There are a number of equine fractures that may be encountered in practice and equine practitioners should be able to diagnose and manage with confidence in the field. These can largely be divided into three categories; traumatic fractures, pathological fractures and those that occur as a result of repetitive stress-related pathology. Donati et al (2018) studied a population of 499 equids with fractures resulting from known kick injuries. The 2nd and 4th metacarpal/tarsal (splint) bones were affected most frequently (15%), followed by the radius and ulna (13.8% each), the tibia (12.2%) and the head (12%). Other commonly encountered sites of traumatic fractures include the distal phalanx. Sites of repetitive stress fractures include the pelvis, the condyles of the 3rd metacarpal bone and proximal phalanx. Pathological fractures may occur secondary to neoplasia or osteomyelitis. This article will focus on the diagnosis and management of traumatic fractures.
Distal phalanx (pedal bone) fractures
Fractures of the distal phalanx (pedal bone) usually occur as a result of trauma such as kicking a solid object, standing on a stone or fast exercise on hard ground. Horses may present with similar signs to those seen in a subsolar abscess; acute severe lameness, heat in the foot, increased digital pulses and focal pain on hooftesters. Horses with an articular fracture may have an effusion of the distal interphalangeal joint. Forelimbs are more commonly affected than hindlimbs (Honnas et al, 1988). Horses may be unwilling to place their heels or toes on the ground. Once an abscess has been ruled out radiography can be used to diagnose most distal phalanx fractures. The foot should be carefully pared and packed to avoid air artefacts and care taken to differentiate between normal vascular channels and fracture lines. Images must include a lateromedial, dorsoproximal-palmarodistal 65° oblique (upright pedal) and dorsal 45° proximal 45° lateral-palmarodistal oblique (pedal bone wing) views (Figures 1a,b and 2a). A 50° palmaroproximal-palmarodistal (navicular skyline) view should also be used to identify abaxial (wing) fractures. In some cases hairline fracture lines may be very difficult to diagnose initially and repeat radiography at ~7 days may be required. In a minority of cases pedal bone fractures cannot be diagnosed on radiographs but can be identified on magnetic resonance imaging (MRI) (Figure 2b). In the author's experience horses in which a distal phalanx fracture is diagnosed on MRI alone are likely to have a history of lameness localised to the foot which has shown an initial improvement to non-steroidal anti-inflammatory drugs and rest. There is recurrence of lameness once exercise resumes, although this is not pathognomonic for fractures. Distal phalanx fractures are categorised into seven types: type I) abaxial non-articular; II) abaxial articular; III) mid-sagittal articular; IV) extensor process; V) multifragment (comminuted); VI) Solar margin; VII) solar margin fractures in foals (Honnas et al, 1988).
Management is usually conservative with box rest and stabilization of the hoof capsule using a bar shoe with quarter clips or a hoof cast. The period of box rest is likely to be 2–4 months depending on the fracture configuration, followed by a period of controlled walking exercise. Most distal phalanx fractures will heal by 4–6 months, although in some cases it may take up to 1 year for the bone oedema and lameness associated with pedal bone fractures to resolve. Radiographic healing by bony union occurs in most cases; however, in some cases, lameness and clinical signs resolve without complete radiographic healing (Kidd, 2011). Internal fixation with lag screws may be considered in some articular fractures. The advent of pre and/or intra-operative computed tomography (CT) makes surgical approaches through the hoof wall more accurate. Solar margin fractures occur more frequently in young horses and those working on hard ground and may be associated with demineralisation of the bone. They may heal by resorption leaving a defect on the bone or by fibrous union (Kidd, 2011). Solar margin fractures may result in a bone sequestrum and subsequent lameness with solar abscessation and/or septic osteitis requiring surgical curettage.
The prognosis following distal phalanx fractures is generally very good for non-articular type I fractures (-91%), type II–III articular fractures had a good prognosis (~70%). Arthritis of the distal interphalangeal joint may develop following type II and III fractures involving the articular margin of the bone. Comminuted (type V) fractures have a poor prognosis (Ohlsson et al, 2005; Rijkenhuizen et al, 2012), euthanasia may be the only realistic option in these cases. Palmar digital neurectomy may be considered in cases of distal phalanx fracture with chronic lameness.
Fractures of the 2nd/4th metacarpal or tarsal bones
The 2nd and 4th metacarpal/tarsal (splint) bones are poorly protected by soft tissues and are therefore subject to injury during blunt trauma. Traumatic fractures can be accompanied by a wound. Horses can present with moderate–severe lameness, pain on palpation and soft tissue swelling of the metacarpal/tarsal region. Fractures are classified as proximal, mid or distal according to their location within the bone (du Preez, 1994). A subset of distal splint bone fractures occur as a result of overstrain, particularly in racehorses.
Fractures may be detected at the time of injury when the wound is digitally palpated or during radiographic examination. Radiography is frequently diagnostic for splint bone fractures, the oblique views (dorsolateral-palmaromedial and dorsomedial-palmarolateral oblique) are the most useful views (Kidd, 2003). Never omit taking the ‘wrong’ oblique because it is remarkable how many fracture planes can be visualised when looking ‘through’ the cannon bone, e.g. a dorsomedial-palmarolateral view to highlight a lateral (4th metatarsal) splint bone fracture. Commonly traumatic fractures are displaced, comminuted and open. In some cases fractures are only detected when the horse develops a non-healing wound or discharging sinus tract as the result of formation of a bone sequestrum.
Fractures of the proximal extent of the splint bones require careful examination to rule out involvement the distal carpal or tarsal joints. The long lateral collateral ligaments of the tarsus and carpus insert in part on to the 4th metatarsal/carpal bones, disruption of the ligamentous insertion as a result of a fracture can result in instability or subluxation of the joint (Figure 3a,b). Internal fixation with lag screws or small bone plates should be considered in horses with closed, displaced fractures of the proximal splint bones.
Simple, minimally displaced fractures of the distal metacarpal/metatarsal (MC/MT) bones in the absence of a wound are typically associated with overstrain injuries such as bone fatigue or secondary to thickening of the suspensory ligament which displaces the splint bone abaxially and increases strain on it. These horses present with mild–moderate lameness and pain on palpation, but typically have less soft tissue swelling (Figure 4). Ultrasound examination of the suspensory ligaments should be performed in cases of distal splint bone fracture, especially in the absence of a wound (Baxter et al, 1992; Jackson et al, 2007).
It should be remembered the majority of traumatic fractures of the 2nd and 4th splint bones respond well to conservative management. Open and comminuted fractures at any level of the bone should be managed with cleaning and debridement of the wound alongside curettage of loose bone fragments and debris. Horses should be box rested until sound at walk and no longer reactive to palpation of the affected bone. Bandaging, antimicrobials and anti-inflammatory drugs are used as necessary. Fractures frequently heal by fibrous union. Complications reported following conservative management include excessive callus formation, slower healing times compared with surgical management and non-union (Jackson et al, 2007).
Segmental ostectomy or removal of fractured MC/MT bones may be considered where there is non-union of the fracture, horses remain lame or reactive to the fracture site or following excessive callus formation. Excessive callus formation as fractures heal may cause impingement of the suspensory ligament with resultant lameness (Baxter et al, 1992). Where ostectomy is performed the proximal third of the bone should be left in-situ to avoid the risk of joint traumatic luxation, although the 4th metatarsal bone can be removed in its entirety (Baxter et al, 1992).
Splint bone ostectomy or removal under general anaesthesia carries a not-insignificant risk of catastrophic fracture of the 3rd metacarpal/tarsal bone (Sherlock and Archer, 2008). This may occur either as a consequence of undetected pre-existing microfractures or as a result of surgical trauma. Given that the outcome of conservative treatment is very good the requirement for and risk of surgical treatment should be considered very carefully.
The outcome following splint bone fractures is good overall following both surgical and conservative treatment, although it is dependent on the location (proximal, mid-body or distal) and the involvement of adjacent structures such as the distal carpal/tarsal joints and the suspensory ligament (Jackson et al, 2007).
Mandibular fractures
Jaw fractures are usually the result of either blunt trauma or horses pulling back while chewing or biting a fixed object, e.g. a fence, resulting in an avulsion. Three types of fractures are seen; those involving avulsion of the incisor teeth are the most common, while fractures involving the horizontal or vertical ramus of the mandible occur less commonly.
Rostral mandibular fractures involving avulsion of the incisors are easily diagnosed on visual appraisal and digital palpation. Radiographs are not usually required. These fractures can be repaired easily using sedation and local anaesthetic blocks such as mental nerve blocks. Minimal soft tissue debridement should be performed. In cases of mandibular fracture where there is concern about dental involvement it is always advisable to leave the tooth in place and reassess viability at a later date rather than perform an extraction at the time of fracture occurrence or repair since most loose or damaged teeth will survive. Although the exact repair technique will depend on the fracture configuration most rostral mandibular fractures can be repaired using tension band wiring, with cerclage wire passed between the incisor teeth or around the canine teeth using either a drill or a large gauge needle to create a tract for the wire (Furst and Auer, 2019). The ends of the tightened wire should be covered with dental impression material to prevent ulceration of the soft tissues while the wires are in place. The integrity of the wires should be checked regularly as cyclical loading, e.g. while chewing, leads to loosening or breaking of implants. Rasping the incisors to take them out of occlusion may reduce loosening of the wires. While the fractures heal the mouth should be washed out daily to prevent accumulation of feed material around the wires, objects such as haynets in which the wires may become trapped should be avoided. Horses will usually eat very well following stabilisation of the fracture, requiring just a short course of phenylbutazone with or without antimicrobials. Wires should be removed at 4–6 weeks post-operatively (Figure 5a,b).
Fractures involving the horizontal and vertical ramus of the mandible may be accompanied by a wound and associated with thickening of the soft tissue and pain on palpation. Radiography provides a definitive diagnosis, using a ventrolateral 45° dorsolateral oblique view. For the most part, in simple, incomplete fractures and some complex fractures the opposite mandible will act as a splint and fractures can successfully be managed conservatively. Complex or bilateral fractures and those extending to the temporomandibular joint may require internal fixation with plates or external fixation devices. CT is very useful to define the fracture planes in horizontal and vertical ramus fractures.
Radial fractures
The medial aspect of the radius is poorly covered by soft tissue and is therefore at risk of fracture following a kick injury. Fractures are more commonly seen at the distal extent of the bone and are often accompanied by small wounds. Where lameness is disproportionate to the soft tissue swelling or wound a fracture should be considered. Standard radiographic views (lateromedial, dorsopalmar, dorsolateral palmaromedial, dorsomedial palmarolateral) are usually diagnostic (Figure 6). In some cases the fracture line is not apparent on the initial images, these horses should be managed as though there is a fracture present and re-radiographed 7–14 days later. Non-displaced fractures are usually managed conservatively through several weeks‘ box rest. Bandaging and splinting of the limb with a lateral and caudal splint may be used following appropriate wound management, some clinicians prefer to leave the limb unbandaged. Cross-tying may reduce the risk of catastrophic fracture progression but requires careful management to avoid complications such as pneumonia. Thomas and Bladon (2018) reported that 17/20 (85%) of conservatively managed horses with a non-displaced radial fracture had a successful outcome. Displaced radial fractures in adult horses have a very poor prognosis for survival.
Olecranon fractures
Olecranon fractures usually occur as a result of kicks or falls. Horses will present with severe lameness and will be unable to extend the elbow and carpus giving them a classic ‘dropped elbow’ appearance similar to that seen in radial nerve paralysis (Figure 7). There will be a variable amount of soft tissue swelling associated with the elbow. Palpation may be diagnostic but usually a mediolateral radiograph, with slight obliquity in the craniocaudal plane is required for diagnosis (Figure 8). To obtain this radiograph the limb must be pulled forward. Fractures are categorised into: Ia) apophyseal physis separation, Ib) apophyseal fractures extending into the metaphysis; II) articular olecranon body; III) non-articular body; IV) multifragment; V) distal oblique ulnar fracture (Donecker et al, 1984). In foals and yearlings apophyseal physis avulsion fractures of the olecranon (type Ia, Ib) are common as a result of the forces placed on the bone by the triceps muscle insertion, left uncorrected these will rapidly lead to flexural limb deformities. In adults type IV and V fractures are the most common configurations.
The majority of olecranon fractures require internal fixation using a combination of plating, lag screws and tension band wiring, therefore it is advisable to refer horses with a suspect or diagnosed olecranon fracture to a surgical facility. Some controversy exists with regard to appropriate coaptation of the limb for transport, traditionally a full limb Robert Jones bandage with a caudal splint has been described (Mudge and Bramlage, 2007), however at the author's hospital we recommend either no bandage or a bandage with a cranial splint extending from the fetlock to the forearm to fix the limb in extension (Wright, 2016), this usually allows the horse to bear weight and travel comfortably.
The prognosis following internal fixation is good, with success rates defined as return to full function reported as ranging from 68–81% (Anderson et al, 1995; Swor et al, 2003; Swor et al, 2006; Jackson et al, 2011).
Tibial tuberosity fracture
Fractures of the tibial tuberosity generally occur as a result of impact with solid objects such as jumps, they have been reported as the second most frequent injury following stifle trauma in event horses (Latimer et al, 2001). Stifle injuries are usually associated with marked lameness and soft tissue swelling. Fractures can be diagnosed on lateromedial and caudolateral-craniomedial oblique radiographs. Fracture fragments are usually displaced cranially and proximally as a result of forces from the quadriceps muscle (Dyson, 1994). Both conservative treatment and surgical treatment have been described. Conservative treatment consisting of box rest, anti-inflammatories and controlled exercise was successful in 80% (12/15) of horses managed conservatively, with an average of 6 months rehabilitation required (Arnold et al, 2003). Surgical treatment involves placement of lag screws and tension band wires or removal of the fragment under general anaesthesia or standing sedation. Wright et al (1995) reported that all six horses treated surgically returned to athletic function (four horses treated with lag screws and two treated with fragment removal).
Conclusion
Traumatic fractures occur with relative frequency in equines. It is important to be aware of the common fracture sites, presenting signs and the imaging required for accurate diagnosis. With this knowledge many of these fractures can be effectively and successfully managed by ambulatory practitioners.
Key Points
- Severe lameness and identification of a fracture is not an indication for immediate euthanasia.
- Radiography is mandatory for diagnosis, practitioners should be aware of the appropriate views for diagnosis of fractures. Technology allows for rapid dispersal of images for a specialist opinion.
- Antimicrobials are an important part of the management of open fractures.
- Many traumatic fractures can be managed successfully by the ambulatory practitioner using appropriate conservative management.