IMPLANTABLE DEVICE FOR LENGTHENING AND CORRECTING MALPOSITIONS OF SKELETAL BONES

Abstract: The invention relates to an implantable device (11) for lengthening and correcting malpositions of skeletal bones, which device has an elongate shape comprising a first end (12), a second end (13), a length dimension (14) and a cross-sectional dimension (15). The device (11) further comprises a lengthening means (16) for bringing the first (12) and the second (13) ends into displacement from each other to a predetermined distance (14') between each other after an activation. Thereby, the lengthening means comprises an absorbent body (16), which is arranged for bringing the first (12) and second (13) ends to the predetermined distance (14') by means of a controlled swelling after the activation, while the length dimension (14) increases more than the cross-sectional dimension (15). The invention can advantageously be implemented for lengthening and also for correcting rotational and angular malpositions of skeletal bones, for example in connection with stabilising fractures, post-traumatic bone defects, bone shortenings, malpsitions, congenital malformations, and bone defects after tumour surgery.

Description: Title Implantable device for lengthening and correcting malpositions of skeletal bones Technical field The present invention pertains to the field of orthopaedic surgery, and more specifically relates to an implantable device for lengthening, and also lor correction ol rotational and angular malpositions of skeletal bones The invention advantageoush can be applied in connection with stabilisation oi fractures, post-traumatic bone defects, bone shortening, malpositions, congenital malformations and bone defects after tumour surgery Background of the invention Within the field of orthopaedic surgery, it is previously known with implantable devices e.g. for e g stabilisation of fractures, lengthening of skeletal bones, or for correction of different malpositions Many of the previousK known devices require that suitable attachments means are driven into the skeletal bone on both sides of the bone portion which is to be influenced, and that subsequently a screw assembly is applied between the attachment means, wherein a screw or the like acting on the screw assembh . alternatively on the attachment means, is allowed to protrude through the skin of the patient Thereafter, by means of turning the screw, the length of the screw assembly can be influenced in accordance with an adapted lengthening scheme Accordingly . in case it is desired to correct a malposition ol a skeletal bone which for some reason occurs by means of a surgical operation a screw assembly oi the above- described type can be applied at one side of the skeletal bone with the aid of two attachment means, hereafter the skeletal bone between the two attachment means can be cut off By means of lengthening the screw assembh in accordance with the chosen lengthening scheme, a gradual bending oi the skeletal bone in question can be obtained Finally . after an appropriate healing time, the screw assembh . the screw and the attachment means can be bv means ot a surgical operation In case onlv a linear lengthening is desired, several screw assemblies in parallel can be applied around the skeletal bone in question. Furthermore, for example in connection with stabilisation of fractures, it is previously known with so-called intramedullary nails, which during use are intended to be inserted into the bone-marrow cavity of a tubular skeletal bone. It is also previously known with such devices for which the lengthening action can be activated and/or controlled from the outside after the implantation. Accordingly, for example the patent publication US-A-5.626.581 discloses a nail assembly for bone lengthening comprising a first nail body portion and a second nail body portion. The assembly further comprises a power package inside either the first or the second nail body portion, wherein the power package comprises a power-supplied hydraulic pump which forces hydraulic fluid from a hydraulic fluid container and into a sealed chamber between the first and second nail body portions, thereby forcing the first nail portion to be extended longitudinally in relation to the second nail portion and increasing the length of the nail. It is also reported that the disclosed assembly may comprise a spring of a heat- sensitive memory material such as nitinol, and a heating system with a battery-powered electrical heater acting on the spring. According to US-A-5.626.581. external activation and/or control of the assembly may be accomplished e.g. by means of providing the heating system with a timer or a suitable circuit for remote control which acts on the heating system. Previously known arrangements for lengthening or correction of skeletal bones which require one or several permanent skin lead-throughs during the treatment time are associated with a large discomfort for the patient and a raised risk of infection. The previously known implantable devices for lengthening and correction of skeletal bones which can be controlled from the outside, or which otherwise can be controlled without any permanent skin lead-throughs. often comprise a large number of mechanical and electronic components, and can be perceived as complicated or unnecessarily expensive. When the external dimensions, the durability and the different lengthening properties are concerned, it may become expensive to tailor-make devices for each individual case in accordance with the prior art. since this often requires a number ot the many different components to be re-dimensioned Furthermore, when devices having small external dimensions are concerned, problems with lack of internal space may arise Summary of the invention Accordingly, a first object of the present invention is to provide a simple and reliable, implantable device for lengthening and correcting malpositions of skeletal bones, wherein the dimensions and the lengthening process of the device can be tailor-made in advance for the configuration and type of tubular skeletal bone in question into which the device is to be implanted, and where the device also can be designed with very small external dimensions thanks to its simple design In accordance with claim 1. this first object of the invention is achieved by means of the device having an elongate shape comprising a first end, a second end. a length dimension and a cross-sectional dimension, and the device further comprising a lengthening menas for bπnging the first and second ends into displacement from each other to a predetermined distance between each other after an activation According to the invention, the lengthening means compπses an absorbent body . which is arranged for bringing the first and second ends to the predetermined distance by means of a controlled swelling after the activation while the length dimension increases more than the cross-sectional dimension A second object of the present inv ention is to provide an implantable device which, in addition to the above-mentioned advantages, also enables correction of rotational and angular malpositions of skeletal bones In accordance w ith claim 2. this second object of the ιn\ ention is achieved by means of the absorbent body of the implantable device further comprising one or several stiffening elements and/or one or several swelling zones having a raised intrinsic swelling capacity in comparison to the remaining absorbent bod\ w hich are arranged tor controlling the swelling so that the first and second ends striv e towards a predetermined angle in relation to each other after the acti ation Further object of the invention will become ev ident trom the following description, while the features enabling these further objects to be achieved are ev ident from the attached, dependent claims Brief description of the drawings In the following, the invention will be described in greater detail with reference to the attached drawings, in which Fig 1 schematically show s a sectional view through an implantable device according to a preferred embodiment of the invention. Fig 2 schematically shows a sectional view through an implantable device according to an alternative embodiment of the invention. Fig. 3 A schematically shows a sectional view through an implantable device according to a particularh preferred embodiment of the invention, before activation. Fig 3B schematically show s a sectional view through the implantable device in Fig 3 A. after activation and subsequent swelling, and Fig 4 schematically show s a sectional view through an implantable dev ice according to another alternative embodiment of the invention Detailed description of preferred embodiments In the following, a particularly preferred embodiment, and a number oi alternative and advantageous embodiments of an implantable device for lengthening and correcting malpositions of skeletal bones according to the invention will be described with reference to the attached Fiεs 1 to 4 The implantable device 1 1 ; 1 1'; 21 : 1 1 1 according to the invention has an elongate shape comprising a first end 12: 12': 22; 1 12. a second end 13; 13'; 23: 1 13. a length dimension 14; 24: 1 14 and a cross-sectional dimension 15: 25; 1 15. Thereby, "cross-sectional dimension " e.g. refers to the outer diameter in case of a circle-cylindrical device, but can also refer to another cross-sectional dimension depending on the geometrical shape of the cross-section. Furthermore, the device 1 1 ; 21 : 1 1 1 comprises a lengthening means 16; 16'; 26; 1 16, 216 for bringing the first 12: 12'; 22; 1 12 and second 13; 13'; 23; 1 13 ends into displacement from each other to a predetermined distance 14'; 24'; 1 14' between each other after an activation. Therebv. "predetermined distance" refers to the maximum distance of the implantable device which is desirable after it has been implanted into a tubular skeletal bone. The predetermined distance has to be adapted for each individual case. According to the invention, and in the particularly preferred embodiment, the lengthening means comprises an absorbent body 16; 16'; 26; 1 16, which is arranged for bringing said first 12; 12'; 22; 1 12 and second 13; 13': 23; 1 13 ends to the predetermined distance 14'; 24'; 1 14' by means of a controlled swelling after the activation, while the length dimension 14; 24; 1 14 increases more than the cross-sectional dimension 15; 25; 1 15. In the particularly preferred embodiment of the implantable device 1 1 '. 1 1 " according to the invention, shown in figures 3A (before activation) and 3B (after activation and swelling), the absorbent body 16'. 16" comprises one or several stiffening elements 18'. 18". 19', 19", and/or one or several swelling zones 20'. 20" having a raised intrinsic swelling capacity in comparison to the remaining absorbent body 16'. 16". Thereby, the stiffening elements and/or the swelling zones are arranged for controlling the swelling so that said first 12'. 12" and second 13'. 13" ends strive towards a predetermined angle a in relation to each other after the activation. Thereby, the stiffening elements 18'. 18". 19'. 19" advantageously are constituted of inserts of metal or plastic, while the swelling zones 20'. 20" advantageously comprise a high content of a superabsorbent. However, it is conceivable with embodiments with another choice of material, or where only stiffening elements or only swelling zones are present. Accordingly, within the scope of the invention, it is conceivable with embodiments in which the first and second ends essentially are in the same plane (α =0) before the swelling and are displaced in relation to the plane (α > 0) by the swelling, or inversely, embodiments in which the two ends initially are displaced in relation to a plane (α > 0) and are brought into the same plane (α =0) by the swelling. In one advantageous embodiment, the absorbent body 16: 16'. 16" primarily is constituted of a matrix of thermosetting melamine formaldehyde plastic on a needled reinforcement material of HT-rayon. Thereby, HT-rayon refers to rayon fibres or filaments having a high tenacity. Furthermore, the absorbent body 16 advantageously comprises micro-crystalline cellulose as a filler. The absorbent body preferably has been compression-moulded to its intended shape during heating. Within the scope of the invention, it is of course also conceivable with absorbent bodies with another matrix material, reinforcement material, or filler. Accordingly, the matrix material can consist of or comprise another polymeric resin suitable for the purpose, the reinforcement material can consist of or comprise another fibre material suitable for the purpose, and the filler can consist of or comprise a suitable superabsorbent. such as for example cellulose acetate. In an alternative embodiment, in addition to an absorbent body of e.g. the type shown in Fig. 1. the device 21 further comprises first 28 and second 29 cylinder members having closed ends 22. 23 and opposite open ends 30, 31. Thereby, the open end 30 of the first cylinder member 28 is at least partially slidably inserted into the open end 31 of the second cylinder member 29, so that the cylinder members 28.29 together form at least one internal cavity 32 within which the absorbent body 26 is arranged. Furthermore, a back stop device 33 is arranged between the open ends 30. 31 for enabling the first 22 and second 23 ends of the implantable device 21 to be irreversibly displaced to the predetermined distance 24' after the activation. Thereby, 'irreversibly " ' refers to the fact that the implantable device cannot be compressed in its longitudinal direction, but can only be extended until the first and second ends of the device have arrived at the above-mentioned predetermined distance between each other. In another alternative embodiment, the device comprises valves 27', 27" for opening or closing a connection between the absorbent body 26 and the environment surrounding the device 21. wherein the valves 27'. 27" are arranged for being controlled by means of radio waves, ultrasonic, induction or magnetic control when accomplishing the activation and/or a deactivation. This embodiment is particularly advantageous when the device according to the invention comprises cylinder members of the above-mentioned type which enclose the absorbent body, but it is also conceivable with embodiments where the absorbent body only is enclosed by a relatively impervious membrane through which the valve or valves are arranged. In still another alternative embodiment, the back stop device 33 comprises at least one spring-loaded member 34 of one of the cylinder members which is arranged for mechanical engagement with a member provided with steps 35 of the other cylinder member. This type of back stop device is schematically depicted in the attached Fig. 2. In still another alternative embodiment, the cylinder members are slidably arranged with seals (not shown) against each other, wherein the internal cavity is divided into at least two portions by a stationary partition wall in which a connection having a check valve has been arranged. In another advantageous, alternative embodiment of the device according to the invention, illustrated in Fig.4. the absorbent body 1 16 is accommodated within a cylindrical member 129 comprising water inlet means for allowing water transport into the absorbent body during the controlled swelling. In this embodiment, the second end 1 13 is connected to a piston means 128 arranged for sliding displacement within the cylindrical member 129, wherein at least one spring member 216 is embedded in the absorbent body 1 16 for exercising a lengthening force in cooperation with the absorbent body on the first 1 12 and second 1 13 ends during the controlled swelling. The spring member 216 is preferably a helical steel spring. However, its also conceivable with embodiments with other geometrical spring shapes and/or materials. In the alternative embodiment, the water inlet means can be constituted by one or several water-permeable portions 1 17 in the cylindrical member 129, by the piston means 128 being water-permeable, or by the piston means 128 consisting of a disc member with a plurality of axially extending through-apertures, which can be accomplished e.g. by means of punching or laser cutting. If desired, the water inlet means can be constituted by the piston means comprising one or several nonreturn valves, for allowing water transport only in a direction towards the absorbent body. In the alternative embodiment, as illustrated in Fig. 4. the cylindrical member 129 preferably is sealed by a wall member 131 between the piston means 128 and the second end 1 13. thereby forming an internal cavity within the cylindrical member 129. The internal cavity is intended to be filled with an aqueous liquid H 2 O for providing at least a part of the water during the controlled swelling. It is also conceivable with embodiments in which opposing spring members (not shown) are provided on both sides of the piston means 128 in order to facilitate the control of the lengthening course of the implantable device. In the described alternative embodiment, the absorbent body 1 16 and the spring member(s) 216 are adapted for bringing the first 1 12 and second 1 13 ends to the predetermined distance by means of exercising a pressure together on the first and second ends after the activation which is larger than about 500 N/cm2. Furthermore, the water inlet means 1 17, 128 advantageously are adapted to the remaining components 1 1 . 1 16 of the implantable device 1 1 1 , so that the water transport (into the absorbent body 1 16) during the controlled swelling generates a lengthening rate of about 1 mm/day. However, it is also conceivable with alternative embodiments with another pressure and/or lengthening rate. In embodiments of the implantable device according to the invention where the absorbent body is enclosed by and stabilised by cylinder members of the above-discussed type, the absorbent body 26: 1 16 paπicularly advantageously comprises cellulose acetate or another superabsorbent. When the cylinder members 28, 29: 129 are concerned, they particularly advantageously are constituted of titanium. However, it is also conceivable with embodiments where the absorbent body comprises another suitable absorbent material, or where the cylinder members are made of another material suitable for insertion into a shaft of a bone. In all embodiments of the implantable device, it is particularly advantageous that the absorption properties of the absorbent body 16: 16', 16"; 26; 1 16 are adapted so that the activation can be accomplished by means of wetting with water originating from a body fluid (BF). In a particularly advantageous embodiment of the invention, the absorbent body 16; 26 is enclosed by a liquid-permeable membrane 17; 27 having permeation properties which are adapted for providing a controlled permeation rate of the water into the absorbent body during wetting. The liquid-permeable membrane 17; 27 is advantageously constituted of cellophane, a stretched polymer film or the like and, in addition to a cohesive effect, provides a possibility to control the rate at which the absorbent body is wetted and, as a consequence, also the swelling rate of the absorbent body and the lengthening rate of the device. In this embodiment, the liquid-permeable membrane preferably is selected in such a way that only water molecules and no other components of the body fluid can penetrate the membrane. However, it is also conceivable with embodiments where the implantable device according to the invention lacks a liquid-permeable membrane. In another advantageous embodiment, the absorbent body 16: 26. or the absorbent body and the liquid-permeable membrane 17; 27 is/are enclosed by a biodegradable, initially water- impervious, barrier layer (not shown), which advantageously comprises a hydrophobic material which is sensitive to body enzymes, or a macromolecular material which can be hydrolysed. Thereby, the barrier layer can be constituted of or comprise for example polylactate or polyurethane-urea (PUU). In this embodiment, the possibilities to control the permeation process and. consequently, also the swelling process of the absorbent body after activation are increased. The present invention should by no means be regarded as being limited to what has been disclosed in the foregoing in connection with the different embodiments, or to what is shown in the attached drawings, but the scope of the invention is defined by the appended claims. Accordingly, within the limits of what is allowable for the case in question, it is also conceivable with embodiments where the above-discussed cylinder members and/or the absorbent body does/do not have a circular cross-section. When embodiments of the device according to the invention where activation and deactivation can be influenced from the outside after implantation are concerned, a method comprising the following steps can be utilised for the lengthening and/or correction: a device according to the invention having appropriate dimensions and lengthening properties for the tubular skeletal bone in question is selected, the device according to the invention is implanted into the skeletal bone using techniques which are well-known to the skilled person. the device is left in its place for 14 days, a lengthening of about 0.5 mm length increase is activated twice a day until the desired lengthening/correction L (mm) is achieved, and the device is left in its place within the skeletal bone for an approximate time of 5 x L weeks before the device is removed by means of techniques which are previously known per se In case the intention is to utilise a device according to the invention, the activation and deactivation of which cannot be influenced from the outside, a method comprising the following steps can be utilised: analysis of the lengthening/correction which is required for the skeletal bone in question, a device according to the invention having appropriate dimensions and lengthening properties is selected. the device is implanted using techniques which are previously known per se, the device is left in its place within the bone for a certain stabilisation time counted from the point in time when the desired lengthening/correction has been achieved, and the device is removed using techniques which are previously known er se. In both cases, the status of the skeletal bone should be regularly supervised by means of radiographs. Accordingly, vvhen the swelling process of the absorbent body 16; 16'; 26; 1 16 is concerned, after the activation having been accomplished by means of an external signal or the device according to the invention coming into contact with body fluid after the implantation, the swelling process is controlled from the outside and/or is predetermined by the choice and adaptation of the components included in the device according to the invention, so that the swelling process at least will compπse: (i) an initial phase during which no swelling takes place and recovery from trauma can take place: (ii) a lengthening phase during which the device according to the invention at a controlled rate gradually adopts the desired length/shape; and (iii) a healing phase during which no further swelling of the absorbent body takes place and healing/stabilisation of the skeletal bone in question can take place.

Claims: Claims 1. An implantable device for lengthening and correcting malpositions of skeletal bones, said device (11; ll';21; 111) having an elongate shape comprising a first end (12; 12';22: 112),asecondend(13; 13'; 23; 113), a length dimension (14; 24; 114) and a cross- sectional dimension (15; 25; 115). wherein said device (11: 11'; 21: 111) further comprises a lengthening means (16; 16'; 26; 116.216) for bringing said first (12; 12'; 22; 112) and second (13; 13'; 23; 113) ends into displacement from each other to a predetermined distance (14'; 24'; 114') between each other after an activation, characterised in that the lengthening means comprises an absorbent body (16; 16'; 26; 116), which is arranged for bringing said first (12; 12'; 22; 112) and second (13; 13'; 23; 113) ends to said predetermined distance (14'; 24'; 114') by means of a controlled swelling after the activation, while the length dimension ( 14; 24; 114) increases more than the cross-sectional dimension (15; 25; 115). 2. An implantable device according to claim 1. characterised in that the absorbent body (16'.16") further comprises one or several stiffening elements (18', 18".19', 19") and/or one or several swelling zones (20'.20"), having a raised intrinsic swelling capacity in comparison to the remaining absorbent body (16', 16"), which is/are arranged for controlling the swelling so that said first (12', 12") and second (13'.13") ends strive towards a predetermined angle (α) in relation to each other after the activation. 3. An implantable device according to claim 2. characterised in that said stiffening elements (18'.18".19'.19") are constituted of inserts of metal or plastic and/or that said swelling zones (20'.20") comprise a high content of a superabsorbent. 4. An implantable device according to any one of claims 1 - 3. characterised in that the absorbent body (16; 16', 16") primarily is constituted of a matrix of thermosetting melamine formaldehyde plastic on a needled reinforcement material of HT-rayon with micro-crystalline cellulose as a filler. 5. An implantable device according to claim 1, wherein the device (21) further comprises first (28) and second (29) cylinder members having closed ends (22.23) and opposite, open ends (30, 31). wherein the open end (30) of the first cylinder member (28) is at least partially slidably inserted into the open end (31 ) of the second cylinder member (29). so that said cylinder members (28.29) together form at least one internal cavity (32). characterised in that the absorbent body (26) is arranged within the internal cavity (32), and that a back stop device (33) is arranged between the open ends (30, 31) for enabling said first (22) and second (23) ends of the implantable device (21 ) to be irreversibly displaced to the predetermined distance (24') after the activation. 6. An implantable device according to claim 1 or 5. characterised in that the device comprises valves (27', 27") for opening or closing a connection between the absorbent body (26) and the environment surrounding the device (21). wherein said valves (27'.27") are arranged for being controlled by means of radio waves, ultrasonic, induction or magnetic control when accomplishing the activation and/or a deactivation. 7. An implantable device according to claim 5 or 6. characterised in that the back stop device (33) comprises at least one spring- loaded member (34) of one of the cylinder members which is arranged for mechanical engagement with a member provided with steps (35) of the other cylinder member. 8. An implantable device according to any one of claims 5-7. wherein the cylinder members are slidably arranged with seals against each other, characterised in that the internal cavity is divided into at least two portions by a stationary partition wall in which a connection having a check valve has been arranged. 9. An implantable device according to claim 1. wherein the absorbent body (116) is accommodated within a cylindrical member (129) comprising water inlet means for allowing water transport into the absorbent body during the controlled swelling, characterised in that the second end ( 113) is connected to a piston means (128) arranged for sliding displacement within the cylindrical member (129), wherein at least one spring member (216) is embedded in the absorbent body (116) for exercising a lengthening force in cooperation with the absorbent body on the first (112) and second (113) ends during the controlled swelling. 10. An implantable device according to claim 9. characterised in that the water inlet means are constituted by one or several water- permeable portions (117) in the cylindrical member (129). 11. An implantable device according to claim 9 or 10, characterised in that the water inlet means are constituted by the piston means (128) being water-permeable. 12. An implantable device according to any one of claims 9-11. characterised in that the water inlet means are constituted by the piston means (128) consisting of a disc member with a plurality of axially extending through-apertures. 13. An implantable device according to any one of claims 9-11. characterised in that the water inlet means are constituted by the piston means comprising one or several nonreturn valves, for allowing water transport only in a direction towards the absorbent body. 14. An implantable device according to any one of claims 9-13. characterised in that the cylindrical member ( 129) is sealed by a wall member (131) between the piston means (128) and the second end (113). thereby forming an internal cavity within the cylindrical member (129) intended to be filled with an aqueous liquid (HO) for providing at least a pan of the water during the controlled swelling. 15. An implantable device according to any one of claims 9-14. characterised in that the absorbent body (116) and the spring member(s) (216) are adapted for bringing the first (112) and second (113) ends to the predetermined distance by means of exercising a pressure together on the first and second ends after the activation which is larger than about 500 N/cm2. 16. An implantable device according to any one of claims 9-15, characterised in that the water inlet means (117, 128) are adapted to the remaining components (112.116) of the implantable device (111). so that the water transport during the controlled swelling generates a lengthening rate of about 1 mm/day. 17. An implantable device according to any one of claims 5-16, characterised in that the cylinder members (28, 29; 129) are constituted of titanium. 18. An implantable device according to any one of claims 5-17, characterised in that the absorbent body (26; 116) comprises cellulose acetate or another superabsorbent. 19. An implantable device according to any one of the preceding claims, characterised in that the absorption properties of the absorbent body (16; 16'; 26; 116) are adapted so that the activation can be accomplished by means of wetting with water originating from a body fluid (BF). 20. An implantable device according to any one of the preceding claims, characterised in that the absorbent body ( 16: 26) is enclosed by a liquid-permeable membrane (17: 27) having permeation properties adapted for providing a controlled permeation rate of said water into said absorbent body during wetting. 21. An implantable device according to any one of the preceding claims, characterised in that the absorbent body (16:16': 26). or the absorbent body and the liquid-permeable membrane (17; 27). is/are enclosed by a biodegradable, initially water-impervious, barrier layer. 22. An implantable device according to claim 21. characterised in that the barrier layer comprises a hydrophobic material which is sensitive to body enzymes, or a macromolecular material which can be hydrolysed.

Inventors: HOEGFORS CHRISTIAN, KARLADANI ABBAS, HOEGFORS, CHRISTIAN, KARLADANI, ABBAS
Applicants: HOEGFORS CHRISTIAN, KARLADANI ABBAS, HOEGFORS, CHRISTIAN, KARLADANI, ABBAS
Application year: 2000
Main classification: A61F2
IPC codes: A61B17, A61F2