DEVICE FOR TIGHTENING A LOOP IN A WIRE OR CABLE

Abstract: A device for tightening a loop formed in a cable or wire (10) used in surgical procedures has a spacer body (32) for engaging the cable or wire adjacent the point at which the loop closes and an adjusting member (34) coupled to the spacer body at a point spaced from the point of engagement of the spacer body (32) with the cable or wire (10). The adjusting member (34) is rotatable relative to the spacer body (32) and is provided with means for securing (39) at least one free end of the wire or cable (10) for rotation therewith. Consequently, rotation of the adjusting member (34) relative to the spacer body (32) causes the free end of the wire or cable to be wrapped around the adjusting member, thereby drawing the loop tight.

Description: DEVICE FOR TIGHTENING A LOOP IN A WIRE OR CABLE The present invention relates to a surgical procedure and, in particular, to a device for use in tightening a loop formed in a wire or cable in the course of such a procedure. A number of surgical techniques have been developed over recent years which involve the fastening of loops of wire or thin flexible cables around bony structures. Some of these procedures are, for example, concerned with the stabilising of certain types of fracture but others may involve the lashing of various types of prosthesis or like device to the skeleton. Examples of such procedures and of devices to be used in them are to be found in US Patents 4,604,995 (Stephens et al. ) , 2,501,978 (Wichman) and 4,790,303 (Steffee). Traditionally, stiff stainless steel wire filament is moulded into a shape and pulled or pushed around the bone. The passage of this stiff wire may cause serious and irreparable damage to the underlying soft tissues, and for this reason a more flexible cable formed, for example, of braided titanium or stainess steel wires would be preferable. The stiff wire is fastened by tightening together the free ends of the wire as described for example in U.S. patents 2,455,609 (Scheib), 1,304,620 (Steinkoenig) and 914,182 (Pfeffer) as the twisting operation simultaneously tightens and fastens the loop. However, the use of twisting in the surgical procedure has disadvantages. Firstly, the twisting operation puts a great deal of strain on the wire which may consequently break, necessitating a repetition of the entire procedure. Worse, it may weaken the wire so that it breaks after the surgical procedure has been completed and the wound closed, having sharp wire ends protruding where they can cause damage to the surrounding tissues and permitting the structures, which should have been held firm by the wire loop, to move. In any event, the twisting operation itself produces a twisted projection wire stub which may cause tissue damage. It is not possible to fasten flexible wire or cable by the means described above. Instead, some form of tensioning of the flexible cable is required to appose bone fragments or the bone to the implant and then this fixed in position by some form of crimping mechanism, examples of which are shown in U.S. patents 2,291,418 (Siebrandt) and 4,966,600 (Songer et al) . These devices are, however, relatively complex in construction and in operation. They are expensive to manufacture and, when used for surgical procedures, must be re-sterilised each time they are used. It would clearly be desirable to provide a tensioning tool of simple construction which could be made sufficiently cheaply to permit it to be provided as a disposable item for one time use only. In accordance with the invention, there is provided a device for tightening a loop formed in a cable or wire, the device comprising a spacer body for engaging the cable or wire adjacent the point at which the loop closes and an adjusting member coupled to the spacer body at a point spaced from the point of engagement of the spacer body with the cable or wire, and rotatable relative thereto, the adjusting member being provided with means for securing at least one free end of the wire or cable for rotation therewith so that rotation of the adjusting member relative to the spacer body causes the free end of the wire or cable to be wrapped around the adjusting member thereby drawing the loop tight. Preferably, both the spacer body and adjusting member are of moulded plastics material . Since the device has only two major parts and, in a preferred embodiment, is of moulded plastics material, it is simple and inexpensive to produce and may be provided as a disposable item. The plastics material used may be radiolucent so that the presence of the device does not obscure the surgeon's view in X-ray pictures of the site at which the loop is being formed. In a preferred embodiment, the device is provided with a ratchet mechanism operable to permit relative rotation of the spacer body and adjusting member in a first direction and to oppose relative rotation of the spacer body and adjusting member in a second opposite direction. The ratchet mechanism permits the surgeon to make gradual adjustments to the tension in the loop by rotating the spacer body and adjusting member one ratchet tooth at a time. Furthermore, the ratchet mechanism prevents slipping of the loop, if the surgeon moves onto tension another device or lets go of the device for any other reason, for example, while crimping to close the loop. Preferably, the spacer body is shaped to engage a crimp tube through which the wire or cable is passed so that, in use, the device engages the cable or wire indirectly. The spacer body may be bifurcater at the region which, in use, engages the crimp tube to form a pair of arms which in use engage the crimp tube at points spaced longitudinally thereof so that the crimp tube can be ' crimped in the region between the points at which it is engaged by the spacer body without disengaging the spacer body from the crimp tube. This ensures that the loop remains tight while the crimp is being formed. The invention also provides a method for forming a loop in a cable or wire comprising the steps of passing the cable or wire around a structure or structures to be enclosed in the loop to form a closed loop; engaging a device for tightening a loop formed in a cable or wire in accordance with any of claims 1 to 17 with the cable or wire adjacent the point at which the loop closes; securing the free ends of the cable or wire to the adjusting member of the said device; rotating the adjusting member of the said device relative to the spacer body thereof to draw the loop tight; and fastening the wire or cable to hold the loop closed. The system of the invention will now be described in detail, by way of example, with reference to the drawings, in which: Figure 1 shows a wire being drawn around a fracture; Figures 2a and 2b show tools suitable for drawing a wire around a bone or other structure; Figure 3 shows a crimp tube for forming a crimp tube for forming a crimp to secure a wire to form a wire loop; Figure 4 shows a wire tensioning tool in accordance with the invention, in part sectional view; Figure 5 shows the tensioning tool of Figure 4 from the side; Figure 6 is a cross-section through the forward part of the tensioning tool of Figure 4; Figure 7 is a part sectional view analogous to Figure 4 showing an alternative tensioning tool construction; Figures 8a and 8b show a wire being threaded into the tensioning tool of Figure 4; Figure 9 shows a torque driver for use with the tensioning tool of Figure 4; and Figure 10 shows a tool for crimping the tube of Figure 3. As described above, one known technique for securing together bone fragments around the sites of certain types of fracture, for example, breaks or splits extending longitudinally of the long bones, involves the use of wire loops passed around the bone fragments and tightened sufficiently to hold the fragments together while the bone knits and heals. In most cases, several separate loops of wire are passed around the bone in the region of the fracture, so as to ensure that the fragments are securely held together. Each loop must be fastened so that it does not come undone, allowing the bone fragments to move and, perhaps, heal out of their proper alignment. Figure 1 shows a length of surgical wire 10 being passed beneath bone fragments 12 at a fracture site using a wire-passer 14. Two preferred forms of wire-passer 14a and 14b are shown in Figures 2a and 2b. It will be seen that each wire-passer 14a, 14b has an elongate handle 13a, 13b which carries, at one end, a specially shaped hook member 15a, 15b. The particular shape of the hook member 15a, 15b- is determined by the particular part of the body in which it is to be used. Each wire-passer 14a, 14b has, however, at its tip an opening 17a, 17b passing through the hook member 15a, 15b. In use, the tip of the wire-passer 14 is slipped beneath the bone or bone fragments 12 around which a wire loop is to be formed. The wire 10 is then threaded through the opening 17 at the tip of the hook member 15 so that, as the wire passer 14 is withdrawn, the wire 10 is drawn beneath the bone or bone fragments 12. Rather than a single filament, the wire 10 used is a braided cable of stainless steel or titanium threads woven together. The resulting cable is more flexible than a single wire and can be secured more reliably by crimping than can a single wire. In accordance with the invention, the ends of the wire 10 are passed through the crimp tube 20 from opposite ends thereof as shown in Figure 3 so that the free ends of the wire 10 extend from the two ends of the tube. In addition to facilitating tensioning of the wire 10 as described below, this also has the advantage that, when the free ends of the wire 10 are removed following crimping, the crimp tube 20 is substantially flush with wire loop. Consequently, since projecting metal components are minimised there is relatively little risk of damage to surrounding tissues. Before the crimp can be formed, the tension in the wire 10 forming the loop must be adjusted. This is achieved using the tensioning tool 30 shown in Figures 4-6 of the drawings. As can be seen from the drawings the tensioning tool 30 comprises a forward spacer body 32 (shown partly in section) and a rear adjusting member or knob 34. Both the spacer body 32 and the adjusting knob 34 are preferably of moulded plastics material, for example, moulded ABS plastic. This enables the tensioning tool to be made sufficiently cheaply that the tensioning tool can be provided as a disposable item for one-time use only. The material used is, ideally, radiolucent so that, during reduction of fractures, the presence of one or more tensioning tools does not prevent the surgeon determining from X-rays when the bone fragments are properly aligned. The forward part of the spacer body 32 is divided to form a pair of parallel arms 33, each of which is formed at its free end with a part circular recess 35, shown most clearly in Figure 5, of dimensions such that it is a fairly tight fit around the crimp tube 20. The recessed ends of the arms 33 are spaced apart from each other so that the overall width of the forward end of the tensioning tool 30 is roughly equal to the length of a crimp tube, so that a crimp tube 20 can be held firmly by snapping the recessed ends of the two arms 33 onto its two ends during tensioning. There is, however, an appreciable gap between the ends of the arms 33, permitting the central part of a crimp tube 20 held between the recesses 35 to be crimped using a suitable tool, while the crimp tube 20 is still held by the tensioning tool 30. At its rear, the arms 33 of the spacer body 32 are joined to form a substantially tubular portion having a cylindrical blind bore 37 formed centrally in it. Adjacent its closed end, the bore 37 is provided with a ring of ratchet teeth 38. Near the open end of the bore 37, the wall of the tubular portion is extended outwards to form a pair of diametrically opposed lugs 39 each of which has an axially-extending opening 41 formed in it. The rear adjusting knob 34 of the tensioning tool 30 has a generally cylindrical hollow shaft 40 dimensioned to be a sliding fit in the rear bore 37 of the spacer body 32. The forward end surface of the shaft 40 is formed with ratchet teeth 42 intended to interengage with the teeth 38 formed in the innermost end of the blind bore 37. At its end remote from the ratchet teeth 42, the shaft 40 carried a knurled knob 44 by means of which the rear adjusting knob component 34 can be rotated relative to the spacer body 32. Midway between the ratchet teeth 42 and the knurled knob 44, the hollow shaft 40 is provided with a pair of diametrically opposed, longitudinally extending slots 46. Each of the slots 46 has sections along its length of three differing widths so that wires of differing diameters may be caught and held in the slots 46, as will be described below. The adjusting knob 34 is secured to the spacer body 32, as shown in Figure 4, by means of a wave ring 48 of resilient metal. The wave ring 48 has at intervals around its circumference outwardsly extending tabs which project through openings 49 formed in the hollow shaft 40 and engage in a circumferential groove 50 formed in the wall of the blind bore 37 at the rear of the spacer body 32. Thus, the wave ring 48 serves to prevent the adjusting knob 34 being withdrawn from the bore 37 in the spacer body. The wave ring 48, however, also serves another important purpose in that it biasses the adjusting knob component 34 towards the interior of the bore 37 in the spacer body 32 and, in particular, it biasses the two sets of ratchet teeth 38 and 42 into engagement with one another. The two parts of the tensioning tool 32 and 34 can only be rotated relative to one another by moving the adjusting knob 34 slightly towards the outer end of the bore 37 in the spacer body 32 so that the ratchet teeth 42 on the end of the 40 can ride over the teeth 38 formed on the end wall of the bore 37. In the 'forward' direction of the ratchet, the necessary axial movement of the adjusting knob and associated shaft 40 is caused by a camming action of the two sets of teeth 38 and 42. In the backward direction, however, the adjusting knob component 34 must positively be pulled back against the biassing force of the wave ring 48 until the ratchet teeth 42 on the end of the shaft 40 of the adjusting knob 34 are clear of those formed on the end wall of the bore 37. The ratchet teeth 38 and 42 are important because they permit the surgeon to tighten the wire loop incrementally by rotating the adjusting knob 34 one tooth at a time. Furthermore, when the surgeon releases the tensioning tool, the ratchet mechanism formed by the teeth 38 and 42 prevents any backward slippage between the two components of the tool and consequent loosening of the wire loop. This is particularly helpful where several wire loops are to be formed around the site of a fracture at the same time. Since there is little risk of slipping, each loop can be tightened a little at a time before finally being fixed, allowing even pressure to be applied around the fracture site. Figure 7 shows an alternative tensioning tool construc¬ tion which provides similar advantages to those of the device of Figure 4. The main components of the tensioning tool of Figure 7, the adjusting knob 34 and spacer body 32, are similar to those described in relation to Figure 4 but their construction in the region where the two parts interengage is different. Instead of the blind bore 37, the spacer body 32 in Figure 7 is provided at its rearward end with a generally cylindrical hollow boss 70.. The main part of the boss 70 is joined to the rest of the spacer body 32 by a stem 72 of smaller diameter than the main part. The stem 72 has formed on it a thin outwardly extending annular spring flange 74 which provides the necessary resilient force in place of the wave ring 48 of Figure 4. The annular end surface of the boss 70 remote from the spacer body 32 is provided with ratchet teeth 76. In the construction shown in Figure 7, the adjusting knob 34 is provided, at the end of the shaft 40 remote from the knurled knob 44 with a sleeve 78 dimensioned to fit over the boss 70 on the spacer body 32. Ratchet teeth 80 are formed on an inwardly extending annular shoulder 82 of the sleeve 78 in a position such that, in use, the two sets of ratchet teeth 76 and 80 co-operate m a manner similar to that described in relation to Figure 4. At its forward end, the sleeve 78 has an inwardly directed flange 82. The sleeve 78 of the adjusting knob component 34 is 'snapped' over the boss 70, the resilience of the material permitting the flange 82 to pass over the spring flange 74. Thereafter, removal of the adjusting knob component 34 is opposed by the spring flange 74 which also serves to urge the ratchet teeth 76 and 80 into engagement with each other. The construction shown in Figure 7 has the advantage that it does not require any additional metallic components whatsoever over and above the two moulded plastic components. It is, as a result, very inexpensive to manufacture and easy to assemble by simple snap-fitting of the two parts together. As mentioned above, it may be necessary or desirable to position two or more wire loops at a fracture site at the same time. For this reason, it is preferred that at least the forward part of the spacer body 32 is of generally tapering triangular cross-section, as shown in Figure 6, so that the tensioning tools used can be placed as close together as possible. In use, the two free ends of the wire loop 10 are passed through the crimp tube 20 from opposite ends of the tube 20. The tensioning tool 30 is then snapped on to the crimp tube 20, the resilience of the plastics material of which the tensioning tool 30 is made allowing the arms 33 to deform in the regions of the recesses 35 at their ends so that the crimp tube 20 is held in the recesses 35. The free ends of the wire 10 are then passed alongside the arms 33 of the tensioning tool 30 as shown in Figure 8a, and then threaded through respective ones of the opening 41 in the lugs 40 at the rearward end of the spacer body 32. The two ends of the wire 10 are then threaded together through the diametrically opposed slots 46 in the shaft 40, as shown in Figure 8b, so that the wire ends pass right through the shaft 40 and are wedged firmly into the slots 46. The shaft 40 may additionally be provided with a transverse screw (not shown) which, in use, is tightened to trap the wire 10 passing between the slots 46 against the inside of the wall of the hollow shaft 40. This prevents the wire 10 inadvertently coming loose from the slots 46 during tensioning. As can be seen in Figure 8, ".he shaft of the tensioning tool 30 may be provided with a mot led lip 43 to guide the wire ends into the slots 46 and thus make it easier to thread the wire 10 into the tool 30. Once threaded, the tool 30 is used to adjust the tension in the wire loop 10 by rotating the knurled knob 44 so as to turn the adjusting knob component 34 relative to the spacer body 32. As the two components of the tensioning tool 30 rotate relative to one another, the wire 10 is wound around the shaft 40, gradually drawing the wire loop tight. It is to be noted that during the tightening of the wire 10, the tensioning tool 30 bears on the crimp tube 20 rather than on the bone fragments or any other biological structure. Furthermore, the wire 10 is drawn up tight from both ends simultaneously, minimising friction between the wire 10 and the bone or bone fragments around which it passes. As the final tension is approached, the ratchet mechanism formed by the teeth 38 and 42 allows the tensioning tool 30 to be adjusted in small increments and permits the surgeon to let go of the tool without any real risk of the wire shipping. The adjusting knob 54 is turned either directly by the surgeon using the knurled knob 44 or using a torque driver 90 of the type shown in Figure 9. The torque driver 90 has a hollow shaft 92 with, at one end a sleeve 94 dimensioned so as to fit over and frictionally engage the knurled knob 44 of the tensioning tool 30. At its other end, the torque driver 90 has a generally disc-shaped handle 96 of relatively large diameter. The large diameter of the handle 96 facilitates the application of relatively large torques to the tensioning tool 30 and also assists in making small adjustments. The torque driver 90 may also incorporate a torque meter so that the wire 10 can be tightened to a predetermined numerical value of torque. It might also be provided with some form of conventional 'pop-off mechanism so that when the desired torque is reached, the torque driver 90 is no longer operatively engaged with the tensioning tool 30. This has the advantage that the risk of overtightening the wire 10 is reduced. Once the required tension has been reached, the crimp tube 20 is crimped around the wire 10 using the crimp tool 100 shown in Figure 10 . The crimp tool 100 has a pair of opposed jaws 101 and 102 which are hinged together at pivot 106. Each of the jaws 101 and 102 is itself hinged part-way along its length at pivots 103 and 104 respectively. The rear part of each jaw 101 and 102 is extended rearwardly to form a handle 107 or 108 and the handles 107 and 108 are formed with interengaging cam surfaces (not shown) so that, as the handles 107 and 108 are moved together about pivot 106 (as shown in dotted lines in Figure 10), the ends of the rear parts of the jaws 101 and 102 carrying pivots 103 and 104 move apart. At the forward end of the crimp tool 100, each of the jaws 101 and 102 is provided with a forward jaw member 111 and 112 connected to the rear parts of the jaws ' at the pivots 103 and 104 respectively. The forward jaw members 111 and 112 are themselves hinged together at pivot 110, close to their forward ends. The forward ends of the two forward jaw members 111 and 122 are shaped to form co-operating die surfaces 113 and 114 so that when a crimp tube 20 is disposed between the die surfaces 113 and 114 and the forward jaw members 111 and 112 are moved together, using the handles 107 and 108, the crimp tube 20 is deformed around the wire 10 to grip it tightly. The forward jaw members 111 and 112 are made sufficiently narrow that they can be placed around the central part of the crimp tube 20, between the arms 33 of the tensioning tool 30. The tube 20 is then crimped with the tensioning tool still in place. It is also to be noted that the forward end surfaces of the forward jaw members 111 and 112 are substantially flat and extend generally transversely of the crimp tool 100 so that the crimp tube 20 can be crimped using the tool as close to the bone as possible. Once a secure crimp has been formed, the crimp tool 100 and tensioning tool 30 are removed and the ends of the wire 10 are cut off, close to the ends of the crimp tube 20 using conventional surgical wire cutters. The crimp thus formed lies flat against the bone, in line with the wire loop and with virtually no projecting ends liable to cause damage to surrounding tissues.

Claims: CLAIMS 1. A device for tightening a loop formed in a cable or wire, the device comprising a spacer body for engaging the cable or wire adjacent the point at which the loop closes and an adjusting member coupled to the spacer body, at a point spaced from the point of engagement of the spacer body with the cable or wire, and rotatable relative thereto, the adjusting member being provided with means for securing at least one free end of the wire or cable for rotation therewith so that rotation of the adjusting member relative to the spacer body causes the free end of the wire or cable to be wrapped around the adjusting member thereby drawing the loop tight. 2. Apparatus according to claim 1 in which the device is provided with a ratchet mechanism operable to permit relative rotation of the spacer body and adjusting member in a first direction and to oppose relative rotation of the spacer body and adjusting member in a second opposite direction. 3. Apparatus according to claim 2 in which the ratchet mechanism includes a first set of ratchet teeth formed on the spacer body and a second set of ratchet teeth, engageable with the first said set, formed on the adjusting member, and resilient biassing means for urging the first and second sets of ratchet teeth into engagement with one another. 4. Apparatus according to claim 2 in which the resilient biassing means acts so as to couple the spacer body and adjusting means together. 5. Apparatus according to claim 3 or 4 in which the resilient biassing means comprises a resilient wave plate engaged in grooves or openings formed in the spacer body and in the adjusting member so as to permit relative rotation but oppose relative axial movement thereof. 6. Apparatus according to claim 3 or 4 in which the resilient biassing means comprises a resilient annular glange formed integrally with one of the spacer body and adjusting member and engageable with an annular surface of the other one of the spacer body and adjusting member. 7. Apparatus according to any preceding claim in which either or both of the spacer body and adjusting member are of moulded plastics material. 8. Apparatus according to any preceding claim in which either or both of the spacer body and adjusting member are of radiolucent material . 9. Apparatus according to any preceding claim including means for guiding the free end of the wire or cable from the point of engagement of the sapcer body with the wire or cable to the means for securing the free end on the adjusting member. 10. Apparatus according to claim 9 in which the means for guiding include at least one projecting lug having an axially extending opening formed therethrough through which the free end of the wire or cable can be threaded. 11. Apparatus according to any preceding claim in which the means for securing the free end of the wire or cable comprises at least one slot of width only slightly greater than that of the wire or cable; the free end of the wire or cable being frictionally engaged by the walls of the slot. 12. Apparatus according to claim 11 in which the or each slot has sections of differing widths for receiving wires or cables of different widths. 13. Apparatus according to any preceding claim in which the means for securing the free end of the wire or cable includes a screw-threaded clamping member for clamping the free end of the wire or cable against a wall of the adjusting member. 14. Apparatus according to any preceding claim which further comprises torque driver means engageable with the adjusting member for rotation therewith and having a radially-extending member of relatively large dimension to facilitate rotation of the adjusting member relative to the spacer body. 15. Apparatus according to any preceding claim in which the spacer body is shaped to engage a crimp tube through which the wire or cable is passed, whereby, in use, the spacer body engages the cable or wire indirectly by means of the crimp tube. 16. Apparatus according to claim 15 in which the spacer body is bifurcated at the region which, in use, engages the crimp tube to form a pair of arms which, in use, engage the crimp tube at points spaced longitudinally thereof, whereby the crimp tube can be crimped in the region between the points at which it is engaged by the spacer body without disengaging the spacer body from the crimp tube. 17. A device for tightening a loop formed in a cable or wire, the device being substantially as hereinbefore described with reference to Figures 3 to 9 of the drawings. 18. A method for forming a loop in a cable or wire comprising the steps of passing the cable or wire around a structure or structures to be enclosed in the loop to form a closed loop; engaging a device " for tightening a loop formed in a cable or wire in accordance with any of claims 1 to 17 with the cable or wire adjacent the point at which the loop closes; securing the free ends of the cable or wire to the adjusting member of the said device; rotating the adjusting member of the said device relative to the spacer body thereof to draw the loop tight; and fastening the wire or cable to hold the loop closed. 19. A method according to claim 18, in which the free ends of the wire or cable are passed through a crimp tube from opposite ends thereof so as to close the loop, the device for tightening the loop engaging the crimp tube. 20. A method according to claim 18, in which the cable or wire is fastened by crimping the crimp tube around it to hold the loop closed. 21. A method according to claim 20, in which the crimp tube is crimped around the wire or cable prior to removal of the device for tightening the loop. 22. A method for forming a loop in a wire or cable, the method being substantially as hereinbefore described with reference to the drawings.

Inventors: CROCKARD ALAN, LUGO BRENDA, MELLOUL RAPHAEL, CROCKARD, ALAN, LUGO, BRENDA, MELLOUL, RAPHAEL
Applicants: HILLWAY SURGICAL LTD, HILLWAY SURGICAL LIMITED
Application year: 1993
Main classification: B25B25
IPC codes: A61B17, B25B25, B25B27