WO2018215471A1

WO2018215471A1 - Trapezium-methacarpal prosthetic implant

Info

Publication number: WO2018215471A1
Application number: PCT/EP2018/063393
Authority: WO
Inventors: Carlo BUFALINI
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-05-24
Filing date: 2018-05-22
Publication date: 2018-11-29
Anticipated expiration: 2019-11-24
Also published as: IT201700056525A1

Abstract

Trapezium-methacarpalprosthetic implant that ensures stability of the implant without limiting the freedom of movement of the hand bones. In particular, this is achieved by the shape of an interposition element.This shape of the implant allows for a freer movement of the bones with respect to one another and with respect to the prosthesis itself.

Description

TRAPEZIUM-METHACARPAL PROSTHETIC IMPLANT

TECHNICAL FIELD

The present invention relates in general to field of joint prostheses for the fingers of the hand and more precisely it concerns a trapezium-methacarpal prosthetic implant.

TECHNICAL BACKGROUND

As is well known, the trapezium-methacarpal joint is located at the base of the thumb and allows all those wide movements that also allow the thumb to be opposed to other fingers.

The trapezium-methacarpal joint involves coupling of the articular surfaces of the first methacarpal and trapezium bone, both covered with a layer of cartilage, as well as the presence of ligaments that keep them close together and in alignment.

These surfaces show a double curvature (defined as "saddle") and are extremely congruent with each other, while allowing a considerable relative mobility of the two bones.

With age or as a result of trauma, the ligaments, especially the anterior ligament, "Beek ligament", may become weaker and longer, inevitably leading to a reduction in joint congruency. The relative movement of the articular surfaces of the methacarpal and trapezium bone thus becomes "defective", thus causing a creep that leads to wear of the cartilage (known as arthrosis), resulting in pain, crackling, subluxation and loss of strength.

Currently, surgery and, if necessary, prosthetic implants can be used to solve the most serious arthrosis problems. These can be divided into two broad categories, total endoprostheses and spacers. The endoprosthesis completely replaces the trapezium-methacarpal joint and consists of a mechanical joint, whose two components are joined to the trapezium bone and the first methacarpal bone respectively (adapted surgically before joining). The spacer consists of a disk of biocompatible material designed to be placed between the trapezium bone and the first methacarpal, in order to reduce the direct rubbing of the two articular surfaces onto one another.

As far as known spacers are concerned, it should be noted that practically no one can maintain reliable stability over time. In fact, after a few months from its insertion, the spacer tends to become unstable, to sublux and degenerate, both because of a lack of capsule-ligamentous restraint, and because of the lack of perfect conformity and anatomical adherence to the adjoining carpal bones. The consequence is that after an initial period with a good functional outcome, the clinical situation degenerates leading to poor grip, pain, and thumb base deformity.

Italian patent No. 1377916, which has the same holder as the present application, describes a trapezium-methacarpal prosthetic implant that allows the elimination of trapezium-methacarpal subluxation, i.e. it reports the first methacarpal on site with respect to the trapezium bone. This implant also reduces friction forces on the first methacarpal. Although this is an improvement on the earlier known technique, it has certain disadvantages. In particular, the shape of the implant, with the flat surface of the interposition disk, limits the movement between the thumb bones, forcing them to male an angle to each other to overcome the limitation. In addition, the interposing disk is difficult to insert due to stabilizing fins required to keep the implant in position. OBJECT OF THE INVENTION

The main object of the present invention is to create a spacer type, trapezium-methacarpal prosthetic implant that eliminates, at least in part, the problems of the prior art.

SUMMARY OF THE INVENTION

These and other objects, which will be better explained later, are achieved by a trapezium-methacarpal prosthetic implant, including: a spacer element with a substantially bi-convex lenticular shape, adapted to be positioned between the trapezium bone (T) and the base of the first methacarpal (I) of the hand; at least first fixing means, adapted, when the implant is positioned in the prosthetic site, to connect the spacer element with the first methacarpal (I) and to keep it firmly in place, without preventing the movement of the first methacarpal, with the first fixing means comprising at least ligament adapted to pass through a first channel in the first methacarpal along a substantially longitudinal direction, the first channel being obtained between the base of the first methacarpal and the external wall of the first methacarpal; at least second fixing means, designed to connect, when the implant is fitted in the prosthetic site, the metaphysis of the first methacarpal (I) with the distal diaphysis of the second methacarpal (II) and to apply, when it is fitted in the prosthetic site, an adduction and lifting force on the spacer element, the second fixing means comprising at least one ligament adapted to pass through the first (I) and second (II) methacarpal through a second and a third channel, the second and third channels being substantially aligned with each other and obtained between the external wall of the first methacarpal and the ulnar wall of the second methacarpal.

The implant according to the present invention ensures the stability of the implant without limiting the freedom of movement of the hand bones. In particular, this is achieved by a bi-convex lenticular shape of an interposition element. This shape of the implant allows for a freer movement of the bones with respect to one another and with respect to the prosthesis itself.

In a preferred embodiment, the ligament is passed through the first methacarpal, through a channel obtained in the first methacarpal and extending in the longitudinal (vertical) direction and having inlet/outlet holes, one situated substantially in the centre of the base of the first methacarpal, the other situated on the side wall of the first methacarpal, proximal to the base of the methacarpal itself: the essentially vertical direction of the ligament allows for a stabilization of the implant without the need to provide additional stabilization elements, thus simplifying the installation of the prosthesis and making the implant less invasive. After vertical passage, the ligament exits the first methacarpal and re-enters more proximally, i.e. closer to the joint margin, crosses the first methacarpal in the direction of the second methacarpal, crosses the second methacarpal and is fastened to the outer side opposite to the first methacarpal. These two artificial ligaments can be independent of each other: they can be divided according to their specific tasks or set in continuity with each other, but with separate purposes. Preferably, the ligaments are passed through the channels (or tunnels) in the bones, pulling them with a looped steel wire that is introduced through a specially cannulated drill bit.

According to a preferred embodiment of the present invention, the prosthesis comprises two main elements: the actual prosthesis in the shape of a biconvex lens and the artificial ligament, i.e. a sort of string that holds the biconvex element in place. Preferably, the biconvex element is made of biocompatible material (e.g. polyethylene "peek", ceramic, titanium, possibly coated with ceramic), has a diameter of about 1 .5 cm and a maximum thickness of about 4 mm. The ligament (consisting of a going thread and a return thread) has preferably a diameter of approximately 0.5-1 mm (i.e. with a single thread of between 0.25 and 0.5 mm) and is made of sterilisable and biocompatible synthetic fibres. In a preferred embodiment, the single wire has a thickness of about 0.4 mm, so the double wire will be about 0.8 mm. The ligament acts in two distinct directions and for different but complementary purposes. The first segment keeps the spacer disk in place and bound to the first methacarpal; the second segment keeps the first methacarpal and prosthesis aligned with the trapezium and in the original position with respect to the second methacarpal; in addition, the second segment exerts a "distracting" action with respect to the trapezium and thus lightens the functional load on the same. The two segments may also be made up of a single ligament, suitably locked so that the first segment provides a tractive force independent of the second segment, for example by locking it onto a small rigid plate (e.g. metal), as shown below.

BRIEF DESCRIPTION OF THE FIGURES

The characteristics and advantages of the prosthetic implant according to the present invention will result more clearly from the following description of an embodiment, made by way of example and not limited with reference to the attached drawings, in which:

Figure 1 shows a schematic frontal view of a portion of the bone structure of a hand, to which a prosthetic implant is applied according to the invention;

Figure 2 shows the spacer element, according to a preferred embodiment of the present invention, with three distinct views. DETAILED DESCRIPTION

With reference to Figure 1 , a trapezium-methacarpal prosthetic implant according to the invention is indicated with 100 as a whole.

This prosthetic implant 100 includes a spacer element 101 to be placed between the trapezium bone, indicated by T, and the base of the first methacarpal of the hand, indicated by I. According to a preferred embodiment of the present invention, the spacer element 101 has the shape of a biconvex lens, with a diameter that can depend on the size of the patient's finger, usually between 1 cm and 2 cm, and a thickness between 3 mm and 5 mm. In a preferred implementation the diameter is about 1 .5 cm and the maximum thickness about 4 mm. Preferably, the biconvex element is made of biocompatible material. The material can be selected from a wide range of possible materials including "peek", polyethylene, ceramic, titanium possibly coated with ceramic. Those skilled in the field will understand that any material that guarantees not only strength and sterility, but also tolerance by the contacted tissues, can be used as an alternative.

According to a preferred embodiment of the present invention, a biocompatible ligament 103 is attached to spacer element 101. Ligament 103 is a kind of double twine with an overall diameter of 0.5-1 mm, preferably 0.8 mm (therefore each single twine has a diameter between 0.25 mm and 0.5 mm, preferably 0.4 mm), made up of sterilisable and biocompatible synthetic fibres, for example, Dynema^®, Kevlar^®, carbon fibres. According to a preferred embodiment of the present invention, both the spacer element and the ligament are radioopaque, i.e. visible by X-rays. Such characteristic and the modalities in order to obtain it are known to the person skilled in the art, for example, the ligament can be submitted to a treatment with barium or made by weaving a metallic wire; If it is not metallic, the spacer element 101 could have, e.g, a radio-opaque ring inside the edge. According to a preferred embodiment, fastening the ligament 103 to the spacer 101 is done by passing the ligament through two holes in the biconvex prosthesis, in its center, and by fixing the ligament to the base of the methacarpal, in a direction perpendicular to the axis of the methacarpal itself (as shown in Figure 2C).

In a preferred embodiment, ligament 103 is made to pass through a hole 105 and a channel 107, obtained in the first metacarpus and extending in a substantially longitudinal, oblique direction, between the centre of the methacarpal base and the external wall of the first methacarpal; as mentioned above, the essentially vertical direction of the ligament allows for a stabilization of the implant without the need to provide additional stabilization elements, as was, for example, the case in technical solution of patent No. 1377916, which required the presence of two fins to be inserted into the bone itself, which made the procedure for installing the prosthesis heavier and increased the invasiveness of the implant. After vertical passage, the ligament exits the first methacarpal through the exit hole 109 from the cortical of the first methacarpal and is fastened hereto, so as to ensure the stability of the spacer disc 101 against the base of the first methacarpal. In the example shown in the figure, this fastening is done by means of a small plate (1 1 1 ) of sufficiently rigid material (e.g. metal, or polyethylene) substantially elliptical in shape and having two holes through which the two ligament wires will pass and will be properly attached in order to fasten the ligament. Such fastening (for example, by a knot) ensures that this first segment of the ligament acts independently of the rest of the ligament; the two segments could very well be distinguished from each other. Figure 1 shows the knotted ligament after passing through plate 1 1 1 , but before it is tightened to stabilize the fastening of the spacer element 101. According to a preferred embodiment of the present invention, the ligament (consisting of two "going and coming" wires) is unique and continues as described below after the fastening at the exit from hole 109, but it is not excluded that two separate ligaments may be used alternatively. According to a preferred embodiment, the exit hole 109 is at a distance of about 2 cm from the base of the first methacarpal. The ligament is then inserted into the first methacarpal through the hole 1 13, which is located more proximally than the base of the methacarpal. Ligament 103 passes through the first methacarpal along a longitudinal direction slightly inclined with respect to the vertical axis, in a canal 1 15 which opens outside through an exit hole 1 17. Following a direction in a substantially straight line, ligament 103 then enters the second methacarpal through an entry hole 1 19, runs along a a channel obtained in the second methacarpal and comes out at the opposite side through an exit hole 123, to be fixed on the ulnar outer side (i.e. opposite to the first methacarpal), preferably, by fastening it to a second metal plate 125, for example, by means of a knot. The ligament so fastened applies an adduction action towards the second methacarpal and a lifting action from the trapezium to the methacarpal base. As mentioned above, the ligament 103 does not need to be made up of a single wire and the two segments need not be joined. The same result could be achieved by means of two distinct and separate segments: a first segment holds the spacer disk 101 in place; a second segment keeps the first and second methacarpal joined, so as to carry out adduction and lifting actions as described above. In this case, for example, an additional plate can be used to block the ligament at the entrance of channel 1 15 (not shown in the figure).

Figure 2 shows a spacer disk according to a preferred embodiment of the present invention. Figure 2A shows a top view of the spacer disk in which the preferably circular shape and the two holes 203 are shown, through which the two wires of the ligament (the "going" and "coming " ones) are made to pass. Figure 2B shows a side view of the disk, in which you can see the biconvex shape of the disk itself. Disc sizes may vary depending on the size of the patient's hand; preferably, the disk surface should cover about ¾ of the trapezium surface, in order to keep the implant attached and prevent dislocation thereof. The width (L) and maximum height (H) ratio should be between 2 and 7, according to the formula 2<L/H<7, in a preferred embodiment, this ratio is about 3.7. Figure 2C shows a section view of the spacer disk, in which you can see the concavity (optional) at the bottom, aimed at accommodating the passage of the ligament 103.

The installation of the prosthetic implant of the present invention is now described. After having made appropriate surgical accesses to operate on the bones of the first and second methacarpal, the area between the trapezium T and the first methacarpal is prepared for insertion of the spacer element 101 with a lenticular biconvex shape. A channel 107 is then created between the inlet/outlet holes 109 and 105. According to a preferred embodiment, the channel 107 is obtained by means of a drill bit that enters from the side wall (creating the hole 109) and crosses the first methacarpal up to its base (hole 105). The ligament that, according to a preferred embodiment of the present invention, consists of a wire that is passed through two holes made in the spacer element (see Figure 2A and 2C) and is then double, will pass through channel 107. The ligament is then fastened at the exit from channel 107 using a knot and a suitable plate 1 1 1 , so as to keep the spacer element 101 in position. Channels 1 15 and 121 , which cross the first and second methacarpal along a lateral direction, are obtained by means of a drill and appropriate surgical guides. Preferably, the drill bit will be cannulated to allow the insertion of the ligament and facilitate its passage. A prosthetic kit for the trapezium-methacarpal joint, consisting of a spacer body, at least one ligament and means of attachment of the ligament to the spacer body, as described above, also forms the subject of this invention. Optionally, one or more of the following elements can be included in the kit: a cannulated drill bit, a protective sleeve for the drill bit, a sliding guide for introducing the drill and make the holes, steel wires with bend (known as Kirschner wires) to help introducing the ligament. The kit may also include a rasp to prepare the site for the prosthesis.

The device so conceived is subject to many changes and variations, all of which fall within the scope of the invention: furthermore, all parts may be replaced by other technically equivalent elements, however, without going beyond the protective scope of the present invention.

In practice, the materials used, provided they are compatible with the specific use, as well as their dimensions, may be varied according to the needs and the state of the art.

Claims

1 . Trapezium-metacarpal prosthetic implant, comprising:

a spacer element (101 ) with a substantially bi-convex lenticular shape, adapted to be positioned between the trapezium bone (T) and the base of the first metacarpal (I) of the hand;

at least first fixing means adapted, when the implant is positioned in the prosthetic site, to connect the spacer element with the first metacarpal (I) and to keep it firmly in place, without preventing the movement of the first metacarpal (I), the at least first fixing means comprising at least one ligament adapted to pass through a first channel (107) in the first metacarpal (I) along a substantially longitudinal direction, the first channel being obtained between the basis of the first metacarpal (I) and the external wall of the first metacarpal (I);

at least second fixing means adapted, when the implant is fitted in the prosthetic site, to connect the metaphysis of the first metacarpal (I) with the distal diaphysis of the second metacarpal (II) and to exercise an adduction and lifting action on the spacer element when it is inserted in the prosthetic site, the at least second fixing means comprising at least one ligament adapted to pass in an oblique durection through a second channel (1 15) in the first metacarpal (I) and a third channel (121 ) in the second metacarpal (II), the second and third channels being substantially aligned along the same direction and obtained between the external wall of the first metacarpal and the ulnar wall of the second metacarpal (II).

2. Trapezium-metacarpal prosthetic implant according to claim 1 , wherein the first fixing means, through the first channel (107), connects the joint between first metacarpal (I) and trapezium bone (T) with the external wall of the first metacarpal (I), a first of the two entry/exit holes of the channel (107) being substantially at the center of the bottom surface of the first metacarpal (I), a second of the two entry/exit holes of the channel (107) being at a distal distance between 2 and 3 cm from the base of the first metacarpal (I).

3. Trapezium-metacarpal prosthetic implant according to any preceding claim, wherein the at least first fixing means and the at least second fixing means are joined together.

4. Trapezium-metacarpal prosthetic implant according to any preceding claim, wherein the at least first fixing means and the at least second fixing means includes at least one biocompatible ligament (103).

5. Trapezium-metacarpal prosthetic implant according to any preceding claim, wherein the bi-convex lenticular shaped spacer element (101 ), having a substantially circular section, is provided with two passing holes extending in substantially perpendicular direction with respect to the plane of the substantially circular section, the two passing holes being substantially symmetrical with respect to the center and wherein the at least first fixing means includes a ligament which is adapted to pass through the two holes and bent back to itself, so that, when the implant is in place, the ligament, after passing through the first channel (107) and fastened to a first fixing plate (1 1 1 ), keeps the spacer element (101 ) in place.

6. Trapezium-metacarpal prosthetic implant according to claim 4, wherein the at least second fixing means includes the continuation of the two ends of the ligament which, after being fixed to the first fixing plate (1 1 1 ) are passed through the second (1 15) and third (121 ) channels and fixed to a second fixing plate (125), so that an adduction force to the bottom of the first metacarpal (I) and a lifting force on the trapezium bone (T) are exercised.

7. Trapezium-metacarpal prosthetic implant according to any preceding claim, wherein the spacer element (101 ) has a surface area equal to about ¾ of the joint surface of the trapezium bone (T).

8. Trapezium-metacarpal prosthetic implant according to any preceding claim, wherein the spacer element (101 ) is made of one or more of the following material: steel, titanium, ceramic, polyethylene, ceramic coated peek.

9. Prosthetic kit for the trapezium-metacarpal joint including: a spacer element (101 ) as defined in any preceding claims; first fixing means as defined in any preceding claims and second fixing means as defined in any preceding claims.

10. Prosthetic kit according to claim 9, including a cannulated drill tip suitable for creating passing channels through first and second metacarpals and an adjustable guide for facilitating the alignment of the drill tip.