Arthritis is a nonspecific term denoting inflammation of a joint. All joint diseases of large animals have an inflammatory component to varying degrees. Arthritic entities of importance include traumatic arthritis, osteochondritis dissecans, subchondral cystic lesions, septic (or infective) arthritis, and osteoarthritis (also called degenerative joint disease).
Traumatic arthritis includes traumatic synovitis and capsulitis, intra-articular chip fractures, ligamentous tears (sprains) involving periarticular and intra-articular ligaments, meniscal tears, and osteoarthritis. Traumatic arthritis is seen in all breeds of horses worldwide.
Clinical Findings and Diagnosis
Traumatic synovitis and capsulitis is inflammation of the synovial membrane and fibrous joint capsule associated with trauma. Typically, the horse is an athlete and presents with synovial effusion in the acute stage, along with general thickening and fibrosis in the more chronic stage. Lameness varies from a mild gait change to severe lameness. Traumatic synovitis and capsulitis is differentiated from other traumatic entities by use of radiography to exclude osteochondral fractures or disease. Tearing of ligaments or menisci (in femorotibial joints) can often be excluded only by diagnostic arthroscopy. Osteochondral fractures are diagnosed with radiographs. Osteoarthritis is the progressive loss of articular cartilage and can be the consequence of any or all of these traumatic entities (also see Osteoarthritis below). Osteoarthritis is diagnosed with radiographs when the changes are sufficiently severe to demonstrate loss of joint space (associated with articular cartilage loss), subchondral sclerosis, and osteophyte or enthesophyte formation. Lesser degrees of osteoarthritis can be defined only with diagnostic arthroscopy. Clinical signs of osteochondral fractures are similar to those of synovitis and capsulitis, as well as those of osteoarthritis; differential diagnosis of these entities is based on radiographs and, in some cases, arthroscopy.
Arthritis generally results in pain and altered function of the joint. If the process is active or acute, there is usually synovial effusion, and the surrounding tissues are swollen and warm. In more severe cases, manipulation of the joint causes pain. In more subtle cases, flexion tests are required to elicit lameness. As the disease process becomes chronic, the range of motion is reduced with fibrous thickening of the joint capsule. Radiographic evaluation is necessary for positive confirmation of a number of disease entities. Arthroscopy is used to accurately assess the amount of damage to the articular cartilage and to establish a prognosis.
Treatment of acute traumatic synovitis and capsulitis includes rest and physical therapy regimens such as cold water treatment, ice, passive flexion, and swimming. NSAIDs (usually phenylbutazone) are used routinely. In more severe cases, the joint is lavaged to remove inflammatory products produced by the synovial membrane, as well as articular cartilage debris that exacerbates the synovitis. Joint drainage alone, without lavage or injection of medication, provides only short-term relief.
Various intra-articular medications have been used. Corticosteroids are the most potent anti-inflammatory agents and are effective in acute traumatic arthritis. However, there are differences in the adverse effects between various corticosteroids and various dosages. Betamethasone products and triamcinolone acetonide are effective with no deleterious adverse effects. Methylprednisolone acetate is more potent and longer acting than the other two drugs but has significant adverse effects that cause degenerative changes in the articular cartilage. Intra-articular sodium hyaluronate has been used effectively for mild to moderate synovitis and has a chondroprotective effect, but it is less effective in severe synovitis or when intra-articular fractures are present. Use of an IV formulation of hyaluronic acid (systemic dose 40 mg) in clinical cases appears to be effective, and this is supported by research data in a controlled model of arthritis in horses. Polysulfated glycosaminoglycans (PSGAGs) are also used frequently for traumatic arthritis entities. PSGAG is effective for synovitis and can help prevent ongoing degeneration of articular cartilage. Although effectiveness of PSGAG when used intra-articularly (250 mg) has scientific support, effectiveness when used IM (500 mg) is less certain. The use of pentosan polysulfate (PPS) at 3 mg/kg, IM, has been shown to be effective as a disease-modifying drug with experimental equine osteoarthritis and has been extensively used in clinical cases outside the USA. Biologic therapies such as autologous conditioned serum are also becoming more commonly used.
Horses with osteochondral chip fragmentation (most commonly seen in the carpus and fetlock joints) are treated with arthroscopic surgery to minimize the ongoing development of osteoarthritis. Fragments are removed, and defective bone and cartilage debrided. Rest periods of 2–4 mo follow, and physical therapy regimens are instituted in the convalescent period. The success rate in returning horses to previous performance level is high when secondary osteoarthritic changes are minimal at the time of surgery. Osteochondral chip fragments that are amenable to arthroscopic surgery and have successful results include those associated with the distal radius or carpal bones; dorsoproximal first phalanx; proximal palmar/plantar first phalanx; apical, abaxial, and basilar fragments of the proximal sesamoid bones; fragmentation of the distal patella in the femoropatellar joint; chip fragments of the tibiotarsal joint; and fragments of the extensor process of the distal phalanx (coffin joint).
For a complete discussion of equine osteochondrosis, see Osteochondrosis in Horses.
In osteochondritis dissecans (OCD), a focal area of the immature articular cartilage is retained, and the matrix in the basal area of this region becomes chondromalacic and acellular. The immature articular cartilage separates from the underlying trabecular bone. The chondral fracture extends horizontally and vertically until a flap is formed. Synovial fluid gains entrance to the underlying medullary space, and subchondral cysts may form (usually only in larger animals). The flap of immature articular cartilage may stay separated and loose, break away completely (“joint mice”), or reattach by endochondral ossification to the underlying bone, especially in pigs, and result in a wrinkled articular surface. The latter occurs only if the joint is rested or protected, which permits reestablishment of the circulation necessary for endochondral ossification. If the flap is torn free by joint motion, it may be ground into smaller pieces during locomotion and disappear, whereas the larger plaques may become attached to the synovial membrane, become vascularized, and ossify. The resultant articular defect, in time, fills with fibrocartilage.
The exact cause of OCD is unknown but is assumed to be multifactorial. Factors include genetic predisposition, fast growth, high caloric intake, low copper and high zinc levels, and endocrine factors.
The most common sites of OCD, which usually is seen in young animals, are the femoropatellar joint, tibiotarsal (tarsocrural) joint, fetlock (metacarpophalangeal and metatarsophalangeal) joints, and the shoulder.
Animals with OCD of the shoulder usually present when <1 yr old with severe forelimb lameness and possibly some muscular atrophy. Animals with OCD in the other joints usually present with synovial effusion and varying degrees of lameness. Diagnosis is confirmed with radiographs.
The history, age, breed, sex, and clinical signs provide useful information; however, radiographs are required to substantiate a diagnosis of OCD.
Treatment of OCD depends on the location and degree of involvement. Femoropatellar joint lesions are associated with the lateral trochlear ridge of the femur, medial trochlear ridge of the femur, or distal patella. They are amenable to arthroscopic surgery, which is recommended in all cases except early lesions characterized by flattening (without fragmentation) <2 cm long on the lateral trochlear ridge. In the tarsocrural joint, OCD lesions are seen in decreasing frequency on the intermediate (sagittal) ridge of the tibia, lateral trochlear ridge of the talus, medial malleolus of the tibia, and medial trochlear ridge of the talus. All lesions are amenable to arthroscopic surgery, and the prognosis is usually good. Surgery is recommended when synovial effusion is present. Lesions without fragmentation in the metacarpophalangeal or metatarsophalangeal joints can be treated conservatively, and most affected animals recover well. If a fragment is present, arthroscopic surgery is recommended. In the shoulder, surgery is usually recommended, although milder cases have been managed conservatively with success. The prognosis with arthroscopic surgery is generally less favorable in the shoulder than in other joints.
Subchondral Cystic Lesions
Subchondral cystic lesions are seen in the femorotibial joint and in the fetlock, pastern, elbow, shoulder, and distal phalanx. The diagnosis is usually made on the basis of localization of lameness with intra-articular analgesia (synovial effusion is variable) and confirmed with radiographs.
Subchondral cystic lesions are most frequent in the femorotibial joint, followed by the fetlock joint. Surgery (arthroscopic) is currently recommended in the femorotibial joint whenever a complete cystic lesion is present. Smaller, dome-shaped or flattened lesions are usually treated conservatively in the initial period. Athletic soundness is achieved in 65%–70% of these horses. Intralesional injection of corticosteroids under arthroscopic visualization, in preference to debridement as done previously, achieves superior results. In cases with collapsed edges to the cystic lesion at arthroscopic surgery, or in cases unresponsive to therapy, arthroscopic debridement with augmentation with fibrin, growth factors, and mesenchymal stem cells have been used. Surgery is usually recommended for subchondral cystic lesions of the distal metacarpus in the fetlock but not as consistently as in the femorotibial joint. Single lesions associated with the pastern and elbow joint are treated conservatively and have a fair prognosis. If possible, surgery is recommended for cystic lesions of the distal phalanx (results with conservative treatment are very poor).
Etiology and Epidemiology
Septic or infective arthritis results from sequestration of bacterial infection in a joint. Infection of a joint develops in three main ways: 1) hematogenous infection, which is common in foals, calves, and lambs (commonly referred to as navel ill); 2) traumatic injury with local introduction of infection; or 3) iatrogenic infection associated with joint injection or surgery (usually in horses). Navel ill is only one example of a hematogenous route of infection, which can also be gained from GI or pulmonary sources.
Clinical Findings and Diagnosis
Septic arthritis is usually characterized by severe lameness and distention of the joint with cloudy, turbid synovial fluid that contains >30,000 WBC/mm3 and a total protein level of >4 g/dL.
In foals, hematogenous osteomyelitis often accompanies septic arthritis. Septic arthritis in foals has been classified into type S (septic joint only), type P (involving osteomyelitis of the adjacent growth plate as well), or type E (involving osteomyelitis of the epiphyseal and subchondral bone). Various organisms may be involved.
In young lambs, Actinobacillus seminis causes polyarthritis, as doChlamydophila psittaci and Erysipelothrix insidiosa. The latter can follow docking, castration, or navel infection. Viruses and mycoplasma may also be etiologic agents in food-producing animals.
In mature goats, caprine arthritis and encephalitis virus (see Caprine Arthritis and Encephalitis) is an important cause of infective arthritis. In young goats, C psittaci and Mycoplasma mycoides are frequent causes.
Bacterial (including Mycoplasma) arthritides are seen in young pigs. In newborn pigs, septic arthritis usually is due to intrauterine or navel infection with Escherichia coli, Corynebacterium,Streptococcus, or Staphylococcus spp. Control is best directed toward reducing the possibility of infection from the environment. Older pigs sometimes develop arthritis as a sequela of infection with Haemophilus, Erysipelothrix, or Mycoplasma spp. Although diagnosis in the early stages is not difficult, the more chronic stages can be confused with articular lesions produced by dietary hypervitaminosis A.
Traumatic injury to joints with contamination and progression to infection is common in horses, and various species of bacteria are involved. Infection associated with intra-articular injection or surgery occurs in horses and is usually associated with Staphylococcus aureus or S epidermidis.
Septic arthritis requires prompt treatment to avoid irreparable damage. Systemic broad-spectrum antibiotics are indicated; the initial choice is based on the most likely pathogen but is subject to change based on culture and sensitivity tests. Systemic antibiotic treatment is often combined with intra-articular antibiotics (to achieve more effective sterilization of the joint) and other local therapy, including joint lavage (initially) and arthroscopic debridement and drainage. Adjunctive treatment with NSAIDs (eg, phenylbutazone) is also done. The effectiveness of treatment is monitored carefully with clinical signs and repeat synovial fluid analyses.
(Degenerative joint disease)
Etiology and Epidemiology
Osteoarthritis is a progressive degradation of articular cartilage and represents the end stage of most of the other diseases discussed above if treatment is ineffective or the initial problem is too severe. For this reason, prompt diagnosis and correct management of traumatic synovitis and capsulitis, intra-articular fractures or traumatic cartilage damage, osteochondritis dissecans, subchondral cystic lesions, and septic arthritis are critical.
Clinical Findings and Diagnosis
Lameness can be localized with analgesia to the affected joint. There are varying degrees of synovial effusion, joint capsule fibrosis, and restricted motion (decreased flexion). Radiographic signs of osteoarthritis include decreased joint space, osteophytosis, enthesitis, and subchondral sclerosis. In less severe cases, articular degradation requires definition with arthroscopy.
Treatment of osteoarthritis is most commonly palliative and includes the use of NSAIDs, polysulfated intra-articular glycosaminoglycans, intra-articular corticosteroids, IV hyaluronic acid, and IM pentosan polysulfate. The use of intra-articular autologous conditioned serum has also been validated. Physical therapy regimens may prove useful. Arthroscopy is commonly performed to diagnose the extent of articular cartilage loss, as well as to treat primary conditions such as articular cartilage separation, meniscal tears, and ligamentous injury. In advanced cases of osteoarthritis, surgical fusion (arthrodesis) may be performed on selected joints. Surgical fusion of the proximal interphalangeal joint (pastern) or distal tarsal joints can effect athletic soundness. Fetlock arthrodesis is also done in valuable animals and makes them comfortable and capable of breeding. Treatment is usually unsuccessful in chronic cases in bulls and cows, but restricted exercise and careful feeding and nursing prolong the life of and can be worthwhile for valuable breeding animals.
Last full review/revision January 2015 by C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, DACVS, DACVSMR