WO2008001324A2

WO2008001324A2 - Locking device for intramedullary nails and intramedullary nail including such device

Info

Publication number: WO2008001324A2
Application number: PCT/IB2007/052520
Authority: WO
Inventors: Claudio Velluti
Original assignee: Osp Ortho Service Provider Srl
Current assignee: Osp Ortho Service Provider Srl
Priority date: 2006-06-30
Filing date: 2007-06-29
Publication date: 2008-01-03
Anticipated expiration: 2008-12-30
Also published as: WO2008001324A3

Abstract

The present invention is generally applicable to the field of bone surgery devices and particularly relates to A locking device for intramedullary nails which device is designed to be at least partly inserted in an intramedullary nail (2) for locking it in position in the medullary cavity (M) of a fractured bone (B). The device comprises at least one fixation screw (3) having an axis of rotation (X) and a threaded axial end (4) for stable screwing into the wall of the medullary cavity (M). The device (1 ) is provided with elastic lock means (5) interacting with the fixation screw (3) to oppose rotation thereof and lock the nail (2) in position within the medullary cavity (M). An intramedullary nail may comprise such device.

Description

LOCKING DEVICE FOR INTRAMEDULLARY NAILS AND INTRAMEDULLARY NAIL INCLUDING SUCH DEVICE

Field of the invention

The present invention is generally applicable to the field of bone surgery devices and particularly relates to a device for locking intramedullary nails in the medullary cavity of a limb to be treated.

The device is particularly suitable for use with intramedullary nails for treating long bone fractures.

The present invention also relates to an intramedullary nail including such device.

Background of the invention

It is known that stabilization of bone fractures, particularly sited in long bones such as the femur, the tibia and the homerus is facilitated using intramedullary nails generally formed of an elongate tubular body suitable to be inserted and fixed in the medullary cavity of the limb to be treated.

For the treatment to be effective, the position of the nail in the medullary cavity of the bone to be treated shall be as stable as possible to prevent excessive mobility thereof due to physiological stresses normally acting thereon.

Typically, proximal fixation of the nail is carried out using one or more threaded through screws, which are inserted in respective holes on the side wall of the nail.

Thus, by tightening the screws into the bone cortex, the various parts of the bone are kept in joined relationship and any translation and/or rotation of the nail in the medullary cavity is prevented.

On the other hand, distal fixation of the nail is carried out using a pair of metal stabilization wires with a pointed end, which are designed to be inserted in the nail through a proximal opening and come out of distal holes for anchorage into the wall of the medullary channel.

In order to impart high stability to the nail, the fixation screws have to be prevented from rotating while being allowed a slight axial translation to follow the movements of the various parts that form the fractured bone, which normally tend to move close to each other as the bone callus is being formed.

A recognized drawback of these known solutions is that the fixation screws are not always adequately locked in the bone cortex but tend to rotate, thereby loosening, due to the physiological stresses acting on the nail. These movements cause the nail to lose stability, and thus effectiveness.

Also, an excessive clearance of a screw in its seat may cause excessive axial motion thereof and in the worst cases may cause the threaded tip thereof to come out of its seat, which would affect the effectiveness of the treatment and possibly cause bone injury.

In an attempt to obviate the above drawbacks, a number of devices have been proposed for locking intramedullary nails in bone cavities, as well as for locking the fixation screws.

From European patent application EP 1365692 an intramedullary nail for treating trochanteric fractures is known whose fixation in the cavity is obtained using a cephalic screw and a pair of metal wires.

The cephalic screw has one or more grooves parallel to its own axis, with which comes into engagement the end of another screw which is designed to interact with the cephalic screw to prevent its rotation without restricting axial displacements thereof.

While this solution ensures the proper position of the cephalic screw during the treatment, it is still inappropriate if two or more screws are used, because the cephalic screws that are closer to the distal part of the nail could not interact with the fixation screw.

Furthermore, the need of the fixation screw requires a further component to be formed and mounted, and makes on-site nail application more difficult and nail fabrication poorly cost effective.

A further drawback of these known solutions is that insertion of the wires and alignment thereof with the exit holes is generally accomplished manually. Therefore, this step requires high skills by the operator and is often time consuming.

Furthermore, forced sliding of the wires, which is required to cause them to exit from their respective holes and further penetration of their tips into the medullary wall, is obtained by hitting the wires at one end thereof with a ram.

Therefore, there is no way to control the precision of the hits and the force applied to the stabilization wires, which involves the risk of damaging both the wires and the fractured bone, as this step is carried out with the nail inserted in the medullary channel.

Furthermore, for this step to be carried out with no risk of hitting the nail to, the metal wires shall extend to a greater length than their corresponding nail for which is intended.

Therefore, the portions of wires coming out of the nail will have to be cut, thereby involving material waist, as well as a considerable increase of the time required for the whole nail insertion operation.

Summary of the invention The object of the present invention is to overcome the above mentioned drawbacks, by providing a locking device for intramedullary nails that is highly efficient and relatively cost-effective.

A particular object is to provide a locking device for intramedullary nails that allows stable positioning of the fixation screws and opposes their rotation once they are inserted in the medullary cavity of the limb to be treated, while allowing them to perform the required axial motion.

A further object is to provide a locking device for intramedullary nails that allows stable simultaneous placement of multiple fixation screws.

Yet another object of the present invention is to provide a locking device for intramedullary nails that has a small number of components, and is thus cost- effective.

One more object is to provide a locking device for intramedullary nails that can be simply and quickly inserted in an intramedullary nail and may be easily removed at the end of the treatment.

A further object is to provide a locking device whose insertion in the nail is highly safe and prevents any risk of damages to the device, as well as to the nail and bone of the human body for which it is intended.

Not least object of the present invention is to provide an intramedullary nail that ensures highly stable positioning in the medullary cavity in which it is inserted.

These and other objects, as better explained hereafter, are fulfilled by a locking device for intramedullary nails as defined in claim 1 , which comprises at least one fixation screw having a rotation axis and a threaded axial end which is designed to be firmly screwed into the wall of the medullary cavity. The device is characterized in that it comprises elastic locking means designed to interact with said at least one fixation screw to oppose rotation thereof and lock the nail in position within the medullary cavity.

Thanks to this feature, the locking device will provide a highly stable positioning of the fixation screws within the medullary cavity while preventing rotation thereof.

Also, the intrinsic elasticity of the locking means will allow the latter to adapt to the geometry and sizes of the screw, while allowing them to perform the required axial movement to accommodate the micromovements of the fracture lines during the bone healing process.

Advantageously, the elastic locking means have an elongate thread-like body which defines a longitudinal axis and preferably has at least one pair of longitudinal arms that are substantially symmetrical with respect to the longitudinal axis, with a predetermined resilience.

Suitably, the longitudinal arms will have first end portions transversely offset with a predetermined spacing to define a passage for the fixation screw.

Advantageously, a plurality of fixation screw may be provided, with substantially parallel and longitudinally offset axes of rotation, which have multiple pairs of flattened portions adapted to interact with the corresponding longitudinal arms.

Thanks to this additional features, the locking device will allow stable and simultaneous positioning of two or more fixation screws designed for proximal and/or distal fixation of the intramedullary nail.

Also, the thread-like body may have a first centering bush at an axial end thereof to facilitate proper positioning thereof in the intramedullary nail.

Thanks to this additional inventive feature, the thread-like body may be fitted into the nail by acting upon a larger portion instead of hitting the external end of the thread-like body.

This will avoid any elastic reaction of the longitudinal arms and will prevent any damage to the thread-like body, the nail and/or the bone to be treated.

Advantageously, the first centering bush may have an at least partly threaded and substantially central bore, which is designed to interact with an external tool to promote insertion/removal of the device into/from the tubular cavity of the nail.

Suitably, a second substantially annular bush may be provided which has at least a partly external thread designed to be screwed into the nail above the first bush to act thereon by exerting an axial thrust and assisting the longitudinal arms in sliding into the tubular cavity of the nail.

Thus, the device may be inserted in the nail in a highly easy and safe manner.

In a further aspect of the present invention, an intramedullary nail is provided for fixation of bone fractures in accordance with claim 14, which comprises a locking device in accordance with one or more of claims 1 to 13.

Brief Description of the Drawings

Further features and advantages of the invention will be more readily apparent upon reading of the detailed description of a preferred but non exclusive embodiment of a locking device for intramedullary nails and an intramedullary nail according to the invention, which are shown as a non limiting example with preference to the annexed figures, in which:

FIG. 1 is a perspective view of a locking device according to the invention is a first preferred embodiment;

FIG. 2 is a front view of the device of FIG. 1 ; FIG. 3 is a rear view of the device of FIG. 1 ; FIG. 4 is a side view of the device of FIG. 1 ;

FIG. 5 is a partially perspective exploded view of a device and a nail according to the invention;

FIG. 6 is a perspective view of a first detail of a locking device according to the invention;

FIG. 7 is an exploded view of the detail of FIG. 6;

FIG. 8 is a top view of the detail of FIG. 6;

FIG. 9 is a partially broken away front view of a portion of the detail of FIG. 6; FIG. 10 is an exploded, sectional front view, as taken along the plane / - / of

FIG. 6, of a detail of a device of the invention, associated to an intramedullary nail;

FIG. 11 is a sectional front view of the device according to the invention, as taken along the plane p of FIG. 1.

FIG. 12 is a front view of a screw fastener that is part of a device according to the invention;

FIG. 13 is a sectional view of the detail of FIG. 12, as taken along the plane

FIG. 14 is a sectional view of the detail of FIG. 12, as taken along the plane /// - ///; FIG. 15 is a partially perspective exploded view of an intramedullary nail according to the invention;

FIG. 16 is a partially broken away front view of the nail of FIG. 15; FIG. 17 is an enlarged view of a detail of the nail of FIG. 16, when inserted in the medullary cavity of a fractured bone.

Detailed description of one preferred embodiment

With reference to the above figures, the locking device according to the invention, generally designated by numeral 1 , may be at least partly inserted in the tubular cavity of an intramedullary nail 2 for treating fractured bones B, particularly long bones such as the femur, the tibia and the humerus. The device 1 will be particularly suitable for locking pertrochanteric nails for fixation of femur fractures, which nails are designed to be locked in the medullary cavity M of a bone by one or more proximal and/or distal fixation screws 3, 3', as exemplary shown in FIG. 17.

As shown in FIG. 1 , a locking device 1 according to the invention has one or more fixation screws 3, 3' having respective axes of rotation X, X' and respective threaded axial ends 4, 4', which are designed to be firmly screwed into the side wall of the medullary cavity M of a fractured bone B.

According to a peculiar feature of the invention, elastic locking means 5 are provided, which are adapted to interact with the fixation screws 3, 3' to oppose rotation thereof and lock the nail 2 in position within the medullary cavity M of a fractured bone.

In the particular embodiment of the figures, which is preferred but not intended to restrict the scope of this invention, the device 1 may include a pair of cephalic fixation screws 3, 3', which are designed to be placed at the proximal end 6 of an intramedullary nail 2, as more clearly seen in FIGS. 15 and 16.

Furthermore, the elastic locking means 5 have an elongate thread-like body 7 which defines a first longitudinal axis W and preferably has at least one pair of longitudinal arms 8, 8' that are substantially symmetrical with respect to such longitudinal axis W, and have a predetermined resilience.

Nevertheless, other configurations may be provided, in which the locking device 1 may include a different number of substantially similar fixation screws 3, 3' inserted at the proximal end 6 and/or the distal end 9 of a nail 2 to lock the latter within the medullary cavity M.

As used herein, the terms "proximal end" and "distal end" are intended to respectively mean the closer ends and the further end with respect to the limb root in which the nail 2 is designed to be inserted, which in the example of pertrochanteric fracture of the femur as shown in FIG. 17, consists of the head H of the femur B.

However, it is understood that the above terms are only used for the better intelligence of the present text. Therefore, in the case of a humeral nail, not shown, the device 1 may be inserted at the open end of the nail in the distal position and come out of side holes formed at the proximal end thereof.

As particularly seen in FIG. 2 and FIG. 3, the longitudinal arms 8, 8' may have first substantially parallel and transversely offset end portions 10, 10', and second end portions 11 , 11 ' diverging with respect to the first longitudinal axis W.

Preferably, the first end portions will be transversely offset with a predetermined spacing d to define a passage 12 for the fixation screws 3, 3'.

The longitudinal arms 8, 8' may be formed of a base material with a predetermined resilience, so that, upon insertion of the screws 3, 3', it can allow elastic deformation of the arms 8, 8' along a substantially transverse direction Y.

The spacing d may be advantageously coincident or slightly smaller than the maximum diameter of the fixation screws 3, 3', to promote elastic deformation.

The base material may be selected from the group comprising metals and alloys thereof or even plastic materials having suitable mechanical strength and chemico-physical and biological compatibility properties, in view of the particular use of the device 1 in the human body.

Thus, the thread-like body 7 may accommodate the suitably selected sizes of the screws 3, 3', to exert thereon a compressive force F which is substantially directed in the transverse deformation direction Y to oppose any movement by the screws 3, 3' about their respective axes of rotation X, X¹. However, the elastic deformations of the longitudinal arms 8, 8' will not hinder the mimimal movements of the screws 3, 3' along the directions defined by their axes of rotation X, X¹.

These movements are required for the screws 3, 3' in order to accommodate the settling movements between the various parts of the fractured bone B during the formation of the bone callus.

Advantageously, the fixation screws 3, 3' may be located between the first end portions 10, 10' of the arms 8, 8', with their respective axes of rotation X, X' lying in a plane of symmetry p of the thread-like body 7 passing through the first longitudinal axis W.

As more clearly seen in FIG. 4, the screws 3, 3' may have respective axes of rotation substantially parallel to and offset from each other.

Furthermore, the screws 3, 3' may be configured in such a manner that, when the nail 2 is inserted in the bone B, both axes X, X¹ pass through the head H of the bone B to prevent rotation of the nail 2 relative to the neck of the bone B during the formation of the bone callus at the fracture site.

Preferably, the fixation screws 3, 3' may have a substantially cylindrical outer surface 13, 13' with one or more pairs of axial flattened portions 14, 14' which are designed to selectively interact with the longitudinal arms 8, 8', as particularly seen in FIG. 11.

Unless otherwise stated, the flattened portions 14, 14' will be designated hereafter by the simple reference, with no prime thereon.

The flattened portions 14 may have substantially similar or at least comparable axial lengths I₁ and will also be angularly staggered to engage corresponding first end portions 10, 10' of the longitudinal arms 8, 8'. While two pairs of flattened portions are provided in the exemplary configuration of the annexed figures, these may be provided in any number, compatibly with the sizes of the corresponding screw 3, 3', without departure from the scope of the present invention.

For each pair, the respective flattened portions 14 may be diametrically opposed to define an angle of about 180° between their respective center lines, and their width ai will be determined by the total number of flattened portions 14 on the screw 3, 3'.

The longitudinal arms 8, 8' may have the known shape of a right cylinder with a circular cross section, like in the examples of FIGS. 6 and 7, or an elliptical or irregular cross section, otherwise they may be even pre-shaped, like in FIG. 1 , for easier insertion and extraction thereof from respective distal holes 15, 15' of the nail 2, as more clearly seen in FIG. 15 and in FIG. 16.

Also, the threadlike body 7 may include a centering member 16, preferably but not exclusively located at the axial proximal end 17 of the thread-like body 7, which has the function of assisting proper positioning thereof in the nail 2.

The centering member 16 may be formed of the same base material as the longitudinal arms 8, 8' and may be fixed thereto in a stationary or removable manner.

The longitudinal arms 8, 8' may be disposed at diametrically opposite positions, substantially symmetrical with respect to the first longitudinal axis W and their axial extension I₂ may be substantially coincident with the axial extension of the tubular cavity 18 of the nail 2, excepting the thickness required for accommodating the centering element 16.

Advantageously, the centering member 16 may be manually handled by an operator during implantation or pre-assembly of the nail 2. Furthermore, the member may have a substantially flat outwardly directed face 19 to allow compression or percussion by the operator for the second distal end portions 11 , 11' of the longitudinal arms 8, 8' to penetrate the bone tissue.

According to a particular configuration, more clearly seen in FIG. 9, the first end portions 10, 10' of the longitudinal arms 8, 8¹ may have respective end sections 20, 20' inserted in corresponding counter-shaped receptacles 21 , 21' formed in the centering element 16.

The arms 8, 8' may be joined to the centering member 16 by either a cold process, such as interference fit, screw mating or interlocks, or by a hot processes, such as welding or bonding.

Moreover, the centering member 16 may have a through or blind bore 22, possibly threaded, substantially at its center, for interacting with an external member 23 such as a plug, a hex-key, a threaded pin.

This will dramatically facilitate removal of the device 1 from the tubular cavity 18 of the nail 2, and will considerably reduce the risk of injuring the bone tissue during such removal step.

In order to facilitate insertion of the thread-like body 7 in the axial direction and stabilize the position of the whole device 1 in the tubular cavity 18 of the nail 2, a substantially annular, at least partly threaded bush 24 may be provided, which is also designed to be inserted in the cavity 18 of the nail 2 at the proximal end 6 thereof.

The bush 24 may have a substantially flat inner face 25 which is designed to operate on the outwardly directed face 19 of the centering element 16, to exert thereon a thrust substantially directed along the axis W to facilitate the sliding motion of the longitudinal arms 8, 8' in the tubular cavity 18 of the nail 2. In the particular application as shown in FIG. 17, the device 1 is partly inserted in a pertrochanteric nail 2 which is located in the medullary cavity M of a femur B, for treating the fracture of the femur T.

The nail 2 comprises a tubular body having a central cavity 18 with a second longitudinal axis Z, which is designed to be inserted in the medullary cavity M of a fractured bone B.

The nail 2 further has a distal end 9, an open proximal end and a side wall 26 on which two lateral through apertures 27, 28 have been formed, which are substantially transverse to said second longitudinal axis Z, for the passage of corresponding screw fasteners 3, 3' which are designed to lock the nail 2 at its proximal end 6.

In order to further enhance the stability of the device and prevent the bone callus from forming inside the nail 2, a threaded cap 29 may be provided, to be inserted in the tubular cavity 18 at its open proximal end 6.

This will further simplify removal of the nail 2 from the medullary cavity M at the end of the treatment.

Also, for the device 1 to be stably positioned in the axial cavity 18, the latter may be designed with a substantially cylindrical lateral surface 30, with a proximal section 31 having a transverse dimension a₂ substantially coincident with the radial dimension a₃ of the bush 24 and of the centering member 16, as shown in the section of FIG. 10.

The proximal section 31 of the axial cavity 18 may be at least partly threaded for easier screw connection of the bush 24.

Furthermore, the substantially cylindrical 19 lateral surface 30 of the axial cavity 18 may have a peripheral abutment surface 32 with a transverse dimension a₄ smaller than the radial dimension a3 of the centering member 16, to prevent device 1 from sliding past a predetermined limit, thereby causing injuries to the limb.

Advantageously, the axial length l-i of the flattened portion 14 of the fixation screws 3, 3' associated to the nail 2 may be greater than the transverse dimension I₃ of the proximal apertures 27, 28 as measured along the axes of rotation X, X' of the corresponding screws 3, 3'.

Thus, typical loads normally acting on the nail 2 may be evenly distributed over the flattened portions 14, thereby increasing the resistance of the whole device 1.

Furthermore, the arms 8, 8' will have such a longitudinal extension I₂ as to allow the end sections 33, 33' of the diverging portions 11 , 11' to come out of the distal through holes 15, 15' of the intramedullary nail 2.

Advantageously, the end sections 33, 33' of the diverging portions 11 , 11' may be pointed, e.g. bit- or chisel-shaped, to penetrate the inner wall of the medullary cavity M.

Thus, the arms 8, 8' will also act as stabilizing wires, for even more stable anchorage of the thread-like body 7, and thus of the whole nail 2, to the bone B to be treated.

The above disclosure clearly shows that the invention fulfils the intended objects, and particularly to provide a locking device for intramedullary nails that allows stable and simultaneous positioning of one or more fixation screws 3, 3', ... and prevents their rotation once they are inserted in the medullary cavity M of the bone B to be treated.

Thanks to its particular configuration, the device of the invention may be inserted in and/or removed from an intramedullary nail in a very quick and simple manner without causing damages to the nail or injury to the bone undergoing the treatment.

The device and nail of the invention are susceptible of many modifications and changes falling within the inventive concept disclosed in the annexed claims. All the details thereof may be replaced by other technically equivalent parts, and the materials may vary depending on different needs, without departure from the scope of the invention.

While the device and nail have been described with particular reference to the annexed figures, the numerals referred to in the disclosure and claims are only used for the sake of a better intelligibility of the invention and shall not be intended to limit the claimed scope in any manner.

Claims

1. A locking device for an intramedullary nail, of the type designed for insertion in the intramedullary cavity (M) of a fractured bone (B), which nail has a hollow tubular body (2) and at least one lateral aperture (27, 28) at one proximal end thereof (6), wherein the device comprises at least one fixation screw (3) having an axis of rotation (X) and a threaded axial end (4) designed to be firmly screwed into the wall of the medullary cavity (M), characterized in that it has elastic locking means (5) designed to interact with said at least one fixation screw (3) to oppose rotation thereof and lock the nail (2) in position within the medullary cavity (M).

2. Locking device as claimed in claim 1 , characterized in that said elastic locking means (5) have an elongate thread-like body (7) which defines a first longitudinal axis (W) said thread-like body (7) having at least one pair of longitudinal arms (8, 8') which are substantially symmetrical with respect to said first longitudinal axis (W), and have a predetermined resilience.

3. Locking device as claimed in claim 2, characterized in that said longitudinal arms (8, 8') have first substantially parallel and transversely offset end portions (10, 10') with a predetermined spacing (d) to define a passage (12) for said at least one fixation screw (3), and second end portions (11 , 11') diverging with respect to said first longitudinal axis (W).

4. Locking device as claimed in claim 2 or 3, characterized in that said at least one fixation screw (3) is located between said first end portions (10, 10') of said arms (8, 8'), with its axis of rotation (W) lying on a plane of symmetry (p) of said thread-like body (7) passing through said first longitudinal axis (W).

5. Locking device as claimed in one or more of the preceding claims, characterized in that said at least one fixation screw (3) has a substantially cylindrical outer surface (13) with at least one pair of axial flattened portions (14, 14').

6. Locking device as claimed in claim 5, characterized in that said flattened portions (14, 14') have predetermined axial lengths (11 ) and are angularly staggered to interact with corresponding first end portions (10, 10') of said longitudinal arms (8, 8') and oppose the rotation of said at least one fixation screw (3) relative to the intramedullary nail (2) in which the device is inserted.

7. Locking device as claimed in claim 5 or 6, characterized in that it comprises a plurality of fixation screws (3, 3', ...) having at least one pair of flattened portions (14, 14') for interacting with corresponding longitudinal arms (8, 8¹).

8. Locking device as claimed in claim 7, characterized in that said fixation screws (3, 3') have respective axes of rotation (X, X') substantially parallel to and offset from each other.

9. Locking device as claimed in one or more of the preceding claims, characterized in that said thread-like body (7) further includes a substantially cylindrical centering member (16), located at an axial end (17) of said thread-like body (7), for assisting proper positioning thereof in the intramedullary nail (2).

10. Locking device as claimed in claim 9, characterized in that said first end portions (10, 10') of said longitudinal arms (8, 8') have respective shaped end sections (20, 20') inserted in corresponding counter-shaped receptacles (21 , 21') of said centering member (16) and said second diverging portions (11 , 11') have pointed end sections (33, 33') to come out of suitable distal holes (15, 15') formed in the nail (2) and allow anchorage of said thread-like body (7) to the bone (B) to be treated.

11. Locking device as claimed in claim 10, characterized in that said centering member (16) has a substantially flat outwardly directed face (19) to allow compression or percussion by the operator for said pointed end sections (33, 33') to penetrate the bone tissue.

12. Locking device as claimed in any preceding claims, characterized in that said centering member (16) has a longitudinal bore (22) substantially at its center, which is designed to interact with an external member (23) to promote insertion/removal of the device into/from the tubular cavity (18) of an intramedullary nail (2).

13. Locking device as claimed in any preceding claims, characterized in that it comprises a substantially annular bush (24) which has at least a partly external thread, said bush having a substantially flat inwardly directed face (22) which is designed to operate on said outwardly directed face (19) of said centering member (16) by exerting a direct thrust thereon substantially along said first longitudinal axis (W) and promote the sliding motion of said thread-like body (7) within the tubular cavity (18) of a nail (2) to be implanted.

14. An intramedullary nail for fixation of bone fractures, comprising a tubular body (2) with a cavity (18) defining a second longitudinal axis (Z), said tubular body (2) being insertable in a medullary cavity (M) of a fractured bone (B), said tubular member further having a distal end (9), an open proximal end (6) and a side wall (26) with at least one lateral aperture, extending across opposite sides with respect to the axis (Z) of said cavity (18) at said proximal end (6) and at least one pair of through holes (15, 15') near said distal end (9) characterized in that it comprises a locking device (1) as claimed in one or more of claims 1 to 13.

15. Intramedullary nail as claimed in claim 14, characterized in that the axial length (11 ) of flattened portions (14, 14') of at least one fixation screw (3) of said locking device is greater than the width (d₅) of at least one lateral aperture (27) as measured along the axis of rotation (X) of the corresponding screw (3) to allow even distribution of the loads normally acting on said nail (2) on said flattened portions (14, 14').

16. Intramedullary nail as claimed in claim 14 or 15, characterized in that said axial cavity (18) has a substantially cylindrical lateral surface (30) with an at least partly threaded open proximal section (31 ) for allowing a threaded bush (24) to be screwed therein and having a transverse dimension (az) substantially coincident with the radial dimension (8₃) of said bush (24).