Fractures vary enormously in pattern; bones vary in their size, texture and strength. To cope with even the most common situations and be a match for every subtle variation of circumstance requires an impressive range of devices and instruments for their insertion. The design of fixation devices has in the past been somewhat haphazard, and aimed at the treatment either of one fracture or the solution of a single fixation problem. There have been attempts to produce integrated systems of fracture fixation: sets of devices which can contend with any fracture situation. The most outstanding system, now firmly established, is that developed by the Association for the Study of Internal Fixation (ASIFor AO (Arbeitsgemeinschaft für Osteosynthesefragen). This group of general and orthopaedic surgeons was founded in 1956 by Maurice E. Miiller to research certain concepts propounded by Robert Danis). As a result of their work, apart from the development of a series of screws, plates and other devices, and the corresponding instrumentation, the Association is responsible for some change in emphasis in the philosophy of fracture treatment. They feel that the common aim - a return to full function in the shortest time - can often best be achieved by the use of internal fixation devices, of such strength and design that external splintage can frequently be discarded, permitting immediate joint freedom, early weight bearing, short-term hospitalisation, and early return to work and other activities. These ideals are often achieved, but it must be stressed that optimum results cannot be obtained without the necessary technical knowledge of the system and a degree of mechanical aptitude, both of which can be acquired by appropriate training and experience.
With any form of internal fixation great importance must always be placed on recognising which cases are best treated in this way. Ii is equally important to recognise which cases are not suited to treatment by internal fixation, and those which may be dealt with either surgically or conservatively. It is in the last group that there is often some difficulty, and it is important to remember the hazards of infection; even though it may be uncommon, it must always be a feared complication which, on occasion, can turn a comparatively minor fracture into a disaster. In certain situations the risks of infection may be reduced and fracture fixation achieved by using minimally invasive techniques (such as closed intramedullary nailing). Disturbance of the fracture haematoma is best avoided if at all possible as this may delay or prevent union: the risks may be reduced by the use of Wave or Less Invasive Plate Systems (see p. 76).
As in many branches of surgery, the core problem is in deciding how many excellent results are required to balance the occasional serious failure, and the compromise to be made between the particulars of a case and the outlook and judgement of the surgeon.
12. Principles of internal fixation and common devices: Cortical bone screws (a): The AO cortical bone screw enjoys widespread use and is probably the commonest of all internal fixation devices. The standard screw has an outside diameter of 4.5 mm (I) and a core diameter of 3.0 mm
(2). The thread form is a modified buttress
(3). oi 1.75 mm pilch (a 15 TPI). The large head has a hemispherical undersurface
(4) and contains a hexagon socket (5) which is used for its insertion.
13. Cortical bone screws (b): To insert an AO screw, the hone is drilled with a 3.2 mm drill (1). preferably using a guide to maintain its perpendicularity. The hole is then tapped (2) and sized, so that lite correct length of screw (from a wide range) can be chosen. This is then inserted using a hex screwdriver (3). In certain circumstances it is necessary to use smaller screws (e.g. in dealing with phalangeal fractures) and screws of 3.5. 2.7, 2.0 and 1.5 mm are available in the AO range.
14. Cortical bone screws (c): When two bone fragments are being approximated with a screw, it is usually desirable lo do so in such a manner thai the adjacent surfaces are compressed one against the other - this improves the quality of the fixation, reduces the risks of non-union, and may be essential if the fracture will otherwise be unsupported (e.g. if a cast is not being applied). To do this, a clearance (or gliding) hole is drilled in the nearest fragment: tightening the screw draws the two fragments together: the so-called lag screw principle.
15. Cortical bone screws (d): Placing the screw*. Two mutually exclusive screw positionings may be used. To obtain the most effective compression, and lo avoid side thrusts which might displace the alignment of bone fragments, screws should be inserted al right angles to the plane of the fracture (I). To offer the maximum resistance lo torsional forces, screws should be inserted al right angles to the cortex (2). In practice, a combination of these two placements may he employed with effect (3).
16. Cortical bone screws (e): In long bones, one or more screws may be used lo hold a fracture in perfect alignment (lllus.). Such an arrangement can seldom suffice without additional support: this may be in the Ibrm of plaster cast, but commonly a plale is used to neutralise any torsional or bending stresses thai the fracture might be subjected lo (neutralising plate). Note that if the stresses are great (e.g. unsupported weight bearing), some of the load must be carried by the bone, otherwise eventual fatigue fracture of the plate is likely.
17. Common devices: Plates (a): There are many different types of plate. Some are quite lightweight and occupy little space (1), being used only to hold major bone fragments in alignment, while others are heavy (2) and sufficiently rigid to allow all external splintage to be discarded. For these lo be successful and to encourage endosteal callus formation, the hone surfaces should be brought together under a degree of compression. One way of doing this is lo use a tensioning device (3) before inserting the screws on the second side of the fracture.
18. Plates (b): Another and more commonly used method of achieving compression is to use a dynamic compression plate (1). This has specially contoured slots (2). rather than plain round holes for the cortical screws, which are inserted eccentrically after using an offset drill guide (3). When the screws are tightened (4) their heads pinch the plate (5). causing the plate to slide slightly so that fracture surfaces are brought together in compression (6).
19. Plates (c): Plates should be placed so that compression loads are taken by bone (I). and tension effects are neutralised by the plate (2). In practice this means that plates should be applied to the convex surface (e.g. the lateral side of the femur). However, in the tibia, plates are often fixed to the anteromedial surface. In the case of the femur, tibia and humerus ideally 8 cortices should be engaged in each major fragment (6 in the forearm). F.nd screws engaging a single cortex (3) may be used to relieve stress.
20. Plates (d): When a Mat plate is applied to a hone using any system to obtain compression, this lends to occur in an uneven manner; the far side may open up as compression occurs on the nearside (1). To avoid this, it is common practice to pre-bend the plale at the level of the fracture (2). Then Ihe far side compresses first (.3). before the rest of the fracture line becomes involved, wilh the plate tending (o straighten out (4). Note too that with Ihe use of appropriate clamps plates may be individually bent to lit snugly against Ihe contours of a hone (5).
21. Plates (e): Plates come in a great variety of shapes and sizes; some have been designed to cope with a specific fracture, while others have been developed to overcome certain inherent problems associated with the use of plates of a standard pattern.
• The low-contact dynamic compression plale (I.C-DCI'I is relieved on its undersurface (1) so thai the bone wilh which it is in direct contact is reduced in area: this minimises the amount of periosteum and bone which may be deprived of its blood supply by pressure from Ihe plale. The screw slots are shaped in such a manner thai interfragmentary bone compression screws (e.g. lag screws) may he inserted at angles up to 40° (2).
• Reconstruction plates have V-cuts (3) between the screw holes which allow the plates to be bent in zig-zag fashion (4) (as well as in other planes) so that they can be used in special situations (e.g. in certain pelvic fractures).
• T- am! L-buttress plates (5) are of particular value in dealing with fractures of the proximal libia (6).
• Lateral tibial head (hockey stick) plates (7) are also used in the proximal tibial area.
• Cloverleaf(8) plates are used mainly for the distal tibia.
• Hook plates (e.g. Zuelzer (9), AO) may be used when one fragment is not particularly suited lo receiving a screw (e.g. fractures of the medial malleolus (10) or certain spinal fractures).
• Carbon fibre plates (which can only be contoured al the time of manufacture) are slightly flexible and allow the formation of bridging callus.
22. Plates (f): The Eggar plate, now only occasionally used, is a lightweight plate which is readily contoured to (it the bone to which it is being applied. Additional support (e.g. with an external plaster cast) is generally required. The plate is lixed to the bone with self-tapping screws which are not fully tightened. This permits slight axial movement, so that as bone absorption at the fracture site occurs the bone ends are not kept apart and union is thereby encouraged.
23. Plates (g): The wave plate has a substantial concavity in its middle third. This allows the easier ingrowth of blood vessels into any cancellous bone onlay grafts which may be placed between the plate and the bone surface. The wave plate also spreads stress concentrations over a wider area, thereby reducing the risks of fatigue fracture. In certain situations it may also act as a tension band.
24. Plates (h): Liss (less invasive stabilisation system) plates arc made of titanium, and are of particular value in osteoporotic bone and for periprosthetic fractures. In the distal femur a preconlourcd range ensures a good lit (a). The plate is introduced through a small distal incision, and secured with screws whose tips (b) are self-drilling. Their caps (c) screw into the holes in the plate which arc threaded to lake them. Proximal screws are inserted through small incisions using a jig.
25. Cancellous bone screws (a): Screws designed for insertion in cancellous bone have a coarse pitch and a narrow thread angle, a combination which at its extremes produces auger forms. AO cancellous bone screws (with diameters of 6.5 or 4.0 mm) may he partially threaded (for use as lag screws) (I). or fully threaded (2) (when used to tix plates in the metaphyseal regions of long bones). The near cortex only is usually lapped, the screw culling its own path in the cancellous bone (3).
26. Cancellous bone screws (b): In the metaphyseal regions cancellous screws gel the best grip if they engage the thin bone of the opposite cortex (which may have to be lapped) (I). If a reduction has been held with a Kirschner wire (2). eammlated 3.5 and 6.5 mm screws may he used when premature removal of ihe wire might threaten the reduction. The near cortex is drilled with a cannulaled drill (3) and the screw inserted (4) over the wire which is then removed.
27. Cancellous bone screws (c):
Partially threaded malleolar screws have been designed to secure small malleolar bone fragments by getting a purchase on the lirm cancellous bone of the distal tibial metaphysis. They have an outside diameter of 4.5 mm and have fluted self-tapping tips. Because of this they are generally inserted without preliminary tapping.
28. Self-tapping screws: Where ihe bone cortex is very thin, self-tapping screws gel a better grip than lapped screws. (Note also that prior to the development of the AO range of bone screws, self-tapping screws were in universal use for all forms of internal fixation; their main disadvantage was that they could be difficult to insert in dense cortical bone.) With the Sherman screw (9/64". 3.6 mm OD) a pilot hole marginally larger than the core diameter (in practice 7/64". 2.X mm) is drilled before insertion of the screw.
used lo treat diaphyseal fractures, and take a number of forms. Rush pins are of solid stainless steel, come in a range of lengths and diameters, and have hooked ends to prevent their migration into the bone cavity. They may be used singly and straight ;ls supplied (e.g. in the ulna), but in the femur (lllus.). tibia and humerus they may be ben! to obtain a measure of 3-point fixation, and paired, to provide belter support and some control of rotation.
29. Blade plates: These are most commonly used at either end of the femur when there is insufficient bone on the epiphyseal side of a fracture to allow an ordinary plale lo be used. Blade plates come in a variety of angles and forms: the plate portion (I) is screwed to Ihe shaft of the bone after the blade or spline (2) has been inserted into ihe bone. Cancellous bone screws (3) may be used for interfragmentary compression.
32. Intramedullary nails (b): Nancy nails are sometimes used in treating long bone fractures in children. They are made of titanium, are flexible, and of small diameter. Singly, they may be used in ihe radius and ulna (I), bin in Ihe humerus (2). libia and femur they are employed in pairs. The nails are beni so that they provide dynamic 3-point fixation. Their sharp ends penetrate Ihe cancellous bone of the metaphysis. thereby providing rotational and axial stability.
30. Dynamic hip screw/dynamic condylar screw: This device uses a large diameter cancellous bone screw (I) which can be drawn (with a small screw (2)) into Ihe sleeve (3) of a plale which is screwed to the shaft of the femur (4). In the femoral neck the soli bone of the head is gripped and the fracture can be compressed; at the distal end of ihe femur (5) il is of particular value in treating T- or Y-fractures. allowing the articular fragments lo be drawn together (a blade plate in such circumstances is harder to insert and less effective).
33. Intramedullary nails (c): Tubular, solid or clover leaf pattern nails are often used to treat shall fractures of the tibia, femur and humerus in adults. In many cases the operation can be performed without exposing the fracture. Reduction is obtained, sometimes with skeletal traction (I) under intensifier control (2). Through a proximal incision (3) the medullary canal is located (4). A rod (5) is passed across the fracture, followed by a reamer (61 to allow the later passage of a close-filling nail (7) over a guide rod (8).
34. Intramedullary nails (d):
Interlocking of the fragments, a well-reamed canal and a close-fitting nail may suffice to resist torsional forces which might jeopardise the fixation. Bone absorption at the fracture site is usually taken up by telescoping (I). If torsional control is poor, an interlocking nail may be used: this employs transversely running locking bolts (2) which pass through holes (3) or slots (4) in the nail. Where reaming is undesirable (e.g. in certain open fractures) solid intramedullary nails (e.g. of titanium) may be used.
35. Tension band wiring: This is used most frequently in olecranon and patellar fractures. The surfaces away from the articular side of the fracture (I) are drawn together and pre-loaded with a high tensile wire (2). while muscle pull (3) acting against the fulcrum of the coronoid (or femoral condyle) brings the rest together (4). The wire is twisted to tighten it (5), and Kirschncr wires (6) may be used if required to preserve longitudinal alignment.
36. External fixators (a): There are many types to deal with a wide range of bone sizes. The pins (2 or preferably 3 in each main fragment) must be rigid (e.g.Ilal-threaded Schanz pins) and are inserted through 'safe' areas to avoid damage to underlying nerves or blood vessels. Single-side (unilateral or cantilever) systems give the best access for dressing open wounds, with bilateral systems now being reserved mainly for arthrodeses. Meticulous care must be taken to avoid pin-track infections.
1.8 mm diameter) Kirschner wires (A) are passed pcrcutaneously through carefully selected sites. Two or more are used at each level. They are generally tensioned and held with wire fixation bolts (B) to a ring (C) which encircles the limb. (The ring may be hinged or have a removable segment to case application.) Two or more rings are applied to each main bone fragment. They are connected together using threaded rods (D) or adjusters (E).
38. (c) Hybrid fixation: This technique is particularly helpful in dealing with metaphyseal fracture. In the Orthofix*™ hybrid system (shown here being used to hold a tibial metaphyseal fracture) a lower or distal ring (A) is secured by means of a Sheffield clamp (B) and three Schanz pins (C) inserted into the tibial diaphysis. The metaphyseal fragments are held with tensioned wires (D). clamped to a second ring (E) which is connected to the other with three reduction units (F).
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