Introduction

Skin injuries with skin deficits and/or ‘degloving’ are relatively common (Figures 72, 73), and management of these injuries can be very difficult. The absence of ‘spare’ (loose) skin on limbs means that large deficits in these sites require particular care. Notwithstanding the best possible care, healing is likely to be prolonged.

Degloving injuries are commonest on the upper limb regions; the skin on the lower limb is probably more firmly attached and seldom ‘degloves’ in the same way as the upper limb and body trunk. These injuries should be treated promptly to restore as much of the skin as possible to its original position (even if it is probably non-viable). Degloving of limbs usually involves at least some horizontal skin laceration and is usually in a downward direction so that the skin hangs around the limb.

The exposed subcutaneous tissues rapidly become dry and infected but remarkably little bleeding occurs in most such cases. The blood supply to the upper margin of the wound is usually intact and so this is less of a problem than the distal wound margin, which is invariably compromised – especially at the most central part of the wound margin. Sloughing of the skin along this margin is common.

Preliminary Approach

The wound should be irrigated with copious warm sterile saline and protected from further contamination by application of a hydrogel to the exposed tissues. This will minimize dehydration and infection. The flap should be restored to its natural position as far as possible, and bandaged onto the site if practicable until a more detailed examination can be performed. This maintains warmth, prevents further contamination and devitalization, and covers the exposed tissues with a biological dressing.

Movement of the limb should be minimized so that tension on the wound is reduced as far as possible. Shear forces will be maximal during movement of the underlying muscles relative to the skin. Large skin deficits should initially be dressed with a hydrogel after warm saline irrigation. There is seldom any spare skin that can be mobilized, and so a prolonged recovery and/or extensive surgical procedures may be expected.

Surgical Procedure

The wound should be carefully examined (possibly even under general anesthesia) and, after superficial irrigation, all obvious foreign matter and devitalized subcutaneous tissues scrupulously removed. Deeper injuries are treated accordingly by lavage, and if indicated by suturing the defects with an absorbable suture material of suitable diameter and pattern. Skin should not be removed unless it is totally devitalized and shredded.

Carefully placed subcutaneous ‘walking sutures’ limit dead space by firmly fixing the skin to the deeper structures, but this may not always be possible. This minimizes tension on any single part of the incision; with careful extension of the skin it may be possible to eliminate tension on the wound line. If the injury is more than 1–2 hours old, the skin will have shrunk significantly, and it may be difficult to restore it to its natural position. The skin wound is closed using interrupted horizontal or vertical mattress sutures with monofilament nylon (4 or 5 metric/1 or 2 USP). Tension across the wound site can be relieved by supported quill sutures.

If there is deep tissue disruption, fluid accumulation must be prevented. A surgical drain exiting the wound below its most dependent aspect is helpful (this may involve a separate skin incision). Firm dressings can be used to apply direct pressure but this must be controlled carefully to prevent further compromise of the cutaneous vasculature. Alternatively the wound can be left partially closed so that fluid can drain freely.

Follow-up Measures

Movement should be restricted depending on the extent and type of wound.

Dressings should be changed as and when indicated. Variable necrosis of at least part of the skin margin is commonly present. In any case, the necrotic tissue will eventually need to be removed and the wound allowed to heal by second intention or by some form of grafting.

Introduction

These wounds involve the upper limb or body trunk regions (Figure 74). Wounds involving muscle damage sometimes bleed quite heavily – this is particularly so if the muscle is lacerated (as opposed to bruised or crushed).

Large flap wounds involving extensive skin and muscle damage are common in horses, particularly when the injury occurs at speed.

Wounds caused by sharp objects (e.g. glass, metal, or sharp plastic) tend to be almost surgical with little maceration but may have multiple lacerations. Those involving kicks or falls at speed are complicated by extensive skin avulsion and deep muscular bruising with laceration and damage. In the case of barbed wire wounds, the edges are often ragged and there may be several cuts in close proximity to one another.

At this stage it may not be possible to decide which tissue is viable. Many extensive wounds that are left to heal by second intention heal largely by contraction. Cosmetic results tend to be good with a significantly smaller scar than the wound (see p. 17). Primary closure of the muscle deficits may shorten the recovery period and improve functional restoration. Fresh injuries are far more amenable to primary closure. The location of the wound is important because muscle damage may be more important over the eyes or on the face than on major muscle masses.

There may be moderate or severe skin deficits that will need to be considered at an early stage. Discoloration of the underlying muscle may be indicative of serious compromise: dark or black muscle may be non-viable or severely desiccated, whereas bright red active muscle is likely to have a good blood supply (there may be more bleeding in this case). Any delays in restoration of the skin to its normal position will result in shrinkage and reduced viability of the flap.

Preliminary Approach

Adequate restraint should be used to permit close examination, which may require sedation with an α-2-agonist (e.g. romifidine, detomidine, xylazine) (see p. 39). Hemorrhage should be controlled (see p. 39), and appropriate anesthesia (regional blocks or local inverted L block) is required for exploration, cleaning, and possible suturing. Local anesthetic infiltration into the wound itself is not conducive to healing, and should be avoided if possible by using regional blocks. In particular, anesthetic with adrenaline should not be used.

The wound should immediately be covered with a hydrogel and the margins of the wound carefully clipped or shaven to establish the full extent of the injury, and in particular the full extent of the underlying muscle damage. The skin flap and the underlying muscles should be handled gently and washed carefully with warm saline. Chemical antiseptics should be avoided as far as possible unless there is gross contamination. Antibiotic powders (such as crystalline penicillin and aureomycin powder) may be cytotoxic and therefore retard healing. If the wound is infected or is likely to be infected then such an approach may be helpful, i.e. the benefit outweighs the disadvantages. The wound should be irrigated with copious warm (body temperature) sterile saline (as much as the horse will allow) to remove superficial contamination and the residues of the hydrogel. Further applications of hydrogel to the wound site will keep the surface moist and protected against further bacterial contamination.

No skin should be removed if at all possible. Replacing the skin into its natural position temporarily will keep it warm, and will provide a biological cover for the underlying muscles so that they will not dry out or become injured further.

Surgical Procedure

All foreign matter and necrotic/nonviable/compromised tissue should be removed from the wound bed by sharp excision (using a scalpel rather than scissors). Assuming that the wound is surgically clean, the deeper layers of muscle are closed carefully with 1 or 2 metric polyglactin (e.g. Vicryl), using a mattress or simple continuous suture pattern.

The skin should be restored to its natural position, although this may be difficult due to shrinkage if there have been any delays. Walking sutures placed subcutaneously between the skin and the underlying muscles are useful in reducing the dead space, ensuring that the skin is firmly placed up against the underlying muscle, reducing the tension on the suture line, and reducing the extent of skin shrinkage/contraction.

If there is extensive muscle bruising and possible necrosis a surgical drain should be inserted. A latex Penrose capillary drain can be used with its exit at a specially made exit portal at or below the most dependent part of the wound.

Vacuum drains can also be useful provided that they can be maintained. Fenestrated tube drains are useful in allowing the wound to be flushed but rapidly block-up and become useless.

The skin wound is closed using either horizontal mattress sutures (if the tension is mild), vertical mattress sutures (where cosmesis is important and tension is mild), simple interrupted sutures (where tension is not significant), or supported quill tension sutures (where tension is high).

A stent made from gauze swabs covered in hydrogel can be used to cover the wound, and serves both as a protection and a means of reducing the tension on the suture line. Dressings are applied over the wound if convenient. Non-steroidal anti-inflammatory drug (e.g. telzenac, phenylbutazone, or ketoprofen) are useful to reduce inflammatory responses and provide analgesia. Pain can be controlled by opioid analgesics such as butorphanol. Antibiotics are advisable and penicillin is probably the antibiotic of choice. It is unlikely that areas with large blocks of underlying muscle will be amenable to bandaging.

Follow-up Measures

Dressings should be changed at appropriate intervals. If there is significant exudate consider more frequent changes and/or the use of a high volume absorbent dressing (e.g. a disposable nappy). If the wound is clean and non-exudative there is usually no extra value in repeated dressings. Intervals of up to 3–5 days are possible if modern wound dressings and hydrogels are used. The tetanus status of the horse should be checked, and toxoid given if there is unknown vaccination history but the horse is known to have been vaccinated, or tetanus antiserum when there is unknown, uncertain, or no previous vaccination.

Introduction

Wounds resulting in penetration of any synovial structure can lead to life threatening infection and extreme lameness and should be treated as an emergency. All joint injuries are serious, and must be recognized at the outset as delay in treatment is potentially catastrophic. Injuries over 12 hours old usually carry a poor prognosis, while those over 24 hours have an almost hopeless prognosis.

Not all wounds extend perpendicularly into the deeper structures and so the skin wound may not directly overlie a joint (Figure 75). Deficits of the joint capsule are a serious complication (Figure 76). Some injuries involving joints or tendons are complicated by fractures. Injuries involving the flexor tendons during full limb extension (i.e. the tendon is at full tension) cause severe damage (or even total disruption). The skin injury may appear to be relatively trivial (Figure 77). Furthermore, the tendon injury may be at a site that is quite a distance from the skin injury. The exact location and extent of the wound should be established.

Careful radiographic and ultrasonographic examinations are essential. Synovial fluid leakage may be obvious or may be difficult to identify; clear yellow, somewhat oily fluid exuding from the depth of the wound could be joint fluid, but the difference between serum exudate and synovial fluid is not always clear, especially when there is some inflammation of the joint that results in a cloudy synovial fluid that lacks normal viscosity. No wound that has synovial fluid drainage should be trivialized or left untreated.

Close observation of the posture of the foot and fetlock when the horse is made to take weight on the leg will help to identify tendon disruption.

Severance of the superficial digital flexor tendon produces only slight dropping of the fetlock, whereas deep digital flexor severance results in toe lifting from the ground and is extremely serious; this is unlikely in a wound without superficial flexor tendon damage. Complete disruption of the suspensory apparatus results in a dropped fetlock and lifted toe. Although disruption of the extensor tendon initially results in knuckling over at the fetlock, the horse quickly adapts. Normal function may be restored as the tendon ends become incorporated in the granulation tissue.

The cause of the wound is a useful factor in deciding on the likely treatment.

Sharp lacerations are usually easier to repair than those complicated by extensive tissue bruising and widespread damage to adjacent structures. If the patient cannot move or is unwilling to move there may be concurrent damage to other structures (joints/bones). The horse should not be moved (an ambulance or trailer may be helpful) as movement can exacerbate a tendon or joint injury and may also cause displacement of fractures. It can also result in dissemination of infection. Significant bleeding is unusual.

Preliminary Approach

The wound site should be packed with hydrogel to prevent ingress of further foreign matter, followed by digital exploration of the wound to assess the full range of injuries. Local anesthesia may be required (regional blocks are far better than local infiltration).

Antibiotics and non-steroidal anti-inflammatory drugs (e.g. phenylbutazone) should be administered parenterally at an early stage. Infection is one of the most dangerous complications of synovial injuries, and intravenous penicillin and gentamicin is probably the best initial combination. If the joint or tendon sheath is open it may be possible to flush the wound using large volumes of saline. The sterile end of a giving set may be introduced directly into the wound as a first aid measure to flush away gross debris and infective organisms.

A hydrogel is then applied to the wound site and a polymeric foam dressing applied. A full Robert Jones’ bandage can be used to limit movement at the wound site. If there is much synovial exudate an absorptive dressing can be used (e.g. a disposable nappy). The horse is then admitted to hospital or referral center for joint/sheath flushing and repair. (This is a specialist procedure.)

Surgical Procedure

Most tendon and joint injuries require general anesthesia for full investigation and repair. The wound may have to be enlarged to allow proper assessment and removal of all foreign matter, damaged and non-viable tissue. Copious flushing (usually from a remote site in the synovial structure, via high pressure systems delivering warm saline) helps to remove foreign matter and bacteria. The final flush should be with a suitable antibiotic solution such as gentamicin solution.

Antibiotic impregnated beads may be used within the structure.

The tissues are reconstructed appropriately; flexor tendons may require prosthetic reconstruction. Drains with continuous flushing mechanism to allow continuous flush after recovery are helpful. The decision to close the wound (primary union) or partially close it or leave it open is a matter for the surgeon.

In many cases a delayed primary union is a useful technique provided that further contamination can be prevented. A rigid limb cast may be required once all infection has been controlled.

Follow-up Measures

Suitable supportive shoes should be applied to assist recovery and avoid excessive forces on the healing site. This may be far more difficult than it seems. For example, simply raising the heel transfers forces away from the deep to the superficial flexor tendon. Axial loading has become common practice but this may be problematical in the long-term, and subsequent wound contraction may result in an intractable tendon contracture.

Sustained broad spectrum combination antibiotics are obligatory. Courses of gentamicin or amikacin and crystalline benzylpenicillin are used, but others may be used according to the suspected or proven infective organisms. Repeated synoviocentesis may be indicated, but this should be performed with care and only when useful information can be gained; there is no merit in sampling when the horse shows no pain and is apparently improving clinically.

Drains should be removed as soon as possible. Supportive bandaging and frog supports should be applied to the contralateral limb. The horses should be strictly confined and then given limited exercise in the later stages of healing. Even with the best treatment there is a high rate of complication, and delays of even 4–8 hours may be catastrophic. Owners may not readily appreciate the severity of the injury (particularly of the flexor tendons).

Introduction

Exposure of bone occurs most often on the distal limb and the face/head (Figure 78). Sequestrum formation occurs when there are fragments of non-viable bone, the periosteum is stripped from the bone, or the periosteum is dried/desiccated. The blood supply to the bone is disrupted, and the outer one-third of the cortex becomes necrotic because it derives its blood supply from the periosteum. Sequestrum formation also occurs when the exposed surface of the bone is infected.

Sequestrum formation often takes several weeks; the necrotic bone is often obscured by unhealthy granulation tissue.

Sequestrum can usually be identified radiographically provided the beam is angled appropriately. Sequestration is not an inevitable consequence of periosteal injury, but is a common feature of those wounds that involve periosteal damage that fail to heal. Grafts will not take on denuded bone.

Preliminary Approach

Wounds with exposed bone may be complicated by open joints (see above). Injuries to the lower limb tend to be more dangerous with respect to bone/periosteal damage. Injuries that occur from sharp lacerations tend to induce minimal periosteal damage, whereas injuries that are severely torn or macerated (e.g. barbed wire wounds) tend to produce extensive periosteal damage. Bleeding is usually minimal. Obvious distortion of the bone suggests that there is a concurrent fracture, and open fractures carry a poor or hopeless prognosis. The horse should not be moved without veterinary advice. A firm hydrogel dressing should be applied before transport.

The extent of concurrent soft tissue damage is then assessed, and the area of bone involved determined, including the possibility of fractures (either partial or non-displaced). Immediate radiography may be necessary to eliminate fracture.

If there is no fracture a moist wound dressing (hydrogel and a conformable absorptive dressing) should be applied and a firm bandage used to provide warmth and support. If there is a possibility of a fracture or tendon or joint involvement, a suitable splint can be placed.