Joints, bursae and tendon sheaths are known as synovial structures. Joints are gliding cartilage end caps of bones, their associated capsule (outer enclosing envelope), and secretory lining (synovial membrane). Joints allow for smooth movement between adjacent bones. Tendon sheaths are fluid lined sacs enclosing and lubricating tendons as they pass through high motion areas (hock, carpus, fetlock). Bursae (bursa singular) are fluid lined, cushioning pouches that underlie tendons as they pass over bony points (point of elbow, navicular are examples).

The anatomy and physiology of synovial structures is intricate and delicate. When these structures are compromised by a wound and subsequent infection, there is the potential for life-threatening disease and chronic pain or lameness.

When wounds penetrate synovial structures, not only are components of the synovial structure often damaged (cartilage, underlying bone, supporting ligaments, tendons, joint capsule), bacteria are usually also introduced and closed bacterial infection of the structure often becomes established.

Joint and tendon sheath infection usually results in severe lameness. Massive inflammation rapidly causes life-threatening damage to the joint or other synovial structure. In tendon sheaths, adhesions (spot-welds) between tendon and sheath can develop as a long-term consequence, causing loss of motion and chronic pain and lameness.

Synovial infections tend to be very difficult to treat. They usually require specific, timely and expensive treatments to return the joint to health and save the horse from chronic lameness. For this reason, it is critical that veterinarians determine early on whether a synovial structure is involved in a wound.

DIAGNOSIS

In some cases, a joint is obviously involved. Perhaps the joint surface is exposed or the joint is wide open. This is relatively rare. More commonly, the communication between wound and synovial structure is more subtle and hard to define. In this instance, veterinarians confirm or rule out the breach of a synovial structure by rapidly performing specific diagnostic tests:

1. Collection and analysis of synovial fluid. If a sample of joint fluid from a joint or tendon sheath near the wound shows signs of infection, that can confirm involvement of that synovial structure.

2. If fluid injected into the joint under pressure exits through the wound, it confirms communication.

3. If a radiographic contrast study of a puncture wound shows it to communicate with a joint. Or, conversely if radiographic contrast material is injected into a nearby synovial structure escapes into the wound, it confirms communication.

Culture can identify specific bacterial species involved. Radiography, ultrasound, arthroscopy and even MRI may help assess the degree of damage to structures and aid our ability to provide a prognosis.

TREATMENT

Rapid diagnosis and aggressive treatment of synovial infection provides the best chance for a full recovery. Treatment usually involves systemic antibiotics, intra-articular antibiotics (injected into the joint), regional limb perfusion.

Arthroscopic exploration of the synovial structure with removal of debris and flushing is the gold standard of treatment. Needle flushing of the synovial structure is also commonly performed and in many cases may be sufficient.

Horses with these wounds often need very careful sterile bandaging and long-term wound care and repeated special treatments. For this reason, these horses are often hospitalized.