Koper Equine

Takeaways

• Fibrotic myopathy is a mechanical lameness that occurs when scar tissue forms in the muscle.

• It most commonly affects the hamstring muscles in the upper part of the hind limb.

• Involves thickening and scarring of connective tissue that can progressively worsen.

• Scar tissue does not behave the same way as normal muscle fibers. It is inelastic and can restrict normal function

• Affected horses display a characteristic gait abnormality.

• Fibrotic myopathy can be caused by trauma, hyperextension, repetitive strain, infection, or repeated IM injections.

• The prognosis for affected horses is generally good, with many returning to full work in about a month.

What is fibrotic myopathy?

Fibrotic myopathy is a type of mechanical lameness that occurs when abnormal scar (fibrotic) tissue forms in the muscle. Unlike normal muscle fibers, scar tissue is inelastic and can restrict the muscle’s natural elasticity, altering its function. This condition can result from various causes, including trauma (such as getting kicked, slipping and falling, catching a foot in a fence, or leaning on the butt bar of a trailer or stocks), hyperextension, repetitive strain (commonly seen in reining, cutting, roping horses and horses involved in activities that require abrupt turns and sliding stops), infection, or repeated intramuscular injections. There is also a congenital form of the disease present at birth.

Fibrotic myopathy most commonly affects the hamstring muscles in the upper part of the hind limb, particularly the semitendinosus, semimembranosus and biceps femoris muscles.

Typically, it affects one leg at a time and involves the thickening and scarring of connective tissue, which can progressively worsen over time. The muscle fibers bond together and eventually harden. Once healed this condition is not usually associated with pain, although it can limit or prohibit performance.

How is fibrotic myopathy diagnosed?

Diagnosis is based on clinical signs and patient history. Affected horses exhibit a distinctive gait characterized by a jerky forward stride, with the foot pulled back slightly before being placed on the ground. In some cases, the hardening of the muscles can be felt. X-rays and ultrasound imaging can help determine the location and extent of muscle damage.

Signs of fibrotic myopathy include

commonly observed signs

• Sudden onset of warm, painful muscles.
• Hind hoof slapping down at the front of the stride
• Short-strided movement in one or both hind limbs.
• Chronic hind limb lameness
• Choppy or short gait
• Visible dents or changes in the rear muscles.
• Resistance to raising, lifting, or bending a limb
• Hesitancy to walk on hard surfaces.
• Chronic cases exhibit hardened areas of muscle

less commonly observed

• Not Engaging or Collecting, Lacks Impulsion
• High-Stepping Gait of One or Both Hind Limbs

How should fibrotic myopathy be addressed?

The initial tearing of the hamstring causes lameness, reluctance to move the limb, and pain and swelling in the rear of the limb. Rest is crucial during the early stages to alleviate pain and limit damage. In milder cases, massage and movement therapy soon after injury may be beneficial.

Fibrotic myopathy can be managed with a combination of treatments, including rest, cold therapy, therapeutic ultrasound, massage therapy, stretching, shockwave therapy, laser therapy, red light therapy, water treadmill therapy, cavaletti exercises, and passive range-of-motion exercises. Within 30-60 days post-injury, enough scarring typically develops to cause the characteristic gait abnormality. By 90 days, the scar is usually fully mature.

For severe symptoms, surgery may be necessary to remove the scar tissue, cut the ligament attached at the stifle or remove ossified tissue. However, scarring can also occur at the surgery site, so this approach does not always restore full range of motion in the affected limb(s). While most horses show improvement after surgery, only about half achieve a full recovery. The procedure is often performed on a standing horse.

Questions to Ask Your Vet

• Is my horse lame due to pain or is this a mechanical problem?
• Is this a short-term issue or a chronic condition?
• Will this condition affect my horse’s ability to do his job?
• Would surgery help this condition?
• How can I best manage his condition going forward?

How can fibrotic myopathy be prevented?

To reduce the likelihood of fibrotic myopathy (and other injuries), ensure good footing, proper warm-ups, and careful conditioning. Avoid sudden hard stops and turns, limit intramuscular injections, and minimize trauma to the hamstring muscles.

Regular massage therapy can help maintain muscle and connective tissue health, and improve exercise recovery, reducing the risk of injury. Think of it as proactive soft tissue care and maintenance.

For a horse with a mild case of fibrotic myopathy, massage can help maintain muscle condition, allowing him to continue an active and functional lifestyle. For a horse with a more severe case, massage can help minimize the impact of compensation patterns caused by the goose-stepping gait, reducing additional wear and tear and alleviating muscle tension.

Prognosis and Relevant Factors

The prognosis for fibrotic myopathy varies depending on the severity of the injury, gait deficit, and scarring, as well as the presence of ongoing pain. Mild, chronic cases often allow horses to perform normally as long as they are careful to avoid re-injury.

For horses not involved in riding, the gait deficit is usually manageable.

Severe cases in riding and performance horses will significantly impact performance and may require a more aggressive approach to recovery.

Summary

Fibrotic myopathy is a mechanical lameness caused by scarring in the hamstring muscles, resulting in a distinctive gait. Depending upon the severity of the gait alteration, and the horse’s use, the condition may or may not be performance-limiting for the horse. While the condition can be managed with massage and movement therapy and /or surgery, preventing re-injury and ensuring proper care are essential for maintaining a horse’s performance and well-being.

Additional Notes

Ossifying myopathy is a related but distinct condition.

• Description: This is a more severe form of fibrotic myopathy where the scar tissue not only becomes fibrous but also undergoes ossification, meaning it turns into bone. This further restricts muscle movement.
• Symptoms: Similar to fibrotic myopathy but often more pronounced due to the added rigidity from the bone formation within the muscle. This can severely impair movement and lead to significant gait abnormalities.
• Cause: Ossifying myopathy can occur as a progression from fibrotic myopathy or independently, often due to severe or repeated trauma to the muscle.

Key Differences

Tissue Changes: In fibrotic myopathy, the muscle tissue is replaced by fibrous scar tissue. In ossifying myopathy, this scar tissue additionally undergoes ossification, forming bone within the muscle.

Severity: Ossifying myopathy is generally more severe due to the presence of bone, which is less flexible than fibrous tissue and more significantly restricts muscle movement.

Management

Fibrotic Myopathy: Management focuses on massage therapy, stretching, movement therapy, and sometimes surgical removal of scar tissue to improve mobility.

Ossifying Myopathy: This condition may require more aggressive interventions, including surgery to remove the ossified tissue, as it can cause more severe mobility issues.

Ossifying myopathy represents a progression or more severe manifestation of myopathy where ossification occurs within the fibrous tissue.