Anatomical fixation implant

IS 2 255 258 T3

DESCRIPTION

Anatomic fixation implant.

This invention relates, in general terms, to a surgical implant (nail) for fixation of body tissue and, more particularly, to an implant for fixation of tissue to a bone according to the preamble part of claim 1 of The patent. Such an implant is known, for example, from EPA-0 611 557.

In procedures such as rotator cuff surgery or labrum tear fixation surgery and hand tendon surgery, tendons or other soft tissues are attached to the bone. Tendons or other tissues are often attached to the bone by passing soft tissue through holes formed in the bone and suturing the tissue in place. Another method of attaching soft tissue to bone employs a fixation device that essentially tacks the tendon to the bone. Unless the tendon or other soft tissue is fully immobilized, the fixation device must be securely embedded in the bone to hold the tendon or other soft tissue immobile relative to the bone surface, resisting forces intended to pull on the tendon. or other soft tissue by pulling it away from the surface of the bone until the tendon or soft tissue has been attached to the bone. Another method of attaching the tendon or other soft tissue to the bone uses a fixation device (suture anchor) with an attached suture. Again, the fixation device must be securely embedded in the bone to resist forces that tend to pull tissue away from the bone surface.

Bioabsorbable soft tissue fixation devices are frequently used because they biodegrade after the tissue has healed and therefore do not cause long-lasting tissue problems and do not require a removal operation.

However, the bioabsorbable fixation implants currently known in clinical use have encountered several problems, especially in the fixation of the labrum or labrum tear. According to references EE Berg and W. Oglesby, J. Shoulder & Elbow Surg. 5, pages 76-78 (1996) and P. Kavli et al. Acta Orthop. Scand. 272, page 24 (1996), the use of bioresorbable tacks and staples in surgical fixation of shoulder instability led to recurrent instability and looseness, causing healing problems. The bioabsorbable nails or studs of the type of bolts that are stronger than staples, have symmetrical heads that are anatomically inappropriate for the fixation of the labrum or impeller tear as can be seen in the schematic Figure 1. The symmetrical head of the tack does not effectively correspond to the surface of the bone because the angle between the head of the tack and the stem is 90 degrees, while the angle between the surface of the bone and the stem is less than 90 degrees. Additionally, this part of the symmetrical head (on the right side of the stem in Figure 1) which does not support the soft tissue, is unnecessary for healing and can irritate the edge of the joint cavity.

US Patent 5,634,926 describes a bone or soft tissue fixation implant having a leg part (stem) and an elongated end part (head) arranged such that the longitudinal axis of the leg part is oriented at an angle of 15 to 55 degrees relative to the surface corresponding to the enlarged end. However, this implant is expressly restricted to those applications where no force is exerted on the implant that will have a tendency to come out of the bone. This implant does not effectively grip the hole drilled in the bone to resist pulling forces because the leg portion is constructed in such a way that it can be easily pulled in the direction parallel to the longitudinal axis of said hole. Therefore, the high muscular forces that carry a labrum tear during healing would pull the leg part at least partially from the hole drilled during healing, causing serious complications.

Another problematic feature of the implant of US Patent No. 5,634,926 is the fact that the enlarged end, even if not symmetrical, still protrudes in all directions from the leg portion. Thus, the part of the end that is directed towards the edge of the joint cavity in the labrum fixation or impeller is ineffective and unnecessary for the soft tissue fixation and can cause irritation at the edge of the gasket cavity. .

WO 97/18762 presents a substantially bioabsorbable implant for fixation of human tissue comprising: an elongated stem having a longitudinal axis, an outer surface and the first end, said first end having the first and second sides, said first end comprises a corresponding surface projecting from said outer surface of said elongated stem, the said corresponding surface oriented at an angle of less than 90 degrees with respect to said longitudinal axis of said stem.

This implant is a fastening means for attaching one piece of human tissue to another piece of human tissue. It is used in human tissues by means of the tubular installation tool that places the aforementioned implant at its front end. By this technique the implant cannot be inserted into a bone for the fixation of the tissue to a bone.

Patent EP-A-0 611 557 presents a substantially bioabsorbable implant for a substantially bioabsorbable implantation of human tissue fixation, composed of: an elongated stem having a longitudinal axis, an outer surface and the first end, said first end having the first and second sides, said first end comprises a corresponding surface projecting from the outer surface of said elongated stem, the said corresponding surface oriented at an angle of less than 90 degrees with respect to said longitudinal axis of said stem, wherein said implant is an implant for fixing human tissue to a bone and has a cannulated stem and said corresponding surface has a width in the direction transverse to the longitudinal axis of said stem that is greater than the width of said stem.

The objective of the present invention is to provide a bioabsorbable fixation implant that is capable of safely and effectively holding the rupture of the labrum or labrum tissue to the bone and / or the super2

ES 2 255 258 T3 folds from cartilage and is designed to optimize fixation ability and avoid unnecessary mass and mechanical irritation of the joint of the shoulder tissues.

It is the main objective of the present invention to provide a fixation implant to achieve effective surgical fixation of soft tissue or tendon tissue to bone.

Another object of the present invention is to provide a fixation implant for fixation of the labrum or rim tissue to the bone and / or the cartilage surface in which the size of the fixation implant is minimized.

Still another object of the present invention is to provide a fixation implant that can be made of materials that are absorbed by the human body over time.

There is also another object of the present invention and that is to provide a fixation implant which can be manufactured economically and which can be used effectively and safely in the fixation of soft tissue to bone.

In summary, the present invention provides a fixation implant that is particularly suitable for use in the fixation of human soft tissue to bone. The fixation implant generally includes at least one stem configured to fit securely within the hole formed in the bone. The stem is of sufficient length relative to the inside diameter of the hole and, in some preferred embodiments, has locking protrusions, such as threads, ridges, or barbs that prevent removal of the stem from the hole in the bone when different types of forces as torsional forces or bending forces are applied to the implant. The stem is cannulated and is generally cylindrical in shape, however, in various embodiments of the present invention, different cross-sectional shapes can be used. In the present invention, the implant has a bent, flattened end portion that protrudes from only one side of the stem. On the other side of the implant the outer surface of the stem and the end part that protrudes from the smooth surface without any protrusion. This smooth surface at the end of the implant prevents irritation of the surrounding tissue. The end portion has a corresponding surface configured to grasp a portion of the soft tissue surrounding the hole between the bone and the corresponding surface. The longitudinal axis of the stem is oriented at an angle of less than 90 degrees relative to the corresponding surface. In this way, the implant anchors the soft tissue, such as the labral tissue, to the bone.

Additional objects and features of the present invention will be more readily apparent on the basis of the following detailed description and the appended claims when considered in conjunction with the drawings.

Brief description of the drawings

Figure 1 is a schematic cross-sectional view of a prior art fixation implant (tack or screw) used in the fixation of soft tissue to the surface of a bone.

Figures 2A and 2B are front and side schematic views, respectively, of the fixation implant according to the present invention. Figure 2C is a schematic cross-sectional view of the fixation implant according to the present invention used in the fixation of soft tissue to the bone surface.

Figures 4A-4E are cross-sectional, enlarged and longitudinal views of the implants of the present invention showing some preferred directions of molecular orientation and / or reinforcing elements.

Figures 5A and 5B are longitudinal cross-sectional views of implants that can be easily removed from the hole drilled in a bone.

Figure 5C is a longitudinal cross-sectional view of an implant of the present invention; This implant can be tightly fitted within the hole drilled in the bone.

Detailed description of the invention

Reference is made to Figure 1 in which the bioabsorbable implant (screw or tack) 1 is shown. This implant comprises a stem 1a and a symmetrical head 1b. The stem of the implant 1a has been inserted into a drilled hole 2a in the bone 2 and the implant 1 fixes the soft tissue 3 on the surface of the bone 2 around the stem 1a and below the head 1b. The implant 1 has a conventional symmetrical head 1b whose diameter is greater than the diameter of the stem 1a. Physiological forces that have a tendency to pull the soft tissue out of its fixed position are directed to the right in Figure 1. Therefore, only the left part 1c of the head 1b in Figure 1 effectively holds the tissue. soft in place; the right part 1d of the head 1b has no beneficial effect on soft tissue fixation. In fact, the right side 1d of the head 1b can cause damage by irritation near the tissues within the shoulder joint. As can be seen in Figure 1, the corresponding underside of the prior art implant does not have good contact with the soft tissue to be treated. This occurs because the corresponding underside of the implant is at right angles to the implant stem, but the angle between the bone surface surrounding the hole and the implant stem is less than 90 °.

Figure 2A and Figure 2B present a side and front view, respectively, of an embodiment of a bioabsorbable implant 4 of the present invention. The implant has an elongated shaft part 4a, preferably equipped with the protrusions 4e, such as threads, ridges or barbs. The stem 4a is cannulated, that is, it contains a longitudinal hole 4b. Such cannulation helps in arthroscopic insertion. The implant 4 has a flattened and bent end portion 4c protruding from only one side of the stem 4a so that on the other side of the stem 4a the outer surface of the stem 4a and the protruding end portion 4c form a smooth surface 4d. The corresponding flattened surface 4f of the end 4c is oriented at an angle β of less than 90 ° relative to the longitudinal axis of the stem 4a. The width "w" of the end part 4c is greater than the diameter "d" of the core of the stem part 4a.

As shown in Figure 2C, the bioabsorbable implant 4 of the present invention is inserted into the drilled hole 5a in the bone 5. The implant 4 fits the soft tissue 6 to the surface of the bone 5 around the hole 5a and below the extreme part 4c. To ensure that the implant is firmly positioned in hole 5a, stem 4a has

ES 2 255 258 T3 the maximum width larger than the inner diameter of said drilled hole 5a in the bone 5. On one side of the implant 4 the outer surface of the stem 4a is gently bent up to the top of the implant. This smooth surface area, 4d, does not have protrusions and therefore will not irritate the surrounding tissue. The end part 4c has no corresponding surface 4f configured to grip a part of the soft tissue 6 around said hole 5a between the bone 5 and the end 4c. The longitudinal axis of the stem 4a is oriented at an angle of less than 90 degrees relative to the corresponding surface 4f. The stem has a longitudinal hole 4b within it. Such cannulated implants are especially advantageous because they can be inserted into the hole drilled along the guidewire, with minimally invasive, arthroscopic surgical techniques.

In a preferred embodiment, the bioabsorbable implants of the present invention are made of absorbable polymers and copolymers or blends of polymers and their alloys. This can be achieved with the melt molding methods known in the prior art. It is also possible to use the techniques of US Patent No. 4,743,257 to mold the absorbable fibers and the binder polymer together in a compression or injection mold to create a structure that is preferably self-reinforcing or that is fiber-reinforced. The implants of the present invention can be molded in a single compression molding cycle. The molding can be done, for example, with an injection molding technique by injecting the molten phase of the polymer into the cavity of the mold having the shape of the implant of the present invention and by cooling the mold so that the molded implant solidifies and can be removed from the mold. The mold cavity can include a variety of reinforcing elements such as a reinforcing fiber bundle, cord, fabric, etc. or the short or long individual reinforcing fibers. Any protrusion on the surface of the stem can be formed within a cavity of the mold or it can be machined onto the surface of the implant after the molding cycle.

The oriented or self-reinforcing structure of the implants of the present invention can also be created by extrusion or by injecting the absorbable polymeric injection solution through an appropriate die or into an appropriate mold at high speed. and pressure. When cooling occurs under the proper conditions, the solution flow orientation remains in the solid material as an oriented or self-reinforcing structure. In an advantageous embodiment, the mold may be in the shape of the implant but it is also possible to manufacture the implants of the present invention by machining and bending (possibly using heat) the injection molded or extruded semi-finished products.

It is also advantageous to make implants from bioabsorbable polymeric materials, molded from melt, in a solid or compressed state, which are described, for example, in Patent Nos. 4,968,317 or 4,898,186.

The reinforcing fibers of the implant can also be ceramic fibers such as bioabsorbable hydroxyapatites or bioactive glass fibers. Such reinforced and bioabsorbable ceramic materials are described, for example, in European Patent Application No. 0146398 and in WO 96/21628.

The implants of the present invention oriented or reinforced by themselves, or reinforced in any other way, can be manufactured by molding the reinforcement of the fiber polymer matrix until obtaining the final product in a mold whose mold cavity has the shape of the final product. Alternatively, the final shape can be mechanically machined (possibly also using heat) in a preform mold such as a string formed in a molten or solid-state mold, as described, for example, in the Patent US No. 4,968,317.

In some advantageous embodiments of the present embodiment of this invention the orientation and / or reinforcing elements of the reinforced structure itself are mainly oriented in the direction of the long axis of the implant stem (Figure 4A) and can be smoothly converted and continues at an end portion in the form of a hook or hoe, as shown in the schematic cross-section of Figure 4E. The reinforcing elements can extend into any protrusion or ridge of the implant stem (Figures 4B and 4C) and in any barb of the end portion. In another embodiment of the present invention, the reinforcing elements are spirally wound around the long axis of the implant (Figure 4D). Additionally, different orientations of the reinforcing elements in elongated samples that are familiar according to composite technology, can be applied to the present invention.

However, a characteristic of the orientation, fiber reinforcement, or self-reinforcing implants of the present invention is that many of the reinforcing elements are oriented in such a way that they can effectively carry different external loads (such as torsional loads). , bend and net load) that are directed to the tissue to be cured (for example, loads on the shoulder joint caused by movements of the muscles in the patient's arm and / or upper body).

According to the advantageous embodiment of the invention, the implant or the layer of the special coating on its surface may contain one or more bioactive substances, such as antibiotics, chemotherapeutic substances, angiogenic growth factors, substances that accelerate wound healing. , growth hormones and the like. Such bioactive implants are especially advantageous in surgical use because they contribute chemically to the healing of damaged human tissue in addition to the provision of mechanical support.

The oriented and / or reinforced materials of implants typically have fracture strength of 100-2000 MPa, bending forces of 100-600 MPa and shear strength of 80-400 MPa. Additionally, they are usually stiff and hard. These mechanical properties are superior to those of absorbable polymers that are not reinforced and that usually show forces between 40 and 100 MPa and are additionally either very flexible.

ES 2 255 258 T3 or brittle (see, for example, Ref .: S. Vainionpaa, P. Rokkanenen and P. Tormala, "Surgical Applications of Biodegradable Polymers in Human Tissues", Progr. Polym Sci., 14, pages 679-716 (1989).

According to the advantageous embodiment of the present invention the end portion may be too bent in relation to the angle "a" between the corresponding surface of the bone and the hole drilled in the bone. This means that the angle "P" in Figure 2 is smaller than the anatomical angle in Figure 1. When the implant is pushed strongly into the hole drilled in the bone, the angle 3 opens slightly to match the bone surface and the compressive force develops within the head of the implant. This compression is advantageous for the adjustment of the soft tissue to the bone.

The implants of the present invention can be sterilized by any well-known sterilization technique depending on the type of material used to make the implant. Appropriate sterilization techniques include thermal sterilization, radiation sterilization such as cobalt 60 or electron beam radiation, ethylene oxide sterilization, and the like.

After the foregoing description of the present invention and some specific embodiments thereof, it will be readily apparent to those skilled in the art that many variations and modifications can be made in this invention without departing from the concept and scope thereof. . The non-restrictive example that follows presents the manufacture and properties of some embodiment of the implants according to the present invention.

Example 1

A simple extrusion machine was used to manufacture poly-L / DL-lactide (molar ratio L / DL 70/30, inherent viscosity 5.8 dl / g, trade name Resomer LR 708, manufacturer Boehringer Ingelheim, Germany) a continuous cylindrical billet 8.6 mm thick, which was cooled to room temperature. The cooled billet was heated to 70 ° C and subsequently extracted to the extraction index of 3 according to PCT / FI 96/00511, Example 1, the entire presentation of which is incorporated herein by reference, in order to increase the strength and ductility of the material. The final oriented part had the diameter of 5 mm. The oriented part was cut into bars 40 mm long. A 1.1 hole was drilled through the bars along the long axis of the bars. A 10 mm long segment at the end of the bars was placed between two heated steel plates (T = 80 ° C) which were compressed to flatten the end of the bar to a thickness of 1 mm. At the same time the uncompressed part (stem) of the bar was bent relative to the flattened part so that the 60 ° angle was formed between the corresponding surface of the flattened part and the long axis of the stem. The hole drilled within the stem was opened by drilling through the hole within the stem and through the joint between the stem and the end portion with the 1.1mm diameter drill head.

The right stems of the implants were shaped by turning to the shapes shown in Figures 5A-5C. In the case of Figure 5A, the stem was turned to receive a smooth-surfaced, cylindrical shape, with the uniform diameter of 3.2mm. In the case of Figure 513, the stem was turned to receive a smooth-surfaced cylindrical shape with segments having a diameter of 3.2 mm at each end of the stem and a 10 mm long segment in the middle of the stem having a diameter of 3.6mm at its center tapering to 3.2mm at each end. In the case of Figure 5C, the stem was provided with threads by turning the spun profile onto the surface of the stem. The inner wire diameter was 3.2mm and the outer wire diameter was 3.6mm. The distance between the threads was 1 mm and the angle of inclination of the threads was 25 °.

The fixation capacity of the implants described above was tested with disengagement tests on porous bovine bone. Holes drilled through the cortical bone have been made into the porous bone in the distal part of the bovine femur with a 3.2 mm diameter drill bit. The cortical part of the drill hole was widened with the 4.5 mm drill head. The implants were threaded into the drilling holes with a special tube-like applicator whose cross section corresponded to the implant cross section. A loop of steel wire (1.5 mm thick) was left at the angle between the bent end and the stem for the disengagement test. The implants were disengaged from the drill hole by fixing the steel wire loop to one jaw of a mechanical torque testing machine and by fixing the bone to another jaw. The maximum force to pull the implant out of the drilled hole was measured. Six parallel samples were tested.

The disengagement force for the implants in Figure 5A was 40 ± 20 N, for the implant in Figure 5B it was 85 ± 30 N and for the implants in Figure 5C it was 170 ± 40 N.