A swelling on the limb that might or might not be accompanied by lameness could be the first sign of bursitis or synovitis. These are similar, moderately common inflammatory conditions of the structures that produce synovial (joint) fluid.
"When synovial structures become inflamed, distension (swelling) and pain can follow," says Joanne Kramer, DVM, Dipl. ACVS, clinical assistant professor of equine surgery at the University of Missouri. "Even worse, by-products of severe inflammation can damage cartilage in joints, tendons in tendon sheaths, or set up adhesions (restrictive bands of scar tissue). Infectious bursitis/synovitis often causes severe lameness."
Bursitis is inflammation of the bursa. "The bursa is a sac between the tendon and an adjacent bone that the tendon glides over," Kramer says. "The sac is lined with a membrane that produces synovial fluid."
Synovitis refers to inflammation that occurs in the tendon sheath (tenosynovitis) or the inner lining of the joint capsule (synovitis). "The tendon sheath is a sac that encloses regions of a tendon, found in areas where the tendon crosses a high-motion joint," states Kramer. "The inner lining of a tendon sheath produces synovial fluid. The joint capsule is a thin, saclike structure that envelops and contains all the elements of a joint, including an inner lining that produces synovial fluid."
Julie Dechant, DVM, MS, Dipl. ACVS, equine emergency clinician at Oklahoma State University, further clarifies: "Problems such as osteoarthritis and bone chips will have associated synovitis and bursitis (inflammation is secondary to the primary injury). But typically, the use of the terms bursitis or synovitis implies that the disease or inflammation is localized to the membrane lining of these structures and there is no other associated injury--no infection, bone chips, or osteoarthritis."
The two conditions can affect several different areas, present with varied clinical signs, and result from multiple causes. Generally, idiopathic (unknown) causes are associated with effusion (fluid buildup), but no lameness, says Kramer.
"Traumatic synovitis and bursitis usually present with effusion and variable degrees of lameness," she adds. "When caused by infection, the clinical signs include effusion and severe lameness to the point where the limb is minimally bearing weight. If secondary to developmental orthopedic joint disease, there will be swelling with the degree of lameness varying, depending on the joint involved and the level of work."
Dechant details areas typically (and not so typically) affected as follows:
Carpal hygroma is an acquired problem in the bursa caused by direct trauma to the carpus (knee) from a fall, lying on hard ground, or pawing and hitting the knee against a hard surface. The problem is primarily cosmetic, with an ugly swelling on the front of the knee. However, sometimes the swelling can restrict flexion of the knee.
Capped elbow (olecranoid bursitis) is similar to carpal hygroma in that it is acquired and associated with a cosmetic blemish. It is caused by trauma, usually from the shoe on the affected leg contacting the elbow during motion or when the horse is lying down.
Capped hock (calcanean bursitis) is caused by trauma and originates from an acquired and/or congenital (false) bursa (traumatic separation of the tissue planes with secondary fluid accumulation). The trauma is usually associated with kicking a wall or gate, and the complaint is usually a cosmetic concern (although lameness can be a problem).
Cunean bursitis is associated with lameness and occurs in conjunction with tarsitis (inflammation of the narrow, lower tarsal, or hock, joints).
Navicular bursitis can be a component of navicular disease and is associated with lameness. Septic or infected navicular bursitis can occur when a nail or foreign body penetrates the frog and causes infection of the navicular bursa and surrounding structures. This is also known as a "street nail injury." This infection causes severe lameness and can be devastating to the horse if not promptly recognized and treated.
Bicipital bursitis is associated with lameness usually due to an injury to the point of the shoulder. Visible swelling is minimal, but pain is evident during palpation or manipulation. The bursitis might be associated with injury to the bicipital tendon or the presence of bone fragments.
Fistulous withers (supraspinatus bursitis) is not commonly seen. This is an infection of the bursa overlying the withers, causing swelling and draining tracts. Treatment is difficult due to its location and problems of trying to drain the bursa. Many different types of bacteria have been associated with these infections, but infection caused by Brucella abortus appears to be more common in horses living in areas with brucellosis in cattle. (Brucellosis is a health risk to people and other animals. Specific testing for brucellosis should be considered for any horse with fistulous withers, and if positive, public health officials must be notified.)
Bog spavin is a swelling of the large tarsocrural joint in the hock. This is a very common cosmetic complaint in young horses, but one needs to eliminate osteochondritis (OCD) as a cause. Lameness is usually minimal or not present, but swelling can be significant and chronic.
Windpuffs are swellings of structures around the fetlock region, either in the joint itself or the tendon sheath around the flexor tendons at the back of the joint. Lameness is minimal or not present, although OCD of the fetlock joint should be ruled out as a cause.
Thoroughpin refers to swelling of the tarsal sheath, which encloses the deep digital flexor tendon as it crosses the hock. The swelling is located just above and in front of the point of the hock. Lameness is typically not present unless associated with injury to the tendon.
Villonodular synovitis is caused by chronic traumatic injury to the fetlock, resulting in thickening of the synovial pad in the front of the fetlock joint. This is a problem in racehorses, causing lameness and joint swelling.
With many of these problems, onset can be gradual or sudden. Says Dechant, "Occasionally the bursitis or synovitis is associated with a specific or recent trauma, and the clinical signs of swelling and/or lameness will suddenly develop. More frequently, the clinical signs gradually develop over time and a specific incident or time-point cannot be determined for its development."
While these problems can develop acutely, all have the potential to develop into chronic problems. "In most situations, the problem is chronic," she adds.
Synovitis and bursitis without lameness commonly develop in two groups of horses--young horses entering training and mature performance horses.
Young horses with conformation problems, such as joints that are too straight or too angled, might be predisposed, says Dechant. The condition also can arise in response to training demands. Young racehorses or performance horses tend to develop cunean bursitis/tarsitis due to the stresses of racing and training. She notes that young show horses are the ones most commonly presented for evaluation of these problems because of owner/trainer concerns about the cosmetic blemish and concerns for future performance.
In mature performance horses, ongoing use and accompanying wear and tear can result in mild, chronic swelling of the hocks, digital tendon sheaths, and fetlocks. "Gaited horses, Standardbreds, or jumping horses may be predisposed to hitting their elbows with their hooves during movement, causing capped elbows," Dechant says. "Horses shod with heel extensions, trailers, or calks may traumatize their elbows when lying down because the modified shoe is more likely to come in contact with the elbow."
Horses of any age which kick in the stall or trailer are at risk for capped hocks.
In making the diagnosis, Kramer recommends a veterinary physical exam consisting of an overall physical exam, detailed observation, manipulation and palpation of the limbs, and a lameness exam. If any lameness is present, diagnostic anesthesia might be necessary to determine if the effusion is the source of lameness.
"Radiographs are useful in identifying underlying joint disease such as osteochondrosis, degenerative joint disease, and traumatic chip fractures," she adds, "while ultrasound evaluation is used to assess tendon and ligament damage.
"The veterinarian will look for evidence of an underlying disease process such as osteochondrosis, carpal chip fractures, tendon damage within the sheath, etc.," says Kramer. "The veterinarian will also check for evidence of a wound that may have entered a synovial structure; this may require distending a joint, tendon sheath, or bursa with sterile saline and looking for saline leaking out of a nearby wound, providing evidence that part of the wound entered the synovial structure."
The synovial fluid might be analyzed for total white blood cell count, total protein, and presence of bacteria. Reports Kramer, "Elevated white blood cell and protein levels or the presence of bacteria would suggest infectious synovitis or bursitis. Elevations in protein only or elevations in protein with mild elevations in red cells or white cells are more suggestive of traumatic, developmental, or other non-infectious causes of synovitis."
Dechant says that ultrasound is useful for further assessing tendon injuries and defining the fluid swelling. "In selected cases, contrast studies using a dye that shows up on radiographs may be helpful to assess the problem."
Treatment and Prognosis
When discovered and treated early, bursitis and synovitis can usually be favorably resolved. Says Kramer, "Synovitis due to osteochondrosis generally yields a good prognosis, but this depends on where the primary lesion is and how extensive the lesion is. Infectious synovitis/bursitis must be treated early and aggressively, or extensive and sometimes permanent cartilage and soft tissue damage in the joint sheath or bursa results.
"However, chronic infectious synovitis, tenosynovitis, and bursitis have poor prognoses," Kramer warns, "because the prolonged exposure to severe inflammation has often caused extensive damage that may not resolve even when the infection is overcome. Well-established infections are much more difficult and costly to treat than acute infections; over time, in the appropriate environment, bacteria can become functionally walled off from the systemic circulation, making difficult the penetration of systemic and local antibiotic therapy and even the horse's own immune cells."
Sudden onset of synovitis or bursitis relative to a mild strain or demands of early training is more likely to have spontaneous resolution of clinical signs; this is more common in young horses. "Otherwise," says Dechant, "the main treatments for most types of idiopathic synovitis or bursitis include combinations of draining the fluid from the swelling, wrapping the leg, applying DMSO topically to the swelling, as well as intra-synovial or intra-bursal injections of corticosteroids and hyaluronic acid. If the swelling responds poorly to injections of corticosteroids and hyaluronan alone, small doses of atropine may be included in the joint injection; the mechanism of this action is not known, but it is anecdotally effective. Intravenous hyaluronan may be useful as a primary or
adjunctive therapy in some horses."
Depending on the severity of the swelling and the treatment used, one should see improvement or resolution of the swelling within one to two weeks.
If these treatments prove unsatisfactory for acquired bursae (carpal hygroma, capped elbow, capped hock), the swelling can be drained with or without other treatments to induce fibrosis (scarring of the tissues) of the cavity, Dechant says. She cautions that any time a bursa or synovial membrane is drained or injected, there is a risk of infection.
After any of these treatments, the horse is usually rested for a couple of days before returning to work. "The legs may need to be cold-hosed or iced and then wrapped after training or work to reduce the recurrence of the swelling," Dechant suggests. If the problem does not resolve, then it should be investigated further.
When lameness is present, the cause of the lameness should be determined and treated specifically. "Typically, this would include rest and/or controlled exercise for management of lameness problems, plus other treatment as indicated for the specific problem, such as shoeing changes, intra-articular medication, etc.," says Dechant.
Underlying problems such as OCD or bone fragments require surgical removal of the chips or fragments. "Surgical treatment may also be necessary for other lameness problems," Dechant reports, "including resection of the proliferative synovial pad in cases of villonodular synovitis or synovectomy (removal of the synovial membrane) in cases of proliferative synovitis where the synovial membrane is chronically thickened and inflamed."
She cautions against surgical removal of the fluid sac in cases of acquired bursae (carpal hygroma, capped elbow, capped hock) for cosmetic reasons--something owners sometimes request. "Lameness is not usually present with these particular problems," says Dechant. "Surgical removal does not eliminate the cause of the blemish (i.e., kicking behavior, gait/occupational trauma) and attempts to heal the lesion, complicated by areas of motion that disrupt surgical repair, may result in a worse cosmetic outcome."
When surgical treatment is the recommended option, several weeks of convalescence are usually required.
There might be no way to prevent the onset of bursitis or synovitis, but owners can minimize problems that result. Suggests Kramer:
- Monitor limbs for abnormal swelling daily;
- Monitor horse for lameness daily;
- Know where the commonly affected structures are for synovitis (knee, hock, and fetlock) and for bursitis (shoulder);
- Have wounds that are near synovial structures, even when they appear superficial, assessed by a veterinarian immediately; and
- Return to work from any layoffs gradually.
Adding to those suggestions, Dechant urges owners of horses which kick to modify the horse's environment to minimize kicking or pawing behaviors. "In my experience," she explains, "horses are more likely to kick when being fed, even if they are in a stall and not directly threatened. Sometimes changing the feed environment, such as feeding in a separated stall, feeding outside, etc., will stop this behavior. If horses kick in the trailer, a different style of trailering (e.g., stock trailer, angle haul, hauling with horse facing backwards vs. traditional two-horse trailer) may be helpful to alleviate the horse's anxiety."
Deep bedding might prevent trauma to the joints when lying down.
"Bandages or a shoe boil roll may be helpful to prevent capped elbows," Dechant states. "If swelling is noticed, prompt treatment by bandaging, drainage, and/or injection may resolve the problem before it becomes chronic. Additionally, prompt treatment, even if it does not resolve the problem, may still prevent chronic distension and thickening of the membrane."
Dechant says that problems associated with bursitis and synovitis can be frustrating to owners, especially those with show horses or horses for sale, where cosmetics are a concern. "Nevertheless, it is important that owners consider the overall welfare of the horse in their decision making," she emphasizes. "When assessing treatment options, do not put a horse's health or soundness at risk by trying to improve a cosmetic blemish. Repeated injections or drainage of the fluid swelling can lead to infection, while surgical treatment could cause infection or a worsened cosmetic outcome."
Make sure that possible health benefits outweight the possible risks.
About the Author
Marcia King is an award-winning freelance writer based in Ohio who specializes in equine, canine, and feline veterinary topics. She's schooled in hunt seat, dressage, and Western pleasure.