Principles of holding fracture

There are two main ways in which a fracture can be held which make a profound difference to the way in which the fracture heals. Rigid fixation blocks the normal callus forma­tion of bone healing. The bone appears to be unaware that there is a fracture if there is no movement at the fracture site. As the bone undergoes normal physiological remodelling, the fracture cleft is gradually obliterated by new bone. This takes about a year. During that time the fixation must share the loads normally taken by the bone. Most implants fatigue under the repetitive load imposed by the human body, and will soon fail if the bone does not heal and take over its original function. Fracture healing is therefore a race against time: the bone must unite before the implant fails or the construct will collapse. Nonrigid fixation (such as plaster of Paris) allows limited movement and loading of the fracture site. The aim is to allow movement and load to stimulate

callus formation without allowing the fracture to re-displace. This delicate balancing act depends on the quality of the fixation, the type of fracture and the compliance of the patient (Fig. 21.11).

  pathophysiology of fracture healing

When a hone breaks there is disruption of periosteum, cortical bone, trabecular bone and the blood vessels which run in the periosteum and the medulla. There is haemorrhage and immediate release of cytokines. This signals to cells locally that damage has occurred. These cytokines attract macrophages which start the cleaning-up process. They also attract undifferentiated stem cells which migrate in and start differentiating into fibroblasts and bone-producing cells. These stem cells probably come from the periosteum and the endosteum, and normally lie latent.

The haematoma around the fracture is invaded with small capillaries while the macrophages remove the haematoma itself. At the same time connective tissue is laid down. The connective tissue slowly organises.

This pattern of layers of organised tissue appears first as a collar arising from the periosteum close to the end of each broken bone. The collars appear to grow towards the collar on the other bone. Eventually, the spurs of callus meet and bridge the fracture site. They become increa­singly thick and strong fibrocartilage stabilises the fracture. This period, which in the adult occurs over the first few weeks after the fracture, is described as the fracture becoming sticky. It may still be possible to angulate the fracture but it is no longer possible to translate the fracture (move it from side to side). Meanwhile, in the fracture cleft itself, osteoclasts continue to resorb haematoma and other dead tissue and to eat away the broken bone ends. This can result in the fracture becoming more obvious on X-ray over the first few weeks and can indeed make fractures visible which were initially invisible (e.g. the scaphoid). The callus of fibrous cartilage around the fracture cleft becomes calcified and then ossified (so that it is visible on X-ray). Ossification starts at the bone ends but in the centre of the fracture cleft, where oxygen levels may be very low, cartilage may be laid down initially rather than bone. This cartilage is then replaced by bone (endochondral ossification). It is not clear whether the callus is derived from the haematoma or from the periosteum, but it is clear that movement stimulates the production of a callus.

While the fracture can no longer be angulated with normal loads, and it is not painful to try, the fracture is said to be clinically united. On X-ray, when the strands of ossified callus can he seen to be stretching continuously from one bone end to another, the fracture is said to be radiologically united. In neither case is the fracture at full strength yet, but at this stage limited activity can be undertaken safely. Finally, the callus forms a fat cuff of woven bone from one bone end to the other. This callus is at least as strong as the bone around it because biomechanically it has widened the diameter of the tube and this confers extra strength. This stage is called consolidation.

Over the next months the woven bone is replaced by Haversian cortical bone which remodels over the following years.

Rigid immobilisation. If the fracture is rigidly immobilised with a plate there is no stimulus for callus formation. Macrophages remove the haematoma and the dead bone ends. The normal process of remodelling produced by osteoclasts tunnelling through the bone and osteoblasts laying down new bone in their wake gradually obliterates the fracture cleft and reconstitutes normal hone. This process is slow and even in a young patient may take up to a year. If the fixation of the fracture is not completely rigid then some callus will form rapidly, but the patient may be able to resume near-normal function because the fracture is held stable if not immobile by the fixation. This partial rigidity therefore offers the best of both worlds, with rapid biological healing combined with the benefits of early mobilisation of the patient.

Types of fixation

Fixation can be divided into external and internal. Implants which are fitted directly on to or put down the inside of the bone and are then covered with soft tissues and skin are classified as internal fixation. Those where the mechanical strength of the construct is outside the skin are defined as external fixation.

Types of internal fixation

Screws can be used to hold plates on to bone or can be used in their own right to hold bone fragments together. In orthopaedics, screws have been standardised to an agreed set of diameters. The threads of the screws also come in two standard forms, one for cortical and the other for cancellous bone. The size of these threads and their pitch (the distance between each thread) is specifically designed to give the best possible grip in healthy human bone. The drills, which create the holes for these screws, are also standardised to allow as snug a fit of the screws as possible without putting undue load on the bone. ‘Taps’ are also supplied which cut the grooves in the bone to take the threads of the screws. Tables are available in every orthopaedic theatre to show which drill should be used for which screw.

Lagging

If a screw is to be used to compress two hone fragments together it is important that the thread of the screw should only grip the distal fragment in which the tip of the screw is embedded. As the screw is tightened the shoulder of the screw (the part that tapers in under the head) presses down on the proximal fragment and compresses the two fragments together. If the thread of the screw engages with the proximal fragment the screw can actually hold the fragments apart. There are techniques used to ensure that the fragments are drawn together as the screw is tightened. First, a screw can be used which has no proximal thread, just a smooth shaft. This is known as a ‘lag’ screw. An alternative strategy is to use a fully threaded screw, but to drill the hole in the proximal fragment to a slightly larger size so that the screw threads cannot engage with the wall of the hole. This is called lagging the drill hole and serves the same purpose as using a lag screw (Fig. 21.12).

Plates

The plates come in several sizes, each designed to be used with a standard set of screws. They are designed to fit on to the curved surface of bone and to be held there by screws. The plates can be used for several purposes and there are specific plates designed for each function (Fig. 21.14).

Buttress plates. Buttress plates prevent one fragment of hone slipping on another. They are especially useful in oblique fractures in load-bearing bones where they will stabilise what is a very unstable fracture configuration.

Dynamic compression plates (DCP). Dynamic compression plates have oval screw holes in them with tapered walls. If the screw holes are drilled into the bone at one end of these holes (there are drill guides to assist in doing this) then the plate slides along the bone as the screw is tightened home. If the plate has already been firmly fixed to the other fragment then the slip can be used to compress the fragments of bone tightly together. This has the benefit of stabilising the construct by increasing the area of contact. It also appears to stimulate healing by putting the bone edges in close apposition.

Neutralisation plates. Neutralisation plates are used to prevent bone ends from being distracted. They can therefore be used to resist angular forces by being placed on the side of a bone which goes into tension when load is applied (the side that opens when the fracture bends). Plates with screws are excellent at resisting tension and this is how they are used in neutralisation. Plates have very little resistance to bending and so should never be put on the side of the bone which is in compression and which will go into concave angulation when load is applied.

Wires

Wires are much less traumatic than plates and screws. They can be used temporarily to hold fragments reduced while plates and screws are applied. They can also be used to resist shear where loads are not great. They are especially useful in children’s fractures where plates and screws could damage the epiphyseal plate (Fig. 21.13). Wires can cross the growth plate without causing long-term effects, and if left protruding from the skin can be removed when the fracture is secure without the need for a further anaesthetic.

Kapanji wires are a technique which can be used in frac­tures where impaction may have left a defect which leaves the fracture unstable when reduced. After the fracture has been disimpacted and reduced, wires are introduced into the fracture cleft on the side of the defect. As soon as the tip of the wire is in the medulla the wire is tilted so that its tip travels proximally and embeds on the inside of the far cortex. One or more wires placed in this way substitute for the missing cortex and work with the intact periosteum on the other side to create a stable reduction.

Figure of eight wiring allows a strong wire suture to be woven over the cortex of bone which is in tension. The con­struct is not prominent and so fits well subcutaneously and is commonly used on the olecranon and on the patella (Fig 21.14).

Nails

Intramedullary nails. Implants driven down the medulla of a long bone suffer from a significant mechanical disadvantage because they must be narrower than the hone into which they are introduced. Nevertheless, the medulla can provide a natural guide for the implant and introducing the nail into one end of the bone (under image intensifier control) minimises the risk of infection from opening the fracture, and preserves the periosteal blood supply. In recent years the scope of intramedullary nails has been increased enormously by the introduction of the locking nail. This system has holes through the nail at each end. Using jigs or an image intensifier, screws can be passed through the bone, the hole in the nail and out through the opposite cortex of the bone. This produces a construct which holds the bone rigidly and is especially resistant to twisting. It allows an intramedullary nail to be used for a far greater range of long-bone fractures. Some of the newer nails can now be passed down the medulla without requiring any reaming in advance, the unreamed nails. This makes the operation quicker and reduces the trauma to the patient.

In summary, internal fixation can allow very accurate reduction of fractures under direct vision, and allows strong and stable fixation so that the patient can rapidly return to everyday activities with the minimum of inconvenience. The disadvantage is that the patient requires carefully planned and complex surgery which carries a risk of infection if sterile technique is not strictly adhered to.

 Disadvantages and complications of internal fixation

 The disadvantages of internal fixation are those of damage to soft tissues, especially blood supply. The rigidity of fixation slows the natural healing process, even though it allows

earlier mobilisation of the patient. Internal fixation is tech­nically demanding, requires a large range of implants and instruments, and is best performed in ultraclean theatres as infection is a disaster. Internal fixation requires careful pre­planning and the best surgery is performed if the fractures are drawn out on stencils first, and the problems of reduction and obtaining mechanical stability planned in advance. This includes size and type of plates, and position of screws. Only in this way can the operation be performed quickly and cleanly (minimising the risk of tissue damage and infection) so that the strongest fixation is obtained.

Internal fixation is best performed under a tourniquet, if possible, in order to obtain a blood-free view. There are complications inherent in using a tourniquet such as cuff damage to nerves as a result of inflation to an excessive pressure, and problems of reperfusion injury if the cuff is left up too long.

Exposure of the fracture may damage the soft-tissue attachments to the bone and produce avascular fragments, which will delay or even prevent fracture union. Soft-tissue dissection should therefore be kept to a minimum, but must be adequate to obtain a clear view and access. All incisions should be designed so that they can be extended safely if necessary — extensile exposure.

The risk of infection can be minimised by cleaning out open fractures and leaving them open, with the fractures stabilised until it is certain that all dead and contaminated tissue has been removed. Only when they are clean should they be closed (delayed primary closure). When internal fixation is used infection is minimised by performing quick, tidy and well-planned surgery, and by adhering to strict theatre discipline on theatre sterility. Surgery should be covered by three doses of a broad-spectrum antibiotic which has good activity against Staphylococcus (the commonest infective organism) and Streptococcus (the second most common).

Internal fixation can also leave unsightly scars, and these should be planned to minimise cosmetic deformity without compromising access.

Drills and screws can damage nerves and vessels. Drill guards should always be used to prevent soft tissues being inadvertently dragged into a spinning drill. When the drill is cutting into the far cortex the hand that the surgeon is using to hold the drill should have a straight finger resting on the limb through which the drill is passing, and only light pressure should be applied to the drill so that when the drill then comes out through the far cortex it will not suddenly pene­trate deep into the soft tissues on the far side of the bone, where it might perforate a nerve or vessel.

Removal of internal fixation

Implants for internal fixation are made of surgical-grade stainless steel and should not corrode. Nevertheless, the alloys contain transitional metals such as chromium and vanadium whose salts are allergenic, toxic and may even be carcinogenic. Despite this, there is little evidence that metal­ware left in patients for long periods causes any chemical or even allergic problems. Children should have metalware

removed if it is likely to compromise growth. It should be removed as early as possible because periosteal bone grows rapidly over the plates and makes their removal difficult. Internal fixation also shields the bone around it from load, and so may cause local osteoporosis. The load passing down the bone may then peak at the end of a plate (a stress raiser) and cause a fracture. Internal fixation of a fracture next to an old plate already embedded in the bone is very difficult to manage. Despite this, it is now normal practice to leave plates and even intramedullary nails in the patient unless there is a specific reason why they should be given another anaesthetic and he subjected to a further operation to remove them.

External fixators

An alternative way to holding a fracture is to insert pins and wires into the bone on each side of the fracture, and to attach these to an external frame which provides the structural integrity. Fixators can be as simple as a set of pins incorporated into a plaster through single- and double-bar fixators, to ring fixators holding the bone through tensioned wires (Fig. 21.15). There is a trade-off between cost, ease of fitting, adjustability, rigidity and convenience to the patient (Table 21.5). The choice of fixator will depend on what is available and the use to which it is to be put.

Uses of an external fixator

Emergency use of the external fixator

Fixators are used for two main reasons in an emergency.

Pelvis. They can be used to stabilise an unstable pelvic fracture to try to reduce life-threatening haemorrhage from the pelvic veins. Closing and stabilising an open pelvis fracture may reduce bleeding by reducing movement of the pelvic veins. This may stabilise clots and reduce haemorrhage. Closing the pelvis may increase the intrapelvic pressure and tamponade the veins to reduce bleeding. A bar fixator attached to pins inserted into the pelvic wings will need to be used. The bar should be set as low as possible to give enough room over the abdomen should a laparotomy be needed.

Neurovascular compromise. If a limb has an unstable fracture and has lost its blood supply the skeleton needs to be stabilised before the vascular repair can be performed. One option is to insert a stent and provide a temporary blood supply to the limb while a definitive orthopaedic fixation is performed. An alternative is to use an external fixator which can be applied quickly to stabilise the fracture so that the vascular surgeon can start work with the minimum of delay. The disadvantage of this approach is that an external fixator may not be the optimal way of stabilising that particular fracture, but once it has been applied the risk of infection from the pin tracks makes a conversion to a plate or an intramedullary nail potentially risky.

  Nonemergency use of the external fixator

Soft tissue damage. If there is extensive damage to the soft tissues then it may not be possible to achieve good cover of the bone. If bone is contaminated and/or exposed internal fixation may not be advisable. Under these circumstances an external fixator may offer the best option. The position of the pins can be planned with the plastic surgeons to enable them to rotate flaps without the fixator or the pins getting in the way.

Leg lengthening and correction of deformity. Over the last decade one of the great advances in orthopaedics has been the discovery that bones can be lengthened gradually — callo­stasis. Segments of bone can be moved across defects and, if the periosteum is left as intact as possible, new bone will be laid down in the defect — bone transport.

In order for the pins of the fixator to be able to move through the soft tissues as the bones move they need to be very thin, and it is now routine to use wires which gain their rigidity by being tensioned on a ring (the Ilizarov technique). The key to the technique is to move the bone so slowly that new bone can be laid down in its track, but not so slowly that the bone unites and prevents any further distraction. The fixation pins must be positioned to avoid damaging vital structures as they carve through the soft tissues. Care must also be taken to avoid overstretching nerves and vessels, and to avoid contractures caused by ligaments, tendons and muscles failing to extend in concert with the bone.

Determining union

Clinical union

A bone is clinically united when putting load on the fracture produces no detectable movement and no pain. The fracture site will not yet be as strong as the bone around it, but it is united.

Radiological union

This is not the same as clinical union. It occurs when the callus around the fracture can be seen to pass from one broken bone end to the other without a gap between. The fracture across the medulla of the bone may still be visible, but the callus around the bone is continuous. The bone should now be able to cope with normal loads, but will not be as strong as the bone around it. From a management point of view, it is the time when movement and loading of the limb should be increased to build up muscle power, mobility and proprioception. If the patient plays sport or works in a job involving heavy labour they should not return to this unless the bone is protected, or until the fracture has consolidated (Fig. 21.16).

Consolidation

Consolidation takes much longer than union, and is defined as the time when the process of fracture healing is complete and the strength of the hone has risen to normal levels or even beyond. The formation of callus around a fracture creates a strong cuff. The diameter of this cuff is greater than the diameter of the bone itself, and so a consolidated fracture can be stronger than the original bone (Fig. 21.17).

Restoring function

When a fracture occurs, there will be damage to soft tissues. Muscles may be bruised or torn. Ligaments may be ruptured, joints filled with blood, and nerves and blood vessels damaged. The original philosophy in orthopaedics was that the key to management of fractures was immobilisation, and of injury was rest. This has now all changed. Fractures are stabilised to allow mobilisation of the limb and the patient. Rigid fixation of the fractures actually inhibits callus formation and slows healing. However, stabilisation of the fractures allows the patient to start moving the soft tissues to promote healing and reduce stiffness. It also allows the patient to return to a normal independent life sooner. Physiotherapy is a key element in the rehabilitation of trauma cases. It:

    allows early mobilisation of the limb while ensuring that loads are not so excessive that the fixation will fail;

    provides instruction and advice to the patient on their own rehabilitation;

    builds the patient’s confidence;

    re-trains proprioception so that the feedback loops between sensors of joint position and tendon load start to co-ordinate with motor nerves serving the muscles.