Implantable system with elastic components

Abstract

System for controlled stress on a reconstructed or renaturalized ligament of a human or animal body, comprising an anchoring element (10) for implantation into a first bone (41), at least one connecting element (20) and a retaining element (30) for holding the at least one connecting element (20) on a second bone (51), wherein at least one elastomer body (115, 117, 119) is arranged in the anchoring element (10) and the elastomer body (115, 117, 119) is arranged in the interior (102) of an outer body (103) of the anchoring element (10) between a contact surface (101) on the bottom (105) of the outer body (103) and a sleeve (114) to which the connecting element (20) is fixed, wherein the sleeve (114) is immovably fixed to the outer body (103) and wherein at least one elastomer body (125) is arranged in the connecting element (20), wherein the elastomer body (125) has a smaller modulus of elasticity than the connecting element (20), wherein the connecting element is tubular and the elastomer body (125) is arranged in a section of an axial cavity (122) of the tubular connecting element (20).

Description

[0001] The invention relates to an implantable system with elastic components for controlled stress on a reconstructed or renaturalized ligament of a human or animal body.

[0002] The human knee joint is stabilized by the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) within the knee joint. In a twisting injury of the knee, these two ligaments, particularly the ACL, are overloaded, resulting in a rupture or tear. If conservative treatment attempts or attempts to repair the ACL fail to stabilize the injured knee, the ACL is often removed, and knee stability is restored with a tendon graft or a synthetic ligament. This procedure permanently removes the damaged natural ligament from the knee joint. However, the artificial replacement ligament can only partially fulfill its function. In particular, sensation is completely lost, leading to overload and thus increased wear and tear on the artificial ligament prosthesis.

[0003] This fact, along with the self-healing tendency of every ligament in the human body, is utilized in a system described in WO 2010 / 124760 A1 for the controlled stressing of a reconstructed or renaturalized ligament. During the healing phase, a connecting element is attached to the two bones to be joined by an anchoring or retention element. This relieves stress on the natural ligament, thus enabling its natural fusion. The anchoring element incorporates a damping mechanism to ensure uniform tensile stress within the system and to allow flexion of the treated knee. Once the natural ligament has healed, the implantable system has fulfilled its function and is no longer required. WO 2010 / 124760 A1 discloses that one or more components of the system are made of a bioresorbable material and dissolve on their own.

[0004] In particular, components of such an implantable system made of metallic material are described by patients as bothersome and painful, and therefore must be surgically or arthroscopically removed after the ligament has healed. Such a procedure carries risks and discomfort for the patient and incurs additional costs.

[0005] DE 10 2009 051 367 A1 discloses an anchoring element in which a spring is arranged, and this spring is located inside an outer body of the anchoring element between a contact surface of the outer body and a sleeve to which the connecting element is fixed. However, this document does not mention that, according to the present invention, an elastomer body is used instead of a spring, and that the sleeve is fixed immovably to the outer body. Since, according to this document, in all embodiments a spring can be compressed by means of a movable sleeve, and an immovable sleeve would not allow any compression of the spring at all, it is in no way suggested to a person skilled in the art to provide an immovable sleeve based on this document.

[0006] US 2010 / 0286775 A1 discloses a different solution with an anchoring element. However, this document does not disclose an anchoring element in which at least one elastomeric body is arranged, and the elastomeric body is located inside an outer body of the anchoring element between a contact surface of the outer body and a sleeve to which the connecting element is fixed, with the sleeve being immovably fixed to the outer body. Instead, this document describes a first and second end with holes for receiving screws suitable for fixing the prosthesis to the musculoskeletal tissue at the first and second ends. None of the embodiments in this document show the fixation of the prosthesis by means of an anchoring element and a retaining element for holding the connecting element.The object of the present invention is therefore to construct as many components as possible of the implantable system from a material that is well tolerated by the human body and causes minimal irritation or pain when in the patient. The implantable system should exhibit an elasticity similar to that of a natural ligament.

[0007] Although US 4,187,558 A discloses an implantable connecting element, the document does not in any way teach an anchoring element in which at least one elastomeric body is arranged within the interior of an outer body of the anchoring element, between a contact surface of the outer body and a sleeve to which the connecting element is fixed, with the sleeve being immovably fixed to the outer body. This document merely describes a first and second end of the connecting element for fixation, which is passed through buttonholes and knotted. None of the descriptions in this document show the fixation of the prosthesis by means of an anchoring element and a retention element for holding a connecting element.

[0008] Further relevant state of the art is taught by EP 0 249 346 A2.

[0009] The problem is solved by the system according to claim 1. Advantageous embodiments of the system according to the invention are specified in the dependent claims.

[0010] The system according to the invention for controlled stress on a reconstructed or renaturalized ligament of a human or animal body comprises an anchoring element for implantation in a first bone, at least one connecting element, and a retaining element that fixes the at least one connecting element to a second bone. According to the invention, an elastomeric body is arranged in the anchoring element and / or in the connecting element and exhibits a defined elastic effect through the interaction of the elastomeric body with the anchoring element or the connecting element.

[0011] By selecting and composing the materials of the elastomer body, a wide range of elastic moduli can be achieved. Through the interaction of the elastomer body with the anchoring element and the connecting element, favorable material and structural combinations can result in an elasticity profile of the system similar to that of a natural ligament. Furthermore, many elastomers are biocompatible, meaning they have no harmful effects on human or animal tissue. Their deformability makes them far less irritating, allowing them to remain in the body even after the ligament has healed.

[0012] Advantageously, the elastomer body is made of polyethylene and / or polyester and / or polyurethane and / or silicone. These materials have biocompatible properties when used in the human body and also possess favorable elastic behavior.

[0013] When an elastomer body interacts with a fastener, it is advantageous for the elastomer body to have a lower modulus of elasticity than the fastener. This means that at low tensile stress on the fastener, the modulus of elasticity of the elastomer dominates, while at high tensile stress, the significantly larger modulus of elasticity of the fastener material dominates. Thus, the strain characteristic of the fastener interacting with the elastomer body corresponds to the strain characteristic of a natural band.

[0014] It is particularly advantageous if the connecting element is braided and / or knitted, spun and / or twisted and / or woven from a plurality of first individual fibers, and each first individual fiber forms an angle τ between 5° and 85° with respect to the longitudinal axis of the connecting element. This allows the connecting element to elongate in the axial direction and achieve an elastic effect, even if the individual fibers themselves are made of a non-elastic or only very slightly elastic material.

[0015] Advantageously, the connecting element is tubular in shape, and the elastomer body is arranged in a section of the axial cavity of the tubular connecting element. The elasticity curve, also called the strain curve, of such a combination exhibits a progressive profile, since the large deformation increases the pressure cross-section and the local stress concentration, also known as the strain factor. Additionally, the progressive profile of the strain curve is influenced by the angle at which the individual fibers of the connecting element are woven, braided, spun, twisted, and / or knitted with respect to its longitudinal axis. With increasing tensile load, the elasticity profile of the elastomer body initially dominates, as it is determined by the radial pressure of the tubular connecting element on the elastomer body.Simultaneously, the individual fibers of the connecting element align from an angle τ to the longitudinal axis without tensile load to an angle of almost 0° to the longitudinal axis under high tensile load. The combination of connecting element and elastomer body can no longer expand further, and its elasticity decreases significantly.

[0016] A similar elongation characteristic is exhibited by a connecting element in which the elastomer is formed as a plurality of second individual fibers and is spun and / or knitted and / or woven and / or twisted and / or braided with a plurality of first individual fibers to form a connecting element.

[0017] It is advantageous if the individual fibers contain a polymer, particularly polyethylene and / or polyester, and the connecting element is formed from a plurality of individual fibers, particularly polyethylene and / or polyester. These polymers exhibit a relatively high modulus of elasticity, so that after stretching the fiber network, the elasticity of the combination is significantly increased. Furthermore, these polymers are biocompatible and therefore suitable for implantation into the body.

[0018] It is also advantageous if an elastomer body is arranged as a damping device inside the outer body of the anchoring element, between a contact surface of the outer body and a sleeve. The connecting element is fixed to the sleeve and leads out of the anchoring element through an opening in the contact surface of the outer body. The elastomer body thus takes on the function of a damping element and can, for example, replace an arrangement of metallic springs.

[0019] It is advantageous if the sleeve is movably mounted within the outer body. When tensile stress is applied to the connecting element, the movable sleeve presses the sleeve itself against the elastomer body, which is itself fixed in place by contact with the anchoring element, thus compressing the elastomer body.

[0020] It is particularly advantageous if the connecting element is arranged in an axial recess in the elastomer body. When the elastomer body is compressed, it also expands in the axial direction, clamping the connecting element in place. This results in a further significant increase in the modulus of elasticity of the combination of anchoring element and elastomer body.

[0021] It is also advantageous if the connecting element is helically or spirally guided around the circumference of the elastomer body. When the connecting element is subjected to tensile stress, a radially inward force acts on the circumference of the elastomer body, compressing it. The stiffness of the elastomer body thus results in a damped elongation of the implantable system. Here, too, the compressibility of the elastomer body decreases with increasing constriction, and the modulus of elasticity increases with increasing compression. If the sleeve is movably arranged within the connecting element, an additional compression in the axial direction is exerted.

[0022] It is also advantageous if the sleeve is fixed immovably to the outer body, especially if the spring curve of the system is not to be influenced by additional axial compression.

[0023] It is further advantageous if the elastomer body has circumferential grooves that do not run parallel to the longitudinal axis of the elastomer body and the connecting element is guided in these grooves. These grooves prevent the connecting element from slipping and ensure a controlled point of pressure application to the elastomer body. Furthermore, such an arrangement simplifies the assembly of the anchoring element and / or the threading of the thread through the anchoring element.

[0024] An elastomer body formed as a plurality of tongue-shaped protrusions is also advantageous. These protrusions are arranged alternately on opposite sides, directed inwards from the inside of the outer body of the anchoring element and radially overlapping. The connecting element is guided in the space between the protrusions. When tensile stress is applied to the connecting element, the tongue-shaped protrusions of the elastomer body deform in the direction of the tensile force. As the deformation of the protrusions increases, the distance between them decreases, and the thread becomes trapped between them. This results in a significant increase in the modulus of elasticity.

[0025] It is advantageous for the elastomer body to have a cylindrical shape. The elastic modulus and compressibility of the elastomer body depend strongly on its shape. The cylindrical shape enables a uniform radial inward force transmission. It also allows for good force transmission in the axial direction.

[0026] The invention will be explained in more detail below with reference to exemplary embodiments and the drawings. The drawings show: Fig. 1 a system according to the invention implanted in a knee joint in schematic representation; Fig. 2 a schematic representation of a strain characteristic of a soft biological tissue compared to other materials; Fig. 3A a first embodiment according to the invention of a connecting element with an elastomer body in schematic representation; Fig. 3B a second embodiment according to the invention of a connecting element with an elastomer body in schematic representation; Fig. 4 a sectional view through a first embodiment of an anchoring element according to the invention with an elastomer body; Fig. 5 a section through a second embodiment of an anchoring element according to the invention with an elastomer body and Fig. 6 a section through a third embodiment of an anchoring element according to the invention with a tongue-shaped elastomer body.

[0027] Corresponding parts are marked with the same reference symbols in all figures.

[0028] Fig. Figure 1 shows the system 100 according to the invention inserted into a flexed human knee joint. In this embodiment, the anchoring element 10 is screwed ventrally into the proximal region of the tibial bone 50, to which a first bone tunnel 51 connects, leading to the joint space 60. A narrow second bone tunnel 41 is drilled through the adjacent distal end of the femur 40. The connecting element 20 is fixed to a retaining element 30 in this tunnel. The retaining element is supported on the outer surface of the femur 40. The connecting element extends through the second bone tunnel 41, across the joint space 60 and through the first bone tunnel 51 to the connecting element, where it is secured.

[0029] Fig. Figure 2 shows a diagram with strain curves of different materials, plotting the applied stress at a specific strain. Curve 71 represents the typical strain curve of soft biological tissue, such as a human ligament. Spring curve 72 was recorded on a rubber-elastic polymer, and curve 73 on tempered steel. As the diagram shows, elastomers exhibit a progressive strain curve similar to that of soft biological tissue. The modulus of elasticity and the damping constant, indicated by the slope of the curve, show a similarly flatter profile at low strain. However, the progression only begins at higher strains and with reduced strength. Metallic elements, such as tempered steel, on the other hand, exhibit a modulus of elasticity that closely resembles the spring curve in the latter, progressive range.

[0030] Surprisingly, it has been shown that the elastic modulus of an elastomer body integrated into a tubular connecting element or otherwise interacting with the connecting element can be approximated to the strain characteristic of a natural band.

[0031] Fig. Figure 3A represents a tubular connecting element 110, in whose axial cavity 122 an elastomeric body 125, shown again separately above the connecting element for clarity, is arranged. A cylindrical elastomeric body 125, preferably with a length l of 20 mm to 100 mm (e.g., 60 mm) and a diameter preferably of 0.5 mm to 10 mm (e.g., 2 mm), is integrated into a tubular connecting element 120 that is, for example, 120 mm long. The connecting element 120 consists of a plurality of first individual fibers 121, which are knitted, braided, woven, twisted, and / or twisted to form a tubular connecting element 120.

[0032] The first individual fibers 121 preferably consist of polyethylene and / or polyester. The connecting element 120 can be made from first individual fibers 121 of a single material or from first individual fibers 121 of different materials. These individual fibers 121 are oriented at an angle τ 123 to the longitudinal axis 124 of the connecting element 120. Due to the interaction of the elastomer body 125 with the tubular connecting element 120, the connecting element 120 exhibits a large extension under low tensile force, i.e., a low modulus of elasticity, which increases sharply as soon as the angle τ 123 between the individual fibers 121 and the longitudinal axis 124 decreases or approaches zero. The angle τ is preferably between 5° and 85°, and particularly preferably between 35° and 55°.

[0033] Fig. Figure 3B shows a connecting element 120' in which the elastomer body is formed from a plurality of second individual fibers 126. These are spun together with the first individual fibers 121 to form a connecting element 121', preferably without an axial cavity. However, the connecting element 121' can also be braided, knitted, twisted, spun and / or woven and may have an axial cavity.

[0034] The Fig. Figures 4-6 each show an anchoring element 110, 110', 110'' in which an elastomeric body 115, 117, 119 acts as a damping element. An anchoring element 110, 110', 110'' has, for example, a cylindrical outer body 103, which is cup-shaped and has an opening 112 at its base 105. The cylindrical outer body 103 includes, for example, an external thread with which the anchoring element is inserted into the first bone 50, see Figure 4. Fig. 1, is screwed in. A sleeve 114 is inserted into the open end face 104 of the outer body 103 and is slidably mounted inside the outer body. The sleeve 114 has a fastening element 111, which consists, for example, of two conical segments. The connecting element 20 is fixed securely between the inner surfaces 118 of the fastening element 111. Under tensile load, the fastening element 111 itself is pressed against the oppositely shaped contact surfaces 113 of the sleeve 114 and is thus firmly fixed in the sleeve 114.

[0035] In Fig. 4 An elastomeric body 115 is located between the contact surface 101 of the outer body 103 and a parallel contact surface of the sleeve 114. The elastomeric body 115 does not completely fill the interior 102, particularly in the radial direction. The elastomeric body 115 has a coaxial recess 116 through which the connecting element 20 passes and exits through the opening 112 of the anchoring element in the direction of the bone tunnel 51.

[0036] When a tensile load is applied, the elastomer body 115 continuously fills the free volume in the interior 102, which is reflected in a flat strain curve. As soon as the elastomer body 115 almost fills the entire volume, the incompressibility of the elastomer leads to an exponential increase in the curve. Thus, the desired progressiveness is achieved according to curve 71. Fig. 2 reached.

[0037] Fig. Figure 5 shows an anchoring element 110' which, with respect to the outer body 103 and sleeve 114, is constructed according to the anchoring element 110. An elastomeric body 119 is inserted into the interior 102 of the outer body 103. The elastomeric body 119 has a cylindrical shape. The base of the elastomeric body is preferably round, but can also be oval or angular. The connecting element 20 is guided helically or spirally around the circumference of the elastomeric body 119 and exits the anchoring element 110' through the opening 112 at the bottom 105 of the outer body 103.

[0038] If a tensile load is applied to the connecting element 20, this tensile force is transmitted radially through the connecting element to the elastomer body 119. Upon application of the tensile load, the elastomer body 119 can be compressed and, with sustained tensile load, reaches its minimum volume and subsequently becomes incompressible. Compression of the elastomer body 119 in the axial direction is minimal, as the majority of the tensile force is dissipated in the radial direction to compress the elastomer body 119.

[0039] To eliminate the additional axial compression caused by the sleeve 114, the sleeve 114 can be fixed in place, e.g. in Fig. As shown in section 6, it should be fixed to the outer body. This results in a less steep rise in the spring characteristic curve.

[0040] To prevent the connecting element 20 from slipping on the circumference of the elastomer body 119, grooves (not shown) can be provided around the circumference of the elastomer body in which the connecting element 20 is inserted and guided.

[0041] Fig. Figure 6 shows a further embodiment of the damping device by means of an elastomer body 117, which forms a plurality of tongue-shaped protrusions 117a, 117b. These protrusions 117a, 117b are arranged axially offset on the inner surface 106 of the outer body 103 and are formed radially inwards. They extend radially beyond the axis of the anchoring element 110' and are spaced apart from each other in the axial direction. The connecting element 20 is held by the fastening element 118 and is guided further around the tongue-shaped protrusions 117a, 117b to the opening 112.

[0042] When a tensile load is applied, the protrusions 117a, 117b are deformed axially towards the base 105 of the outer body 103. This corresponds to the flat region of the strain characteristic curve 71 in Fig. 2. As the tensile load increases, the connecting element 20 is wedged between the now adjacent protrusions 117a, 117b. Once the protrusions 117a, 117b have deformed to the point of contact with the base 105 of the outer body 103, no further compression is possible. This corresponds to the progressive course of the strain characteristic curve 71 in Fig. 2.

[0043] The slope and onset of the progressive section of the strain curve can be varied by selecting the material for the elastomer body 115, 117, 119. Suitable materials for the elastomer body 115, 117, 119 are polyethylene, polyester, polyurethane, or silicone, or a mixture of these materials. Furthermore, the strain curve is determined by the free volume in the interior 102 of the outer body 103, as well as the shape, diameter, and length of the elastomer body 115, 117, 118.

[0044] All described and / or designated features can be advantageously combined within the scope of the invention. The invention is not limited to the described embodiments.

Claims

[1] System for controlled stress on a reconstructed or renaturalized ligament of a human or animal body, comprising an anchoring element (10) for implantation into a first bone (41), at least one connecting element (20) and a retaining element (30) for holding the at least one connecting element (20) on a second bone (51), wherein at least one elastomer body (115, 117, 119) is arranged in the anchoring element (10) and the elastomer body (115, 117, 119) is arranged in the interior (102) of an outer body (103) of the anchoring element (10) between a contact surface (101) on the bottom (105) of the outer body (103) and a sleeve (114) to which the connecting element (20) is fixed, wherein the sleeve (114) is immovably fixed to the outer body (103) and wherein at least one elastomer body (125) is arranged in the connecting element (20), wherein the elastomer body (125) has a smaller modulus of elasticity than the connecting element (20), wherein the connecting element is tubular and the elastomer body (125) is arranged in a section of an axial cavity (122) of the tubular connecting element (20). [2] System according to claim 1, characterized by , that the elastomer body (115, 117, 119, 125) is made of polyethylene and / or polyester and / or polyurethane and / or silicone. [3] System according to one of claims 1 to 2, characterized by , that the connecting element (20) is braided and / or twisted and / or knitted and / or woven from a plurality of first individual fibers (121) and at least a part of the first individual fibers (121) form an angle (τ; 123) between 5° and 85° with respect to the longitudinal axis (124) of the connecting element (20). [4] System according to claim 3, characterized by , that each first single fiber (121) contains a polymer, in particular polyethylene or polyester, and the connecting element (20) is formed from a plurality of these first single fibers (121). [5] System according to claim 1, characterized by , that the connecting element (20) is guided spirally around the circumference of the elastomer body (119). [6] System according to claim 1 or 5, characterized by , that the elastomer body (119) has grooves around its circumference which do not run parallel to the longitudinal axis of the elastomer body (119) and the connecting element (20) is guided in these grooves. [7] System according to any one of claims 1 to 6, characterized by , that the elastomer body (115, 117, 119, 125) has a cylindrical shape.

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