SURGICAL DEVICE FOR IMMOBILIZATION OF BONE FRACTURE

Abstract: Reinforced, resorbable surgical device for immobilization of bone fracture comprises at least one organ (3), which is formed of resorbable polymeric matrix containing resorbable reinforcing elements, such as fibers, threads, twines or structures constructed of them. The reinforcing elements of the organ are constructed of polyglycolide fibers which are embedded in resorbable polyester matrix. This matrix is constructed of poly- beta -hydroxybutyrate or of glycolide/lactide copolymer, the said copolymer comprising at least 80 mole % glycolic acid repeating units or of poly-dioxanone.

Description: SURGICAL DEVICE FOR IMMOBILIZATION OF BONE FRACTURE This invention relates to a reinforced, resorbable surgical device for immobilization of bone fracture as defined in the preamble of the claim 1. The device comprises at least one organ, which is used to reinforce a fractured or weakened bone of a human or animal subject. The said organ is formed of resorbable polymeric matrix containing resorbable reinforcing elements, such as fibers, threads, twines or structures constructed of them. There are several demands the osteosynthesis devices, which are applied to the fixation of the bone fractures, must fulfill. They must be strong enough for a good fixation and they must be tissue compatible to preserve the undisturbed osseous union. Traditionally the osteosynthesis devices are plate-like perforated samples which are fixed to the bone by screws. Usually such surgical devices have been manufactured of austenitic steel, titan or other metals or metal alloys, which fulfill the demands of the tissue environment. Generally such conventional biostable surgical devices are removed at a separate subsequent operation, when the healing of the fracture has proceeded by means of the growth of the bone tissue far enough. The use of metallic surgical elements causes, however, many kinds of problems. Many metals and metal alloys corrode in tissues causing inflammation and infections, which are problematic and are eliminated only after removing the surgical device. The corrosion is often found in contact points of plates and screws. Because of the large difference in stiffness between bone (Youngs modulus E = 6-20 GPa) and metals (E = 100-200 GPa) , rigid metallic fixation prevents the rapid proliferation of primary callus and deprives the bone of the normal stresspattern. The long-term result of stress-protection is a mechanically inferior bone structure in the region of the plate because of osteosporosis and atrophy. Refracture is therefore a possibility after the removal of the plate. The possibilities to use other than metallic materials as surgical devices have been • studied extensively during the last years. On the basis of these studies polymers and polymer composites seem to be in this respect promising materials. Several kinds of osteosynthesis devices have been proposed and manufactured by using polymeric materials. The Finnish application for patent, FI-83 3351, (Tormala et al), relates to resorbable (soluble) osteosynthesis device, where band-like or thread-like fixing element(s), which are fastened to the bone and/or tightened to their place to go over the fracture site and/or osteosynthesis plate, is applied. Here resorbable material means a tissue compatible synthetic or modified polymeric material, which retains its tissue-supporting properties certain periods of time (typically weeks or months) and is gradually degraded biologically into tissue compatible components which are absorbed by living tissues and replaced by healing tissues (about during months or 1-2 years). The most studied in surgery applicable resorbable polymers are polyglycolides (PGA), polylactides (PLA) and their copolymers. Their manu acturing and applications as sutures etc. are disclosed in several patents e.g. in U.S. Pat. No. 2 668 162, U.S. Pat. No. 2 676 945, U.S. Pat. No. 3 297 033, U.S. Pat. No. 3 636 956 and Can. Pat. No. 808 731. The application of moulded PGA as bone plates and medullary rods is expressed in U.S. Pat. No. 3 739 773. Surgical devices of poly-dioxanone are disclosed in U.S. Pat. No. 4 052 988-. Surgical devices of poly-β-hydroxy butyric acid (PHB) or pόly-β-hydroxy propionic acid are disclosed in G.B. Pat. No. 1 034 123. U.S. Pat. No. 4 343 931 discloses surgical devices manufactured of polyesteramides (PEA) which contain long-chain molecular units, and which are copolymers of diamine, hydroxy acid and diacid: n o o o !! I! I! II -0-CH 2 -C-NH(CH ) -NH-C-CH 2 -0-C -(CH ) -C- The mechanical properties of the surgical devices manufactured of resorbable polymers are typically comparable to those of the biostable polymeric materials e.g. the tensile strength values between 40-70 MPa are typically obtained. In the most cases these mechanical properties are too modest to demanding bone surgical applications. U.S. Pat. No. 4 279 249 discloses the resorbable surgical device of polylactide (PLA) or polylactide copolymer very high in lactic acid units, which device is reinforced with resorbable polyglycolide fibers. This structure has good mechanical properties but the resorption rate of polylactide is very slow (no appreciable resorption occurred for PLA 100 at 12 months; see P. Christel e_t al. Biomaterials , 1980, Eds. G.D. Winter, D.F. Gibbons and H. Plenk, Jr., Wiley, p. 271-280) and it is difficult to control which can be seen from the contradictory literature values (see e.g. D.E. Cutright, B. Perez, J.D. Beasley, W.J. Carson and W.R. Posey, Oral_ 1 _Surg_._ 37 (1974) 142; Vert, M., Chabot, F., Leray, J. and Christel, P., Makromol . Cheπ _ Suppl. 5 (1981) 30; Miller, R.A., Brady, J.M. and Cutright, D.E., J^ Biomed. Mater. Res. 11 (1977) 711). The purpose of this invention is to present new combinations of materials for the resorbable surgical device especially for the organ immobilizing the bone fracture. By means of these combinations it is possible to avoid the drawbacks of the prior art combinations. According to this invention it has been unexpectedly found that very strong reinforced resorbable organs, which can be applied as osteosynthesis devices or as their components, with good resorption properties can be manufactured when polyglycolide fibers, threads, bands, fabrics or structures of the same kind are applied as reinforcing elements in the resorbable, polyester matrix which is constructed of (a) poly-β-hydroxybutyrate or of (b) glycolide/lactide copoly er, the said copolymer comprising at least 80 mole % of units derived from glycolic acid or of (c) of poly-dioxanone . The organs of the invention have good mechanical properties (initial tensile strength 200-400 MPa) caused by the partially fibrous reinforced structure. Because the. resorption rates of the matrix polymers of the organs of the invention are clearly more rapid than that of PLA the organs of the invention are especially suitable in healing of fractures of cancellous bone where fixation of several weeks is needed whereafter the rapid absorption of organs is desired. The enclosed drawing, in which some embodiments of the invention is clarified, together with the following description describe the invention more closely. In the drawings, Fig. 1 shows the invention in connection with the conventional fixing technique and Fig. 2 and 3 show the invention in connection with the technique in accordance with the devices of FI-833351. The organs according to the invention can be applied as - absorbable bone plates 3, which are affixed to the broken bone 1 with pins or screws 4, these being preferably absorbable (Fig. 1), as - medullary rods or bone pins for the fixation of the severed bone ends or fixation of the fractured bone to another bone (not shown) or as - osteosynthesis- plates or beams 3, which immobilize the broken bone 1 in cooperation with fixing element(s) 5 (e.g. Fig. 2 and 3) (e.g. FI Pat. Appl.. No. 833351). In the case of the conventional osteosynthesis device (Fig. 1) the bone 1, which includes the fracture 2, is immobilized by means of the osteosynthesis plate 3 which goes beyond the fracture 2 and which is fixed to the bone by means of nails or screws 4. In the case of the solution of the invention FI 833351 (e.g. Fig. 2 and 3) the fixing element(s) 5 and 5', which are constructed about fibers, have been tightened to go over the fracture 2 of the bone 1 and/or over the osteosynthesis plate 3. In the case of Fig. 2 the osteosynthesis plate 3 has been located at least partially into a groove 6 in the bone and in the case of Fig. 3 the osteosynthesis plate or - beam 3 has been located totally inside the immobilized bone, into a channel 7 which has been drilled through the fracture plane. The maximal reinforcing effect of the materials of the invention is achieved by means of reinforcing elements, when they are divided in fiber form into the reinforced matrix. Fibers can be continuous or short fibers and they can be also weaved or collected to different kinds of reinforcing structures. Also other than fibrous reinforcing elements, such as bands or foils can give the desired effect. One especially favourable solution of the device of the invention is such where the resorbable plate or beam 3 and/or fixing element 5, 5' have been coated with a thin inorganic material layer, which is hydrophobic and slackens therefore the diffusion of the water from tissue solutions into the osteosynthesis plate or beam. If the resorption needs enzymatic activity the inorganic surface layer delays also effectively the enzymatic resorption. As a consequence the decrease of the strength of the osteosynthesis device is in the beginning slow and is accelerated rapidly when the inorganic layer is decomposed. Suitable inorganic coatings in this connection are many ceramics as oxides, carbides, nitrides, suicides and silicates, their mixtures and many metals, such as gold, silver and titan, metal alloys and alloys of metals and ceramics. The following non-limiting examples illustrate the present invention. EXAMPLE 1 A mixture of 70 wt-% of glycolide/lactide copolymer (containing 90 mole % of glycolic acid repeating units) and 30 wt-. of polyglycolic sutures (size 2-0, Dexon (^_) of Davis & Geek) was compression moulded in a pressure mould to cylindrical bars (length 70 mm and radius 4.5 mm) at 185°C 8 min with the pressure of 2000 bar. The bars had the initial bending strength of 230 MPa and after the hydrolysis in destilled water at 37°C for 8 weeks they had lost their mechanical strength. After 12 weeks the resorption had clearly begun and after the hydrolysis in the above conditions for 12 months the bars were absorbed appreciable as could be seen from the decrease of the dimensions of the bars, strong erosion on their surface and disintegration of the structure. When the bars were coated by a thin (ca. 100 nm) layer of gold using the sputtering method the loss of the mechanical strength was in the beginning slower than in the case of non-coated bars but after the hydrolysis of 12 months differences between the non-coated and the coated bars were negligible. The ethylene oxide sterilized bars were successfully applied clinically to immobilize malleoral fractures of 20 adult patients. The bars were placed within the cancellous bone in drill channels across the fracture surfaces. The fixation was reinforced by means of the resorbable flexible fixing device (suture) according to the Finnish application for patent, FI-833351. The fractures were healed with eventless union and no removal operation of the resorbable device was needed. EXAMPLE 2 A mixture of 70 wt-% of poly-β-hydroxybutyrate (Mw = 5 2 • 10 ) and 30 wt-% polyglycolic sutures (size 2-0 Dexon <B) of Davis & Geek) was compression moulded in a pressure mould to bars of dimensions 70 x 4 x 4 mm at 190°C 12 min with the pressure of 2000 bar. The bars had the initial bending strength of 280 MPa and after the hydrolysis in destilled water at 37°C for 20 weeks they had lost their mechanical strength. After the hydrolysis in the above conditions for 12 months the " absorption of the bars was clearly in progress as could be seen from erosion on their surfaces and disintegration of the structure. EXAMPLE 3 A mixture of 70 wt-% of poly-dioxanone and 30 wt-% of polyglycolic sutures (size 2-0, of Davis & Geek) was compression moulded in a pressure mould to cylindrical bars (length 40 mm and radius 2.0 mm) at 150°C 8 min with the pressure of 2000 bar. The bars had the initial tensile strength of 270 MPa and after the hydrolysis in destilled water at 37°C for at least 16 weeks they had lost their mechanical strength. After 26 weeks the resorption had clearly proceeded as could be seen of the disintegration of the structure. The bars were successfully applied to immobilize the osteothomies of the femurs of anesthetized rats using the bars as intermedullary rods. The fractures were healed with eventless union and no removal operation of the resorbable device was needed.

Claims: Patent claims 1. Reinforced, resorbable surgical device for immobilization of bone fracture comprising at least one organ, which organ immobilizes the fractured bone in relation to another bone and/or which organ goes beyond or perforates the fracture being in connection with the parts of bone, which are on the opposite sides of the fracture, and which organ is formed of resorbable polymeric matrix containing resorbable reinforcing elements, such as fibers, threads, twines or structures constructed of them, c h a r a c¬ t e r i z e d in that the reinforcing elements of the organ are constructed of polyglycolide fibers which are embedded in resorbable polyester matrix which is constructed of (a) poly-β-hydroxybutyrate or of (b) glycolide/lactide copolymer, the said copolymer comprising at least 80 mole % glycolic acid repeating units or of (c) poly-dioxanone. 2. Surgical device of Claim 1, c h a r a c t e r¬ i z e d in that the organ is bone plate or beam fixed to the bone by fixing elements. 3. Surgical device of Claim 1, c h a r a c t e r¬ i z e d in that the organ is medullary rod or bone pin. 4. Surgical device of Claims 1-3, c h a r a c- t e r i z e d in that the resorbable organ has been at least partially coated by inorganic (metallic and/or ceramic) surface layer.

Inventors: KILPIKARI JYRKI, MERO MATTI, PAETIAELAE HANNU, ROKKANEN PENTTI, TOERMAELAE PERTTI, VAINIONPAEAE SEPPO, VIHTONEN KIMMO, KILPIKARI, JYRKI, MERO, MATTI, PAETIAELAE, HANNU, ROKKANEN, PENTTI, TOERMAELAE, PERTTI, VAINIONPAEAE, SEPPO, VIHTONEN, KIMMO
Applicants: MATERIALS CONSULTANTS OY
Application year: 1985
Main classification: A61B17
IPC codes: A61B17, A61L31