When our dogs incur a muscle injury however slight, we typically give them a couple of days rest and then return to normal exercise. Is this approach sufficient to restore the dog’s muscle strength or are we risking re-injury?

Muscle injury involves tearing muscle fibres and disruption of vascular (circulation) or connective tissue support. The most severe muscle injury will involve a complete rupture of muscle fibres across the muscle belly. Less severe injuries may only affect a few muscle fibres and we may not see any outward signs of such an injury.

What causes muscle injuries in dogs?

Muscle injuries can be caused by a range of incidents including:

• Laceration or puncture where the skin is cut or torn and the underlying muscle damaged.

• Contusion such as when the dog contacts an object or the ground as in the case of a slip.

• Forceful muscle contraction such as when the dog props or performs sudden action.

What are the stages of muscle healing in dogs?

Several phases of healing occur regardless of the cause or severity of the injury.

Inflammation phase

Sometimes referred to as the acute stage, the inflammation phase is the first 72 hours after injury. This phase is characterised by the following:

• Accumulation of fibrin (blood clotting agent) at the site of the injury which forms a hematoma (bruising, blood clotting)

• Inflammatory immune response with production of neutrophil and macrophage (M1) to remove necrotic debris at the site of the muscle fibre rupture.

• Restoration of vascular supply to the injured muscle fibres with capillary regrowth.

• Accumulation of substances such as fibronectin that binds extracellular components including collagen and fibrin. The fibrin – fibronection network forms the scaffold for adhesion of platelets and fibroblasts – cells that hold tissue together and produce an extracellular matrix upon which the muscle fibres can regenerate during the repair phase.

Repair phase

The repair phase starts from 3 days to up to 6 weeks after injury. During this phase, there is competition for regeneration of functional muscle fibres and production of fibrous scar tissue. In the repair phase an extracellular matrix comprised of fibroblasts including collagen is produced. This matrix provides a structure upon which muscle fibres can regenerate at the injury site.

However, when there is an

• inadequate source of myoblasts (substrate for production of muscle fibres),

• inadequate vascularisation (blood flow),

• inadequate innervation (transmission of neurological signals) or

• excessive stress across the injury site that creates a gap

then excessive collagen deposition and fibroblastic activity occurs. This leads to excess fibrous scar tissue forming at the site of the muscle injury. This fibrous tissue creates a barrier to regenerated muscle fibres crossing the injury site thus preventing the muscle returning to its pre-injury tensile strength. This leads to an increased the risk of re-injury.

Remodeling phase

The remodelling phase occurs 6 – 12 weeks after the injury. During this phase, normal tissue regeneration required for muscle function occurs. The ratio of functional muscle fibres and scar tissue depends on the size of the gap as well as the level of mobilisation and stress at the injury site.

How to reduce excessive scar tissue forming?

The type of healing (ratio of regenerated muscle fibres to scar tissue) that occurs can be influenced by appropriate stress and motion at the injury site.

General recommendations for optimal muscle healing is an initial immobilisation period of 3 – 5 days post injury until the repair phase as started. After a brief period of immobilisation, controlled activity for 4 – 6 weeks, depending on the severity of the injury is advised. This protocol is recommended to accelerate the generation of collagen type 1 fibre and restore muscle strength.

During the remodelling phase, applying appropriate stresses can help align regenerated muscle fibres parallel to the line of action. Without mobilisation, the muscle fibres will orient inappropriately across the lines of stress and tension. If muscle fibres regenerate in this fashion, it reduces the muscle’s strength and prolongs the remodelling phase.

Mobilisation during this phase also helps restore vascularity to the injury site by promoting capillary regrowth around the borders of the injury.

During the remodelling phase, excessive stress can widen the injury gap and cause greater formation of fibrous tissues.

In a study of rats with an induced partial muscle tear to the gastrocnemius muscle, it was found that

• In the group of rats that received no treatment post injury, the muscle did not have significant tensile strength for at least one week post-injury.

• In the group that was immobilised for five days before returning to normal activity, they showed accelerated growth of Type 1 collagen which allowed the muscle to regain sufficient tensile strength to reduce the risk of re-injury when the rats were allowed to return to normal activity. In this group, seven days post injury, the rats showed no signs of re-rupture in the injured muscle.

• In the rats that were immobilised for only two days and then recommenced activity, there were signs of fibrin clot containing fibronectin still present after seven days post injury which suggests that the muscle was not strong enough to withstand mechanical forces of returning to full exercise. In this group, three weeks after the initial injury, a fatty necrosis in the centre of the injury site was present. The fatty necrosis was surrounded by loose connective tissue and encased in dense collagenous matrix which suggests a re-rupture of the muscle had occurred leading to more scar tissue forming. There was also evidence of poor penetration of regenerated muscle fibres into the injury site.

Conclusions from this one study are that a longer period of immobilisation before returning to normal activity improves the penetration and alignment of regenerated muscle fibres and resorption of connective scar tissue.

How to avoid the side effects of prolonged rest period after an injury?

While immobilisation post muscle strain seems to be beneficial for restoring a dog’s muscle function, a prolonged period of immobilisation can result in muscle atrophy (loss of muscle tone and strength), loss of flexibility and co-ordination or muscle contracture. Here are some tips for addressing the side effects of a rest period.

Massage treatments

Daily massage treatments during the repair stage in rats with muscle injury has been shown to enhance the body’s immune response to aid muscle healing. Specifically, following massage, a significant increase in the circulating immune cells namely, macrophages (M1 – responsible for removing debris from initial injury site) and (M2 – aids in repair and restoration) were observed. After four days of daily massage treatments, the rats showed an enhanced recovery of muscle strength, recovery of passive mechanical properties such as the relaxation response, and diminished infiltration of immune cells (leukocytes and monocytes) compared to a control group.

Massage is also effective in relieving muscle tension to prevent muscle contractures during the period of immobilisation.

Passive range of motion and stretching

Passive range of motion exercises involve a therapist gently moving the dog’s immobilised limb through its normal range of motion without the dog actively engaging the muscles. Moving the dogs’ joint through the range of motion promotes cartilage regeneration, reduces the likelihood of adhesions forming between the fascia and muscles, and stimulate circulation to reduce oedemas (blood clotting and bruising).

When passive range of motion exercises are performed daily post injury it can help avoid the onset of muscle contracture and keep the joints mobilised. A study of dogs who had undergone surgery for ruptured cranial cruciate ligaments showed that those dogs that received a therapist lead rehabilitation programme (compared to home exercises) comprising massage, passive range of motion exercises, and weight bearing exercises had restored normal range of stifle motion by the end of the study. In the dogs that received the rehabilitation programme, stifle flexion and extension was significantly greater at week 3 and 6 post surgery than the home exercise group.

Please leave a comment to share your tips for rehabilitating a dog after a muscle strain. Full Stride provides canine massage and exercise therapy to help maintain dog’s mobility and aid their rehabilitation after an injury. For more information please contact me or message me via the Full Stride Facebook page.

You may also be interested in these related articles:
https://www.fullstride.com.au/blog/rehabilitation-nutrition-for-dogs-recovering-from-muscle-injury
http://www.fullstride.com.au/blog/passive-range-of-motion-exercises-for-dogs

Until next time, enjoy your dogs.

Sources:

Lehto, M., Duance, V. C., & Restall, D. (1985). Collagen and fibronectin in a healing skeletal muscle injury. An immunohistological study of the effects of physical activity on the repair of injured gastrocnemius muscle in the rat. Bone & Joint Journal, 67(5), 820-828.

Marcellin-Little, D. J., & Levine, D. (2015). Principles and application of range of motion and stretching in companion animals. Veterinary Clinics: Small Animal Practice, 45(1), 57-72.

Millis, D.L, Levine, D & Taylor R.A (ed) 2004 Canine Rehabilitation and Physical Therapy, Elsevier Inc, Missouri USA

Monk, M.L, Preston, C.A & McGowan, C.M 2006 “Effects of early intensive postoperative physiotherapy on limb function after tibial plateau leveling osteotomy in dogs with deficiency of the cranial cruciate ligament” Australian Journal of Veterinary Research, Vol 67, No. 3

Waters-Banker, Christine (2013) “Immunomodulatory effects of massage in skeletal muscle”, Theses and Dissertations – Rehabilitation Sciences, Paper 18