The Problem with Puncture Wounds
It is uncanny how some of the smallest, seemingly innocuous wounds can become the most life-threatening. Those located around synovial structures (joints, tendon sheaths and bursas) often fall into this category. Early recognition of synovial structure involvement followed by aggressive therapy wins the battle in many cases, but not all. The statistics are worse when recognition or therapy is delayed. Having owners who are caring but also knowledgeable about limb anatomy is an important first step. Owners are often the first responder – making the decision on whether to contact their veterinarian. It is an easy decision to make when blood is spurting, flesh is hanging, or bone is visible but not so easy when the wound is a puncture or just an inch or so in length. Perhaps some of the following information will be helpful in highlighting the importance of small but badly placed wounds.
Puncture wounds are often overlooked as harmless, but objects that create punctures (nails, tree branches, pitch fork tines, etc) usually travel beyond skin level into deeper tissues and may tract considerable distance away from the entry site. A good example of this is a “street nail.” The “stepped-on nail” can penetrate just the insensitive lamina or extend deeper to the digital cushion, the coffin bone, or one to all three synovial structures (coffin joint, navicular bursa, digital flexor tendon sheath) located within the foot. Although the damage to the tissues is initially limited to the path of the penetrating object, and the horse may be reasonably sound, bacteria carried in by the object can multiply and invade surrounding tissues. When combined with soil particles, only a few bacteria are needed to overwhelm the horse’s ability to fight off a developing infection on its own. Determining the path of a penetrating object through the foot can be simple if the object is still in place, but much harder if the foreign material has been removed. In the latter case, contrast radiographs may be obtained using either iohexol (a radiographic dye) or a sterile surgical probe if the entrance to the tract is still visible. Other diagnostics which can be useful in more chronic cases include synovial fluid sampling of the coffin joint and tendon sheath, to evaluate the cellularity of the synovial fluid, ultrasound imaging of the coffin joint, navicular bursa, and tendon sheath or the use of MRI. Ultrasound and MRI imaging can eliminate the risk of iatrogenically spreading an infection into a synovial structure if it is not already present.
Once confirmed that the puncture wound involves a synovial structure, aggressive therapy is required to eliminate infection and debris from within the space to avoid the destruction of tendons, cartilage and bone and to minimize the development of scar tissue which can alter movement. Treatment options have evolved over the past several years to include more refined surgical approaches to the navicular bursa which minimize further damage to the soft tissues of the foot, provide better delivery of potent antibiotics using regional limb perfusion and reduction of inflammatory mediators within the synovial space through the use of conditioned serum products such as IRAP. Treatment is also directed at preventative measures against support limb laminitis while the injured foot regains its original soundness.
A successful outcome is dependent on early recognition, a global approach to therapy, and a bit of good fortune. Remember that although we were brought up to believe that good things come in small packages, this is not an adage that should be applied to punctures and small wounds. The right thing is always to assume the worst and be appreciative when it isn’t.