Abstract:
A novel disposable axial external fixation device for reducing bone fractures, of the type comprising an extendible rod-like middle body and oppositely located bone screw clamps which are articulated to the respective ends of the rod like middle body by means of ball joints. Advantageously, a ball-and-socket joint is mounted to each clamp within a main body with which a clamping mechanism for clamping bone screws clamping is associated or co-operates. Also provided is an ancillary member adapted for releasable association with one end of each clamp to better adapt each clamp for use in different conditions of installation of the fixation device.

Description:
FIELD OF THE INVENTION 
     This invention broadly relates to an improved axial external for stabilizing bone fractures in orthopedic surgery. 
     More particularly, the invention relates to a disposable axial external fixation device of the type comprising an extendible rod-like middle body and oppositely located bone screw clamps which are articulated to respective ends of the rod-like middle body by means of ball joints. 
     PRIOR ART 
     In this specific field, unilateral external fixation devices have been employed to foster recovery of bone fractures, holding the bone fragments firmly in place. 
     Such external fixation devices usually comprise a middle body of substantially cylindrical shape which is axially extendible and has bone screw clamps articulated to its respective opposite ends by means of ball joints. The clamps are connected to rod-like bone screws which have been implanted into the cortex of a broken bone on opposite sides of the fracture. Usually, two or three screws are adequate to guarantee a hold. 
     A known external fixation device for stabilizing tibia fractures is disclosed in European patent application No. 0609409 in the name of the same Applicant. 
     A variety of fixation device to cope with different topologies of fractures and traumatisms are normally available from their suppliers. 
     Thus, tibia and femur fixators, humerus fixator, joints, such as the ankle and the elbow, fixators and wrist fixators are available. 
     All these fixation devices are comparable in structure and include similar componentes; however, different types of fractures lead to the necessity of producing a plurality of fixators having different sizes and configurations. 
     Such a comprehensive stock of different fixators unavoidably reflects in increased manufacturing cost of each typology because of standard mass production methods being impracticable. 
     Also, the current technological tendency to produce fixators which have portions or parts moulded out of transparent materials to X-radiation makes even less economical the supply of varied and different types of fixators. 
     The underlying technical problem of this invention is to contrive a unilateral external fixation device, for reducing bone fractures, having structural and functional features which make the device essentially disposable, avoiding a strain of its parts above their support capacity. 
     SUMMARY OF THE INVENTION 
     The principle of this invention is that of providing a bone screw clamp with a ball joint mounted to each clamp, and means for locking the ball joint in a prefixed angular position through a permanent set of the ball joint. 
     Based on this principle, the technical problem is solved according to the invention by fixation device as previously indicated and defined in the characterizing portions of claims  1  and following. 
     The features and advantages of an external fixation device according to the invention will be apparent from the following description of an embodiment thereof, given by way of the non-limitative example with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  shows a vertical perspective view of an axial unilateral external fixation device according to this invention; 
         FIG. 2  shows an exploded perspective view of the fixation device shown in  FIG. 1 ; 
         FIG. 3  shows a further sectional view of a bone screw clamp of the fixation device according to the invention; 
         FIGS. 4 and 5  show sectional schematic views of a detail of the clamp in  FIG. 3  in two different conditions of its operation. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to the drawing views, an axial unilateral external fixation device for reducing bone fractures in orthopedic surgery, realized according to the present invention, is totally shown at  1 . 
     The fixation device  1  comprises a rod-like middle body  2  having an axis x—x, and having opposite ends  3 ,  4  which are articulated to the respective bone screw clamps  5 ,  6 . 
     Advantageously, both the rod-like middle body  2  and the clamps  5 ,  6  are made out of a transparent material to X-radiation, such as a polyetherketone plastics matrix known as “Peek”, which is reinforced with a predetermined amount of carbon fibers in order to obtain a suitable rigidity. 
     More particularly, the rod-like middle body  2  is axially extendible since it is formed by a first  8  and a second  9  mating parts of prismatic shape. The parts  8  and  9  telescopically slide on each other. 
     Each of said parts  8 ,  9  comprises a first portion  8 ′,  9 ′ of elongate semicylindrical shape which is integrally formed with a second cylindrical end portion  8 ″,  9 ″ of short length. Each part,  8  and  9 , is therefore L-shaped if seen sideways. 
     The semicylindrical portions  8 ′,  9 ′ are coupled to each other in a sliding manner by means of a driving groove  7 , longitudinally formed in the portion  8 ′, and a corresponding slide  7 ′ longitudinally formed in the other portion  9 ′. In particular, the portion  8 ′ essentially has a C-shaped section, while the other portion  9 ′ comprises a longitudinal rib having a T-shaped section to define said slide  7 ′. 
     Of course, other driving/sliding combinations can be foreseen without coming out of the scope of the invention. 
     Advantageously, means for stopping said parts  8  and  9  in their sliding movement is provided. 
     This stop means comprises a locking screw  11 , perpendicularly extended to the axis x—x, which locking screw has a threaded end portion  12  engaged in a threaded hole  13  formed in the slideway  7 ′. In addition, the portion  8 ′ of the part  8  is formed with a clearance slot  10  which longitudinally spans most of the portion  8 , as shown in  FIG. 2 . The screw  11  goes through the slot  10 , preferably with a smooth section of its shank  14 , to ease the sliding movement of the portions  8  and  9  on each other. 
     The screw  11  is a socket head screw (Allen screw) for convenient operation with a wrench. 
     By loosening and tightening the screw  11 , the extension of the rod-like middle body  2  of the fixator  1  can be adjusted as necessary, depending on the different dimensions of the broken bone. On the contrary, no rotations of the parts  8  and  9  about the axis of the rod-like middle body  2  occur, because of the C- and T-shaped sections of the driving groove and of the slide. 
     In the compact setting of the rod-like middle body  2 , the portions  8 ′ and  9 ′ of the parts  8  and  9  are fully superposed, with one abutting the cylindrical end portion  9 ″,  8 ″ of the other. 
     As mentioned above, the opposite ends  3 ,  4  of the rod-like middle body  2  are articulated to the respective clamps  5 ,  6  of the bone screws by means of ball joints. 
     Each joint comprises a ball-and-socket joint  16  mounted to each clamp  5 ,  6 . 
     In particular the ball-and-socket joint  16  includes a cylindrical socket  17  which is delimited by a ball-retaining rim  17   a  and provided in each clamp  5 ,  6 , and a ball head  18  lodged in the socket  17 . The ball head  18  has a shank  19  adapted to be received in a corresponding socket  15  on each of the ends  3 ,  4  of the rod-like middle body  2 . 
     The socket  15  lodging the shank  19  is formed near-centrally in the end portions  8 ″ and  9 ″ of the parts  8  and  9 . Briefly, the socket  15  lies along the axis x—x, and the shank  19  is held in the socket  15  by a releasable locking means, such as a lockpin  27  passing through a hole  28  formed transversal to the axis x—x in the portion  8 ″, and a corresponding hole  28 ′ transversal to the shank  19 . 
     Each of the clamps  5  and  6  comprises a main body  20 , substantially prismatic in shape, wherein the cylindrical socket  17 , which lodges the ball head  18 , is formed. 
     A side flange  26  is removably associated with the main body  20  for constraining the clamp onto bone screws, in the example two screws  21  lying in a plane parallel to the lying plane of the axis x—x, and being placed a predetermined distance away therefrom. 
     More particularly, the main body  20  has a side wall  25  of shaped contour. The contour of the flange  26  substantially mates with the side wall  25 , such that the side wall  25  and the flange  26  will joint join like the jaws of a vise, so locking the bone screws. 
     Preferably, the removable coupling of the body  20  and the flange  26  occurs by means of the engagement of a pair of screws  21  in corresponding threaded seats  22  provided in the main body  20 , through clearance holes  23  in the flange  26 . The threaded seats  22  are formed in the side wall  25  of the body  20 . 
     This particular configuration enables the bone screws to be held in the clamp substantially alongside the ball-and-socket joint, thereby achieving a highly compact structure of the overall clamp. 
     Advantageously, locking means  40  of the ball-and-socket joint  16  in a selected angular position is also provided. This locking means  40  comprises a slider  41  which is guided for movement inside the cylindrical socket  17  of the main body  20  in the direction toward the ball head  18 , by the action of a driving means  42 . 
     This driving means  42  comprises a shaft  47  which transversely extends to the socket  17  and is provided with a cam  47   a  acting on the slider  41 . The shaft  47  can be manually rotated with a suitable wrench, and is purposely formed with a recessed hexagon  43  at an accessible end thereof. 
     Specifically, the slider  41  is formed with a cylindrical rim having a plurality of contrate teeth  44 , i.e. all extending towards the same direction parallel to the axis of the rim. These teeth  44  are intended to bite into the surface of the ball head  18 , upon actuation of the driving means  42 , and form a plurality of impressions of a suitable depth therein, e.g. a few tenths of a millimeter deep. In this way, the ball head  18  becomes set permanently, and the ball-and-socket joint  16  is practically locked in a positive manner. 
     A stroke limiting means  45  of the slider  41  is provided so that the teeth  44  bite a predetermined depth into the ball head  18 . This limiting means  45  comprises a radial nose  46  formed integrally with the shaft  47  and appearing externally of the main body  20 , which is arranged to abut against a stop  48  formed on the main body  20 , at an appropriate angular setting of the shaft  47  relative to the main body  20 . 
     With the radial nose  46  abutting the stop  48 , the plurality of teeth  44  of the slider  41  will have sunk the maximum anticipated depth into the surface of the ball head. 
     In assembling one of the clamps,  5  or  6 , first the ball head  18  of the joint  16  is inserted into the cylindrical socket  17  with the shank  19  abutting out of the main body  20 . Then the slider  41  with its teeth  44  facing the ball head  18 , and finally the shaft  47  to stop the previous parts from coming off, is assembled. The shaft  47  is positioned such that an end portion of the cylindrical socket  17  is left available for receiving an additional cylindrical member as described herein below. 
     The cylindrical socket  17  at the free end of the main body  20  is also used for holding an ancillary member  30  which effectively makes the clamp,  5  or  6  more versatile, depending on the different installations of the fixation device. 
     For example, an ancillary member  30  is illustrated in the drawings by a T-connection member  31 , for connecting the clamp  5  to a ring of a ring fixator known in the art as the Ilizarov system. 
     The connecting member  31  comprises a cylindrical shank  32  pivotally fitted in the same cylindrical socket  17  that accommodates the ball head  18  of the ball-and-socket joint  16 . 
     A locking screw  29  engages in a threaded hole  29 ′, transversely formed at the shank  32  and through a slotted hole provided in the main body  20  close to the end thereof opposite to the ball joint  16 . The connecting member  31  further comprises a plate-like portion  33  which is integrally formed with the shank  32  and perpendicularly extends to it. This portion  33  has oppositely located flanges which are penetrated by slotted holes  34  for connection to a ring of an external fixation device of the Ilizarov system. 
     In this way, a clamp  5  or  6  provided with the connecting member  31  can be fastened to a ring of the Ilizarov system to produce a so-called “hybrid splint”, that is an external fixation device comprising an axial fixator and at least one ring, so combining the advantageous features of ring fixation devices and unilateral axial fixation devices. 
     Another ancillary member  30  is illustrated in the drawings by a metaphysis clamp  35  for clamping to bone screws which lie in a plane substantially perpendicular to the axis x—x and, therefore, transversal to the lying plane containing said bone screws held between the walls  25  and  26  of the clamps  5  or  6 . 
     More particularly, a metaphysis clamp  35  allows to secure the fixation device to bone screws implanted in the proximal or the distal end portions of a tibia, or implanted in the distal end portion of a femur. 
     The metaphysis clamp  35  is held in one of the clamps  5  or  6 , in the same way as the connecting member  31 . In fact, the metaphysis clamp  35  would include, as same as the connecting member  31 , a cylindrical shank  36  which fits in the cylindrical socket  17 , and one end  37  integrally formed with the shank  36  and perpendicularly extended to the latter. 
     Such a end  37  is configured with a U-shaped portion which is integrally formed with the shank  36 , in eccentric position therefrom. Such a U-shaped portion basically comprises a pair of walls  38 ,  39  extending parallel to and spaced from each other. A semi-cylindrical groove  38 ′,  39 ′ is provided at the bottom of each wall  38 ,  39  on the same side, which groove defines a semi-socket for accommodating a corresponding metaphysis bone screw, that is a screw implanted in the proximal or the distal end of a tibia, or the distal end of a femur, in a plane substantially perpendicular to the plane of the axis x—x. 
     Advantageously, the portion  37  includes means for clamping metaphysis bone screws. This clamping means comprises a slider  50  which is mounted on the portion  37  for sliding movement along a direction concurrent to the direction in which the flange  26  is clamped against the wall  25 . 
     Such a slider  50  comprises a rectangular base  49  formed with a window  49   a , and has two plate-like lugs  51 ,  52  which are integrally formed with the base  49  at the short sides thereof. 
     The plate-like lugs  51 ,  52  cooperate with the walls  38  and  39  to clamp the metaphysis screws therebetween. More particularly, the slider  50  is sliding mounted on a narrowing end of the wall  39  through the window  49   a , such that the lug  51  is faced toward the portion  37  and is movable between the walls  38  and  39 , parallel thereto. 
     At the free ends of the lugs  51  and  52 , and on the same side are provided respective semi-cylindrical grooves  51 ′,  52 ′, each defining a semi-socket accommodating a corresponding metaphysis bone screw. With the slider  50  assembled to the portion  37 , the grooves  38 ′ and  51 ′ face to each other, and so do the grooves  39 ′ and  52 ′, ready for clamping onto a corresponding metaphysis screw. 
     A locking screw  53  passes through a hole laterally formed in the slider  50  and engages in a threaded hole formed close to the free end of the wall  39  for locking the slider  50  in place, clamping onto the metaphysis screws. 
     In this way, i.e. with the screws, including the side ones between the wall  25  and the flange  26 , and the metaphysis ones between the slider  50  and the portion  37 , all brought to a tightened state by displacements occurring all in the same direction, their mutual positions are retained even when their diameters change, for example, from screws with a diameter of 6 mm to screws with a diameter of 8 mm throughout. 
     The fixation device of this invention does solve the technical problem and offers a number of advantages, among which the foremost is that the clamps are of universal utility, unlike prior solutions. 
     In fact, the middle body  2  can have opposite clamps associated with it, which serve different functions but stem all from a common basic structure. 
     Furthermore, the fixation device made of a transparent material to X-radiation allows the orthopedic surgeon to radiograph the affected region without suffering interference from bulky objects. 
     Also, it should be noted that the middle body accounts for a major portion of the overall length of the fixation device according to the invention, and allows the fixator length to be adjusted for almost any traumatic situations. 
     It should be further noted that the multiple impressions produced by the contrate teeth in the surface of the ball head, so that in practice the ball-and-socket joint can be locked in any desired angular position, also forbid re-use of the clamps, which are therefore disposable clamps. This offers an additional advantage from both the sanitary and the safety standpoints.