The treatment of equine lameness is a complex subject. Lameness in horses has a variety of causes, and treatment must be tailored to the type and degree of injury, as well as the financial capabilities of the owner. Treatment may be applied locally, systemically, or intralesionally, and the strategy for treatment may change as healing progresses. The end goal is to reduce the pain and inflammation associated with injury, to encourage the injured tissue to heal with normal structure and function, and to ultimately return the horse to the highest possible post-recovery performance.
The process of healing
Bone
Bone heals by formation of a callus over the defective area. Speed and quality of healing is directly related to the blood supply and fracture stability. Rest is required immediately following injury to reduce movement of the fracture site. Stability may be improved through use of surgical implants or casting, depending on the location of extent of the fracture. Shock wave therapy is sometimes employed in the case of splint bone fracture or stress fractures to the cannon bones, to improve blood flow to the area. Fractures within a joint, such as chip fractures in the knee, hock, or fetlock, require arthroscopic surgery to prevent secondary arthritis of that joint.
In some cases, the callus may place pressure on surrounding soft tissue structures. The callus of a splint bone fracture can push on the adjacent suspensory ligament, leading to lameness from secondary suspensory desmitis. Treatment usually involves the removal of the offending callus.
On average, bone heals better than soft tissue. It requires less time to heal and, unlike soft tissue which is always weaker after healing, bone heals to 100% strength. However, fracture healing in horses is complicated by their size, flightiness, and desire to stand. Horses are at risk of re-injury of the fracture site, especially when trying to rise after lying down, or when recovering from anesthesia following fracture repair. Forced recumbency is not an option for horses, making healing more difficult. Weight bearing on a single front or hind limb increases the likelihood of support limb laminitis. Additionally, the cost of casting or surgical fixation makes treatment financially unattainable for some owners. While limb fractures are no longer a death-sentence for horses, it is still considered a very serious injury. In general, a horse is more likely to survive if it is small in stature and has a good temperament that will tolerate the months of inactivity required for healing. Fractures that are open, comminuted (very fragmented), or located higher on the limb tend to have a poorer prognosis.
Synovial joints Lameness is most commonly associated with injury to synovial joints, or those joints containing articular cartilage, a joint capsule, and a synovial membrane. Joint disease may affect the joint capsule and synovial membrane, articular cartilage, subchondral bone (the bone underneath the cartilage), menisci, or any ligaments associated with the joint. Damage to any of these tissues leads to inflammation, which is especially problematic in the joint. While degeneration of articular cartilage is a common disease process in working animals, resulting in osteoarthritis, cartilage is aneural (does not contain nerves) and does not produce pain. Pain associated with osteoarthritis is secondary to joint capsule pain, due to joint distention and reduced range of motion, or to pain from the underlying bone, which may become damaged following erosion of the articular cartilage.
Inflammatory products, such as inflammatory mediators and cytokines, damage articular cartilage and have been shown to weaken intra-articular ligaments. Therefore, treatment of joint disease should not only address the primary injury producing inflammation, but also the inflammatory cycle that leads to further tissue damage. Cryotherapy, joint lavage, systemic anti-inflammatories, or intra-articular medications are used to reduce joint inflammation. In the case of severe joint pathology such as an osteochondral chip, intra-articular fracture, osteochondritis dissecans lesion, or ligamentous or meniscal injury, arthroscopy may be required to ensure normal function of that joint. Debris within the joint, such as from a chip fracture, can cause long term damage to the synovium and articular cartilage leading to osteoarthritis, and is therefore best removed. Following acute injury, joints often benefit from specialized physical therapy, such as swimming, to prevent the loss of range of motion associated with joint capsule fibrosis.
Treatment of joint cartilage injury is difficult and often unrewarding. Partial-thickness defects do not heal. The body will try to repair full-thickness cartilage defects using scar tissue or fibrocartilage, both of which are poor substitutes for normal, healthy articular cartilage. Current treatment includes arthroscopy-produced microfratures within the subchondral plate. These microfractures encourage an inflammatory response within the defect, which recruits stem cells to the area. Unfortunately, these cells differentiate into fibrocartilage, rather than normal joint (hyaline) cartilage, leading to inferior tissue repair at the site of injury. Bone marrow aspirate concentrate (BMAC) has shown some benefits when grafted into the area following microtrauma. However, the primary treatment for degenerative joint disease involves reducing the inflammatory process that is known to accelerate articular cartilage degeneration.
Tendon and ligament
Tendon is primarily composed of elastic type I collagen. However, mature tendon contains cells that have a limited ability to regenerate. Following injury, tendon lays down type III collagen, or scar tissue, which is stronger than type I collagen but stiffer and less-elastic. This makes it less distensible and more likely to re-injure when the horse begins to stretch the tendon during strenuous work. Certain treatments may improve the final tendon fiber quality, and subsequently increase the likelihood that the horse will return to full performance post-injury.
Healing of soft tissue injury is often monitored using ultrasound to assess the lesion size and fiber pattern. Monitoring soft tissue injury with ultrasound allows for a more scientific determination of when to introduce exercise back into the horse's rehabilitation program, and for quick intervention should the injury worsen. Recently, a new ultrasound technique called color Doppler ultrasonography has been used to assess equine tendon injuries. Color Doppler measures the degree of blood flow to a lesion, allowing for more accurate assessment of healing.
Rest and hand-walking Rest is almost always recommended for treatment of lameness because it reduces forces placed on damaged tissue, allowing the normal process of healing to occur. Type and severity of injury determines the duration and degree of rest required. Aggressive limitations of activity may be required in cases of fracture. Horses are kept tied for the several-month duration of healing, to prevent them from lying down and potentially re-injuring the bone while trying to stand. In other cases, rest may be contraindicated. Animals with a history of upward fixation of the patella, polysaccharide storage myopathy,Valberg SJ. A Review of the Diagnosis and Treatment of Rhabdomyolysis in Foals. Proc. AAEP 2002(48) 117-121. and equine recurrent rhabdomyolysis are often best kept on a schedule of regular exercise. Rest may be counterproductive if the lameness is secondary to osteoarthritis. In this case, mild exercise improves joint mobility and lameness can worsen with confinement. Rest may vary from strict confinement (“stall rest”), to small paddock or pasture turnout, to reduction of exercise intensity. Horses are often unpredictable when on prolonged stall rest, which greatly increases the risk of re-injury when hand-walking is begun. Sedation or additional forms of restraint may be needed to help control the horse during this initial period of increased exercise intensity. While rest may be implemented as the only form of treatment, specialized treatment often improves overall recovery, and is recommended if the client desires the animal to return to full athletic function.
Soft tissue and bone strengthen with exercise and weaken if it is not actively used. Horses that undergo long-term stall rest require a slow, progressive rehabilitation program to try to prevent re-injury of the original tissue or injury to a new area now weakened by prolonged disuse. In some cases of soft tissue injury, low-impact exercise, such as hand walking or walking under tack, can be more beneficial if introduced in the early healing phase rather than adhering to strict stall rest alone. Tendons and ligaments heal by formation of scar tissue, which is less elastic and lacks the very regular, organized pattern of fibrils of normal tissue.Dahlgren LA. Review of Treatment Options for Equine Tendon and Ligament Injuries: What’s New and How Do They Work? Proc. AAEP 2005 (51) 376-382. Exercise helps to encourage proper fiber alignment, and subsequently leads to a tissue that is closer to its original elasticity.
In cases of acute injury, joints benefit from rest to allow for reduction of the inflammatory process within the joint. Hand walking is often recommended during times of stall rest to help prevent adhesion formation and fibrosis within the damaged joint, to maintain range of motion, and prevent atrophy of the articular cartilage. Hand walking is used in cases of cellulitis to reduce edema formation in the tissues. Cellulitis leads to an extreme degree of swelling, which can persist after elimination of the underlying cause and result in long-term lameness. Therefore, reduction of edema is a very important part of treatment, and walking is often performed multiple times each day.Getman LM Alternative Therapies for Cellulitis. Proc. ACVS (2011) 585-587.
Cryotherapy, thermotherapy, and compression
Cold application to the skin (cryotherapy) is used to decrease pain and inflammation of acute soft tissue injuries. At a cellular level, cold application decreases the formation of exudate and diapedesis of inflammatory cells, thereby reducing edema. Cryotherapy has also been shown to reduce metabolism and thus oxygen demand of tissues, helping to prevent hypoxic tissue damage. Cold is often applied to the site of injury by hosing cold water onto the area (hydrotherapy), icing, or medical devices such as the Game Ready system that provides both cold therapy and compression. Cold salt-water spas are also available, and are used to bathe a patient's injury in aerated, hypertonic, cold water. This combines the benefits of cryotherapy with the osmotic effect of salt, producing better analgesia and reduction of inflammation.
Heat (thermotherapy) is usually applied at least 48–72 hours after the initial injury. It is used to improve blood flow and subsequently healing, and to increase extensibility of tissues. Improved blood flow can also encourage fluid reabsorption, which reduces swelling, and encourages phagocytic cells to enter the site of the injury. Liniments are sometimes used to increase heat to an area. Both heat and cold have been shown to decrease muscle spasm and pain.