Complex and open fractures

Abstract

Clinical challenges Cats often present with traumatic injuries of the limbs, including complex and open fractures, frequently as a result of road traffic accidents. On initial assessment, complex and open fractures may appear to require expertise beyond the experience of the general practitioner and, in some cases, referral to a specialist may be indicated or amputation should be considered.

Practical relevance Many cases, however, can be managed using straightforward principles. This review describes a logical and practical approach to treating such injuries. It discusses general principles of fracture management, highlights the treatment of open fractures, and describes the use of external skeletal fixation for stabilisation of both open and complex fractures.

Equipment Most fractures can be stabilised using equipment and expertise available in general practice if the basic principles of fracture fixation are understood and rigorously applied.

Evidence base Many textbooks and journal articles have been published on the management of fractures in companion animals, presenting case studies, case series and original biomechanical research. The simple strategy for managing complex injuries that is provided in this review is based on the published literature and the author’s clinical experience.

Fixation need not be complex

Any fracture that is difficult to repair may be referred to as ‘complex’. However, the term is most commonly used to describe a comminuted (multifragmented) fracture of the diaphysis, in which there is no contact between the main proximal and distal fragments after reduction. ¹ Complex fractures may also be open – ie, there is communication between the fracture and the exterior. Complex fractures are caused by high-energy impact: when force is applied to bone very rapidly, the bone absorbs a large amount of energy before finally ‘blowing’ apart, with subsequent dissipation of the energy into the surrounding soft tissues. This results in severe soft tissue devitalisation, predisposing to infection and problem fracture healing.

Cats often suffer complex fractures, partly as a result of their small body size and their tendency to stray into the path of cars. Road traffic accidents (RTAs) are reportedly the fourth most common cause of death in cats, with cats under 2 years old most at risk.^2,3 A study of 233 cats with fractures found that 25/33 humeral fractures, 4/15 radial and ulnar fractures, 81/89 femoral fractures and 96/96 tibial fractures were complex or open. ⁴ Tibial fractures are also reported to have a higher infection rate (up to 15%), potentially due to the limited soft tissue coverage in that part of the leg.^5,6

An open fracture is one of the few genuine orthopaedic emergencies: the animal’s prognosis will be significantly poorer if the fracture is not treated immediately.

Where massive soft tissue or neurovascular damage has occurred, it may be in the best interests of the cat to amputate the leg straightaway. In less extreme cases, however, cats can often be returned to good function without prolonged reconstructive surgery by using minimally invasive techniques. With complex fractures, anatomical alignment and reconstruction is rarely possible, and therefore a method is chosen that preserves the biological healing potential of the fracture as much as possible. The least invasive method of achieving this is with the application of an external skeletal fixator (ESF), with or without a ‘tied-in’ intramedullary (IM) pin.

As with any technique there is an initial learning curve; however, most surgeons will rapidly become comfortable with constructing and applying simple frames, using standard equipment available in most practices. Gaining proficiency with this technique will enable veterinary surgeons to treat fractures in limbs that they may previously have considered to be unsalvageable.

First-line approach to open fractures

An open fracture is one of the few genuine orthopaedic emergencies: the animal’s prognosis will be significantly poorer if the fracture is not treated immediately and appropriately. That said, a full clinical examination and identification of concurrent, potentially life-threatening injuries must always be the priority: 59–72% of animals with limb fractures also have significant non-orthopaedic injuries to other body systems.^7,8 The thorax (± abdomen) must always be radiographed if the animal has been involved in an RTA; depending on the clinical examination findings, this may be performed as a priority prior to administration of a general anaesthetic. Initial survey films of the fractured limb may also be obtained at this stage to determine whether the limb is salvageable. In all cases, the limb should also be carefully assessed for vascularity and evidence of neurological damage, prior to starting treatment (Figure 1).

Figure 1

(a) The distal limb of this cat was cold, and no pulse could be felt or detected using Doppler ultrasonography. The cat had been shot, causing an open, severely comminuted fracture of the distal tibia (b). (c) Pricking the pads with a hypodermic needle failed to elicit bleeding, as did subsequently cutting a nail short. The decision was, therefore, made to amputate the limb

Treatment protocols

Classification of open fractures (see box on page 57) is useful in directing treatment protocols. ⁹

Following assessment, triage and appropriate analgesia and stabilisation, the protocol should be to:

• Sedate or anaesthetise the patient.

• Remove any gross debris from the skin, and apply sterile gel into any wounds, prior to clipping the affected area widely – aiming for a 4–5 cm margin of clip.

• Flush the wounds copiously with at least 2–3 l of sterile fluid (saline or Hartmann’s), through an IV giving set with a three-way tap and syringe attached. Gentle pulses of pressure are preferable to strong jets, which may force contaminants deeper into the tissues.

• Take a swab for bacteriological culture and sensitivity after performing lavage/ debridement – you want to know what bacteria remain in the wound, not the contaminants that were there at the start. Although positive cultures taken at this stage are more sensitive at predicting infection, the infecting organism is only present in 42% of cases, and so swabbing and culture should be repeated subsequently if signs of infection develop.^9,10

• Administer broad-spectrum antibiotics and cover the wound(s) with sterile dressings – the hospital environment is a major source of contaminating organisms at this stage (nosocomial infections). Useful antibiotics that can be administered intravenously include cephalosporins (cefuroxime, 20 mg/kg IV q8h) or clavulanic acid-potentiated amoxicillin (20 mg/kg IV q8h). Following initial intravenous administration, antibiotics can be continued orally until bacteriology results are available. Note that if no growth has developed on bacteriological culture, the antibiotics should be stopped after 5 days. If culture is positive, ensure the sensitivity is appropriate and, if necessary, continue antibiotic treatment for up to 6 weeks. ⁹

The next stage of management will depend on the type of open fracture.

Primary determinants of infection

It is now recognised that rather than the time elapsed (the so-called 6 h ‘golden period’), it is the degree of contamination, extent of tissue injury and vascular compromise that are the primary determinants of whether infection becomes established. ¹¹

Fracture classification

• Type I Bone penetrates skin from within; low energy, often simple fracture; minimal muscle damage; wound <1 cm deep (Figure 2)

  Figure 2

  Type I open fracture of the distal tibia. A sharp spike of bone has penetrated the skin

• Type II Wound >1 cm deep; communicates with fracture; high energy moderate soft tissue and muscle damage

• Type III (a–c) Increasingly severe wound; loss of soft tissue and bone (Figure 3)

  Figure 3

  Type III open fracture of the distal tibia; a typical shearing injury is seen

• Type IV Near amputation or amputation of limb; severe soft tissue and neurovascular injury (Figure 4). NB Prompt surgical amputation is usually indicated in these cases

  Figure 4

  Type IV open fracture. This limb clearly cannot be salvaged, and amputation was completed surgically

Type 1 fractures

Following appropriate management, as described above, most type 1 fractures can be managed as closed fractures, with definitive stabilisation performed at the time of initial wound management. It is prudent to manage any wounds in the vicinity of the fracture in the same way, even in the absence of any communication with the bone.

Type II and III open fractures

Management will depend on the extent of the soft tissue damage.

• Stabilisation of the fracture Whether temporary or definitive, the aim of stabilisation is to reduce pain and prevent further damage. Stabilisation helps reduce infection by reducing dead-space, facilitates revascularisation by stabilising the soft tissues, and facilitates muscle and joint mobility, thereby improving venous and lymphatic drainage and reducing oedema. In most cases, external skeletal fixation is indicated for initial stabilisation (Figure 5).

  Figure 5

  ESF used temporarily to stabilise an open distal tibial fracture during wound management, until enough soft tissue coverage was present to allow definitive stabilisation

• Subsequent wound management As for other wounds, this should involve haemostasis, copious lavage, debridement of devitalised tissues and establishment of drainage. Wounds may be allowed to close by second intention healing, or delayed reconstructive procedures may be required. The principal factors to consider in determining whether immediate wound closure is appropriate are the level of contamination, and the likelihood of ischaemia. If there is any doubt, it is always better not to close the wound. For more detailed discussion of the management of shearing injuries, readers are referred to an earlier JFMS review. ¹²

• Bone grafting The high incidence of non-union associated with open fractures makes grafting desirable in most cases. Autogenous cancellous grafts or bone substitutes are appropriate; cortical grafts are contraindicated in the face of possible infection. Grafting may be performed at the time of fracture stabilisation, or may be delayed if there is insufficient soft tissue coverage to retain and revascularise the graft.

Distal tibial fractures and tarsocrural (sub)luxations

Fractures of the distal tibia or tarsocrural (sub)luxations in cats should be rapidly reduced and stabilised, due to the high risk of vascular compromise to the foot associated with these injuries.

Diagnostic imaging

Initial survey films of a conscious or sedated animal are useful for triaging a patient or determining whether referral may be appropriate, but not for planning a fracture repair. For fracture planning, good quality orthogonal views must be taken of the limb, and should include the joint above and below the fracture. Oblique views may be required to further define fracture or fissure lines. A radiograph of the contralateral limb is often useful for measuring or pre-contouring implants, which can save surgical time.

Radiographs should be examined methodically (using a bright spot light if necessary) to carefully evaluate the fracture and to check for any abnormalities of the periosteum or medullary cavity that may indicate other pathology, especially in older cats. The adjacent soft tissues and skin should be assessed for swelling as well as for gas shadows, which may indicate an open fracture. The growth plates of young animals should be carefully examined, as abnormalities are often very subtle and easy to miss. Growth plates may remain open beyond 48 months in neutered male cats, ¹³ although this is rarely linked to clinical problems. ¹⁴

Practical tips

• Beware fissures or complex fracture lines: take a minimum of two orthogonal views, and further oblique views, or use different exposures and a spotlight if suspicious. Implants will split fissures; identify them in advance and avoid them.

• Small bone ‘chips’ adjacent to joints may have ligaments attached (eg, collateral ligaments of the hock attach to the malleoli). Don’t remove these when debriding shearing injuries.

Choice of appropriate fixation method

For anything other than very simple fractures, it is useful to make a ‘fracture plan’ (Figure 6). With conventional film–screen radiographs, the fracture can be traced on two views and reconstructed graphically. Measurements should be made of the length of the largest fragments, and the distance of fracture lines from joints, to determine the size and number of the appropriate implants, and plan their placement pre-operatively. Where digital systems are used, ensure the images are ‘real size’, or incorporate a scale on the image, before making the same measurements.

Figure 6

(a,b) The fracture is traced and measurements are made of the fragment sizes and proximity to joint spaces. Although only a single view is shown here, this is done for both views

Fractures that are anatomically reconstructable and closed

If a fracture is anatomically reconstructable, and closed, consider using open reduction and internal fixation (ORIF). The fracture fragments are anatomically reduced and stabilised using rigid internal fixation (plates and screws), leading to primary or direct bone union. The advantages are that this allows load sharing between the implants and the bone, reducing the stress on the implants and protecting them from fatigue failure. It also achieves early stability, resulting in decreased pain and early limb use. The main disadvantage of ORIF is that it usually requires an extensive approach, and the associated damage to the soft tissues is not ideal if the soft tissues and blood supply are already compromised. The surgery is also technically more demanding, resulting in prolonged surgery times, which will increase the infection risk (and costs), and requires expensive equipment. More recently, however, a technique of minimally invasive plate osteosynthesis has been described to stabilise minimally displaced tibial fractures. ¹⁵ This involves inserting an epiperiosteal plate percutaneously through small epiphyseal incisions; the plate is then effectively slid along the length of the bone, and secured in place by proximal and distal screws.

Fractures that are not anatomically reconstructable or are open

If the fracture is not anatomically reconstructable (eg, complex fractures), or is an open fracture, an alternative strategy is often used, referred to as the minimally invasive ‘biological’ or ‘gardening’ approach (in contrast to the ‘carpentry’ approach described above!). This involves using ‘bridging’ or‘buttress’ fixation, with either an ESF or a bridging/buttress plate. The two main fragments are approximately aligned to avoid gross length/angular/torsional abnormalities, either through closed reduction or via a minimally invasive approach; only the main proximal and distal fragments are stabilised, with minimal disruption of the intermediate fragments. Application of an ESF causes less disruption of the soft tissues than a plate, and thereby better preserves the ‘extraosseous’ blood supply that is vital in the early stages of healing. Fracture healing is indirect/ secondary, with callus formation. The main disadvantage of buttress fixation is that there is minimal load sharing with the bone; therefore, strong implants are required to withstand the forces acting on the fracture.

Figure 7 shows a cat with bilateral complex radial and ulnar fractures in which a minimally invasive approach was used. Closed reduction was performed and the fractures were stabilised with type II ESFs.

Figure 7

(a,b) Cat with bilateral comminuted radial and ulnar fractures stabilised with type II ESFs, applied following closed reduction

Advantages and limitations of external skeletal fixation

As long as certain criteria can be met, most fractures will heal. The fundamental requirements for healing are the establishment of an adequate blood supply at the fracture site, and stability of the main fragments. As mentioned, perfect anatomical alignment and reconstruction of complex fractures is rarely possible, and so stabilisation is achieved using either external skeletal fixation or a buttress plate. Interlocking nails can also be used, but are not widely available. A study by Wallace et al on feline radial and ulnar fractures found that an ESF necessitated a higher rate of revision surgery (4/14 cases) compared with a plate (1/10). ¹⁶ However, it was proposed that this may have been because ESFs tended to be used for the more complex fractures.

As discussed, an ESF provides all the advantages of the minimally invasive approach, whereas the buttress plate has some of the disadvantages of the ORIF approach. In addition, when external fixation is used for open fractures, the implants do not have to be placed in or near the fracture site. A further advantage of ESFs is that the frames can be adjusted; for example, if postoperative radiographs suggest that the repair is suboptimal, or to reduce the strength of the frame as healing progresses, thereby allowing increased loading on the bone, which will generally promote the healing process. For these reasons, and because of the relative inexpense of the equipment and level of experience needed to apply an ESF compared with a plate, this technique is often more appropriate.

It should be noted that, although external fixation is ideal for fractures below the elbow and stifle, the presence of the body wall means that only unilateral (and therefore weaker) frames can be used above these joints. For fractures of the humerus or femur, the frame can be adequately strengthened, if necessary, with the addition of an IM pin, which markedly increases resistance to bending forces acting at the fracture site. Nonetheless, in certain cases, such as an older animal with expected prolonged healing time, a buttress plate (± IM pin) may be preferred. Internal fixation may also be preferred in very fractious cats, as the patient will require fewer re-examinations.

The fundamental requirements for healing are the establishment of an adequate blood supply at the fracture site, and stability of the main fragments.

Basic steps in external skeletal fixation

A summary of external skeletal fixation is presented here. More detailed descriptions can be found elsewhere.^17,18

ESF implants

A basic linear ESF is composed of multiple fixation pins that pass through the main bone fragments and are held by clamps to one or more external connecting bars. All fixation pins pass through both cortices, but may exit through one or both skin surfaces depending on whether the frame is unilateral (type I) or bilateral (types II and III). Type I (uniplanar) constructs (Figure 8) with a tied-in IM pin (Figure 9), or type II frames (Figure 10) are usually adequate for most complex feline fractures. Epoxy putty may occasionally be used to attach pins to the connecting bar; for example, when a fragment is very small and multiple pins have to be placed close together or at slightly different angles (Figure 11).

Figure 8

Type I ESF – a simple uniplanar, unilateral frame, incorporating threaded pins

Figure 9

Type I ESF with a tied-in IM pin, used to stabilise a fractured femur. The cat also had bilateral sacroiliac subluxations, which were stabilised using a transsacral screw and wires

Figure 10

Type II ESF – a simple uniplanar, bilateral frame. The frame could be strengthened by including a greater proportion of bilateral pins

Figure 11

(a–d) Very distal, comminuted femoral fracture in a cat, stabilised using a modified type II ESF. Some of the distal pins are attached to the connecting bar using epoxy putty. The epoxy putty is added after radiographs have been taken to check on satisfactory pin placement and alignment, prior to ‘setting’ the frame. An additional bar has also been added to increase the strength of the frame

Fixation pins must not exceed 25% of the bone diameter as determined from the radiographs (see box for pin sizes usually appropriate for use in cats).

Suggested pin sizes

• Metatarsals/metacarpals: 0.9–1.2 mm

• Tibial diaphysis: 2 mm

• Radius (mediolateral): 1.2 mm

Fixation pins should ideally be placed through ‘safe corridors’, to avoid major neurovascular tracts, muscle masses and tendons. These have been described for dogs,^19,20 and the same principles apply for cats. The aim should always be to engage a minimum of six cortices in each of the main proximal and distal fragments – additional pins may be used if a stronger frame is required (eg, for complex fractures or in older cats). Pins may be smooth or threaded (Figure 12); positive profile threaded pins provide the best holding power.

Figure 12

The three main types of fixation pin. From left: a negative profile threaded (Ellis) pin, a smooth pin and a positive profile threaded pin

The ‘bone–pin’ interface is critical to frame stability. Pins should be inserted using a low speed (50–150 rpm), high torque drill to minimise heat production. A small pilot hole should be drilled prior to insertion of positive threaded pins, again to reduce heat production. Hand-drilling is not recommended, as unavoidable wobble tends to produce too large a hole.

Applying an ESF

Applying the frame

• After routine pre-operative preparation, the limb is ‘draped out’. The ‘hanging limb’ technique (Figure 13) may be used, as this helps to align the fracture fragments (and fatigue the muscles).

  Figure 13

  The leg is hung for draping, and may be kept in this position during surgery

• The two main fragments are identified and gently manipulated into alignment, ideally using closed palpation.

• It is helpful to identify the proximal and distal joint spaces, to avoid inadvertently placing pins too close to them – this can be done by carefully placing a small hypodermic needle into each joint space (Figure 14).

  Figure 14

  Small hypodermic needles have been placed into the stifle to define the joint margins and help prevent inadvertent placement of a pin too close to the joint. The most proximal and distal pins are placed first, parallel to the joint surfaces

Placing the fixation pins

• Wherever possible, pins are placed through normal skin, and not through wounds.

• Avoid penetrating muscle masses with pins.

• Palpate and stabilise the large fracture fragment into which the pin is to be inserted.

• Make a sharp skin incision with a number 11 scalpel blade, and bluntly dissect through the soft tissues using mosquito forceps to create a portal to the bone. A portal of 0.5–1 cm will help to avoid the soft tissues binding up in the drill or pin. This can be further avoided by always using a drill guide or small Gelpi retractor.

• Place the most proximal and distal pins first, preferably parallel to the adjacent joint surfaces (Figure 14). The pins should be placed slowly, so as not to generate excess heat.

• Manipulate the fracture into satisfactory reduction and alignment, and then attach the connecting bar(s). It should be possible to insert a finger between the skin and the clamps, to allow for postoperative swelling. If standard Kirschner–Ehmer clamps are being used, the bar(s) must be preloaded with the appropriate number of clamps, as determined in the fracture plan. With the IMEX-SK kits, or if Kirschner–Ehmer split clamps are being employed, clamps can be added to the bar(s) at any stage.

• Insert the remaining pins through the clamps:

  – Pins should be no closer than three times their diameter to a fracture line or joint surface.

  – Threaded pins should be inserted parallel to each other, and perpendicular to the bone. This is easiest, most biomechanically sound, and makes best use of the bone stock.

  – Non-threaded pins should be placed at an angle of 70° to the long axis of the bone to increase pull-out resistance.

  – Flex and extend the limb at the end of the procedure, and enlarge any skin incisions if the skin is impinging on the pins.

Use of a tied-in pin for femoral and humeral fracture fixation

For femoral and humeral fractures, an IM pin may also be used, in which case the IM pin is placed first. For retrograde placement, a minimal approach is made to the fracture site, and the pin is placed so as to disturb the fragments as little as possible: only handle the main proximal and distal fragments, leave the intervening ones alone to preserve blood supply. The IM pin must be undersized to allow subsequent placement of the fixation pins (eg, a 1–2 mm Kirschner wire in a cat). If a minimal approach is being made to the fracture site, it is often worth adding a cancellous bone graft at the same time. The proximal end of the IM pin (which exits the humerus or femur) can then be bent round and attached to the ESF frame with a clamp (Figure 9).

Postoperative assessment of the repair

Stability

Does the fracture feel stable? The cat should not leave theatre if you are not completely happy with the stability of the repair. If it does not feel stable, then no matter how good the postoperative radiographs look, the fracture will not heal.

Apposition and alignment

As ever, at least two orthogonal radiographic views should be obtained, with oblique views as necessary. The ideal of having the fractured ends of long bones in contact by at least 50% in both craniocaudal and mediolateral planes is not usually possible with complex fractures. However, the other aspects of ‘spatial alignment’, as defined by Aron et al, ²¹ are pursued:

• Reconstruction of normal bone length Most animals will cope with 10–15% loss of long bone length (by increasing extension of the associated joints, or increasing flexion of joints in the contralateral limb).

• Adjustment of the two main bone fragments to within 5° of normal torsional or axial angulation It is essential to ensure that the joint surfaces are parallel – mediolateral deformity tends to have more severe consequences on adjacent joints than craniocaudal malalignment.

If spatial alignment is suboptimal, it may be possible to improve the repair by loosening the clamps and manipulating the frame (Figure 15).

Figure 15

(a) Suboptimal fracture alignment – the joint surfaces are not parallel. This was easily corrected (b) by loosening the clamps and manipulating the fragments using the fixation pins. (Note these pins are all too long, but this will not cause significant morbidity)

Implants

Are they well positioned, away from joints and fracture lines? Are the implant–bone interfaces good, with both cortices fully engaged? If Ellis pins have been used, the junction between the threaded and non-threaded parts is a weak point, and must be protected by being placed within the medullary cavity. If pins have to be removed and replaced, the cat should be taken back to theatre. Minor adjustments (advancing or withdrawing pins a little) can, however, be undertaken outside of theatre (eg, during radiography).

It is essential to critically evaluate the repair. If it is suboptimal, take the animal back to theatre and correct any problems at this stage. A problem that develops as a consequence of a suboptimal repair will be much more difficult to deal with at a later date, especially if it is further complicated by fracture disease or non-union.

Postoperative care

A bandage is usually applied to the limb for 3–4 days postoperatively. An inner layer is placed between the frame and the skin to reduce skin movement and swelling, and absorb discharge (Figure 16). This layer is maintained until the pin tracts have stopped discharging. Cats are prone to distal limb swelling, particularly of the paw, and so the distal limb should be included in the bandage for the first 24–48 h. Thereafter, the distal limb/paw should be left undressed to encourage the animal to use the leg, and any swelling should be relieved by gentle massage.

Figure 16

Hydrocellular foam dressings (Allevyn; Smith and Nephew) are placed around the pins to absorb any discharge. Dry (used) surgical scrub brush sponges are placed between the dressings and connecting bars to reduce skin movement around the pins

Follow-up radiographs should be taken every 3–4 weeks in immature animals, and 4–6 weeks in mature animals, until the fracture has healed. Fracture healing occurs by indirect or secondary processes, and so some callus should be evident; this will be minimal with a very strong, stable frame, and more exuberant with instability.

Practical tip

• Always keep the surgical kit sterile until you have assessed the postoperative radiographs.

General fracture complications

Anyone who performs enough surgery will eventually encounter complications. It is important to be honest in assessing why a fracture complication has occurred, and to learn from any mistakes. The most common reason a fracture fails to heal is instability and, unfortunately, this is usually the fault of the surgeon, rather than the implants.

Osteomyelitis

Acute osteomyelitis can develop within 3–5 days, resulting in increased lameness and localised swelling, progressing to more extensive swelling and limb oedema. As osteomyelitis becomes established, discharging sinuses may develop.

Radiography

In acute osteomyelitis, few bony changes may be apparent; it may take 10–14 days for any signs of irregular bone lysis, sclerosis or periosteal new bone formation to develop. It is often difficult to differentiate between osteomyelitis and exuberant callus, particularly in the early stages. Callus tends to be more centred around the fracture site, whereas osteomyelitis tends to spread along the periosteum/bone away from the fracture site.

Treatment

Samples should always be obtained and sent for culture (for aerobic and anaerobic bacteria and fungi). Sampling from draining tracts is of limited use as it produces mainly contaminants. Instead, fine needle aspirates should be obtained from deeper tissues; ultrasound guidance may be useful. The microbiology of osteomyelitis is discussed by Bubenik and Smith, ²² who report that in most cases a single organism is isolated (a staphylococcal species 46–74% of the time). Therefore, amoxicillin-clavulanate or cefazolin are appropriate antibiotics to use while awaiting culture and sensitivity results.

In chronic osteomyelitis, sinus tracts should be explored and debrided, and necrotic tissue removed and sent for culture. Copious lavage is required, and rigid stabilisation is essential if the fracture has not healed. Antibiotic-impregnated beads or sponges may be implanted, and systemic antibiotics are required for 6–8 weeks. Any loose implants must be removed, and the fracture restabilised if necessary. If fracture healing is complete, all implants should be removed, as metal and other foreign materials reduce the number of bacteria required to cause and maintain infection. Aggressive treatment produces a favourable response in up to 90% of cases. ²³

Fracture disease

Fracture disease most commonly occurs when an animal fails to use a limb in the early post-operative period, either through pain or due to extended immobilisation. Animals show a progressive deterioration in limb use, with development of muscle atrophy, joint stiffness and muscle contracture. Young animals and those with fractures associated with extensive soft tissue damage are particularly at risk. Radiography reveals osteopenia, delayed or non-union of fracture and degenerative changes in the adjacent joints.

Fracture disease carries an almost hopeless prognosis, and is much easier to avoid than to treat. Early limb use should be facilitated through proper fracture fixation and provision of good analgesia and, if fracture disease is suspected, early and aggressive treatment should be instituted. Unfortunately, most of these cases cannot be salvaged and progress to amputation.

Sampling for culture

Tissue or bone are the preferred samples for both anaerobic and fungal culture. Samples should be placed in a small amount of saline (just enough to cover the material) to help prevent desiccation. Samples may be collected for anaerobic culture using swabs, which must be rapidly placed into charcoal transport medium. Swabs are not recommended for fungal culture, however, as the hyphae do not adhere well to the swab (personal communication, Idexx Laboratories).

Delayed and non-union

Delayed union always precedes non-union, the difference being one of degree. Clinically, patients will show poor limb use that does not improve with time. There may be palpable instability and pain at the fracture site, and eventually muscle atrophy and joint stiffness become apparent.

With delayed union, fracture healing is slower than expected, but callus and progression of healing is evident on sequential radiographs. Delayed union rarely necessitates surgical intervention if the implants are stable – most cases will progress to union if allowed more time, and the owners ensure that the animal’s exercise is appropriately restricted.

If there is no radiographic progression of healing over a period of 3 months, this constitutes a non-union. ²⁴ Non-unions are classified according to their biological activity into viable and non-viable non-unions. Viable non-unions show variable amounts of callus, but it does not bridge the fracture gap. Non-viable non-unions result from severe interruption of the blood supply to the fracture and carry a poorer prognosis. Non-unions invariably require surgical intervention to stimulate healing. The aforementioned study of fractures in 233 cats, ⁴ reported a non-union rate of 0.85%, although the authors defined non-union as failure to heal within 9 months. Other studies have reported non-union rates as high as 5.2% (18/344 cats). ²⁵

The main cause of delayed or non-union of fractures is instability at the fracture site. Other significant causes include excessive fracture gap or loss of bone fragments, severe comminution (which is more likely to be associated with poor blood supply to fragments, sequestration and instability), loss of blood supply and infection. Creating too rigid a fixation can also be counterproductive, as it can result in excessive ‘stress protection’, where the beneficial microstrains are absent, leading to delayed or non-union with a generalised loss of bone mineral density. In such a case, the fixation should be weakened, if possible – for example, by removing some fixation pins from an ESF, or the IM pin in a tied-in frame.

Treatment of non-unions

The priority is to ensure or establish stability at the fracture site, as most fractures will eventually heal (even in the presence of infection) if rigid stability is provided. The fracture site should be surgically approached, lavaged and debrided of any infected or necrotic tissue, and tissue samples sent for culture and sensitivity. If the implants are functional and rigid stability exists, the implants should be left in situ. If any implants are non-functional, then these must be removed (and sent for culture). Healing should be stimulated by debriding any fibrous tissue from the fracture gap and applying cancellous bone graft or bone substitute materials.

If the overall fixation is compromised, then all the implants should be removed, and the fracture restabilised. In such a case, the sclerotic fracture ends should be drilled to open up the medullary canal (facilitating re-establishment of a blood supply). If possible, the fracture ends can be cut to create a transverse fracture line, as compression can then be applied, ideally using a bone plate, to create rigid stability. Finally, appropriate postoperative management should be ensured, to encourage controlled weightbearing. Physical therapy, ideally under the supervision of a trained animal physiotherapist, can help improve limb function in these animals.

Key points

• Always examine the whole animal, as the majority of animals with limb fractures also have significant non-orthopaedic injuries.

• Open fractures are genuine emergencies: prompt and intensive treatment is essential to prevent the inevitable contamination becoming established infection.

• Always reduce and stabilise injuries of cats’ hocks promptly, due to the high risk of the blood supply to the distal limb becoming compromised.

• Complex fractures do not necessarily require complex fixation. By ensuring stability of the major fragments, and protecting and encouraging a blood supply, most fractures will heal uneventfully with relatively straightforward fixation techniques.