RO128477A2 - Bioresorbable self-tapping cannulated screw for ligament fixation - Google Patents

Abstract

The invention relates to a bioresorbable self-tapping cannulated screw made of a composite material of the polymer-ceramics type, i.e. poly-L-lactic acid and tricalcium beta-phosphate, for the fixation of soft tendinous tissues or bone-tendon-bone grafts during joint reconstruction surgery. According to the invention, the screw () comprises, at its distal end which represents the screw tip, a cone-shaped zone () provided with a double-pitch thread with three self-tapping channels () of constant depth, stretching all along the said zone. At the proximal end, the screw has a cylindrical shape () of a length which is equal with two thirds of its total length, provided with a double thread having a constant pitch allover its length, continued up to 1 mm from the proximal end (), so that the screw can be completely inserted into the bone. In the truncated cone-shaped part of the screw, the thread () is more aggressive in order to easily penetrate the cortical bone, while, in the cylindrical part, the thread () has a larger leading angle in order to prevent the graft damage. The screw is cannulated, having inside a hexagonal channel whose size is variable along the screw length.

Description

The invention relates to a bioresorbable cannulated self-tapping screw for ligament fixation made of polymer-ceramic composite material, usable for fixing soft tendon tissues or bone-tendon-bone grafts during joint reconstructive interventions.

Anterior cruciate ligament (ACL) reconstruction is a typical application for bioresorbable interference screws, this procedure involving either the use of a soft tissue (tendon) graft or a bone-patellar-tendon-bone graft [McGuire DA, Barber FA, Elrod BF, Paulos NO. Bioabsorbable interference screws for graft fixation in anterior cruciate ligament reconstruction. Arthroscopy 1999; 15: 463–473], [Weiler A, Hoffmann RF, Stahelin AC, Helling HJ, Sudkamp NP. Biodegradable implants in sports medicine: The biological basis. Arthroscopy 2000; 16: 305-321], Other applications include ligament repair procedures with bone graft fixation or tenodesis (ligament locking) procedures in sports trauma.

Interference fixation is one of the most commonly used methods of fixation in the reconstruction of the cruciate ligament. The surgical procedure involves the use of a tendon graft or with bone pills, inserted through the tunnels and fastened with screws inside the tunnels. The purpose of the interference screw is to mediate the relationship between the bone tunnel and the bone pill, while at the same time fixing the pill in the tunnel.

The use of bioresorbable interference screws raises several problems related to their tendency to be removed from the bone due to loads during the recovery treatments, the risk of fracture of the area at the tip of the implant or of thread deflection due to the small size, absorption sometimes incomplete due to poor blood flow to the bone. Thus, most of the bioresorbable screws made of polymeric materials (polylactic acid, polyglycolic acid) or biocomposites (polylactichidroxyapatite acid, polylactic acid-tricalcium phosphate), in order to prevent damage to the bone screw, require a separate procedure for preparing the implantation site, but it is tarodare Speaking of spongy bone, the surgical gesture of tapping is imprecise (the bone is tightened), creating difficulties in assessing the exact diameter of the screw required for stable ligament fixation.

In this context, the creation of a self-tapping screw from bioresorbable material seems to be a necessity dictated by the specific conditions for performing the surgical intervention. Avoiding additional implant preparation activities provides a significant advantage for orthopedic surgeons, as the surgical technique is laborious and complex. In this context, any additional activity means a risk of complications and prolongation of the operating time, elements that can be avoided if the screw variant described in the present invention is used.

In the scientific literature and other international patents related to this subject, several existing design variants for interference screws are presented. The differences between these variants are given by both the outer geometric shape (conical or cylindrical tronconic), the thread geometry and its pitch, as well as the shape of the inner channels (hexagonal, triangular, star). Biomechanical studies performed on several types of existing screws show that the fixing force of the system with interference screws has about the same value for similar types of screws, even if they come from different manufacturers or are made from different biomaterials. Also, it is emphasized that the type of screw, diameter and number of channels for self-tapping significantly influence the torsional strength and pull force of the bone screw [Current Concepts in ACL Reconstruction, Freddie H. Fu, Steven B. Cohen, ISBN : 978-1-55642-813-5, SLACK Incorporated NJ, USA] It has also been shown that at the same diameter of the tunnel, the quality of the fixing (which is assessed by the force of the pull) increases by 120% with increasing diameter. outer screw from 6.5 mm to 9 mm [Weiler A, Peine R, Pashmineh-Azar A, Abel C, Sudkamp NP, Hoffmann RF, Tendon healing in a bone tunnel: Pa I: Biomechanical results after

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Patent application

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• ν biodegradable interference fit fixation in a model of anterior cruciate ligament reconstruction in sheep, Arthroscopy, 2002; 18: 113-123].

Currently, several models of bioabsorbable interference screws for ligament reconstruction are known and used clinically (trade names for screws marketed by different companies in the field: Biocryl, Milagro, Phantom, Bioscrew, Sysorb, Matryx), made from different biomaterials (poly acid). -L-lactic PLLA, polyglycolic acid-PLGA, polylactic acid-hydroxyapatite composite, polylactic acid-tricalcium phosphate composite), with different geometries and sizes. The practice shows that these screws, although they have the desired characteristics of biocompatibility and are compatible with modern imaging techniques, present a lack of resistance to insertion in the spongy bone. Thus, for all these screws, the requirement for bone tapping before insertion remains a mandatory additional activity of the surgical technique, implying, depending on the quality of the anatomical bone structures, the use of a tarod or a dilator before implanting the bone screw.

Another existing variant is the iFix screw model, made of polyether-ketone (PEEK) and equipped with a single channel for self-tapping. In this screw model, the thread has a constant profile and pitch over the entire length, being provided with a connecting radius to avoid grafting. But this screw model has a major disadvantage, namely that the biomaterial from which it is made is not absorbable, being possible to modify its mechanical properties in time due to the deterioration of the material.

Further models of existing screws in international patents are described [US Patent 0198288 A1, US Patent 6589245 B1], Such a bioresorbable screw is provided with four channels for self-tapping, located on the distal trunk side of the screw, step the screw is constant, as is its profile, and in order to facilitate the insertion in the bone, the screw consists of two assembled parts, of different materials, which raises manufacturing problems, mechanical characteristics and different degradation rates. Also within the scope of the invention is also known a model of cannulated bioresobable screw, with a truncated geometric shape, but which is not self-tapping. Also, in another patent there is presented an interference screw model whose thread is different as a profile for the tip area with respect to the cylindrical area, but only in the sense that the profile on the distal side does not have a radius of connection, its purpose being that to facilitate the penetration of the screw into the bone, but this screw is not provided with channels for self-tapping.

The technical problem solved by the type of bioresorbable cannulated self-tapping screw of the present invention is the elimination of the need to prepare by tapping the insertion channel, both by using a composite bioresorbable material that confers mechanical properties that ensure the integrity of the screw during its insertion into the bone. , as well as a special design that guarantees self-tapping without damaging the bone or graft.

The bioresorbable cannulated self-tapping screw for ligament fixation according to the invention solves this technical problem by the fact that it is made of polymer-ceramic composite material, respectively poly-L-lactic acid and tricalcium β-phosphate, usable for fixing tendon or soft tissues. bone-tendon-bone grafts during joint reconstructive interventions. The screw is formed, on the distal side - the tip of the screw, from a conical area provided with a double pitch thread and with three channels for self-drilling having a constant depth and extending the entire length of this area. At the proximal end, the screw has a cylindrical shape of length equal to two thirds of its total length and provided with a thread with two starts. The thread of the screw has a constant pitch throughout its length and continues up to 1 mm from the proximal end, so that the screw can be fully inserted into the bone. The shape of the thread differs for the two areas of the screw, at the truncated side the thread is more aggressive to penetrate the cortical bone more easily, and at the cylindrical side, the thread has the greater angle of attack so as not to injure the graft. The screw is cannulated, having a hexagonal channel of different size present throughout the length of the screw to increase the mechanical strength during insertion.

The advantages of the invention are that the design proposed for the screw eliminates the need for the tapping operation of the insertion channel, and the mechanical characteristics of the material of its father during insertion.

which is made the screw allows to maintain i

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Other advantages include protecting the graft in which the proposed screw is fixed vis-à-vis its invasive action (related to the use of tendons grafts, which can be damaged by an overly aggressive profile of the screw thread, which would ultimately lead to fixation compromise).

The screw described in the invention, made of bioresorbable composite material, can be delivered sterile packaged and used in combination with a reusable screwdriver and a guide wire from Ni-Ti alloy.

Detailed description of the invention

The invention is further illustrated in connection with Figures 1-4 which represent:

- Fig.1, isometric view - interference screw and guide screw constructed and assembled in accordance with the principles of the present invention

- Fig. 2, side view of the cannulated self-tapping screw

- Fig. 3, isometric and orthogonal views of the cannulated self-tapping screw

- Fig. 4 shows an axonometric cross-section of the cannulated self-tapping screw

The bioresorbable cannulated self-tapping screw 1 for ligamentous fixation of bone or tendon tissue, according to the invention, has a complex design, self-tapping type, which can be manufactured by injection of powders or by rapid manufacturing processes and can be used in peri-articular ligament reconstructions, by means of a screwdriver 2 and a guide wire 3, as shown in Figure 1.

The outer geometric shape of the screw (figure 2) is described by two zones, one truncated 4 at the distal part of the screw - the tip of the screw, and the other cylindrical 6 at the proximal part - the head of the screw. The truncated area has a length approximately equal to one third of the total length of the screw. The conical profile makes the screw easy to insert, at the same time it ensures a higher fixation resulting from a gradually increasing diameter. Upon introduction, the screw engages in the cortical bone at the end of the bone tunnel and clogs almost the entire inlet, thus offering the possibility of guidance.

Inside the screw is cannulated (fig. 3A-D), the geometric shape of the channel 10 being hexagonal along its entire length. Semicircular channels 11 are also provided, at the intersection of the flat faces of the hexagon, in order to reduce the concentrated tension at this level and thus avoid breaking the screw during insertion. The constructive shape of the screw provides that towards the conical tip of the implant we have a hexagonal cannulation with another size step, smaller distally 12, so that the thickness of the tip associated with the properties of the composite biomaterial used to prevent rupture during insertion maneuvers. The inner channel continues throughout the length of the screw, allowing the use of a guide wire 3 of Ni-Ti alloy for further guidance of the insertion of the screw into the bone.

The screw is provided on the outside with a thread with two starts, with a constant pitch along its length, which continues up to 1 mm from the proximal end, so that it can be inserted completely into the bone. The proximal end 7 of the screw is rounded to avoid graft injury and at the same time reduce conflict with peri-articular tissues if insertion is incomplete due to implant position.

On the outer trunk area 4 of the screw there are provided three channels for self-tapping 5, distributed at 120 °, which extend along the entire length of the truncated part and which have a constant depth.

The geometry of the thread is different on the two areas of the screw in order to improve the contact with the bone and, consequently, the resistance to tearing. Thus, the thread depth is greater for the cylindrical area compared to the truncated one, ensuring better screw placement in the cortical bone. Also, on the trunk side the thread 8 is more aggressive to penetrate the cortical bone more easily, and on the cylindrical side the thread 9 has a smaller angle of attack so as not to injure the graft. The transition from one shape of the thread profile to another is made progressively, without the introduction of additional sharp edges. Because currently the length of the femoral tunnel is 25-30 mm and the diameter is 8-10 mm (8mm for quadruple graft, semitendinosus-gracilis and 10mm for bone-tendon-rotulian graft), it is recommended âX

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s execution of the screws in the following types: 8mm x 30mm, 9mm x 30mm, 10mm x 30mm, 11mm x 30mm, 8mm x 35mm, 9mm x 35mm, 10mm x 35mm, 11mm x 35mm.

The screw thread is provided with connecting radii to avoid injury to the graft or bone.

The additional guide system also includes a screwdriver 2 with hexagonal - negative profile of the screw channel and having a cannulated hole along its entire length, about 1.2 mm in diameter to allow the passage of guide wire 3 from Ni-Ti alloy.

Guide screwdriver 2 and guide wire 3 are designed to be reusable, being sterilizable like other medical instrumentation metal parts.

The composite biomaterial used in the execution of this screw is based on poly-lactic acid and tricalcium β-phosphate (ΡΙ_Ι_Α-βΤΟΡ) and has all the attributes of biofunctional performance and NMR compatibility (nuclear magnetic resonance).

The screw is recommended to be made of composite material based on poly-L-lactic acid (70%) and tricalcium β-phosphate (30%). Poly-L-lactic acid decays slowly and is generally better tolerated than other resorbable polymeric biomaterials (such as polyglycolic acid), and the addition of a reinforcing element such as bioactive ceramic materials (such as tricalcium phosphate or hydroxyapatite) brings more many advantages: the ceramics used have an osteoconductive character, increase the adhesion of the screw to the bone, can buffer the products resulting from the acid degradation of the polymer and thus reduce the possible adverse reactions. Another advantage of the composite biomaterials used in the execution of the screws is that the mechanical, biological and physiological properties can be adapted to the requirements of clinical functionality much better than in the case of the use of individual homogeneous biomaterials.

The mechanical properties of the PLLA ^ TCP resorbable composite material and the specially profiled screw tip make it easy to implant into the bone, without requiring the use of a tar or cutter. The digital three-dimensional model of the screw was obtained by computer-aided design, its design being verified using the specific analysis techniques assisted by the finite element method, by varying its characteristic parameters (angles of thread geometry, thread pitch, angle at the tip screw, thread pitch depth, number of channels for self tapping).

Regarding the clinical use of the screw described in the invention, it is implanted with the aid of a reusable screwdriver and a guide wire of NiTi alloy (Figure 1). The truncated shape of the distal part of the screw acts as an element of interference between the soft tissue graft or the bone graft and the perforated tunnel wall. Thus, when fully inserted, the threaded screw acts as a wedge that prevents the ligament graft from slipping out of the tunnel. In the case of bone fixation procedures, the screw is inserted into the bone part of the graft, allowing the soft tissue on the lateral half to integrate into the surrounding bone tissue. Due to the specific design, both the body and the screw thread contribute to the graft pressing in the bone tunnel. The 1.5mm depth of the screw thread of the invention ensures a larger volume of bone fixed in the thread, which favors the resorption of the composite biomaterial from which the screw is performed and of the bone integration, an extremely important aspect especially for the osteoporotic bone.

The method of clinical use of the interference screw is relatively simple because it does not require special accessories for implantation or additional procedures (such as tapping), with sufficient screwdriver and guide wire. The only intraoperative step required during the preparation for graft fixation is to locate and forgo the fixation tunnels within the femur and tibia [Marinescu R., Lăptoiu D., Reconstructive surgery of the anterior cruciate ligament - arthroscopic techniques, Carol University Publishing House Davila, 2004, Bucharest ISBN 973-7918-95-9],

The screws made will be packed in special polyethylene double bags and sterilized by gamma irradiation at 25kGy, in boxes with carbon snow [J.C. Middleton and A.J. Tipton, "Synthetic Biodegradable Polymers as Medical Devices" Medical Plastics and Biomaterials Magazine, 1998], [Bernkoft, M., Sterilization of bioresorbable polymer implants, Medical device technoloay, May / June 2007, JK 26-28],

Claims (3)

claims 1. Bioresorbable cannulated self-tapping screw, for ligament fixation, made of composite biomaterial, usable for fixing soft tendon tissues or bone-tendon-bone grafts during joint reconstructive interventions, characterized in that said composite biomaterial is of polymer-ceramic type respectively poly-L-lactic acid and tricalcium phosphate, and is formed, at the distal part - the tip of the screw, from a conical area (4) provided with double-step thread and three channels for self-tapping ( 5) having a constant depth and extending the whole length of this area, at the proximal end the screw having a cylindrical shape (6) of length equal to two thirds of its total length and provided with a thread with two starts, the thread of the screw having a constant pitch along its entire length and continuing up to 1 mm from the proximal end (7), so that the screw can be inserted completely in the bone, the shape of the thread being different for the two areas of the screw, at the truncated side the thread (8) being more aggressive to penetrate the cortical bone more easily, and at the cylindrical side, the thread (9) having the greater angle of attack for not to injure the graft, the screw being cannulated, having a hexagonal channel with different size on the length of the screw. 2. Screw, according to claim 1, characterized in that, at the truncated side, it is provided with three channels for self-tapping, evenly distributed, at 120 ° to each other, extending over the entire length of the truncated area. 3. Screw, according to claim 1 or 2, characterized in that it is manufactured in the following types: 8mm x 30mm, 9mm x 30mm, 10mm x 30mm, 11mm x 30mm, 8mm x 35mm, 9mm x 35mm, 10mm x 35mm , 11mm x 35mm.