A DEVICE IN INSTRUMENTS

Abstract: An arrangement in instrumentaria or external fixation and stabilization of fractured skeletal parts, comprising at least one connecting element (5) which extends along the skeletal parts to be healed and on which there is mounted at least one holding device (6) for pins (3) inserted in each skeletal part, wherewith a first assembly part (7) of at least the one holding device can be displaced along the connecting element and locked thereto at selected positions therealong, and wherewith a second part assembly (8) of the holding device is rotatably connected to a lockable to the first part of the holding device and provided with means for locking the pins. This rotatable connection between the aforementioned parts of the holding device comprises a ball-and-socket coupling with line abutment between the ball and at least one of the ball seatings capable of being pressed against the ball.

Description: A device in instruments DESCRIPTION Technical Field The present invention relates to an arrangement in instru- mentaria for fixating and stabilizing fractured skeletal parts and being of the kind set forth in the pre-characte- rizing clause of Claim 1. Background Prior Art Instrumentaria of the aforesaid kind and similar kinds are known in the art, see for example in this regard pages 4-11 in the publication "Complications of External Skeletal Fixation" published by Charles C. Thomas, Springfield, Illinois, USA. Of the instrumentaria described in this publication, the instrumentarium most used is that proposed by Hoffmann (vide Figure 6 and 9) , although this instru¬ mentarium is encumbered with a number of drawbacks, of which the most serious resides in the fact that consider¬ able manipulating forces are required firstly to lock a first part of a holding device, said part being lockable in turn to a connecting rod, to a second rotatable part of said device, and to lock the pins to said second part. A further drawback resides in undesirable sliding and/or rotation between mutually locked parts of the instrument¬ arium when large forces are applied thereto. The US Patent Specification 4 135 505 describes and illustrates an instrumentarium in which the connection between a connecting rod or bar and a pin-holding device comprises a ball-and-socket coupling, the ball of which is introduced between and lies against ball seatings in the form of bevelled surfaces, the ball seatings being urged into engagement with the ball by means of screws. in a more recent instrumentarium, designated ORTHOFIX (Registered Trade Mark) the connection between a connecting ^ between a connecting rod and a pinholding device com¬ prises a ball-and-socket coupling, in which the ball is introduced between and lies against the ball seatings which present abutment surfaces in the form of part- spherical surfaces,wherewith the one seating can be urged against the ball by means of a rotatable cam shaft. In a further instrumentarium, proposed in recent times and manufactured and retailed by EX-FI-RE systems, Kristiansand, Norway, the connection between a part of a holding device,which is capable of being locked to a connecting rod, and a pin-locking part of said arrange¬ ment comprises a ball-and-socket coupling. A knurled or servated ball is introduced between a first seating, in the form of a part-spherical surface, with surface abut- ment between the ball and seating, and a second seating in the form of a hollow nut, which is screwed onto the first seating in a manner to urge the seatings towards one another and therewith lock the ball therebetween. The three last mentioned instrumentaria. are encumbered essentially with the same disadvantages as those des¬ cribed with reference to the instrumentarium proposed by Hoffmann. Summary of the Invention It is the object of the present invention to eliminate at least partially the drawbacks encountered with known instrumentaria of the aforedescribed kind, and to provide an improvement in instrumentaria which enables the two parts of the holding device to be locked together and the one part of the holding device to be locked to said pins with the aid of relatively small actuating forces, and which improvement will ensure that the said parts remain firmly locked when the instrumentarium is in use, and that the various components of the holding device are capable of being adjusted to a selected one of a large number of possible positions in relation to one another and in relation to the skeletal parts to be healed, and _hat these procedures can be carried out in a simple and ready manner. This object is fulfilled with the arrangement according to the invention which has the characterizing features set forth in the characterizing clauses of the following Claims. Brief Description of the Drawings Figure 1 illustrates in perspective the leg of a human being and an instrumentarium for the fixation and stabili¬ zation of fractured skeletal parts of the bone, this instrumentarium incorporating the arrangement according to the invention; and Figures 2 and 3 are exploded views of parts of the arrange¬ ment illustrated in Figure 1. Description of a Preferred Embodiment Figure 1 illustrates an instrumentarium which comprises two mutually identical assemblies 1 and 2 having attached there¬ to and extending therebetween identical pins 3. The pins 3 are of substantially circular cross-section and are in¬ serted into prebored holes in fractured parts of the bone of a leg 4, illustrated schematically in chain lines, so as to fixate and stabilize the fractured bone until healed. It will be understood, of course, that the instrumentarium can be used in conjunction with skeletal parts other than the bones of a leg, and that at times it may be sufficient to use solely one of the illustrated assemblies 1 and 2, together with the pins 3, as a complete instrumentarium. The construction of the assembly 1 , the manner in which it is mounted and its method of use will now be des¬ cribed in greater detail. The Assembly 1 comprises three major components, namely a connecting device in the form of a rectalinear steel tube and two mutually identical holding devices 6, each of which comprises a first part 7, which is constructed for axial movement along the tube 5 and can be locked to the tube in selected positions therealong, and a second part 8, which is rotatably connected to the first part 7 and capable of being locked thereto and which is provided with pin locking means, described in more details herein¬ after. The first part 7 of the assembly 1 comprises a steel plate 9 having provided therein four mutually parallel holes 10, 11, 12 and 13, of which only the hole 13 is provided with a screwthread, and a steel plate 14 having provided there¬ in four mutually parallel holes 15, 16, 17 and 18, of which the hole 15 is provided with a screwthread, and with a fifth hole 19 the axis of which extends vertically to the axes of the lastmentioned holes and which intersects a slot 20 (vide Figure 1 ) extending between the hole 16 and the outer surface of the plate. Only that part of the hole 19 which is located on one side of the slot 20 is screw- threaded. The hole 12 in the plate 9 is defined by a cylindrical inner wall 12a having a sharp annular edge 12b. The hole 17 in the plate 14 is defined by a cylindrical inner wall 17a having a sharp annular edge 17b. The sharp edges 12b and 17b have a locking function, which will be described in more detail hereinafter, and in order to retain an effective edge locking action, even after having used the instrumentarium for a long period of time. the edges must be hard and wear resistant. This is achieved by hardening the plates 9 and 12, at least in the regions of the edges 12b, 17b of respective holes 12, 17, or alter¬ natively by forming said edges on separate annular inserts and subsequently press-fitting the inserts into irrespective holes. The edges 12b, 17b consist of stainless, acid- proof steel and have a hardness of 220-250 Brinell. The other part 8 of the assembly 1 comprises a steel shaft 21 which has the form of a crank-like lever and which has located on one end thereof a stainless steel ball 22 having a smooth outer surface which is hardened to a Brinell hard¬ ness of 220-250, and the other end of which shaft has located thereon a substantially parallelepipedic body 23 which is provided with three V-shaped recesses or grooves 24 on one side thereof and with three V-shaped recesses or grooves 25 on the opposite side thereof, and further com¬ prises a parallelepipedic body 26 which has three V-shaped recesses of grooves 27 on one side thereof. The bodies 23 and 26 are provided with respective holes 28 and 29, of which only the holes 28 are provided with screwthreads. The second part 8 of the assembly 1 is intended to be fitted to the first assembly part 7, by passing the second part 8, without the body 26, through the hole 12 in the plate 9-with the body 23 leading until the ball 22 lies against the annular edge 12b, the diameter of the ball being larger than that of said annular edge. The plate 14 is then securely fitted to the plate 9 with the aid of screws (not shown) , which are passed from two directions through the holes 10, 13, 15, 18, wherewith the ball 22 abuts the annular edge 17b, the diameter of the ball being larger than that of said edge. When tightening the screws, the screw inserted through the mutually opposing holes 13, 18 is tightened to an extent which is assumed to corres¬ pond to the extent to which all said screws are to be finally tightened, whereas the remaining screws are tighte¬ ned to an extent which is just sufficient to enable the ball 22, which thus lies against the mutually spaced plates 9 and 14 solely in line abutment with resprective edges 12b and 17b, is able to rotate and pivot upon manual activation of the shaft 21. The thus assembled parts 7 and 8 are then fitted to the tube 5, which passes through the holes 11 and 16 in respective parts, and a screw (not shown) is screwed into the hole 19 and tightened, sufficiently to urge together the two parts of the plate 14 located on opposite sides of the slot 20, so as to loosely clamp the assembly to the tube. A further assembly, comprising first and second parts 7 and 8 and assembled in a manner similar to the first- mentioned assembly, is then fitted to the tube 5 and the positions of the two assemblies are adjusted in relation to the positions of the pins 3 previously inserted in the skeletal parts to be healed, such that the pins lie in the aforesaid recesses or grooves 24 or 25. This adjustment to the positions of the two assemblies is effected by displacing the parts 7 and 8 axially along the tube 5 and by rotating and/or pivoting the shaft 21 , which due to its cranklike configuration enables a suitable position of adjustment to be achieved from a plurality of possible adjustment positions, such that the instrument- arium is as stable as possible and the various screws can be readily reached for subsequent manipulation. The body 26 is then fitted to the body 23, with the recess 27 facing either the recess 24 or the recess 25. Which of the recesses 24 or 25 is chosen depends on the accessability of said recess and/or the accessability of the screws (not shown) , which are inserted through the holes 28 and 29 and which urge the bodies 23, 26 towards one another so that the selected recess 24 or 25 and the recess 27 are brought into line abutment with the pins 3, thereby requiring but a relatively small tightening force on the screws. Subsequent to making minor adjustments to the settings of the assemblies 6, the screw passing through the holes 10, 15 and connecting the plates 9 and 14 is tightened, the holes 10, 15 being located at a further distance from the ball-and-socket coupling 12b, 17b, 22 than the holes 13, 18, whereby the annular edges 12b and 17b are pressed into line abutment with the spherical surface of the ball 22, which means that the force required to tighten the assembly and the locking force achieved are respectively smaller and greater than the comparable forces required and achieved in the case of a surface abutment. Solely the material from which the ball 22 and the plates 9 and 14, and the sharp annular edges 12b, 17b are made has a significance in achieving an optimal locking effect. The positioning of the two annular abutment lines between the said edges and the ball is also important however. It has been found that when the ball and the plates are made from the aforedescribed material, the abutment lines should be spaced at a short distance apart. In this regard, a radius drawn from the centre of the ball to the tangent of each abutment line to the spherical surface of the ball should form, together with a line passing through the centre of the ball and located in the vertical plane in Figure 2, a maximum and also an optimum angle of about 67.3°. When this angle is exceeded, the surface of the ball will be plastically deformed by the shear forces generated, there¬ with impairing the locking effect. In conjunction with the aforesaid critical, optimum angle the ratio between the dia¬ meter of each annular edge 12b, 17b and the diameter of the ball 22 is 0.90-0.91. In tests carried out with identical materials in the ball 22 and the spherical edges 12b, 17b having a Brinell hard¬ ness of 220-250, there was achieved a maximum locking torque force, of 35Nm at optimum angles. This torque force was obtained when applying a tightening torque to the screw passed through the holes 10, 15, of 4 Nm and was not ob¬ served to increase with increased torque. With other conditions equal, the locking torque can be increased to above 50 Nm when the surface hardness of the edges and ball is selected so that the ratio is at least 2:1. The relatively large lever arm effect between the ball-and- sock coupling and the holes 10, 15 enables a smaller torque to be applied than that required when the aforesaid distances are equal or when the screw inserted in the holes 13, 18 is tightened subsequent to tightening the screw inserted in the holes 10, 15. Finally, the screws inserted through the holes 19 are fully tightened, wherewith the instrumentarium is able to fulfill its intended function. Although the invention has been described with reference to a preferred embodiment thereof illustrated in the accompanying drawings, it will be understood that the invention is not restricted to this embodiment and is limited solely by the scope of the following Claims.

Claims: C L A I M S 1. An arrangement in instrumentaria for external fixation and stabilization of fractured skeletal parts, comprising at least one connecting element (5) which extends along said skeletal parts and on which there is mounted at least one pin-holding device (6) for firmly holding a pin (3) inserted in each skeletal part, where¬ with a first assembly part (7) of at least the one holding device is displaceable along the connecting element and capable of being locked thereto in selected positions therealong, and wherewith a second assembly part (8) of the pin-holding device is rotatably connected with and lock- able to the first assembly part and is provided with means (23-29) for locking the pins, c h a r a c t e r i z e d in that the rotatable connection between the aforesaid assembly parts (7, 8) comprises a ball-and-socket coupling having line abutment between the ball (22) and a sharp annular edge (12b, 17b) on each of the ball seatings against which the ball can be urged. 2. An arrangement according to Claim 1 , c h a r a c t e r i z e d in that the linear abutment extends along two substantially parallel circular lines on the surface of the ball (22) , irrespective of the position to which the ball is rotated and swung in relation to the ball seats (12b, 17b). 3. An arrangement according to Claim 1 or 2, c h a r a c t e r i z e d in that the ratio between the diameter of each edge (12b, 17b) and the diameter of the ball (22) is approximately 0.9. 4. An arrangement according to any of the preceding Claims, c h a r a c t e r i z e d in that the ball seatings (12b, 17b) can be urged into engagement with the ball (22) by means of devices (at 10, 15 and 13, 18 respectively) connecting said seatings, of which elements one is located at a greater distance from the ball than the other. 5. An arrangement according to any of the preceding Claims, c h a r a c t e r i z e d in that the ball (22) is mounted on the second assembly part (8) , which has the form of a preferably crank-like arm (21) which projects from the first assembly part (7) and the end of which remote from the ball is provided with said means (23-29) for locking the pins (3) . 6. An arrangement according to any of the preceding Claims, c h a r a c t e r i z e d in that the means (23-29) for locking the pins (3) incorporates two locking devices (23, 26) which can be urged towards one another and which are provided_with. mutually facing V-shaped grooves (24, 25, 27) into which the pins are inserted and pressed there- against in line abutment therewith. 7. An arrangement according to Claims 5 and 6, c h a r a c t e r i z e d in that the one means (23) constitutes a part of the aforesaid second assembly part (8) and is provided with at least one V-chaped groove (24 and 25 respectively) ' on two mutually opposing sides thereof.

Inventors: HAMMER RICHARD, HAMMER, RICHARD
Applicants: HAMMER RICHARD, HAMMER, RICHARD
Application year: 1986
Main classification: A61B17
IPC codes: A61B17