WO2000038584A1

WO2000038584A1 - External fixator structure for the treatment of fractures, dislocations and post-traumatic rigidity of the elbow joint

Info

Publication number: WO2000038584A1
Application number: PCT/EP1999/010312
Authority: WO
Inventors: Giovanni Faccioli; Sander Ten Veldhuijs
Original assignee: Orthofix S.R.L.
Priority date: 1998-12-24
Filing date: 1999-12-22
Publication date: 2000-07-06
Also published as: IT1302480B1; ITVI980244A1; AU2101100A; ITVI980244A0

Abstract

An external fixator structure for the treatment of fractures, dislocations and post-traumatic rigidity of the elbow joint includes a pair of clamps (5; 6) for bone screws (S; T) to be inserted into bones (U; O) from opposite sides respect to the anatomical axis of the joint (t), a pair of extremity elements (2, 3) connected to the corresponding clamps (5, 6) by means of respective universal joints (13; 14) provided with stops (21, 22), a central element (4) for the articulated connection of the extremity elements with a pair of slides (23; 24) connected by a bolt (25) defining a mechanical axis (m) of the fixator structure, stops (30; 36) associated to the slides, distraction means (46) capable of acting on the central element (4) for distraction of the mechanical axis (m) so as to take the load off the cartilage of the joint and favour mobility in the case of post-traumatic rigidity. The distraction means include a first auxiliary unit (46) composed of a third slide (47) which can anchored along the longitudinal guiding means (2'; 3') facing one of the first two slides and a second auxiliary unit (58) acting on the extremity elements for angular distraction.

Description

"EXTERNAL FIXATOR STRUCTURE FOR THE TREATMENT OF FRACTURES, DISLOCATIONS AND POS -TRAUMATIC RIGIDITY OF THE ELBOW JOINT"

DESCRIPTION Field of the invention

This invention concerns the orthopaedic and bone surgery sector, and has as specific subject an external fixator structure for the treatment of fractures, dislocations and post-traumatic rigidity of the joints of the upper limbs, in particular the elbow. Prior Art

The technique that utilises the so-called external fixator structures for the treatment of bone fractures and dislocations as well as post-traumatic rigidity has been well-known for years in orthopaedics and bone surgery. These devices are essentially made up of at least a pair of clamps which support screws or pins inserted into extremities of a fracture and which are anchored in a pre-established direction to a central unit situated outside the limb. Once the fracture and/or dislocation has been reduced in the operating theatre, the fixator structure remains assembled on the limb until complete healing is reached.

It is also well-known that fractures and dislocations near joints, especially the elbow, in the presence of ligament instability, can be very painful and disabling, considerably limiting mobility of the patient in activities which require extensive bending and extension of the elbow, as well as supination and pronation of the forearm. In order to avoid permanent disability, it is not sufficient to reduce and correctly stabilise the fracture but it is necessary to accompany these procedures with precocious mobilisation of the joint to restore normal functionality of the limb as soon as the clinical conditions of the patient make this possible.

Devices for the treatment of fractures, dislocations and post-traumatic rigidity of the elbow which permit partial mobility of the joint are already known. Examples of these devices are described and illustrated in the European patents no. 624 352 and no. 460 944 and in the patent of the United States no. 5,372,597.

These known devices are essentially composed of a pair of rigid elements, substantially curved and shaped to clasp the humerus and the forearm respectively, where screws previously inserted into the ends of the fracture are fixed. The curved rigid elements are reciprocally connected by a pair of articulated joints in the shape of a protractor, placed on opposite sides of the limb and aligned along a transversal axis substantially coinciding with that of the joint axis.

The protractor joints are provided with adjustment means which make it possible to selectively vary the angle of the rigid elements around the rotation axis, so as to carry out angular distraction of the joint and permit its mobility.

One of the drawbacks of these known devices is that they are rather cumbersome, especially in the transversal direction and on both sides of the limb, they require excessively long assembly times and, moreover, they are quite expensive.

In order to simplify the fixator structure and utilise already existing devices, use was made of fixators for short bones such as the hip fixator designed by Dr. Pennig, described and claimed in the German patent no. 4231443, essentially made up of two or more elongated stirrup-shaped elements, provided with clamps for bone screws at the ends, where the elongated elements are reciprocally hinged together by a threaded pin provided with a flat washer on which a screw nut or blocking hand grip is screwed.

This device is also rather cumbersome and, furthermore, does not permit compression/distraction action either in a longitudinal or rotational direction. Presentation of the invention

A primary aim of this invention is to produce an external fixator structure for the treatment of joints, in particular the elbow joint, which possesses characteristics of great flexibility and efficacy in precocious recovery of limb mobility.

Another aim is to design an external fixator structure for the treatment of fractures, dislocations and post-traumatic rigidity of the elbow which makes it possible to distract one or the other of the two bones separately.

A further aim is to create an external fixator r structure for the treatment of fractures, dislocations and post-traumatic rigidity of the elbow which makes it possible to carry out a forced and controlled angular distraction and compression.

Another aim is to produce an external fixator structure of the type described above which possesses a simplified, extremely compact device, easily installed and relatively inexpensive.

A last aim is to manufacture an external fixator structure of the type described above which is easily dismounted to permit complete cleaning and sterilisation.

According to this invention, an external fixator structure for the treatment of fractures, dislocations and post-traumatic rigidity of limb joints, especially the elbow, is foreseen which, in accordance with claim 1, includes:

- a first and second clamp for bone screws to be inserted into the respective bones from opposite sides with respect to the anatomical axis of the joint;

- a first and a second elongated rigid element connected to the said first and said second clamp respectively, by means of respective universal joints provided with stop means which can operated separately;

- a central element representing an articulated connection between the said first and said second rigid element with a substantially transversal rotation axis, where the said central element can be positioned so that this transversal axis is substantially aligned to the said anatomical axis;

- blocking means associated to the said central element to block the said first and the said second rigid element in a variety of angular positions around the said transversal axis; characterised in that it foresees adjusting means associated to said central element capable of distancing its transversal axis from the anatomical axis to allow distraction of the joint axis and to favour mobility of the post-traumatic rigidity.

In particular, the first and second elongated element present first and second longitudinal guides respectively; the central element includes a first and second slide mounted so as to slide smoothly on the first and second longitudinal guiding means.

The claims from 3 to 13 define the detailed characteristics of the fixator structure in accordance with the invention.

Brief description of the drawings

Other characteristics and advantages of the invention will be further clarified in the light of the following description of a type of preferred but not exclusive external fixator structure, illustrated by way of a non-limiting example with the help of the enclosed drawings, where:

FIG. 1 represents a general perspective view of the external fixator structure according to the invention applied to an elbow and fixed to the humerus and ulna bones ;

FIG. 2 represents a lateral overall view of the fixator structure of Fig. 1;

FIG. 3 represents a lateral overall view of the fixator structure of Fig. 1; FIG. 4 represents a lateral part-sectional view of an accessory of the fixator structure of Fig. 3;

FIG. 5 represents a frontal part-sectional view of a detail of the overall view of Fig. 3; FIG. 6 represents a lateral view of a part of the external fixator structure of Fig. 3;

FIG. 7 represents a frontal view of a detail of the fixator structure of Fig. 6;

FIG. 8 represents a prospective view in elevation of a detail of the overall fixator structure of Fig. 1;

FIG. 9 represents a lateral part-sectional view of the detail of Fig. 8;

FIG. 10 represents a view in elevation of the detail of Fig. 8 ; FIG. 11 represents a view from below of the detail of Fig. 8;

FIG. 12 represents a prospective view in elevation of the parts of another detail of the fixator structure of Fig. 1; FIG. 13 represents a view in elevation of the detail of Fig. 12;

FIG. 14 represents a lateral part-sectional view of the detail of Fig. 12;

FIG. 15 represents a view from below of the detail Of Fig. 12;

FIG. 16 represents a prospective view of another detail of the fixator structure of Fig. 1;

FIG. 17 represents a frontal part-sectional view of the detail of Fig. 16; FIG. 18 represents a view in elevation of the detail of Fig. 16. Detailed description

Referring to the above-mentioned figures, a type of the fixator structure according to the invention is illustrated, indicated overall with the reference number 1, which includes a pair of extremity elements or rods 2 , 3 connected to each other by a connecting central element 4.

In their turn, the extremity elements 2,3 are coupled to clamps 5,6 to block the two groups of bone screws, indicated with S, T respectively.

The two groups of screws S, T can be inserted, for example, into the humerus 0 and the ulna U respectively of the arm of the patient who has suffered a fracture and/or dislocation of the joint, or a joint subject to post-traumatic rigidity, having an anatomical axis a, after having made corresponding holes in the areas of the bones by means of a special reamer.

Preferably, the extremity elements 2, 3 are substantially identical and have the shape of elongated stirrups, with respective longitudinal axes a, b, elongated central holes 2 ' , 3' with rounded ends and substantially parallel lateral walls 7, 8.

As is known, the clamps 5, 6 can be formed by pairs of jaws or half 5', 5", 6 ' , 6" having a transversal section substantially semi-elliptical, with substantially level facing sides and provided with positioning grooves, not visible in the drawings, for the screws S, T.

In order to facilitate the surgeon's work, the jaws 5', 5", 6', 6" are preferably hinged together in correspondence with an extremity 5"', 6"' and can be reciprocally tightened by means of one or more blocking screws 11, 12 to hold the groups of bone screws S, T together.

To permit turning of the clamps 5, 6, these are connected to the extremity elements 2, 3 by means of respective universal joints 13, 14.

Every universal joint 13, 14, of a known type, for example similar to those used in the Orthofix axial fixators of the 10.000 series, includes a sphere 15, 16 integral with one of the jaws 5', 5", 6', 6" of a respective clamp 5, 6.

Each of the spheres 15, 16 can be inserted into the axial socket of a corresponding expanded head 9, 10 and kept in this position by respective ring nuts 17, 18 provided with bayonet attachments, essentially composed of internal projections which can be selectively inserted into external annular rings formed in the expanded heads 9, 10.

Stops are provided for each joint 13, 14 which can be operated, from the outside to block/unblock the spheres 15, 16 of the expanded heads 9, 10 with an angular position corresponding to that of the bone screws .

These blocking means can, for example, be composed of cylindrical blocks 19, 20 inserted into the axial seats of the expanded heads 9, 10 and capable of working together with the spheres 15, 16 of the joints. In particular, the blocks present a concave face with a bending radius substantially corresponding to that of the spheres 15, 16 and a substantially level opposite face. In the expanded heads 9, 10 transversal holes are foreseen into which eccentric hollow pins 21, 22 are inserted whose external surface is to co-operate with the substantially level face of each block 19,20. The cavity of each pin 21, 22 presents, at least at one end, a hexagonal socket for the insertion of a hexagonal key.

Inserting the key and rotating the eccentric pins

21, 22 clockwise and anticlockwise, an axial movement of the blocks 19, 20 is obtained; the concave face of these blocks exerts friction against the external surface of the spheres 15,16, so blocking the spheres 15, 16 and, therefore, the clamps 5, 6 in the pre- established position.

The central connection element 4 is shaped in such a way as to mutually unite the extremity elements 2, 3 around a transversal axis rn, so permitting angular adjustment as well as longitudinal adjustment of these elements 2, 3 with respect to this axis m.

For this purpose, the central connecting element 4 can be made up of a first slide 23 and a second slide 24, which can be coupled respectively with the extremity elements 2,3 which, in turn, can be reciprocally coupled, by means of a connecting bolt 25, with the transversal axis m. In particular, slide 23 presents a substantially U- shaped body with a transversal portion 26 which unites two substantially parallel lateral portions and indicated 27, 28 respectively. The lateral portion 27 is of such a size as to be easily inserted into the elongated hole 2' of the extremity element 2 and presents, compared to the projecting portion 28, an inter-space slightly greater than -the thickness of the external wall 7 of the extremity element 2. Furthermore, the lateral portion 27 presents a through- hole 29 which also passes through the transversal portion 26 for insertion of the bolt 25.

The lateral portion 28 presents an internally threaded hole into which a stop dowel 30 is screwed. The dowel 30 has a substantially cylindrical shape with one extremity provided with a rounded edge, to avoid injury, and a hexagonal central cavity 31 for insertion of a hexagonal key. The opposite end is level and provided with an annular washer which serves to exert a more uniform blocking pressure which resists wear.

In this way, rotating the stop dowel 30 clockwise, the lateral portion 27 is compressed against the surface of the extremity element 2 and, therefore, the slide 23 is blocked in a pre-established position along the elongated hole 2'.

The second slide 24, substantially similar to the first 23, presents a transversal portion 32 which unites two lateral substantially parallel portions indicated 33, 34 respectively.

The lateral portion 33 is of such a size as to be easily inserted into the elongated hole 3' of the extremity element 3 and presents, compared to the other lateral portion 34, an inter-space slightly greater than the thickness of the external wall 8 of the extremity element 3. Moreover, the lateral portion 33 presents a through-hole 35 which also passes through the transversal portion 32, for insertion of the connecting pin 25. The portion 34 presents an internally threaded transversal hole into which a second stop dowel 36, similar to the previous one, is screwed. This latter presents a central hexagonal cavity 37 for insertion of a key, not illustrated in the drawings .

In this way, rotating the stop dowel 36 clockwise, the lateral portion 33 is compressed against the external surface of the extremity element 3 and, therefore, the slide 24 is blocked in a pre-established position along the elongated hole 3'.

The connecting bolt 25 presents, along its entire length, a through-hole with a diameter slightly greater than that of a Kirschner wire, a threaded end portion 25' and a hexagonal head 25" to be positioned on the base 25 of the slide 23 forming an anti-rotation element .

The face of the transversal portion 32 furthest from the lateral portions 33, 34 presents a raised edge 38 with parallel sides which define lateral guides for a plate 39. This latter presents, at one end, a semicircular notch, to be inserted into a corresponding circular groove 41 in the smooth part of the bolt 25, so as to avoid axial sliding and, therefore, to prevent the bolt from coming out of the two slides 23, 24. The plate 39 is positioned on the level side of the portion 32 of the slide 24 and is kept in position by means of a screw 42 inserted into a threaded hole 43. The parallel sides of the raised edge 38 prevent rotation of the plate 39 around the screw 42. A blocking hand grip 44, with a substantially triangular shape, presents a cylindrical body with a threaded axial hole and -internal threading corresponding to that of the threaded end 25' of the connecting pin 25. As a precautionary measure, on the threaded end 25' of the bolt 25, an annular groove can be made for an elastic ring, non illustrated in the drawings, which makes it possible to exert controlled resistance when turning the hand grip 44.

In this way, slides 23, 24 can be blocked on their respective extremity elements and can be reciprocally connected by the bolt 25, having previously placed a washer 45 between the level surfaces of the two elements 2, 3. The mechanical axis m of the connecting element 4 must be aligned as far as possible to the anatomical axis a of the elbow joint. For this purpose, a Kirschner wire K can be inserted laterally into the distal diaphysis of the humerus 0 at a position corresponding to the joint axis t, identified by the surgeon by means of a brilliance amplifier. The Kirschner wire K so installed will serve as a guide for the insertion of the slides 23, 24 and, therefore, for the positioning of the connecting element 4.

After positioning the articulation of the element 4, the angle between the extremity elements 2, 3 can be blocked by rotating the hand grip clockwise so as to force the frontal parts of the elements 2, 3 against the washer 45.

According to this invention, first distraction means acting on the central connecting element 4 are foreseen, so making it possible to carry out distraction of the joint immediately after reducing the fracture/dislocation, in order to favour bending/extension movements, take the load off the cartilage as well as to favour mobility of the joint in the case of post-traumatic rigidity. In particular, the distraction means can include a first auxiliary distraction unit, indicated overall with the reference number 46, which can be mounted on the ulna extremity element 2 (i.e. that which supports the group of bone screws T inserted in the ulna) , as illustrated in Fig. 1, or on the humeral extremity element 3 (i.e. that which supports the group of bone screws S inserted in the humerus) , or on both simultaneously.

The auxiliary unit 46 is essentially made up of a third slide 47 having a substantially U-shaped body with a transversal portion 48 which unites the two lateral portions 49,50 substantially parallel to each other. The distance between the opposite sides of the lateral portions 49, 50 is slightly greater than the width of the lateral wall 7 of the element 2.

Furthermore, there is a threaded hole in the lateral portion 49 for a stop dowel 51 having a hexagonal cavity 52 for the insertion of a hexagonal key. Preferably, towards the internal extremity of the lateral portion 50, there is a protruding sloping edge 53 to prevent rotation of the slide with respect to the lateral wall 7 of the element 2.

Finally, in the area connecting the transversal portion 48 and the lateral portion 50, an internally threaded hole is foreseen into which a manoeuvring screw 54 is inserted. This screw 54 presents a pushing extremity 55 and a head 56 with a hexagonal cavity 57 for a hexagonal key.

In this way, it will be possible to block the slide 47 on the extremity element 2 in such a way that the manoeuvring screw 54 is aligned to the lateral portion

34 of the slide 24, with its pushing extremity 55 placed on the adjacent face of this portion 34. After blocking the slide 47, the manoeuvring screw 54 can be rotated clockwise so as to force the slide 24, so causing the mechanical axis m to move away from its initial position and consequently bringing about distraction of the joint. In this way, an articular space will be created between the bones of the joint, so favouring its mobility.

Obviously, the small auxiliary unit 46 can be dismounted and remounted on the humeral extremity element 3 inverting the position of the elements, so as to obtain corresponding distraction of the mechanical axis m from the anatomical one t.

The distraction means can also include a second auxiliary unit for compression-distraction, indicated overall with the reference number 58, acting on the extremity elements 2, 3 to cause controlled, forced rotation of the joint around the mechanical axis m.

In particular, the compression-distraction unit 58 can be composed of an internally threaded tubular body

59 with longitudinal axis 1, into which a threaded rod

60 can be inserted. At the end of the tubular body 59, a first cylindrical transversal appendix 61, having the same diameter as the central holes of the hollow eccentric pins 21, 22, is fixed.

Similarly, a bush 62 is fixed to the end of the threaded rod 60, free to rotate around the longitudinal axis of the rod but not to travel longitudinally along it . To this bush 62 is fixed a second transversal appendix 63, also with an external diameter inferior to the internal diameter of the hollow pins 21, 22.

The threaded rod 60 presents, at the end near the bush 62, an expanded head 64 with a hexagonal cavity for the insertion of a hexagonal key.

Alternatively, L-shaped extension arms 65, 66 can be mounted on the appendixes 61, 63, which serve to keep the distraction-compression unit 58 at a distance from the fixator structure, so enlarging the total stroke of the device.

In this way, after installing the fixator structure on the joint, it will be possible to insert the transversal appendixes 61, 63 or the extension arms 65, 66 into the holes of the hollow eccentric pins 21, 22 and rotate the head 64 of the threaded rod with a hexagonal key, so causing lengthening or shortening of the device along its axis 1 , as schematically illustrated in Fig. 1. The lengthening or shortening of the micrometrically controlled unit will favour extension and bending of the joint, shortening mobility recovery times in the cases of fracture/dislocation and post- traumatic rigidity. When operating, after preparing the instruments, the surgeon can locate the anatomical axis t of the joint by means of an x-ray, then he can establish a reference point for the fixator structure inserting the

Kirschner wire K into the distal diaphysis of the humerus 0. The fixator structure 1, complete with clamps 5, 6, will then be placed near the elbow, inserting the Kirschner wire K into the hole of the connecting bolt 25 of the central element 4 and adjusting the angle of the extremity elements 2, 3 in relation to the central element 4, after unblocking the stop dowels 30, 36 of the slides 23, 24.

Then the surgeon can install the groups of screws S, T in the humerus O and the ulna U and restrain them to the clamps 5, 6. The spherical joints 13, 14 will be blocked in the best position to keep the ulna 2 and humeral 3 extremity elements as parallel as possible to the ulna and humerus, so as to favour bending/extension and supination/pronation of the limb.

Any errors in aligning the fixator structure, verifiable by means of both frontal and lateral x-rays, can be corrected by unblocking the spherical joints of the clamps and slides of the connecting element 4.

Having so arranged the fixator structure, establishing the best position of the joints and slides, the surgeon can remove it temporarily in order to reduce the fracture or dislocation, then the fixator structure can be replaced in the initially established position.

Once the fixator structure has been installed, the surgeon can reduce the articulation in order to favour recovery of limb mobility. For this purpose, the elbow will be extended as far as possible, the distraction unit 46 will be positioned on the ulna extremity element 2 and both the hand grip

44 and the stop dowel 36 of the slide 24 will be released. Then the manoeuvring screw 54 will be rotated clockwise to move the humerus 0 away from the ulna U, carrying out distraction of the axis . In this way, pressure will be taken off the joint cartilage, so favouring joint movement, avoiding growth of heterotopic bone formation and accelerating recovery of joint mobility.

A few days after the operation, the bending/extension of the limb can be helped by installing the compression-distraction unit 58 onto the fixator structure and carrying out micrometrically controlled angular movements on the extremity elements 2, 3.

From the above, it can easily be seen that the fixator structure of this invention reaches all the prefixed objectives and, in particular, its characteristics of great flexibility and efficacy in precocious recovery of limb mobility must be underlined, as well as its capacity to separately distract one or the other of the bones in the joint, and finally its extremely compact simplified structure, as well as the fact that it is easy to install and relatively inexpensive.

The structure of the external fixator structure of this invention is susceptible to numerous modifications and variations which all fall within the concept of the invention and defined in the enclosed claims. All the details can be substituted with others equivalent while remaining within the scope of this invention.

Wherever the technical characteristics mentioned in any of the claims are followed by reference numbers or letters, these reference symbols have been introduced with the sole aim of rendering the claims more intelligible, and consequently they have no limiting effect on the protective scope of each identified characteristic .

Claims

1. External fixator structure for the treatment of fractures and dislocations as well as post-traumatic rigidity of limb joints, in particular the elbow joint, including:

- at least a first (5) and a second clamp (6) for bone screws to be inserted into the respective bones

(U; 0) from opposite sides of the anatomical axis of the joint (t) ; - at least a first (2) and a second extremity element (3) defining respective longitudinal axes (a, b) , connected to the said first (5) and said second (6) clamp by means of corresponding universal joints (13; 14) provided with stops (21, 22) which can be operated separately;

- a central element (4) for the connection of the said first and second extremity elements (2; 3) around a mechanical transversal rotation axis (m) , this said central element (4) to be positioned so that the said mechanical axis (m) is substantially aligned to the said anatomical axis (t.) ;

- stopping means (30; 36) associated to the said central element (4) to block the relative longitudinal position of the said first (2) and said second (3) extremity element in relation to said mechanical axis

⁽m) ; characterised in that it foresees first distraction means (46) capable of acting on the said central element (4) to keep the said mechanical axis (m) at a distance from the said anatomical axis (t) in order to take the load off the cartilage,^" favour movement and guide the joint in the case of instability.

2. External fixator structure according to claim 1, wherein said first and second extremity elements (2; 3) comprise respective guiding means (2'; 3') parallel to the said longitudinal axes (a, b) , the said central connecting element (4) being made up of a first (23) and a second (24) slide mounted on said longitudinal guiding means (2' ; 3') .

3. External fixator structure according to claim 2, wherein said stopping means (30; 36) are associated to the said first and second slide (23; 24) to block them selectively in a pre-established position along the respective longitudinal guiding means (2'; 3').

4. External fixator structure according to claim 3, wherein said first and second slides (23; 24) are reciprocally connected by means of a transversal bolt

(25) defining said mechanical axis (m) and inserted into respective through-holes (29; 35) of each slide (23; 24) .

5. External fixator structure according to claim 4, wherein said connecting bolt (25) presents a guiding through-hole for a Kirschner K wire to be inserted into said anatomical axis (t) of the joint.

6. External fixator structure according to claim 5, wherein said connecting bolt (25) presents one end

(25") with an anti-rotation shape to be positioned in a complementary socket on one of the said slides (24) and with the other opposite end threaded (25') on which a hand grip can be mounted (44) .

7. External fixator structure according to claim 6, wherein said cylindrical portion of the bolt (25) presents, near the said threaded end, a groove (41) for a shaped plate (39) anchored to the respective slide (24) to prevent the bolt (25) from coming out of the said through-hole (29; 35) of each slide (23;24) when in use.

8. External fixator structure according to claim 3, wherein between the said first (23) and the said second slide (24) , a flat washer (45) is to be placed, acting on the opposite surfaces of said first and second extremity elements (2; 3) to distribute the axial load more uniformly and to guide rotation between the two elements (2 ;3) .

9. External fixator structure according to claim 3, wherein said distraction means include a first auxiliary unit (46) formed by at least a third slide

(47) to be anchored to one of the said extremity elements (2; 3) along the respective longitudinal means (2'; 3) in a position facing one of the said slides (23; 24) .

10. External fixator structure according to claim 9, wherein said third slide (47) supports a manoeuvring screw (54) with one end free (55) destined to co- operate with the facing slide (23; 24) to keep it a distance from its original position so as to bring about longitudinal distraction of the joint axis and create an articular space to favour recovery of joint mobility.

11. External fixator structure according to claim 10, wherein said manoeuvring screw (54) presents an expanded head (56) at the other end with at least one hexagonal socket (57) for the insertion of a manoeuvring key.

12. External fixator structure according to claim 1, wherein said stopping means of the said universal joints (13; 14) consist in hollow eccentric pins (21; 22) with through-holes.

13. External fixator structure according to claim 12, wherein second distraction means are provided, including a second auxiliary micrometric compression- distraction unit (58) , said second auxiliary unit being provided with appendixes (61; 63) to be inserted into respective through-holes of said hollow eccentric pins to bring about angular distraction of the joint.