Soft tissue injuries are a relatively common cause of lameness in the athletic horse. These injuries can be difficult to diagnose, manage, and can take considerable time for complete healing to occur.
Soft tissues make up the connections between the bones and provide the power to move the skeletal system. Soft tissue is primarily made up of strong fibers called collagen. Collagen fibers in tendons are tightly arranged in parallel bundles, whereas skin collagen is loosely arranged. Injuries that cause lameness in horses that are soft tissue in origin primarily occur in the tendons and ligaments of the lower limbs.
The definition of a tendon is a fibrous cord by which muscle is attached to bone. They are divided into flexor and extensor tendons and are attached to the muscles and when contracted, either flex or extend the limb. Tendons have high tensile strength, are elastic, and are capable of absorbing and storing energy. Tendons are the “cables” that control the movement of the limb and locks the joints into position. During exercise they can stretch and retract from 1″to 3″. A ligament is a band of fibrous tissue that connects bones or cartilage. Ligaments hold joints, bones and other structures together and add stability to the limb. Ligaments are much shorter and stiffer than tendons. They also have less stretch and elasticity than tendons. Ligaments also have greater resistance to forces of torque, shearing, bending, and twisting than tendons.
Injury can occur from external trauma or from mechanical overload. Mechanical overload is when these structures are stretched beyond their normal capacity. Injury occurs when the individual fiber bundles are stretched beyond their capacity and rupture. Ruptured fibers and bundles start to fill with fluid, the beginning of the inflammatory response. Injury can occur in one catastrophic event or from repetitive low-grade fiber disruptions that add up to a large-scale inflammatory response. The correct term for a tendon injury is a strain and a ligament injury is termed a sprain. There are several factors that contribute to injury. When external trauma is the cause of the injury it can be from blunt trauma or from a restriction on the leg. An example of blunt trauma is having a leg caught in a panel. An example of a restriction is a poorly applied bandage or wrap that has slipped. Mechanical overload can be caused by working on uneven or deep surfaces, muscle fatigue from poor or inadequate training, or from long toes and long sloping pasterns.
Once we have localized the lameness to the soft tissues then an ultrasound exam is the next procedure to perform. The ultrasound exam helps to further refine the diagnosis as to the extent of the damage, the best specific treatment protocol and to determine the prognosis for full athletic recovery. Further ultrasound exams can determine the progress of healing and adjust the course of therapy to suit the degree of healing. There are other diagnostics that can be used to diagnose soft tissue injuries. Examples of are nuclear scans, CAT scans, and MRI scans. These modalities exist but they are more expensive and with limited availability compared to ultrasound.
The ultimate goal of any treatment plan is to reverse the disease process and promote healing. The first course of treatment is to reduce inflammatory response (pain, swelling, and heat). Reducing the amount of inflammation helps to prevent any further damage to the soft tissue and to hope fully reverse what damage has occurred. In this is first phase of treatment we use non-steroidal anti-inflammatory drugs (NSAIDS), Dimethylsulfoxide (DMSO), topical steroids, hypothermia (cold hosing, ice water, cold packs, and poultices), supportive wraps and rest. All of these help control the initial inflammatory response. Once the inflammatory response is controlled there are several other treatment options that can be used to further the healing of the injury and in some cases decrease dramatically the convalescent down time. The following list is just a few of the treatments that have been used in past. Tendon splitting, intra-lesional steroid injections, extra corporeal shockwave therapy, stem cell injections, controlled exercise, hyaluronic acid injections (iv or intra-lesional), and rest. No one treatment has turned out to be the preferred treatment or “gold standard”. This is due to various degrees of efficacy, the nature of the injury, the cost of the treatments or a combination of these reasons. Unfortunately, soft tissue injuries can require a long period of time to heal, even with aggressive therapies. Many times, sedatives must be used to control patients during the rest phase. So, patience on the owner/trainers part is a must for the horse to return to its former soundness, if possible.
Soft tissue injuries can occur in all disciplines of the athlete horse. These injuries can be from one incident, or from an additive effect of minor fiber disruptions. The ultrasound exam is excellent diagnostic aid and helps to gauge the healing process and response the therapy. Treatments vary with effectiveness and expense and can still be very time consuming. It is not uncommon for soft tissue injuries to require a long duration of time to have the tissue and horse completely healed.