NO176344B - Secure Element - Google Patents

Description

The present invention relates to a fastening element of the type specified in claim 1's preamble, as well as an application thereof as specified in claim 6.

A preferred embodiment according to the invention will be described in detail in the following with a view to the reconstruction of a finger joint, but the invention is not limited to this. The invention can be used for other similar joints, such as toe joints, elbow joints, etc. The invention can also be used for reconstructions after amputation or other defects.

Finger joint reconstructions involving prostheses are primarily performed on MCP joints that have been rheumatically altered. Prostheses known for this purpose include "Swanson's Silastic" finger joints. Such joints consist of a material similar to silicon, are elongated in shape and have ends with mainly circular cross-sections. The ends can be adjusted and fixed in the medullary cavity of each leg. The central part of the prosthesis is elastically deformable and thus forms the real joint mechanism.

The St. George prosthesis, a cemented prosthesis, is also known in connection with finger joint reconstruction.

A disadvantage of these conventional prostheses is that the attachment element supporting the actual prosthetic mechanism loosens and/or damages the surrounding tissue with unwanted displacement of the prosthesis in the direction of the load. Attempts have therefore been made in recent years to use clamping devices made of titanium, which are fixed in the medullary cavity of the bone, so that it becomes bone integrated, as described by Hagert et al., "Metacarpophalangeal Joint Replacement with Osseointegrated Endoprostheses" in Scand. J. Plastics. Reconst. Sorrow. 20, pages 207-218, 1986. It is already known to attach permanent oral and extraoral attachment prostheses in the bone tissue. This dental bone integration technique has been developed over the last 25 years by Professor Brånemark and his colleagues with excellent results when placing fixtures in the jawbone to hold teeth or bridge arrangements. But the experiments conducted by Hagert to apply this technique to the reconstruction of finger joints have not met expectations. The unacceptable results are obviously due to the completely different conditions encountered when applying this "dental technique" to prosthetic reconstruction of finger joints. In known technology, e.g. the fastening device placed at right angles to the longitudinal axis of the leg. In the finger joint, the fastening device is placed along the axis of the leg. Naturally, this creates completely different loads and pressures on the fastening elements.

DE-B^ 2 338 136 discloses an anchoring element provided with external threads and which can be screwed into a leg. The element essentially has the form of a hollow cylindrical sleeve which holds a prosthetic part at its end close to the joint. The known anchoring element exhibits slits extending from its open insertion end towards the prosthetic part and has a surface which can at least partially grow together with the bone tissue and thus along its longitudinal axis achieve a permanent anchoring in the interior of the bone, as the anchoring element comprises a material that is biocompatible with the bone tissue . However, the walls of the anchoring element are not designed so that they will be able to adapt to the surrounding bone tissue when screwed in. Such an adaptation is only achieved after the element is fully screwed in by introducing an expansion element into the inner bore of the anchoring element, the expansion element being dimensioned to press the slotted wall end outwards.

In FR-A]_ 2 615 72 6 an anchoring element is shown which is anchored in a similar way as in the discussed DE-B3_ 2 338 136. However, the outer side of the element is not provided with external threads, but is provided with rifles and is therefore to a higher degree than the anchoring element according to the above-mentioned resistance depending on the introduction of an expansion body in its inner bore.

The same is also the case for the anchoring of the shaft in the hip prosthesis which is shown in FR-A;j_ 2 267 380 which has a longitudinal slot without external threads and whose shape deviates substantially from the cylindrical sleeve. In this case, an expansion of the anchoring element (shaft) is achieved by introducing an expansion body into the slot itself.

Today, the main problem in orthopedic prosthetic surgery is still that the bone anchoring unit comes loose. But with a success rate of dental implants of more than 90% over a 20-year period, a number of other problems arise that have so far been unnecessary to factor into the calculation. One of the biggest problems is increased wear on the joint mechanism. A different type of prosthesis pattern than the one that has been in use until now is necessary if the bone integration method is to be used. In order to be able to replace the joint mechanism without disturbing the bone anchorage, the prosthetic system must be divided into components where the element for the joint mechanism can be separated from the actual bone anchorage element. Furthermore, if the two-stage method is to be used, it must be possible to connect the joint mechanism in the second stage if the patient, or at least the patient's reconstructed joint, is not to remain immobile. Two factors must therefore be taken into account in the calculation. Firstly, the joint mechanism is subject to wear and tear and must therefore be replaceable. Secondly, the joint mechanism must be replaceable in order to use the two-step method.

It has now surprisingly been found that the difficulties and disadvantages of the technique described above can be eliminated by the present invention.

The invention is based on extensive experimental biological analyzes of the structure and function of joints during a disease or in a defective state after wear or inflammatory breakdown of bone tissue, and thorough studies of the vascular supply to the bone marrow. It has been shown that when synthetically replacing damaged articular cartilage and ligaments, bone and marrow tissue must be treated as a structural and functional unit. It is absolutely necessary to include in the calculation cooperation between bone and marrow tissue, especially over a longer period of time, if the hard tissue is to function as a support element.

The invention is thus based on the fact that when attaching a prosthetic replacement for a joint surface and ligaments to parts of the skeleton near the joint, the interaction between bone marrow and bone tissue must be taken into account. This means that a mounting element in the marrow cavity of a long bone must be anchored by mechanical elements that will allow communication between marrow and bone tissue along the entire length of this element, as far as is technically possible, taking particular account of the connective layer between the marrow and the compact bone in the wall of the medullary cavity.

The fastening element is thus characterized by what is stated in the characterizing part of claim 1. Further features appear from requirements 2-5.

Thus, the invention is directed to a fastening element for supporting a joint mechanism where the fastening element is essentially rotationally symmetrical, at least partially hollow, and it comprises a material that is compatible with the tissue in the leg. The attachment element has a surface which can be at least partially bone-integrated with the tissue, so that permanent attachment is achieved in the longitudinal axis inside the bone. The invention is also directed at a reconstructed joint.

The fastening element is fixed inside the bone by cutting the bone close to the joint, so that the marrow cavity in the bone is exposed; to make a space in the bone cavity near the joint; fit a guide sleeve into the space and screw the fastener into the medullary cavity, while the guide sleeve is used to center

the fastening element.

Other features and advantages of the invention will be clear from the following description of a preferred embodiment according to the invention with reference to the accompanying drawings.

Fig. 1 is a section of a cross-section of a reconstructed finger joint with a fastening element according to the invention,

fig. 2 shows a fully reconstructed finger joint,

fig. 3 shows how the fastening element is placed in the long leg,

fig. 4 is one. perspective section of the fastening element,

fig. 5 is a cross-section along the line 5-5 in fig. 4,

fig. 6 is a section of a cross-section along the line 6-6 in fig. 4 and illustrates part of the joint mechanism according to the invention,

fig. 7 shows the assembly of the joint mechanism of the fastening element according to the invention.

Fig. 8 to 10 show some further embodiments and show how the effect of the non-rotatable wedge between the fastening element and the guide sleeve can be achieved and/or improved.

In fig. 1, the parts of a long leg on each side of a finger joint mechanism 1 are labeled 2 and 3 respectively.

A rotationally symmetrical fastening element 4 is shaped by a

hollow, mainly sleeve-shaped object 5 with external threading 6 and decreasing wall thickness. The open insertion end 7 of the object 5 tapers and is equipped with slots 8 and 9, starting from the open end 7.

The end 13 (Fig. 6) of the fastening element 4 closest to the joint mechanism 12 is placed in a guide sleeve 11. The shown sleeve 11 is mainly cylindrical and is provided with longitudinal grooves along its bone marrow-adapted outer surface. These grooves can conveniently be identical to an axial section of rotationally symmetrical threaded fastening devices as used in dental practice. The guide sleeve 11 surrounds the joint end 13. The joint end 13 of the object 5 is thus locked against the inner surface 14 of the guide sleeve 11 by a wedge effect when the object 5 has been screwed sufficiently far into the bone tissue. The joint end 13 accommodates the connecting parts 15 of the joint mechanism 1, which are removable. The connecting parts 15 can be centered plugs (Fig. 7) which protrude from the joint mechanism 1. Such plugs cooperate with corresponding recesses 16 in the fastening element 4 or a connecting piece (not shown) which is suitably placed between the guide sleeve 11 and the joint mechanism 1 .

One or more holes can be directly connected to the bone marrow-adapted outer surface of the fastening element 4 with the hole edges towards the surface, so that they form cutting edges. Self-threading is thus achieved when the object 5 is screwed into the leg 2. The removed bone tissue 17 is taken up inside the fastening element 4 as shown in fig. 5.

As the thickness of the wall of fastening element 4 gradually decreases towards the insertion end 7 and/or as element 4 has the longitudinal slits 8 and 9, the requirement for good deformation is met, and the risk of concentrated load, which causes particular difficulties in prior art, is greatly reduced extent. Arrows B-B in fig. 1 denotes the flexibility of the open end 7, i.e. its ability to adapt to the surrounding tissue. The same applies to arrows A-A.

The slots 8 and 9 can suitably be equipped with cutting edges, and since the cavity occupies the chips 17, as illustrated in fig. 5, the fastening element 4 is in itself its own manufacturing tool. At the same time, optimal conditions for normal anatomical and physiological situations are ensured, so that disturbances in the remaining biological tissue, i.e. marrow and bone tissue, are minimal. Fig. 2 shows the joint reconstruction which has been achieved with fastening element 4 in place. Fig. 3 illustrates how fastening element 4 is placed in the bone 2. When fastening element 4 is in use, it is placed in the connecting zone between marrow and bone tissue. The wall thickness of the sleeve-like object 5 decreases towards the slot insertion end 7 and ends in a sharp cutting edge 12. The edges of the longitudinal slots 8 can also be in the form of cutting edges. The chips 17 that appear when the fastening element 4 is screwed into the marrow cavity are thus transferred to the hollow space inside the object 5, as shown in fig. 5.

During surgery, the part of the long leg 2 that is close to the joint is cut, and the medullary cavity is opened. A probe (not shown) is then inserted into the medullary cavity to locate a suitable longitudinal axis for insertion of the fastening element 4. The probe is used as a direction finder to center the fastening element 4 as desired. A recess for the guide sleeve 11 is then carefully drilled into the opened medullary cavity. After insertion of the guide sleeve 11, the sleeve-like object 5 is screwed down into the marrow cavity through the guide sleeve 11. The probe has of course been removed beforehand. The joint end 13 of the fastening element 4 expands somewhat outwards and upwards as illustrated at 18, so that its diameter is somewhat larger than the lower opening of the guide sleeve 11. Thus a wedge effect will take place between the joint end 13 and the guide sleeve 11 (when the sleeve 11 is moved to the position illustrated with dashed lines in Fig. 6), so that both the guide sleeve 11 and the sleeve-like object 5 are placed as desired.

The fastening element 4 and the guide sleeve 11 consist of or are made of titanium or are coated with titanium. The structure of the titanium surface is such that integration is promoted, at least over parts of the surface in question. Advantageously, the surface can have irregularities consisting of microscopic indentations, as described in Swedish patent 7902035-0, with indentation diameters of between 10 and 1000 nm, preferably 10-300 nm. Alternatively, the chemical composition of the titanium surface can be given certain positive tissue reactions, e.g. as described in Swedish patent 8505158-9.

Fig. 8 shows how the upper end 19 of the sleeve 11, which faces the flange 20 of the element 4, is equipped with a protruding edge 21 which is made so that it cooperates with threads 22 on the flange 20. The element 4 and the sleeve 11 are thus non-rotatably locked when the object 5 has been screwed sufficiently far into the bone tissue.

An alternative locking effect between the sleeve 11 and the element 4 is achieved by the assembly shown in fig. 9, where axially located recesses are made so that they cooperate with the inner surface of the sleeve 11.

A further locking effect can be achieved by the assembly shown in fig. 10, by a special thread 24 on the upper edge of the element 4, which is screwed into the tissue.

Claims (6)

1. Fastening element (4) provided with external threads and screwable into a leg, which fastening element (4) has the shape of a cylindrical sleeve, the fastening element (4) being adapted at its joint-closer end (13) to hold a prosthetic part (1), and where the fastening element (4) is at least partially hollow, and exhibits slits (7, 8) extending from the open insertion end (7) towards the prosthetic part (1) and has a surface that can at least partially grow together with the bone tissue (2 ) to achieve along its longitudinal axis a permanent anchoring in the interior of the leg, as the fastening element (4) comprises a material which is biocompatible with the bone tissue, as the fastening element preferably either consists of titanium or is titanium-coated, characterized in that the wall thickness of the fastening element (4) decreases successively in the direction towards the insertion end (7) and that the wall is flexibly deformable, as the fastening element (4) adapts when screwed in the surrounding bone tissue, and that the slits (8, 9) exhibit cutting edges. 2. Fastening element according to claim 1, characterized in that it exhibits a guide sleeve (11) surrounding the end near the joint (13), the end near the joint (13) being torsionally fixable to the guide sleeve (11). 3. Fastening element according to claim 1 or 2, characterized in that the end close to the joint (13) is designed for pluggable reception of connecting parts (15) of the prosthetic part (1). 4. Fastening element according to claim 3, characterized in that a connecting element is arranged between the prosthetic part (1) and the control sleeve (11). 5. Fastening element according to any of claims 1-4, characterized in that its outer surface exhibits a radial outer surface, which at least partially has micropits with a diameter in the range 10 - 300 nm. 6. Application of a fastening element (4) provided with external threads and screwable into a leg, which fastening element (4) has the form of a cylindrical sleeve, the fastening element (4) being adapted at its end near the joint (13) to hold a prosthetic part (1) ), and where the fastening element (4) is at least partially hollow, and exhibits from the open insertion end (7) towards the prosthetic part (1) extending slits (7, 8) and has a surface that can at least partially grow together with the bone tissue (2) to achieve along its longitudinal axis a permanent anchoring in the interior of the bone, the attachment element (4) comprising a material that is biocompatible with the bone tissue, the attachment element preferably preferably either consisting of titanium or coated with titanium, where the wall thickness of the attachment element (4) decreases successively in the direction towards the insertion end (7) and that the wall is flexibly deformable, as the fastening element (4) adapts to the surrounding bone tissue when screwed in, and that the slots (8, 9) exhibit cutting edges, for fastening a prosthetic part which is a de l of an artificial finger joint.