K2 = 3600/Nh2, wherein K, and K2 = the angle distance between the splits at the first K, and second K2 end of the hollow means 1 and Nhl and Nh2 = the number of the splits in the first (Nhl) and second (Nh2) end of the hollow means 1, whereby most commonly NU and whereby (K, + K2)12, wherein the entire angle distance between two adjacent splits in the direction of the periphery of the hollow means 1, wherein preferably adjacent splits begin alternately at opposite ends of the hollow means 1, in case the number of the splits at the opposite ends of the hollow means 1 is equal.

Nhl K K In the manner described above it is possible to bring about an equal division in the position of the splits regardless of their number and thus to attain that the position of the splits seen in the direction of the periphery of the hollow means 1 alternates in a manner that first ends EP (beginnings) of the adjacent splits are at the opposite ends of the hollow means 1. It is advantageous that the splits extend to the central part of the hollow means and that their second ends TP pass each other in the longitudinal direction of the hollow means 1, wherein in the central part of the hollow means 1 there is created a zone 15 (cf. Fig. 1a) formed of interlapping split parts, the length of the zone being determined by the second ends TP (finishing ends) of the splits beginning at both ends of the hollow means 1.

The splits do not necessarily have to be straight but they can also be e. g. oblique in relation to the direction of the longitudinal axis of the hollow means 1 or they can be wound spirally around the longitudinal axis of the hollow means 1 in the wall 'I a thereof. Further, it is possible to arrange a different number of splits at different ends of the hollow means 1, wherein they can be placed according to the requirements of 9 each individual case. The taper pin 3 can be symmetrical, it can have the same diameter from one end to the other, or it can be conical or it can have a variable diameter. It can also be flat or have a triangular, quadrangular or polygonal cross section. Other possible forms for the cross section include e.g. the ellipse or a kidney-shaped configuration. In a corresponding manner, the cross section form of the outer surface of the hollow means 1 andlor the inner hole 4 situated therein can have the same forms as the afore-mentioned taper pin. It is possible to obtain instruments in accordance with the invention for various purposes also by combining hollow means 1 and taper pins 3 having different configurations.

The hollow means 1 of the instrument in accordance with the invention can have projections or protrusions constructed on its surface, such as diverse flake-like or ridge-like projections, which are penetrated at least partially to the surrounding tissue when the taper pin 3 is pushed into the hollow means which is placed inside the tissue. The projections increase the fastening of the fixation by preventing external forces from causing gliding between the fixated tissue parts and the bolt.

The fixation instrument of the invention is used e.g. in fixation of bone fractures in a manner that the bone fragment is fixed temporarily to the bone by forceps, as shown in Fig. 3a. Subsequently, a bone canal 10 is drilled through the fragment and the bone underneath it, the drill canal having approximately the same or a slightly greater diameter than the outer diameter of the hollow means 1 of the fixation instrument in accordance with the invention at its non-extended state (cf. Fig. 3b).

Consequently, it is possible to push the hollow means 1 (e.g. one according to Fig. 2b) into the drill canal 10 as shown in Fig. 3c. Subsequently, in accordance with Fig. 3d, it is possible to place the taper pin 3 into the central hole 4 situated in the centre of the hollow means. As a result, there is attained, in accordance with Fig. 3e, a fixation of the bone fragment to the bone in a manner that the fixation instrument expands at its entire length in the radial direction shown by the arrows of Figs. 3d and 3e, wherein the fixation instrument 1, 3 is locked to the bone efficiently caused by friction forces and simultaneously immobi- lises the bone fragment in an efficient manner against the effect of various forces which possibly attempt to move it.

Thus, by applying instruments according to the invention it is possible to efficiently attach andlor immobilise osteotomies, joints to be ankylosed, fractures, ligaments, as well as joint damages inside the joint or the like, against forces affecting from all the directions without having to carry out a time-consuming threading for the screw andlor without causing, due to the base of the instrument, an effect which could damage the joint surface of the adjacent joint.

According to one advantageous embodiment it is possible that various projections, such as spirals, flakes or ridges or other projections of a corresponding type, are constructed on the surface of the parts of the hollow means 1, these projections facilitating the locking of the fixation instrument to the surrounding tissues. Fig. 5 shows as an example the hollow means 1 of the invention, having parallel splits 2 and 2' situated at both ends of the wall and passing each other, the cylindrical hollow means 1 having ridge-like or flake-like projections 14 on its surface. It is obvious that projections of other types than those illustrated in Fig. 5 can also be employed on the surface of the fixation instruments in accordance with the invention to improve its mechanical locking to the surrounding tissues as an effect of the taper pin 3.

The most important advantage of the surgical instruments (bolts) of the invention over prior art bolts, manufactured of metals, biostable plastics or plastic composites, is that the instruments of the invention loose their rigidity in an advantageous manner upon healing of the fracture due to absorption of the polymer material, which prevents formation of osteoporosis. Compared to known biodecomposing instruments, by applying instruments of the invention a better rigidity for the fixation is brought about, because the instruments of the invention fixate the tissue at their entire length. Since the instrument in accordance with the invention is manufactured entirely of soluble material or materials it dissolves after a suitable period of time into metaboluble compounds. Thus, no removal operation is required in connection with the instruments according to the invention. Consequently, the surface structure of the instruments in accordance with the invention can also be of the type

11 that the instrument can be inserted in a manner that the instrument cannot come off or slacken up and it cannot be removed or slackened up without breaking the instrument andlor the bone.

Fixation instruments in accordance with the invention can be manufactured of biodecomposing (biodegradable or resorbent) polymers, copolymers, polymer alloys or composites, e.g. of poly-a-hydroxide acids and other alifatic biodecomposing polyesters, polyanhybrides, polyorthoesters, polyorganophosphatsenes and other bioabsorbent polymers disclosed in numerous publications, e.g. in FI-952884 and WO90104982 as well as the reference publications mentioned in the aforementioned publications.

Instruments in accordance with the invention can be manufactured of biodecomposing polymers by using one polymer or polymer alloy. The instruments can also be reinforced by reinforcing the material by fibres manufactured of resorbent polymer or polymer alloy, or resorbent glassfibres, such as P-tricalsiumphosphate fibres, bio-glassfibres or CaAl fibres (cf. e.g. EP-146398).

Instruments according to the invention can also contain layered parts comprising e.g. a flexible layer, a surface layer improving the toughness and/or operating as the hydrolysis barrier and a stiff inner layer.

Surgical instruments in accordance with the invention can be manufactured of biodecomposing polymers and of suitable biodecomposing reinforcement fibres by means of various methods used in plastic technology, such as injection molding, extrusion and fibrillation and molding related thereto (cf. e.g. publication US-4968317) or by means of compression molding, wherein the pieces are shaped of the raw material by employing heat andlor compression.

It is possible to manufacture instruments of the invention of aforementioned raw material also by using so-called dissolvent techniques, in which at least part of the polymer is dissolved to a suitable dissolvent or softened by means of a dissolvent and the material or the material alloy is compressed into a piece by means of pressure and possibly by means of slight heat, wherein the dissolved or softened polymer glues 12 the material into a macroscopic piece wherefrom the dissolvent is removed by evaporation.

It is natural that the instruments of the invention can also contain various additives for facilitating the processability of the material (e. g. stabilizers, antioxidants or softeners) or for changing its properties (e.g. softeners or ceramic powder materials or biostable fibres, such as carbon fibres) or for facilitating its treatment (e.g. colorants).

According to one advantageous embodiment the instruments of the invention contain some bioactive agent or agents, such as antibiotics, chemotherapeutic agents, agents activating healing of wounds, growth factor, anticoagulant (such as heparin) etc. Such bioactive instruments are particularly advantageous in clinical use, because they have, in addition to their mechanical effect, also biochemical, medical and other effects in various tissues.

The invention and its function is illustrated by means of the following Example.

Example 1

Absorbent, hollow polyglycolide (PGA) bolts having a cylindrical cross section were manufactured. First there was manufactured for the hollow means 1 by sintering Dexon sutures (manufacturer: Davis & Geck, England; size USP 2), according to Example 3 of publication US4743257 to be closed, preforms having the length of 80 mm and having projections (ridges) of the type according to Fig. 5 on their surface in a manner that the maximum diameter of the preform (= the maximum distance between the ends of the projections in the perpendicular direction against the longitudinal axis of the preform) was 4.5 to 4.6 mm. The distance between the ends of the adjacent projections in the longitudinal direction of the preform was 2 mm. The projections formed uniform, curved structures on the surface of the means in a manner that each projection extended around the means. A hole was drilled by a bore of 1.5 mm through the preform and the preform was split according to the principle of Fig. 2b at both ends by three longitudinal splits having a length of 50 mm, the distance between the splits 13 being 1201% by sawing the split preforms at both ends by a fast rotating diamond disc having a thickness of 0.5 mm. Thus, on the periphery of the hollow preform altogether six splits were formed, the distance between which being 600 seen from the direction of the cross-section periphery of the means. The used taper pin was a cylindrical, sintered PGA rod having a length of 80 mm and a diameter of ca. 2 mm.

To provide comparison material, a prior art type hollow means 11 was manufactured according to Fig. 6, the means 11 having a similar surface profile, a length of the profiled part and a drill hole as in the bolt of the invention, but which was provided with a cylindrical base 12 having a thickness of 1 mm and a width of 8 mm. Further, this hollow means was sawed split at its end at a length of 40 mm by three sawings 13, distance between which being 1200, in accordance with Fig. 5, wherein a nonexpandable profiled part having a length of 30 mm remained under the base. Polyglycolide rod having a length of 80 mm and a thickness of 20 mm was used as the taper pin also in this bolt structure.

A cutting (osteotomy) was made in the horizontal direction in a distal part of a femur of cow 4 cm above the knee joint by means of a bone saw. The osteotomy was fixated by two instruments manufactured according to the afore-mentioned manufacture technique or by two instruments of Fig. 6 having a base 12, placed into parallel drill canals made with a bore of 4. 5 mm, the canals being drilled in a perpendicular manner against the osteotomy level at a distance of 3 cm from each other through joint surface.

The fixated osteotomies were tested by pulling off the fixated bone piece in the direction of the longitudinal axis of the femur. The maximal strength required for opening the osteotomy was measured. Four parallel measurements gave the two instruments of the invention an average hold strength of 700 N and the instruments of prior art were given a hold strength of 540 N, i.e., a result superior with 30 per cent was attained by means of an instrument according to the invention. Thus, the instrument of the invention was distinctly better in view of the tensile load endurance, because it locked the bone fragment in its place when extended at its entire length.

1k 14 It is obvious that in accordance with the invention it is possible to construct also instruments which expand in a guided manner bypositioning the splits unsymmetrically on the periphery of the instrument. Thus, unsymmetrical active zones and effects caused thereby can be brought about in certain surgical objects.

Claims

1. Instrument manufactured of at least partially absorbent, polymeric material, material alloy or composite, the instrument comprising at least one elongated hollow means (1), at least one split (2) situated in the wall (1 a) of the hollow means (1), a taper pin (3) or the like penetrating the wall (1 a) and placed in the central hole (4) of the hollow means (1), to fixate (a) tissues or parts thereof in relation to each other or (b) implants, such as plates, ligaments, fascios, sutures etc. to tissues, wherein the hollow means (1) is arranged to be pushed at least partially into a hole, drill canal, groove or the like made in a tissue, such as bone, cartilage or connective tissue, and wherein the taper pin (3) or the like is arranged, when placed in the central hole (4), to enlarge the diameter perpendicular against the longitudinal direction of the means (1), characterized in that said splits (2, T; 5, 6, 5', 6; 7, 8, 9, T, 8', 9') are divided into two groups in a manner that the first group (2, 5. 6, 7, 8, 9) begins at a first end of the hollow means (1) and the second group (7, E, 6, T, 8', 9) begins at a second end of the hollow means (1) and that at least some of the splits (2, Z; 5, 6, 5'. 6; 7, 8, 9, T, 8, 9) of the first and second group together andlor with splits (16) at the central part of hollow means (1) extend to the entire length of the hollow means (1) so that the splits (2, 7; 5, 6, E, 6; 7, 8, 9, T, 8', 9; 16) make it possible for the hollow means (1) to expand in a perpendicular direction against the longitudinal direction thereof, substantially at the entire length of the hollow means (1) when said longitudinal taper pin (3) or the like is situated in the central hole (4) of the hollow means (1).

2. Instrument as set forth in claim 1, characterized in that at least some of the splits (2, 2; 5, 6, S, C; 7, 8, 9, T, 8', 9) beginning at the opposite ends of the hollow means (1) extend to the central part of the hollow means (1) passing each other, wherein a zone (15) is formed at the central part of the hollow means (1), in which zone (15) the splits (2, Z; 5, 6, S, C; 7, 8, 9, T, 8', 9) are interlapping each other in the longitudinal direction of the hollow means (1).

3. Instrument as set forth in claim 1, characterized in that the splits (2, T; 5, 6, E, 6; 7, 8, 9, T, 8', 9) are at least partially straight, in the 16 longitudinal direction of the hollow means (1), in an oblique angle in relation to the longitudinal axis of the hollow means (1) andlor curved.

4. Instrument as set forth in claim 1, characterized in that the splits are advantageously formed in a manner that their positioning on the periphery of the wall (1 a) in the perpendicular direction in relation to the longitudinal direction of the hollow means (1) is based on formulae of the relation between the angle distance and the end where the splits (2, Z; 5, 6, 6, C 7, 8, 9, 7, 8', W) are inserted K, K2 K, and K2 Nhl and NU ' NW K K 3600/Nhl and 3600/Nh2, wherein the angle distance between the splits at the first K, and second K2 end of the hollow means (1) and the number of the splits in the first (Nhl) and second (Nh2) end of the hollow means (1), whereby most commonly NU and whereby (K, + K2)12, wherein the entire angle distance between two adjacent splits in the direction of the periphery of the hollow means (1), wherein preferably adjacent splits begin alternately at opposite ends of the hollow means (1), in case the number of the splits at the opposite ends of the hollow means (1) is equal.

5. Instrument as set forth in claim 1, characterized in that projections (14), such as ridges or flakes, are constructed on the surface thereof.

6. Instrument as set forth in claim 1 or 5 of the claims, characterized in that at least a part of the projections (14) extends around the stem part.

7. Instrument as set forth in any of claims 1 to 6, characterized in that at least absorbent polymer, polymer alloy, co-polymer or composite has been used in the manufacturing thereof.

17

8. Instrument as set forth in any of claims 1 to 7, characterized in that it is reinforced by bioabsorbent fibres chosen from the following fibres: bioabsorbent polymer fibres, bioabsorbent ceramic fibres, or bioabsorbent glassfibres andlor it is reinforced by biostable fibres chosen from the following fibres; glassfibres, carbon fibres, polymer fibres.

9. Instrument as set forth in any of claims 1 to 8, characterized in that it is manufactured of self-reinforced bioabsorbent material.