Linda A. Dahlgren
Crush Injuries and Compartment Syndrome
Horses are prone to many types of traumatic injuries, including blunt trauma from falls or collision with another horse or object, entrapment injuries associated with stall or fence boards, and kick injuries. Aside from the immediately obvious damage to the skin and underlying soft tissues, more extensive tissue damage frequently occurs but does not become apparent for a period of 4 to 7 days. The resulting tissue trauma can be from a crushing type of injury or the development of compartment syndrome. The attending veterinarian must be aware of these potential complications associated with the acute trauma and include this information in the treatment plan and in discussions of prognosis and cost of treatment with the owner. This chapter describes crush injuries and compartment syndrome and the available diagnostic tools and treatments.
Crush Injuries
Horses are exposed to trauma in the form of sharp lacerations, degloving wounds, blunt trauma, and abrasions or burns. Most of these incidences are managed with routine veterinary care and heal uneventfully. However, wounds resulting from high-energy impact can be exceedingly difficult to treat successfully. The energy imparted to the tissues at the time of injury can result in a substantial area of tissue damage, including damage to the nerves and vessels supplying the distal limb. At the time of injury, it can be challenging to accurately determine the exact magnitude of the injury because the full extent is not grossly apparent. Frequently, high-energy injuries go through an extensive debridement phase, resulting in much greater tissue damage than is apparent at the time of injury. The treating veterinarian should be aware of this potential for increased severity of the injury and should include this information when discussing prognosis and treatment plans with the owner.
Wounds that result from entrapment are particularly challenging to treat because of the considerable soft tissue damage and potential for thrombosis of blood vessels and damage to peripheral nerves. Examples include a limb caught in a fence or cattle guard or under a stall door, severe abrasions caused by stepping through broken trailer floorboards, rope burns, and crush injuries. Full assessment of all structures involved and an accurate prognosis can sometimes only be achieved after several days to a week of treatment, serial reexamination, and specialized imaging.
Initial Assessment
The initial assessment of a severe injury should be similar to that for many other types of injuries. A thorough examination of the structures involved is critical, including palpation of pulses, evaluation for normal skin sensation, and consideration of limb temperature. Assessment includes evaluation of the integrity of synovial structures, blood vessels, nerves, bones, and tendons and ligaments. Radiographs are indicated to rule out fractures in many cases, and ultrasound evaluation may be used to evaluate the soft tissues. Routine wound management is indicated initially. Care should be taken in the early stages following an injury to be conservative in the amount of tissue that is debrided from a wound. Removal of tissues that are potentially viable is contraindicated. Over the course of the 3 to 10 days following injury, the demarcation between living and irreparably damaged tissues will become apparent, and debridement of the wound can be done sequentially over time. Any tissue that remains viable plays a critical role in achievement of functional wound coverage in the distal portion of the equine limb.
Imaging
Viability of tissues in the distal limb can be difficult to determine by physical examination alone. In these cases, vascular phase scintigraphy and venography may be helpful in guiding treatment decisions. The pool and bone phases of scintigraphy are used commonly to aid in lameness diagnosis and may be useful with crush or entrapment injuries to diagnose occult fractures. However, it is the less-used vascular phase that can be especially helpful in assessing vascular perfusion to the distal limb. In the 5 to 7 days following a high-energy injury, the viability of tissues can be impossible to determine with traditional subjective methods of assessment (warmth, color, swelling, response to stimulation, and quality of arterial pulses). Objective methods such as intravenous fluorescein dye, Doppler ultrasound, and contrast arteriography are less than ideal.
In one published series of three cases (severe rope laceration, severe degloving laceration, and pastern laceration following entanglement in a fence), vascular scintigraphy allowed accurate assessment of distal limb perfusion. Both technetium-99m methylenediphosphonate and technetium-99m pertechnetate were used successfully in these cases. Because the long-term cost associated with treating severe injuries can be high, the moderate expense of scintigraphy can be justified if it can help determine the integrity of the vascular supply to the distal limb and whether treatment is reasonable or if the prognosis is grave. Vascular integrity can also be assessed with venography of the distal limb. The advantages of this technique include the use of equipment commonly found in ambulatory equine practice and decreased cost, compared with scintigraphy. A tourniquet such as an Esmarch bandage is placed proximal to the injury. Contrast agent is injected through a catheter placed in a peripheral vein distal to the tourniquet, and radiographs are taken immediately (see Suggested Readings for details of the procedure). Arteriography is contraindicated because of increased incidence of thrombus formation and vasospasm. When an adequate volume of fluid is applied to the venous side, the fluid pressure results in retrograde filling of the arterial circulation.
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