WO2015133967A1

WO2015133967A1 - Skull bone device

Info

Publication number: WO2015133967A1
Application number: PCT/SE2015/050254
Authority: WO
Inventors: Claes Lauritzen
Original assignee: Claes Lauritzen
Priority date: 2014-03-07
Filing date: 2015-03-06
Publication date: 2015-09-11

Abstract

The invention concerns a device (10, 40) for pulling apart a first and a second skull bone segment (23a, 23b). The device (10, 40)comprises a first (11, 41, 61) and a second (12, 42, 62) displacement element, wherein each displacement element (11, 41, 61; 12, 42, 62) is provided with a hook member (21, 22) configured to be hooked on to an edge of the first and the second skull bone segment (23a, 23b), respectively, wherein the first and second displacement elements (11, 41, 61; 12, 42, 62) are configured to be moveable in relation to each other along a longitudinal axis of the device so as to allow a variation of a distance between the first and second hook members (21, 22). The device further comprises a guiding arrangement (13, 43, 63) configured to guide the first and second displacement elements (11, 41, 61; 12, 42, 62) when moved along the longitudinal axis, and a resilient member (16, 17, 46) configured to, when arranged in a stressed state, press the first and second displacement elements (11, 41, 61; 12, 42, 62) away from each other along the longitudinal axis so as to increase the distance between the first and second hook members (21, 22).

Description

Skull bone device

TECHNICAL FIELD

The present invention relates to a device for pulling apart a first and a second skull bone segment.

BACKGROUND ART

During the first 12-18 months after birth, the human brain triples its own weight and thus grows violently. The calvaria, i.e. the skull bones surrounding the brain are joined together with fibrous tissue. This tissue that separates the calvaria is referred to as suture and yield to the pressure of the growing brain. The sutures later ossify (turn into bone) subsequent to the most dramatic brain growth period. Some of these sutures may stay non-ossified for an extended time, but will have nothing to do with the actual skull growth once this has entered a much slower growth phase at approximately 18 months.

Sometimes sutures ossify too early and cannot yield to the pressure of the brain. This condition is referred to as premature fusion of the skull sutures or simply craniosynostosis. This can occur between any of the calvarial bone segments and give in such instances rise to typical skull deformities, totally dependent on where the craniosynostosis has taken place.

Craniosynostosis may appear as a relatively mild condition affecting merely the beauty of the child but can also be a very severe condition seriously threatening eyesight, breathing and, ultimately, life. The treatment for this condition is separation of the bones accommodating the growing brain and its demand for space. Also this separation of the bones can be performed in such a way that not only function, but also the normal shape of a skull will be preserved or restored.

Craniosynostosis surgery was in its inception very simple and aimed at just separating the prematurely fused bones. More often than not, these bones fused back again and the outcome of surgery was rarely successful. With the development in the late 1960s of craniofacial surgery, methods were developed and successfully carried out to treat children with craniosynostosis. Surgery was however extensive, demanding exceptional intensive care resources and always necessitated blood transfusions.

As an alternative to this extensive remodelling carpentry of skull bone a much simpler method has been proposed and utilised entailing the use of safety pin like stainless steel springs that are inserted between bones that have been separated surgically. These springs act slowly but steadily to separate the bones in a desired direction. Used in combination, cuts in the bone together with such springs have proven to be effective enough and also safe when used early in children with craniosynostosis.

The spring is positioned between bone segments in an osteotomy line (i.e. bone cut) under the skin until it is removed during a second operation. Being placed under the skin; the springs are not adjustable or controllable after being positioned. In addition, surgical operations always entail risks and using implanted springs, even though very effective when it comes to treating children with craniosynostosis, results in the need for a second operation. A second operation also adds cost to the total cost for the treatment of a patient with craniosynostosis.

WO2007/064257 discloses a device that makes use of an implantable elastic member and a resorbable bar that may be left in the body, which makes it possible to dispense with the second operation. However, since there is a general desire not to leave anything in the body due to possible long-term effects, a second operation may still be needed. Further, the procedure for attaching the device of WO2007/064257 includes the formation of holes and notches in the skull bone which may be regarded as being more complicated than inserting the steel springs described above.

There is thus a need for further developments in this field. SUMMARY OF THE INVENTION

The object of the present invention is to provide a device which is easy to use, which improves controllability, and which minimizes the risks involved in treatment and surgery of craniosynostosis and other craniofacial conditions. The invention concerns a device for pulling apart a first and a second skull bone segment, and it is characterized in that the device comprises a first and a second displacement element. Each displacement element is provided with a hook member configured to be hooked on to an edge of the first and the second skull bone segment, respectively. The first and second displacement elements are configured to be moveable in relation to each other along a longitudinal axis of the device so as to allow a variation of a distance between the first and second hook members. The device also comprises a guiding arrangement configured to guide the first and second displacement elements when moved along the longitudinal axis, and a resilient member configured to, when arranged in a stressed state, apply a force directed to press the first and second elements away from each other along the longitudinal axis so as to increase the distance between the first and second hook members.

The device described herein can be applied with its longitudinal axis positioned across a gap between two adjacent skull bone segments with its hook members penetrating the skin of the patient and being hooked on to the edges of the bone segments. As the resilient member is set in its stressed state, it will slowly press the displacement elements away from each other and slowly pull the bone segments apart.

Each hook member preferably comprises a hook that simply is hooked on to the edge of the corresponding bone segment. After use, such hook members can be unhooked and removed without any requirement for a second surgical operation. The term hook member includes also variants where a thread, wire, or similar, is hooked on to notches etc. in the bone segment edge, and variants where a hole is made in the bone segment inside the edge and where a thread, wire, or similar is thread through the hole and out together with itself through a hole in the skin of the skull. Also such hook members can be removed without any requirement for a second surgical operation. In the case of a wire that is thread through a hole in the bone segment, it may be "unhooked" and removed by cutting off one of the two wires close to the skin and pulling the other. The stress load controls the pulling, i.e. the displacement of the skull bone segments. All parts of the device except for the hook members can be placed outside of the skin of the patient which simplifies the use and the design and the choice of materials of the device. With most parts of device being placed outside the skin, the device and the stress load can easily be controlled and adjusted if needed. The displacement elements can be provided with scales to indicate their relative longitudinal movement so as to indicate the degree of displacement of the skull bone segments over time.

When the device is installed, the resilient member exerts continuously a bone segment pulling force so the process of pulling the skull bone segments apart becomes automatic, dynamic and continuous. There is, for instance, no need to tighten screws etc. on a regular (e.g. daily) basis.

Each hook member, or a part connected thereto, preferably comprises a sharp tip for easy penetration through the skin. Normally, this penetration should be made from the inside of the skin and outwards to avoid contamination. This means that the sharp tip should be arranged at an outer end of the hook member (or of the part connected to the hook member), i.e. at an end opposite to the end hooked on to the edge of the bone segment. The end with the sharp tip can then be connected to its corresponding displacement element.

Parts intended to penetrate the skin or be placed inside the skin during the process of adjusting the skull bone segments should be made of a biocompatible material that does not have any negative effects on the body. Suitable biocompatible materials include, but are not restricted to, silicon, carbon fibre, titanium or metal alloys. As an alternative or complement, bio-resorbable material may be used. As an example, a hook can be made in a resorbable material where a thread/wire made of e.g. a metal alloy is included to increase the tensile strength. The thread can easily be pulled out when the resorbable material has dissolved. Since it normally is difficult to exactly predict the dissolution rate for a resorbable material it is in many situations preferable to use a non-resorbable material for the hook.

The first and second displacement element may, for instance, be arranged in a row along the longitudinal axis with a common guiding member arranged to hold them in place. As an alternative, they may be arranged on top of, or beside, each other such that they at least partly overlap, wherein the overlap typically decreases when the first and second displacement element are pressed away from each other along the longitudinal axis. The displacement elements preferably have an elongated shape such as to extend along the longitudinal axis.

In an embodiment the hook member comprises a bent end portion intended to be hooked on to the segment edge. The bent end portion allows the hook member to be hooked on to the respective skull bone segment by a simple and fast action. When installing the device, the bent end portion is simply hooked around the edge of the skull bone segment (with the resilient member set in a stressed or non-stressed state, or simply not yet engaged to the displacement elements). The hook members have no or little impact on the bone material; they merely affect the relative position of the skull bone segments as a result of the resilient member exerting a force onto the hook members via the displacement elements.

The sharp tip of the hook member (or of a connected part) allows the hook member to pierce from inside and out a hole in the skin when to be installed. The hook member is removable though the same hole, from inside and out, after completion of the skull bone segment displacement.

The bent end portion is preferably configured to partly or fully straighten out when exposed to a force exceeding a certain magnitude. Once desired positions of the skull bone segment are reached, each hook member can thereby be easily removed by quickly and distinctively applying a pulling force that exceeds the threshold magnitude. Thus, if a sufficient force is applied the bent end portion will straighten out and the hook member will unhook from the skull bone segment and allow easy removal. As a result, no additional surgery is needed and no part of the device will be left in the body after completion of the pulling apart of the skull bone segments. It may be that the hook members can be removed by carefully turning and pulling them outwards without having to straighten them out. Whether this is possible depends, for instance, on the detailed structure of the particular device used.

In an embodiment the device is configured to exert a pulling force of 6-8 N when arranged for pulling apart the skull bone segments. That is, the resilient member exerts a pulling force of 6- 8 N when arranged in a stressed state. A force above a magnitude of around 12 N would, in such an example, be suitable for partly or fully straightening out the bent end portion. The hook members are designed to, and their material composed to, exhibit these properties. The pulling force is mainly determined by the choice and adaptation of the resilient member.

In an embodiment at least one of the hook members is attached to its corresponding displacement element via a rod member. Preferably, the rod member and the hook member form an integral part. Preferably, one end of such an integral part forms the hook member to be hooked on to the edge of the bone segment, whereas the opposite end is provided with the sharp tip described above. When such an integral part is installed (after penetrating the skin from the inside and out and pulling the rod outwards so as to position the end with the hook at the edge of the bone segment), the rod member can be connected to its corresponding displacement member. If desired, the length of the rod member can be adjusted simply by cutting it off at some distance from the sharp tip.

The rod members facilitate that the distance between the respective hook members and the respective displacement elements is adjustable. The distance can be adapted to an individual skull shape by adjusting the length of rods, thereby providing a flexible device which may be adapted to fit different skull shapes and different needs for adjustment. The device can thereby, by adapting length of the rods, be simply adapted to different individuals. The end of the rods can be snipped off such as to give the rods the appropriate length after the hook members has been properly hooked onto the edge of the skull bone segments and engaged to the displacement elements.

In an embodiment of the invention each hook member is connected to its corresponding displacement element so that the force exerted by the resilient member can be transmitted to the hook members.

In an embodiment the device is configured to fix the hook members in a rotational direction. This ensures that the hook members do not unintentionally and/or prematurely disengage from the skull bone segment by an accidental rotation of the hook member.

In an embodiment the device comprises locking means configured to lock the position of the first and the second hook member in relation to the first and the second displacement element in order to prevent rotational movement around the longitudinal axis as well as longitudinal movement of the first and second hook member relative the respective displacement elements. The locking means makes sure that the hook members, e.g. via the rod members, move with the displacement elements as the displacement elements are subjected to a force which presses the first and second displacement elements away from each other along the longitudinal axis, thereby also increasing the distance between the hook members. Pulling apart of the skull bone segments is facilitated.

In an embodiment of the invention the guiding arrangement extends along at least part of the longitudinal edge of at least one of the first and the second displacement element such as to only allow movement of the first and second displacement elements along the longitudinal axis. The guiding arrangement thus holds the first and second displacement elements substantially in place in relation to each other in a lateral and a vertical direction of the device.

In an embodiment of the invention the guiding arrangement comprises a guiding opening arranged on the first displacement element configured to guide the second displacement element. Such a design is suitable when the displacement elements are arranged on top of or besides each other. Preferably a guiding opening is also arranged on the second displacement element configured to guide the first displacement element.

Alternatively, or in conjunction with the guiding arrangement as outlined above, the guiding arrangement also comprises a separate guiding member that is configured to guide both displacement elements. Such a guiding member may extend along at least part of the longitudinal edges of the first and the second displacement element, thereby controlling the longitudinal movement of both displacement elements upon being exposed to a force by the resilient member. Guiding, in longitudinal direction, of the displacement elements allows for proper and controlled pulling apart i.e. displacement of the skull bone segments along the longitudinal axis. In an embodiment of the invention the resilient member is a closed loop made of an elastic material. The closed loop of elastic material, for example an elastic band, is detachably arranged to engage with the first end (or other part) of the first and the second displacement element and to exert a force upon the first and second displacement element when arranged in a stressed state such as to force the first and second displacement element away from each other. One or more closed loops of elastic material can be provided to the device.

In an embodiment of the invention the resilient member is a spring. The spring may be any spring suitable to exert a force upon the first and second displacement element such that they are pressed or pulled away from each other in opposite direction along the longitudinal direction. For example, the spring may be a ring spring, a compression spring, a tension spring, a canted coil spring etc. A first end or part of the spring is arranged to act on the first displacement element and a second end or part of the spring is arranged to act on the second displacement element. The device may be provided with more than one spring, wherein the combined forces of the springs preferably being centrally distributed such as to exert a pulling or pushing force on the first and second displacement elements relative each other only along the longitudinal axis.

One benefit with the invention is that the device is arranged outside the skin of the infant skull during its operations. It is thus desirable that the device is as little in the way as possible. In an embodiment of the invention the first and second displacement element are bent such as to conform to an infant skull shape. Such a design benefits the usability of the device, the device preferably being as discrete as possible as it is intended to be arranged at the periphery of an infant's skull. The conformity of the bent form with the skull shape makes the device less protruding and thus less likely to be subject to impact which might affect the displacement of the skull bone segments. The guiding arrangement may also be bent to conform to the skull shape.

The invention also concerns a method for displacing skull bone segments involving a skull bone segment displacement device comprising a first and a second displacement element configured to be moveable in relation to each other along a longitudinal axis, a first and second hook member, a guiding arrangement configured to guide the first and second displacement elements when moved along the longitudinal axis and a resilient member. The method comprises the step of:

- hooking said first and second hook member on to the edge of a first and second skull bone segment respectively,

- arranging the resilient member in a stressed state so as to , apply a force directed to press the first and second elements away from each other along the longitudinal axis so as to increase the distance between the first and second hook members.

The method may further comprise the step of inserting said first and second hook member through a first and second point of penetration in the skin of a skull. As described above, the hook members are preferably installed through the skin from inside and out to avoid contamination. However, in principle it is possible to insert the hook members from outside and in. If so the bent end portion of the hook member is preferably provided with the sharp tip.

The method may further comprise the step of fixing the first and second hook member to the first and second displacement element respectively,

The method may further comprise the step of exposing the hook members to a force exceeding a certain magnitude such as to partly or fully straighten out a bent end portion of respective hook members. The force is preferably exerted by pulling the hook members in a direction away from the skull bone segment. The hook members are preferably disengaged from the first and second displacement element respectively prior to exposing the hook members to a force. The device may thereby be removed from the skull.

BRIEF DESCRIPTION OF THE DRAWINGS

In the description of the invention given below reference is made to the following figures, in which:

Figure 1 shows, in a perspective view, parts of device according to a first embodiment of the invention;

Figure 2a shows, in top view, a part of the device of Figure 1;

Figure 2b shows, in side view, the part of Figure 2a; Figure 2c shows, in cross-sectional view, the part of Figure 2a;

Figure 3 shows, in side view, the device according to a first embodiment of the invention during operation;

Figure 4a shows, in a perspective view, parts of device according to a second embodiment of the invention;

Figure 4b shows, in perspective view, a part of the device of Figure 4a; and

Figure 5a-c shows, in perspective view, parts of the device according to the invention.

DETAILED DESCRIPTION

In the following several embodiment of the invention are shown and described. The invention is not limited to the embodiments shown; they merely represent examples of the invention.

Figure 1 shows a first embodiment a device 10 for pulling apart a first and a second skull bone segment 23a, 23b according to the invention. The device 10 comprises a first 11 and a second 12 displacement element of elongated shape which are configured to be moveable in relation to each other along a longitudinal axis of the device 10. Figures 2a, 2b and 2c show the first displacement element 11.

The device 10 further comprises a guiding arrangement 13 configured to guide the first and second displacement elements 11, 12 when they are moved along the longitudinal axis. The guiding arrangement 13 comprises a guiding opening 14 arranged on the first displacement element 11 and a guiding opening 15 arranged on the second displacement element 12. The first displacement element 11 is arranged on top of the second displacement element 12 such that they partly overlap and are slidable in relation to each other. The guiding opening 14 arranged on a first end the first displacement element 11 guides the second displacement element 12 and the guiding opening 15 arranged on the first end of the second displacement element 12 guides the first displacement element 11 such that they are movable only in longitudinal direction relative each other.

Two resilient members 16, 17, shown as elastic loops in Figures 1 and 3, are arranged on each side of the overlapping parts of the elongated first and second displacement elements 11, 12 by means of protruding elements 20a, 20b, i.e. each resilient member 16, 17 cooperates with a protruding element 20a of the first displacement element 11 and a protruding element 20b of the second displacement element 12. When arranged in a stressed state the resilient members 16, 17 are exerting a force upon the first and second displacement elements 11, 12 such that the first end of the first displacement element 11 is moved towards the first end of the second displacement element 12, each displacement element 11, 12 being guided by a guiding opening 14, 15 on the respective other displacement element 11, 12. Thereby, the second end 18 of the first displacement element 11 is moved away from the second end 19 of the second displacement element 12 upon exertion of a force from the resilient members 16, 17. The second ends 18, 19 are defined as the ends of the first and second displacement elements 11, 12 being pressed or pulled furthest away respective each other along a longitudinal axis. The other ends, the respective first ends of the first and second displacement elements, are arranged to cooperate with the resilient member.

The second ends 18, 19 of the first and second displacement elements 11, 12 are provided with engagement means (in this example a hole) for engagement with a first and second hook member 21, 22.

As shown in figure 3, first hook member 21 and first rod member 21a forms an integral part. The first rod member 21a is connected to the first displacement member 11. Similarly, second hook member 22 and second rod member 22a forms an integral part, and the second rod member 22a is connected to the second displacement member 12. The second ends 18, 19 are pushed apart due to the force exerted by the resilient members 16, 17 in stressed state. The hook members 21, 22 are subsequently pulled apart. Bent end portions of the hook members 21, 22 are hooked on to an edge of the first and the second skull bone segment 23a, 23b, respectively, thereby pulling the skull bone segments 23a, 23b apart. The rod members 21a, 22a extend through the skin 24. The first and second displacement elements 11, 12 are arranged outside the skin 24 and are bent to conform to the skull shape.

The integrated hook member/rod members have been installed by pushing and pulling the hook/rod through the skin from inside and out. After installation, the hook/rod members were connected to their corresponding displacement element. The outer end of each rod member, i.e. the end opposite to the hook, was initially provided with a sharp tip for facilitating penetration of the skin. The sharp tips are not shown in figure 3 since the rods have been cut off to adjust their length to the particular application.

Figure 4-5 show a second embodiment of a device 40 for pulling apart a first and a second skull bone segment 23a, 23b according to the invention. A first and second displacement element 41, 42; with the first end of the first displacement element 41 and the first end of the second displacement element 42 facing each other, are arranged to slide in longitudinal direction in a guiding member 43. The guiding member 43 partly surrounds the displacement elements 41, 42, i.e. the guiding members 43 longitudinal edges are extending along and folded around the longitudinal edges of the displacement elements 41, 42 such as to form a rail for controlling the longitudinal movement of the displacement elements 41, 42 relative each other.

The first end of the first displacement element 41 and the first end of the second displacement element 42 are provided with a respective protruding member 50a, 50b being arranged perpendicular to the longitudinal direction, extending upwardly. Each respective protruding member 50a, 50b cooperates with a respective end of a resilient member in the form of a ring spring 46. When the ring spring 46 is arranged in a stressed state, it presses the first and second displacement elements 41, 42 away from each other along the longitudinal axis so as to increase the distance between their respective second ends 48, 49.

The second ends 48, 49 are provided with a respective upwardly directed loop, allowing cooperation with respective hook members 21, 22 via rod members. The hook members 21, 22 of the second embodiment are the same as the ones in the first embodiment. The hook members 21, 22 are configured to partly or fully straighten out when exposed to a force exceeding a certain magnitude.

The first and second displacement elements 41, 42 are further provided with downwardly directed loops at their second ends 48, 49. The rod members are intended to cooperate with the first and second displacement elements 41, 42 by running through the loops. Such cooperation is seen in Figure 5a-c. The hook members are fixed in a rotational direction by locking means 55. The locking means 55 prevent rotational movement of the first and second hook member 21, 22 around the longitudinal axis as well as longitudinal movement of the first and second hook member 21, 22 relative the respective displacement elements 41, 42. The locking means 55 is provided with a through-hole in its body; through which the rod member 21a is fitted.

In Figure 5b a screw member 56, arranged perpendicular to the through-hole in the locking member 55, is arranged to push onto the rod member 21a such as to fix its position in the through-hole in the locking member 55. The screw member 56 tightens the locking means 55 to the rod of the first hook member 21. In Figure 5c a cut-out of the body of the locking means 55 in arranged in contact with the first displacement element 41 such as to lock the position of the rod member 21a, i.e. the hook member 21, in relation to the first displacement element 41 which prevents longitudinal movement of the hook member 21 in relation to the first displacement element 41. Rotational movement as well as longitudinal movement of the first hook member 21 relative the first displacement elements 41 is thereby prevented once the screw 56 is tightened and the locking means 55 body fitted to be in contact with the first displacement element 41.

Figure 6 shows another example embodiment of displacement elements 61, 62 described herein. Each displacement element 61, 62 is provided with a curved protruding member 60a, 60b for cooperation with the resilient member in line with the protruding members 50a, 50b described in relation to Figure 4.

Each displacement element 61, 62 is further provided with a slit 63 along a longitudinal central axis of the displacement element 41, 42 which extends from the first end towards the protruding member 60a, 60b. The protruding member 60a of the first displacement element 61 fits in and is slidable along the slit 63 of the second displacement element 62. The protruding member 60b of the second displacement element 62 fits in and is slidable along the slit 63 of the first displacement element 61. The slit 63 forms part of the guiding arrangement.

The displacement elements 61, 62 are allowed to be placed on top of and partly overlap each other, i.e. with the protruding member 60a, 60b of one displacement element 61, 62 being placed in the slit 63 of the other displacement member 61, 62 and vice versa. This improved stability of the device 10, 40.

Figure 7a and 7b show another example of a locking means 71 according to the invention having a similar purpose as the locking means 55 described herein. The locking means 71 comprises a curved resilient plate capable of resuming its original shape spontaneously after contraction. The locking means 71 is further provided with two through-holes 72 arranged to receive the rod member 21a.

In order to apply the locking member 71 to the rod member 21a the plate is pressed together in the direction of the extension of the rod member 21a such that it is contracted. The rod member 21a is subsequently entered through the through-holes 72. Once the desired position of the locking means along the rod 21a has been reached, the locking means 71 is released, i.e. the contracting force is removed from the plate. As the contracting force is removed, the locking means 71 lock against the rod member 21a by increasing the friction between the plate and the rod member 21a at the through holes 72. Movement between the locking member 71 and the rod member 21a is thereby hindered. In its locking position, part of the plate of the locking member 72 is in contact with the displacement element 61. The locking element 71 in its locked position thereby prevents rotational movement around the longitudinal axis as well as longitudinal movement of the rod member 21a relative the displacement element 61. A locking member 71 in locked position is shown in Figure 7b.

The invention is not limited by the embodiments described above but can be modified in various ways within the scope of the claims. For instance, the resilient member may be a compression spring. The embodiments of the different parts of the device described herein are all combinable, for example the overlapping first and second displacement elements of the first embodiment may be provided with a guiding arrangement or a resilient member as described in conjunction with the second or third embodiment. The hook members can be connecting to any part of the respective first and second displacement element, not just the second ends.

Claims

1. Device (10, 40) for pulling apart a first and a second skull bone segment (23a, 23b), characterized in

that the device (10, 40) comprises

a first (11, 41; 61) and a second (12, 42; 62) displacement element, wherein each displacement element (11, 41, 61; 12, 42, 62) is provided with a hook member (21, 22) configured to be hooked on to an edge of the first and the second skull bone segment (23a, 23b), respectively,

wherein the first and second displacement elements (11, 41, 61; 12, 42, 62) are configured to be moveable in relation to each other along a longitudinal axis of the device so as to allow a variation of a distance between the first and second hook members (21, 22),

a guiding arrangement (13, 43; 63) configured to guide the first and second displacement elements (11, 41; 61; 12, 42; 62) when moved along the longitudinal axis,

a resilient member (16, 17; 46) configured to, when arranged in a stressed state, apply a force directed to press the first and second displacement elements (11, 41, 61; 12, 42, 62) away from each other along the longitudinal axis so as to increase the distance between the first and second hook members (21, 22).

2. Device (10, 40) according to claim 1 wherein the hook member (21, 22) comprises a bent end portion intended to be hooked on to the skull bone segment (23a, 23b) edge.

3. Device (10, 40) according to any of claims 1 or 2, wherein the hook member (21, 22) or a part connected to the hook member comprises a sharp tip for penetration of skin.

4. Device (10, 40) according to any of the above claims, wherein a bent end portion of the hook member (21, 22) is configured to partly or fully straighten out when exposed to a force exceeding a certain magnitude.

5. Device (10, 40) according to any of the above claims wherein the device (10, 40) is configured to exert a pulling force of 6-8 N when arranged for pulling apart the skull bone segments (23a, 23b).

6. Device (10, 40) according to any of the above claims, wherein at least one of the hook members (21, 22) is attached to its corresponding displacement element (11, 41, 61; 12, 42, 62) via a rod member (21a, 22a).

7. Device (10, 40) according to any of the above claims wherein the hook members (21, 22) are made of biocompatible material.

8. Device (10, 40) according to any of the above claims wherein the hook members (21, 22) are configured to be fixed in a rotational direction.

9. Device (10, 40) according to any of the above claims wherein the guiding arrangement (13, 43, 63) extends along at least part of the first and the second displacement element (11, 41, 61; 12, 42, 62) such as to prevent movement of the first and second displacement elements (11, 41, 61; 12, 42, 62) in other directions than along the longitudinal axis.

10. Device (10) according to any of the above claims wherein the guiding arrangement (13, 63) comprises a guiding opening (14, 64) arranged on the first displacement element (11), said guiding opening (14) being configured to guide the second displacement element (12).

11. Device (40) according to any of the claims 1-9, wherein the guiding arrangement (43) comprises a separate guiding member that is configured to guide both displacement elements (41, 42, 61, 62).

12. Device (10, 40) according to any of the above claims, wherein the resilient member (16, 17) is a closed loop made of an elastic material.

13. Device (10, 40) according to any of the claims 1-11, wherein the resilient member (46) is a spring.

14. Device (10, 40) according to any of the above claims, wherein each hook member (21, 22) is connected to its corresponding displacement element (11, 41, 61; 12, 42, 62) so that the force exerted by the resilient member (16, 17, 46) can be transmitted to the hook members.

15. Device (10, 40) according to any of the above claims, wherein the first and second displacement element (11, 41, 61; 12, 42, 62) are bent such as to conform to an infant skull shape.

16. Device (10, 40) according to any of the above claims, wherein the first and second displacement element (11, 41, 61; 12, 42, 62) at least partly overlap and wherein the overlap is arranged such as to decrease when the first and second displacement elements (11, 41, 61; 12, 42, 62) are pressed away from each other along the longitudinal axis.

17. Device (10, 40) according to any of the above claims, wherein the device (10, 40) further comprises at least one locking means (55, 71) configured to lock the position of the first and the second hook member (21, 22) in relation to the first and the second displacement element (11, 41, 61; 12, 42, 62) in order to prevent rotational movement around the longitudinal axis as well as longitudinal movement of the first and second hook member (21, 22) relative the respective first and second displacement elements (11, 41, 61; 12, 42, 62).

18. Method for pulling apart skull bone segments (23a, 23b) involving a skull bone

segment displacement device (10, 40) comprising a first and a second displacement element (11, 41, 61; 12, 42, 62) configured to be moveable in relation to each other along a longitudinal axis, a first and second hook member (21, 22), a guiding

arrangement (13, 43) configured to guide the first and second displacement elements (11, 41, 61; 12, 42, 62) when moved along the longitudinal axis, and a resilient member (16, 17, 46)

said method comprising the step of:

hooking said first and second hook member (21, 22) on to the edge of a first and second skull bone segment (23a, 23b) respectively,

arranging the resilient member (16, 17, 46) in a stressed state so as to apply a force directed to press the first and second displacement elements (11, 41, 61; 12, 42, 62) away from each other along the longitudinal axis so as to increase the distance between the first and second hook members (21, 22).

19. Method for pulling apart skull bone segments (23a, 23b) according to claim 18, the method further comprising the step of:

inserting said first and second hook member (21, 22) through a first and second point of penetration in the skin (24) of a skull.

20. Method for pulling apart skull bone segments (23a, 23b) according to any of the claims 18-19, the method further comprising the step of:

fixing the first and second hook member (23a, 23b) to the first and second displacement element (11, 41, 61; 12, 42, 62) respectively.

21. Method for pulling apart skull bone segments (23a, 23b) according to any of the claims 18-20, the method further comprising the step of:

exposing the hook members (21, 22) to a force exceeding a certain magnitude such as to partly or fully straighten out a bent end portion (21a, 22a) of respective hook members (21, 22).