The joint is the union of two bones allowing varying degrees of movement. There are two main types of joints, depending on whether they contain a cavity or not. In joints with a cavity or synovial joints, the bone ends are covered with cartilage and joined at the periphery by a joint capsule. The deep face of the capsule is lined by the synovial membrane, which secretes the synovial fluid or synovia used for the nutrition and lubrication of the cartilage. The capsule is reinforced by the external ligaments. Some joints contain menisci and internal ligaments such as the cruciate ligaments in the stifle joint. Inflammation, arthritis, and osteoarthritis are therefore common in horses.
Joint inflammation in horses
Degeneration of a joint often begins with a mild degree of inflammation of the synovial membrane (synovitis) and/or joint capsule (capsulitis). This inflammation of mechanical origin can be induced by excessive and repeated flexion-extension of the joint, such as during certain intense exercises or when landing after passing an obstacle. But a bad conformation or a bad shoe will also be predisposing causes. Inflammation of the synovial membrane produces a modified synovial fluid, the nutrition of the cartilage is altered and as the fluid loses its viscoelastic and lubricating properties, the friction between the cartilage surfaces increases. The products of cartilage degradation in turn cause synovitis, creating a vicious circle of joint inflammation that leads to progressive and chronic joint degeneration. Progressively, the joint capsule thickens, reducing joint mobility and the bone underlying the cartilage (subchondral bone) changes. On the edges of the joint, bone formations or osteophytes develop. This is called arthrosis or osteoarthrosis because the bone is involved. Arthritis refers to joint diseases where inflammatory lesions are severe and predominant. It has an infectious (septic arthritis) or undetermined (possibly autoimmune) origin. In the horse, it is more commonly referred to as degenerative joint disease than as osteoarthritis. When it affects the small tarsal joints, it is called spavinitis and if it affects the interphalangeal joints, it is called phalangeal forms.
Osteoarthritis and osteoarthritis in the horse
The treatment of degenerative joint diseases is decided according to the stage of evolution. But in all cases, the treatment of acute synovitis with rest and anti-inflammatory drugs must be taken seriously in order not to enter the vicious circle of self-sustained joint inflammation. In addition to medical therapy administered orally, intramuscularly, or intravenously, the veterinarian will often recommend intra-articular injection of hyaluronic acid or a corticosteroid. If an intra-articular fragment is suspected to be the cause of the inflammation, it must be excised or fixed with screws. This is most often done under arthroscopy. This means that the surgical instruments are introduced through a very small opening and manipulated under visual control thanks to a glass fiber optic connected to a camera. Parthroscopy can also be used for exploratory or diagnostic purposes to evaluate the cartilage surfaces and soft tissues present in a joint (menisci, cruciate ligaments, carpal ligaments). A key to success in the treatment of degenerative joint disease is early recognition of the problem. If the problem is acute but does not present permanent structural changes, the prognosis can be very good. On the other hand, in the presence of a chronic degenerative phenomenon of the cartilage with possible osseous modifications, the response to treatment will be much less good, the lesions being most often irreversible. Research is currently focused on stimulating cartilage healing and on techniques for replacing damaged cartilage with healthy cartilage. Future developments in this area should therefore improve the prognosis of horses with cartilage damage. Osteopathy can be a solution in less severe cases.
Joint problems related to the hoof
Phalangeal form is the common name used to describe, mainly in adult horses, a condition of the distal digital joints (pastern and foot) characterized by osteophytes (bony proliferations around the phalanges) with or without articular cartilage involvement. In the latter case, lameness is usually much more intense. These bony proliferations (also called exostoses) are the result of direct trauma to the phalangeal region, osteoarthritis of the pastern and foot joints, or abnormal stresses on the bony insertion of tendons, ligaments, or capsules. This last etiology of phalangeal form is mostly observed in individuals with a bad conformation, such as a horse that is too tight in the front and cranial. The most developed phalangeal forms induce a significant reduction in interphalangeal mobility and in some cases spontaneous arthrodesis (fusion of the joint) is observed. The extent of the lesions can be assessed by radiological examination.
Treatment focuses on improving the animal’s comfort by reducing pain with anti-inflammatory drugs and stabilizing the progression of the disease with orthopedic shoeing and proper foot trimming. In severe cases involving the articular cartilage of the pastern, surgical arthrodesis is recommended. This surgery, performed under general anesthesia, consists of placing screws or plates on the bones surrounding the joint cavity to achieve complete immobility. This surgical technique removes the pain induced by the movement of the affected joint.
Eparvin in horses
Eparvin is the common name used to describe a degenerative joint disorder of one or more of the three distal tarsal (hock) joints. Most commonly, both hocks are affected, and the first symptoms of the condition are seen at about 7-8 years of age. Horses with poor conformation, such as bent hocks or cow hocks, are predisposed to developing this condition.
Initially, the symptoms are subtle and consist of a mild, intermittent lameness that may shift from one limb to the other. Over time, the lameness becomes more pronounced and permanent. Eparvin lesions are irreversible, but the condition can be controlled by modification of shoeing and the addition of oral or local anti-inflammatory drugs.
In chronic cases, surgical treatments are used to perform an arthrodesis. In this way, the joint cavity disappears as well as the related pain.
Osteochondrosis in horses
Osteochondrosis is a disorder of the locomotor system that appears during the development of the foal. It is a defect in the ossification process that mainly affects the bone under the cartilage of the bone ends. Osteochondrosis is a multi-factorial condition that affects any bone and can affect any breed of horse.
The manifestations of osteochondrosis are varied: osteo-cartilaginous fragment (osteochondrosis dissecans), cartilage erosion, flattening or crushing of the subchondral bone and subchondral cyst. Clinically, joint distension is usually the first symptom observed, but for some joints such as the shoulder and stifle, this observation is not easy to make. The second most common symptom is mild to moderate lameness. Radiological examination is the complementary examination of choice to objectify these lesions. Treatment is essentially surgical and consists of excision of the fragments or curettage of certain areas under arthroscopic visualization. The prognosis will depend on the location and number of osteochondrosis lesions and will vary from reformation for sport to excellent for competition.
Arthritis in the horse
Septic arthritis, like septic tenosynovitis, is a bacterial infection of a synovial structure. In the adult horse, trauma or intra-synovial injection is usually the cause of these conditions, whereas in the foal, a hematogenous origin is much more frequent. In all cases, these conditions must be considered and treated as emergencies. Indeed, the bacteria and their toxins that are introduced into the joint will quickly cause an excessive inflammatory reaction from the synovial membrane. The substances released by the inflamed synovial membrane will then degrade the cartilage and synovial fluid leading to major joint damage.
Clinically, septic arthritis is a very painful condition with a hot, distended, and painful joint. It should be noted that in foals, given the hematogenous origin of the problem, it is common to have several infected joints at the same time. The definitive diagnosis will be made after puncture of synovial fluid and examination of its cellular content (cytology). When there is a strong suspicion of septic arthritis, and even before having the results of the cytological examination, the veterinarian will start a treatment that consists of a combination of lavage and joint drainage. Broad-spectrum antibiotic therapy, non-steroidal anti-inflammatory drugs, and regular monitoring of progress are also part of the basic treatment regimen. The prognosis depends on the speed of the intervention and the germ involved, but it is often reserved for the competition because osteoarthritis sets in. If the infection has also affected the underlying bone structures, the prognosis is poor.
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