Recent Advances in Arthritis Treatments – A Summary

Introduction of joint disease and importance

Osteoarthritis (OA) or degenerative joint disease is a frequently encountered problem in horses and results in considerable costs to the equine industry. It is a progressive disease characterized by joint pain, inflammation, synovial effusion, limited range of motion, and progressive deterioration of articular cartilage. Osteoarthritis is a nonspecific term that may be used to include injury solely of the articular cartilage, but frequently, multiple structures associated with the synovial joint are simultaneously affected.

This lecture and the below notes represent what will be discussed on this topic.

A synovial joint is composed of two apposing layers of articular cartilage and underlying subchondral bone. The articular cartilage acts as a smooth gliding surface for joint mobility. Surrounding the joint is a synovial membrane, which is responsible for synthesizing synovial fluid, hyaluronan, and lubricin, which provide for viscosity and lubrication. The joint capsule is connected to the synovial membrane, and has a fibrous portion composed of dense connective tissue, which is continuous with the periosteum or perichondrium of the surrounding bones. The joint capsule, collateral ligaments, surrounding musculotendinous units, and intraarticular ligaments (such as the cruciate ligaments in the stifle joint) provide stability of the joint.

Pathophysiology of joint disease

Proposed mechanisms of joint injury include traumatic arthritis, physiologic trauma secondary to inflammation, or athletic activity leading to injury. Traumatic arthritis is a broad term encompassing single or repetitive trauma to one or any combination of the above structures. A subclassification has been developed to clarify this type of injury. Type I is traumatic synovitis and capsulitis, without cartilage or surrounding soft tissue damage. Type II involves damage to articular cartilage or complete rupture of major supporting structures, such as collateral ligaments and Type III is posttraumatic arthritis, in which articular cartilage progressively deteriorates, accompanied by secondary changes in the surrounding soft tissues or bone.

A second cause of OA is persistent inflammation. With persistent synovitis, secondary inflammatory changes within the joint may progress to OA, even with normal joint loading. A third mechanism of injury is repetitive high-impact loading of the normal joint during athletic activity, which results in repetitive microtrauma. Whatever the inciting cause, damage to articular cartilage and continued inflammation within the joint can lead to progression of disease. As a consequence, persistent OA or injury to the joint capsule may result in joint capsule fibrosis and decreased range of motion.

Diagnosis of joint injury

Horses with clinical OA have various presentations. Some horses demonstrate significant lameness, but others may appear asymptomatic. Synovial effusion may be palpable, but the volume of effusion does not directly correlate to severity of disease nor does it confirm OA. Flexion tests can increase suspicion of joint injury, but these tests do not rule out injury or confirm it to a specific joint. Intraarticular analgesia is the most specific method of localizing pain to a joint, with improving or resolving lameness seen following injection.

Osteoarthritis can be diagnosed via multiple imaging methods. Radiography is the most common (although it is extremely insensitive with early OA) and may reveal one or several of the following changes: periarticular osteophytes, subchondral bone sclerosis or lysis, loss of joint space that may be asymmetric (suggesting cartilage loss), osteochondral fragmentation, or ankylosis. Ultrasonography may reveal synovial effusion, periarticular osteophytes, synovitis, capsulitis, damage to surrounding soft tissue structures, and, in some instances, thinning cartilage or defects within subchondral bone. Computed tomography and contrast arthrography can also demonstrate changes in bone and intraarticular ligaments encountered in osteoarthritis. Magnetic resonance imaging is the most sensitive method in diagnosing cartilage injury, and can simultaneously evaluate surrounding structures. Both CT and MRI are more sensitive in identifying lesions, compared with radiography, because of the dimensional aspect of imaging. Nuclear scintigraphy can be useful, but as OA becomes chronic, this technique may have a lower yield because of lack of specificity, and another type of imaging is typically required to confirm the diagnosis.

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