GB2274993A

GB2274993A - Bone fixation apparatus

Info

Publication number: GB2274993A
Application number: GB9401640A
Authority: GB
Inventors: Christopher John Chadwick
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-02-13
Filing date: 1994-01-28
Publication date: 1994-08-17
Anticipated expiration: 2014-01-28
Also published as: GB9302945D0; GB2274993B; GB9401640D0

Abstract

A bone fixation apparatus comprises an implant 1 for insertion into a first bone region 25, the implant having at least first and second attachment regions, and a plurality of fixation members 2, fixation members being arranged to link the attachment regions to a second bone region 26, such that the first and second bone regions are held in a stable relation. A highly suitable implant 1 comprises a pin, the fixation members 2 comprising stiff wires. The wires may be guided through holes or slots in the pin 1. The fixation apparatus is particularly suitable for the treatment of humeral, low femoral shaft and femoral supracondylar fractures. <IMAGE>

Description

SURGICAL APPARATUS The invention relates to surgical apparatus, and particularly to apparatus for use in the treatment of bone fractures.

Conventional techniques for the fixation of bone fractures frequently utilise plates and metal screws. The plates and screws are used to hold the bone in position and allow the bone to reunite across the fracture. This technique is known as internal fixation.

Although these conventional techniques are effective in most cases, considerable surgical exposure is required, and particular difficulties are often experienced with low supracondylar humeral fractures. The problem with internal fixation in these cases is that the configuration of the humerus does not allow screws to get a good hold in the bone of the distal fragment (humeral condyles). These problems are particular severe in elderly osteoporotic women.

Accordingly, the invention provides bone fixation apparatus comprising: an implant for insertion into a first bone region, the implant having at least first and second attachment regions; and a plurality of fixation members, the fixation members being arranged to link the attachment regions to a second bone region such that the first and second bone regions are held in a stable relation.

Preferably, the implant comprises a pin.

The attachment regions may each comprise one or more holes formed adjacently to first and second ends of the implant.

Preferably, the first attachment region comprises a first group of holes formed in the implant, adjacent to a first end of the implant and the second attachment region comprises a second group of holes formed in the implant, adjacent to a second end of the implant.

Alternatively, the first attachment region may comprise a first elongate slot formed in the implant, adjacent to a first end of the implant and the second attachment region may comprise a second elongate slot adjacent to a second end of the implant.

Preferably, each hole in the first and second groups has a central axis which is inclined at an angle with respect to a central longitudinal axis of the implant.

Preferably, the central axis of the or each hole in the first attachment region lies substantially in a first plane, and the central axis of the or each hole in the second attachment region lies substantially in a second plane which is inclined to the first plane.

Preferably, the angle formed between the central axis of the implant and the central axis of each of the holes in the first and second group is between 100 and 800. Preferably, this angle is 600.

For particular applications, this angle could vary between the first and second attachment regions.

The first and second elongate slots may also lie in first and second respective planes.

Preferably, the first and second planes containing the first and second groups of holes, or the first and second slots, make an angle of between 20 and 200 with respect to one another. The angle may for example be in the range 80 to 120.

The angle between the first and second planes may be adjustable. For example, one end of the implant may be rotatable with respect to the other end.

Preferably, first and second tie holes are provided at tips of the first and second ends respectively of the implant.

Preferably, the first and second groups each comprise three holes.

Preferably, the fixation members comprise stiff wires.

Preferably, a first set of stiff wires are provided for the first group of holes, and a second set of stiff wires are provided for the second group of holes.

Preferably, when the first and second sets are inserted into the first and second groups of holes the first set crosses, and overlays, the second set.

Preferably, where the first set overlays the second set, none of the wires of the first set come into contact with wires of the second set.

The holes or slots may be shaped such that the angle of one set of wires can be adjusted with respect to the angle of the other set of wires.

The implant is arranged for insertion into a passageway bored into the first bone region.

Preferably, the implant is arranged for insertion into a passageway formed in the humeral condyles from medial to lateral.

Preferably, the implant is arranged such that one or more holes of the first and second groups are exposed on either side of the first bone region, and the remaining hole, or holes, of the first and second groups are fully, or partially, located within the passageway.

A plurality of implants may be provided, of different sizes, to suit different sizes of humeral condyles.

Preferably, the fixation members are insertable as follows : fixation members are inserted into and then through the exposed holes of the first and second groups and then through the first bone region into the second bone region, the fixation member or members inserted into the exposed hole or holes of the first group crossing, and overlaying, any fixation members inserted into the second group; the remaining fixation members are located into the remaining holes of the first and second groups by using the already inserted fixation member or members as a reference.

Penetration of the bone by the fixation members may be aided by drilling or rotation of the fixation members as they are inserted into the bone.

An alignment tool may be provided to aid location of the fixation members into the remaining holes, the alignment tool being arranged to use an already inserted fixation member as a reference.

Preferably, the alignment tool comprises a handle region and a head region, the head region having a set of inclined bores or a slot formed within it, corresponding to the spacing and configuration of the first or second groups of holes in the implant or the configuration of the first or second elongate slot. The alignment tool is arranged to be used by passing the head over an already inserted fixation member, aligning the head to be substantially parallel to the central axis of the implant, by reference to a fixation member already inserted at the opposite end of the implant, and passing the remaining fixation members through the remaining holes or slot, and into the second bone region.

After a required number of fixation members have been inserted and passed into the second bone region, a tie wire may be inserted into one or other of the tie holes and secured to a part of the bone so as to provide an extra means of fixation.

For certain applications, a single hole may be provided, adjacent each end of the implant, each hole receiving a single fixation member.

There may be means to lock at least one fixation member in an associated hole.

For example, screw-threaded locking means may be provided. In a further embodiment, each end of the implant may have a pair of holes each for the passage of fixation members, the central axis of one hole of each pair lying in a first plane, the central axis of the other hole of the pair lying in a second plane, the two planes being inclined at an angle to one another and intersecting along the longitudinal axis of the implant.

The planes may intersect at an angle of from 10 to 300. For example the angle may be 5 .

A jig may be provided to assist in drilling the passageway into the humeral condyles by aligning a drill bit across the condyles from medial to lateral.

Preferably, the jig comprises a handle portion and a bifurcated head, a first arm of the bifurcated head having a location region and a second arm of the bifurcated head having an adjustable hollow sleeve, the locating region being in line with a central axis of the hollow sleeve.

The jig is such that in use it may be placed across the humeral condyles from medial to lateral, the location region being placed adjacent to one of the condyles and the sleeve being adjusted such that it abuts the opposing condyle, the sleeve being then lockable into position, an appropriately sized drill bit being insertable into the hollow sleeve to drill the passageway in the desired location.

By way of example, specific embodiments of the invention will now be described, with reference to the accompanying figures in which : Figure 1 is a perspective view of an embodiment of the bone fixation apparatus of the present invention; Figure 2 is a top view of an implant pin forming part of the apparatus of Figure 1; Figure 3 is a schematic side cross-sectional view along the line AA' of the implant pin of Figure 2; Figure 4 is a schematic diagram showing an "X-ray" type view of a typical example of a fractured bone, fixed into place using the fixation apparatus of Figure 1; Figure 5 is a view showing an alignment tool and its use in conjunction with the apparatus of Figure 1; Figure 6 is a front view of a jig, for use with the apparatus of Figure 1, for drilling a hole into a bone.

Figure 7 is a schematic diagram showing an "x-ray" type view of a typical example of a fractured bone, fixed into place using a second embodiment of fixation apparatus; Figure 8 is a top view of an implant pin according to the second embodiment; Figure 9 is a cross-sectional view of the implant pin of Figure 8 viewed along axis BB'; Figure 10 is a top view of an alternative alignment tool for use with the second embodiment of the invention; Figure 11 is a cross-sectional view of the alignment tool of Figure 10 viewed along axis CC'; Figure 12 is a cross-sectional view of yet another embodiment of implant pin; Figure 13 is a cross-sectional view of part of a still further embodiment of implant pin; Figure 14 is a transverse cross-sectional view of yet another embodiment of implant pin; Figure 15 is a longitudinal cross-sectional view of part of the pin shown in Figure 14;; Figure 16 illustrates yet another embodiment of bone fixation apparatus according to the invention; Figure 17 illustrates the embodiment of Figure 16 in use; Figure 18 is a partial view of yet another embodiment; and Figure 19 is a partial view of a still further embodiment.

Figure 1 shows a bone fixation apparatus comprising an implant pin 1 and six stiff wires 2. The implant has two sets of three holes 3,4 disposed towards each of its ends. Each end also has an extra hole 5,6 through which a small diameter flexible tie wire (not shown) may be passed.

Referring to Figures 2 and 3, it can be seen that the two sets of holes 3,4 have angled bores. As can be best seen from Figure 3, the left hand set 3 are disposed at an angle of approximately 60 to a central axis of the implant, represented by the line A-A' and sloping from left to right.

Similarly, the right hand set 4 are disposed at an angle of approximately 600 to the central axis, but slope from right to left.

Referring to Figure 2, it can also be seen that the two sets 3,4 are tilted with respect to each other about the central axis of the implant. The tilting, typically of the order of 8 , ensures that when straight stiff wires are passed through the holes they will cross, but not interfere with each other (as shown in Figure 1).

In use, the implant pin 1 is inserted into a hole formed in the humeral condyles 25. The implant is passed across the condyles from medial to lateral. An appropriate sized implant is used such that the first, outer most hole 7,8 of the two sets 3,4 protrudes from the bone. The implant is orientated such that the inclined bores of the holes 3,4 enable the stiff wires to pass into the humerus on either side of the coronoid fossa 26, as shown in Figure 4.

Insertion of the stiff wires into the holes 3,4 of the implant proceeds as follows. First stiff wires are inserted into each of the outer most holes 7,8 of the sets 3,4. These wires are then passed into the humerus, bridging the fracture 9. Passage of the stiff wires into the bone is assisted, usually by rotation of the stiff wires or by drilling. Once the two outermost wires have been inserted, an alignment tool is used to assist location of further stiff wires into the inner holes, which are not directly visible. Figure 5 shows an example of an alignment tool 10. The tool 10 has a handle region 11 and a head region 12. The head region 12 has a series of bores 13, 14, 15 formed within it identical in layout to the first set of holes 3.

The alignment tool is, in use, passed over a first wire 16 (which has already been inserted into the implant and the bone by direct vision) and aligning the head parallel to the central axis of the implant. Once the head and the implant are aligned, a second stiff wire 17 is passed through the bore into the corresponding hole 14 and, as the holes in the head of the alignment tool have the same configuration as the holes in the implant, the wire 17 may be simply located and pushed home into the implant with the assistance of rotation or drilling. Insertion of the remaining stiff wire 18 of the set 3 can be achieved in similar fashion.

The alignment tool 10 is reversible such that insertion of the stiff wires into the set of holes 4 proceeds in identical fashion to that of the set 3.

A jig for alignment of a drill to make a hole for the implant 1 in the humeral condyles is shown in Figure 6. The jig has a handle 19 and a bifurcated head, a first arm of which 20 has a location point 21, and a second arm of which 22 has a moveable hollow sleeve portion 23. The sleeve may be locked into any desired position by means of thumb screw 24.

In use, the two arms are located in the desired drilling position across the humeral condyles. The sleeve 23 is moved in towards the location point 21 until the humerus is gripped between the two arms, from medial to lateral.

The sleeve is then secured into position by the thumb screw 24 and the hole drilled by inserting a drill bit (not shown) into the sleeve 23, attaching a drill (not shown) and forming the hole.

The fixation system described is particularly useful in the treatment of humeral fractures, but with minor adaptations, where necessary, may find application in other types of fracture, such as low femoral shaft and femoral supracondylar fractures. The holes 5 and 6 provided at the end tips of the implant may not always be necessary, or even provided, but, in certain types of fractures they may be useful. Small diameter tie wires may be passed through these holes and located around a portion of bone. This has been found to be particularly useful in severe cases, for instance where the bone has fragmented into multiple portions, and when the fracture is so oblique as to interfere with the fixation of the stiff wires into the second bone fragment.

The inclining of the bores of the two sets of holes 3, 4 is particularly arranged such that the stiff wires will pass around the coronoid fossa 26. The triangular arrangement of the stiff wires and the implant ensures the stability of the bone around the fracture. In this manner, movement of the region around the fracture is restricted, allowing the area to heal. Furthermore, within a short period following an operation to fix the bone, the patient is often able to move the arm and achieve a good range of joint movement almost immediately.

As an alternative to providing a thumb screw 24 on the jig, the sleeve portion may be threaded. Other modifications to the jig and alignment tool may also be envisaged. The alignment tool could take reference from one or more datum points on the implant. Alternatively, the alignment tool could be combined with the drill jig.

Although the particular embodiment described is for use with fractures of the humerus, implants may be provided in which the angle of sloping, and arrangement of the holes in the implant may be varied for use with fractures in other bones of the body.

An alternative arrangement of the attachment regions would be in the form of slots rather than a group of holes. This would allow for variation in the angle subtended by the fixation members in respect of the central longitudinal axis of the implant.

Figures 7, 8 and 9 show such an alternative arrangement of implant, in which the holes 3 and 4 of the implant are replaced by elongate slots 27 and 28. Such an arrangement is particularly useful in the treatment of humeral fractures further removed from the distal end of the humerus than the low supracondylar fractures as shown in Figure 7, or in an embodiment designed for use in low femoral shaft fractures and supracondylar fractures of the femur.

The elongate slots 27, 28 allow a greater deal of angular adjustment for the stiff wires 2.

In order to provide a greater degree of purchase within the bone, implants may be provided with an area of central embellishment. This embellishment may for instance be in the form of a screw thread or fins.

A special alignment tool 29, shown in Figures 10 and 11, is provided to facilitate the insertion of the stiff wires 2 into the implant. The alignment tool has a head 30 with an elongate slot 31.

Insertion of stiff wires into the implant can be accomplished using the alignment tool in a similar manner to that described for the first embodiment, and will not be described in further detail here.

For certain applications, particularly complex fractures, it may be desirable to be able to vary the angle between the first set of wires and the second set of wires. Figures 12 to 15 show three examples as to how this could be achieved.

In Figure 12, the implant pin 1 is formed in two parts, la and lb.

They are interconnected by a screw threaded arrangement lc, so that one end can be rotated with respect to the other end, to adjust the angles between the planes which respectively contain the holes 3 and the holes 4. The arrangement would work equally well with the slotted version of the implant pin.

Instead of using a screw threaded connection lc, a simple sliding connection could be provided, as shown at ld in Figure 13.

Yet another possibility is for each hole, or each slot, to have angled side walls, as shown in Figure 14, so that the wires can be angled within the holes or slots as desired. In addition to being angled in the transverse direction, as shown in Figure 14, the holes or slots may also be angled in the longitudinal direction, as shown in Figure 15.

Turning now to Figures 16 to 18, embodiments are shown that have been developed especially for fractures somewhat removed from the humeral condyles, such a fracture being illustrated in Figure 7. These embodiments might also find application in supracondylar femoral fractures.

Instead of using a plurality of fixation members such as those illustrated at 2, a single fixation member 2 is utilised as illustrated in Figure 16. There is one fixation member 2 for each end of the implant pin 1.

Slightly thicker implant and fixation members may be necessary. For example the implant may have a thickness of 6 mm and each fixation member may have a thickness of 3 mm, for humeral fractures.

In use, as shown in Figure 17, it can be seen that the fixation members negotiate the medullary canal of the humeral diaphysis, rather than penetrating the opposite boney cortex as in the original embodiments. To promote this penetration, the angle of penetration of the implant by the fixation members is increased to substantially 750 and the fixation members 2 are provided with blunt rounded ends as can be seen in Figure 16.

Because the fixation members 2 lie within the medullary cavity, rather than penetrating the boney cortex, the exact length of the fixation members 2 is not critical. They may for example be made in a series of standard lengths ranging from 12 cm to 28 cm. Because they are of fixed length and designed to be inserted fully, they may be provided with a fixation mechanism whereby their ends are secured to the implant 1 without substantial protrusion.

In the embodiment shown in Figures 16 and 17, this fixation is achieved by internally threading the holes in the implant 1 and providing the fixation members 2 with externally threaded ends.

An alternative fixation arrangement is shown in Figure 18 in which each fixation member 2 is provided with dimples 2a. Each end of the implant 1 is provided with an axially aligned internally threaded hole 2b. A small screw 2c with a rounded end can be screwed into the hole 2b until the rounded end engages in one of the dimples 2a.

In a further version of this embodiment, a plurality of dimples 2a may be provided, spaced apart along the length of a fixation member. This allows for a certain amount of adjustment of the active length of each fixation member 2. The fixation member is inserted into the medullary canal by the desired amount, and the screw 2c is engaged with the most appropriate dimple 2a. Any unused portion of the fixation member 2 protruding from the implant 1 can then be cut off adjacent to the implant 1.

Yet another possibility is to use circumferential grooves instead of dimples.

Turning now to Figure 19, this is a cross-sectional view through one end of an alternative implant pin 1. At the one end, there is a pair of holes la and lb. Each hole has its own associated fixation wire, marked respectively 2a and 2b. It can clearly be seen from Figure 19 that the axis X of hole la lies in one plane and the axis Y of hole lb lies in another plane, the two planes being inclined at an angle to one another and intersecting along the longitudinal axis Z of the implant pin.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLANS

1. Bone fixation apparatus comprising : an implant for insertion into a first bone region, the implant having at least first and second attachment regions; and a plurality of fixation members, the fixation members being arranged to link the attachment regions to a second bone region such that the first and second bone regions are held in a stable relation.

2. Bone fixation apparatus as claimed in Claim 1, in which the implant comprises a pin.

3. Bone fixation apparatus as claimed in Claim 1 or Claim 2, in which the attachment regions each comprise one or more holes formed adjacently to first and second ends of the implant.

4. Bone fixation apparatus as claimed in Claim 3, in which the first attachment region comprises a first group of holes formed in the implant, adjacent to a first end of the implant and the second attachment region comprises a second group of holes formed in the implant, adjacent to a second end of the implant.

5. Bone fixation apparatus as claimed in Claim 3, in which the first attachment region comprises a first elongate slot formed in the implant, adjacent to a first end of the implant and the second attachment region comprises a second elongate slot adjacent to a second end of the implant.

6. Bone fixation apparatus as claimed in Claim 4, in which each hole in the first and second groups has a central axis which is inclined at an angle with respect to a central longitudinal axis of the implant.

7. Bone fixation apparatus as claimed in Claim 6, in which the central axis of the or each hole in the first attachment region lies substantially in a first plane, and the central axis of the or each hole in the second attachment region lies substantially in a second plane which is inclined to the first plane.

8. Bone fixation apparatus as claimed in Claim 7, in which the angle formed between the central axis of the implant and the central axis of each of the holes in the first and second group is between 100 and 800.

9. Bone fixation apparatus as claimed in Claim 8, in which the said angle is 600.

10. Bone fixation apparatus as claimed in Claim 8, in which, for particular application, the said angle varies between the first and second attachment regions.

11. Bone fixation apparatus as claimed in Claim 5, in which the first and second slots lie in first and second respective planes.

12. Bone fixation apparatus as claimed in any one of Claims 7 to 11, in which the first and second planes containing the first and second groups of holes, or the first and second slots, make an angle of between 20 and 20 with respect to one another.

13. Bone fixation apparatus as claimed in Claim 12, in which the said angle between the planes is in the range 80 to 120.

14. Bone fixation apparatus as claimed in Claim 12 or 13 in which the said angle between the planes is adjustable.

15. Bone fixation apparatus as claimed in Claim 14, in which one end of the implant is rotatable with respect to the other end.

16. Bone fixation apparatus as claimed in Claim 13, in which the first and second groups each comprise three holes.

17. Bone fixation apparatus as claimed in any one of the preceding Claims, in which the fixation members comprise stiff wires.

18. Bone fixation apparatus as claimed in Claim 17, when dependent on Claim 16, in which a first set of stiff wires are provided for the first group of holes, and a second set of stiff wires are provided for the second group of holes.

19. Bone fixation apparatus as claimed in Claim 18, in which when the first and second sets are inserted into the first and second groups of holes the first set crosses, and overlays, the second set.

20. Bone fixation apparatus as claimed in Claim 19, in which none of the wires of the first set come into contact with wires of the second set.

21. Bone fixation apparatus as claimed in Claim 3, or Claim 4, in which the holes or slots are arranged to receive fixation members in the form of stiff wires, the holes or slots being shaped such that the angle of one set of wires can be adjusted with respect to the angle of the other set of wires.

22. Bone fixation apparatus as claimed in any one of the preceding Claims, in which the implant is arranged for insertion into a passageway bored into the first bone region.

23. Bone fixation apparatus as claimed in Claim 22, in which the implant is arranged for insertion into a passageway formed in the humeral condyles from medial to lateral.

24. Bone fixation apparatus as claimed in Claim 23, in which the implant is arranged such that one or more holes of first and second groups are exposed on either side of the first bone region, and the remaining hole, or holes, of the first and second groups are fully, or partially, located within the passageway.

25. Bone fixation apparatus as claimed in Claim 23 or Claim 24, in which a plurality of implants may be provided of different sizes, to suit different sizes of humeral condyles.

26. Bone fixation apparatus as claimed in any one of the preceding Claims, in which the fixation members are insertable as follows fixation members are inserted into and then through the exposed holes of first and second groups and then through the first bone region into the second bone region, the fixation member or members inserted into the exposed hole or holes of the first group crossing, and overlaying, any fixation members inserted into the second group; the remaining fixation members are located into the remaining holes of the first and second groups by using the already inserted fixation member or members as a reference.

27. Bone fixation apparatus as claimed in Claim 26 in which an alignment tool is provided to aid location of the fixation members into the remaining holes, the alignment tool being arranged to use an already inserted fixation member as a reference.

28. Bone fixation apparatus as claimed in Claim 27, in which the alignment tool comprises a handle region and a head region, the head region having a set of inclined bores or a slot formed within it, corresponding to the spacing and configuration of the first or second groups of holes in the implant or the configuration of the first or second elongate slot.

29. Bone fixation apparatus as claimed in any one of the preceding Claims, in which first and second tie holes are provided at tips of the first and second ends respectively of the implant.

30. Bone fixation apparatus as claimed in Claim 1, in which a single hole is provided, adjacent each end of the implant, each hole receiving a single fixation member.

31. Bone fixation apparatus as claimed in any one of the preceding Claims, including means to lock at least one fixation member in an associated hole.

32. Bone fixation apparatus as claimed in Claim 31, in which screw threaded locking means are provided.

33. Bone fixation apparatus as claimed in any one of the preceding Claims, in which each end of the implant has a pair of holes each for the passage of fixation members, the central axis of one hole of each pair lying in a first plane, the central axis of the other hole of the pair lying in a second plane, the two planes being inclined at an angle to one another and intersecting along the longitudinal axis of the implant.

34. Bone fixation apparatus as claimed in Claim 33, in which the said planes intersect at an angle of from 10 to 300.

35. Bone fixation apparatus as claimed in Claim 34, in which the said angle is 50

36. Bone fixation apparatus as claimed in any one of the preceding Claims, in which the jig is provided to assist in drilling the passageway into the humeral condyles by aligning a drill bit across the condyles from medial to lateral.

37. Bone fixation apparatus as claimed in Claim 36, in which the jig comprises a handle portion and a bifurcated head, a first arm of the bifurcated head having a location region and a second arm of the bifurcated head having an adjustable hollow sleeve, the locating region being in line with a central axis of the hollow sleeve.

38. Bone fixation apparatus as claimed in Claim 37, in which the jig is such that in use it may be placed acrosS the humeral condyles from medial to lateral, the location region being placed adjacent to one of the condyles and the sleeve being adjusted such that it abuts the opposing condyle, the sleeve being then lockable into position, an appropriately sized drill bit being insertable into the hollow sleeve to drill the passageway in the desired location.

39. Bone fixation apparatus constructed and arranged substantially as herein described, with reference to Figures 1 to 6, or Figures 7 to 11, or Figure 12, or Figure 13, or Figures 14 and 15, or Figures 16 and 17, or Figure 18, or Figure 19 of the accompanying drawings.