Common pathological conditions of the Musculoskeletal System

Muscular System Disorders

Myopathies - Diseases that primarily cause damage to muscles or muscle tissue. They may be present at birth or occur due to nutritional imbalances, injury or ingestion of a poison. They may be inflammatory or non in flammatory

  • Inflammatory myopathies: includes infectious or immune-mediated disease
  • Non-inflammatory: include congenital conditions such as floppy labrador syndrome and systemic disease with muscle function pathology. Common symptoms include muscle pain, weakness, atrophy, loss of function with lameness coupled with typical symptoms associated with inflammation or infection as appropriate

Rhabdomyolysis- Muscle disorder of racing greyhounds, working dogs and horses appears to be triggered by an inadequate supply of blood to the muscle after exercise, causing kidney disease and destruction of muscle cells. Signs in dogs include muscle pain and swelling that becomes noticeable 24-72 hours after racing or overuse. In severe cases, stiffness, deep or fast breathing, collapse, and kidney failure may occur. Urine tests are used to confirm the diagnosis. Treatment includes supportive care such as fluids, bicarbonate, body cooling, rest and muscle relaxants.
In horses, signs are usually seen after the horse begins to exercise. Excessive sweating, tachypnoea, tachycardia, reluctance or refusal to move and firm painful hindquarters.

Muscular or tendon trauma - Injury/trauma of the muscles and the associated tendons can cause many forms of myopathy e.g.
Abnormal contracture of the shoulder muscle - usually occurs after trauma in hunting or working dogs. Signs include noticeable lameness, pain and swelling in the shoulder region
Inflammation of the biceps brachii tendon and its covering - can occur in one or both forelimbs. It usually affects mature, large dogs. The injury may be direct, indirect or due to overuse or migration of bone and cartilage fragments
Achilles tendon disruption (dropped hock) - most often afflicts fully grown working and athletic dogs, and is usually the result of trauma. The tendon can be partially or completely ruptured or torn away from the bone. Signs include severe lameness that keeps the animal from putting weight on its leg, overextension of the tarsus, a stance in which the heel touches the ground. Swelling, pain and torn or thickened tendons may be seen

Muscle tumours - tumours that originate in the skeletal muscle can be benign or malignant. Malignant tumours can spread and invade nearby muscle and other parts of the body

Joint disorders

Luxating patella - The knee cap comes out of the groove and slides one side to the other causing the leg to lock up and the leg becomes difficult and painful to bend

Bone disorders

Rickets - rare disease of young, growing animals that causes soft and deformed bones. It is commonly caused by insufficient phosphorus or vitamin D in the diet. Signs include bone pain, swelling, bowed limbs and fractured.

Ruptures and hernias - Involve failure of the muscles that line a body cavity allowing organ(s) to protrude outside of the body cavity. Hernias involve natural openings which either fail to close during normal development or which become weakened or enlarged. As such, they are normally still enclosed by endothelial linings or the integument examples include inguinal hernia, umbilical hernia, pernieal hernia, diaphragmatic hernia/rupture, abdominal wall rupture

Elbow dysplasia

Hip dysplasia - occurs when the ball and socket joint of the hip does not 'fit together properly' resulting in rubbing, which damages the surface of the joint leading to pain and arthritis

Arthritis can be categorised as the following:

  • Immune mediated: Includes polyarthritis, rheumatoid arthritis and lupus erythematosus. It usually involves multiple joints and is associated with pyrexia and other signs of systemic disease. Treatment requires immunosuppression therapy
  • Inflammatory: is seen as joint pain and usually follows surgery or medication. Can be infectious or non-infectious
  • Degenerative: Has a gradual onset. Crepitus is felt on extension/flexion of the joint and the condition generally improves with exercise. Treatment is with NSAIDs, diet and glucosamine supplementation. Weight reduction will help reduce pressure on the joints

Osteomalacia - Develops similar to rickets in mature bones. Because bones mature at different rates, both osteomalacia and rickets can develop in the same animal

Mataphyseal osteopathy - Associated with abnormal metaphyseal bone formation, usually in the distal long bones of large breed growing dogs. Signs include lameness, pyrexia, depression, anorexia and swollen and painful growth plates

Hyperparathyroidism:
Primary hyperparathyroidism - PTH-secreting tumour of the parathyroid gland; in most cases only one gland has a tumour and malignant tumours are uncommon
Secondary hyperparathyroidism - is related to malnutrition - nutritional deficiency of calcium and vitamin D or nutritional excess of phosphorus. The calcium:phosphorus imbalance triggers calcium from bone leading to bone mass weakness which cause pain, lameness, reluctance to stand or walk. Also related to long-term CKD

Osteomyelitis: most commonly caused by infection of the bone. In addition to the usual symptoms associated with infection as well as pain, swelling, and loss of function

Panosteitis: Causes bone inflammation, primarily of long bones in young, rapidly growing dogs of large and giant breeds the animal will be lame and feverish have no appetite and show signs of pain when the affected bones are handled. It appears spontaneously and only lasts as long as the dog is growing

Neoplasia: osteosarcomas usually affect the long bones. There may be minimal swelling but the area may be painful and lame. Pathological fractures may occur and amputation is required. Fibrosarcomas affect the bones of the axial skeleton including the skull and mandible

Bone fractures: May occur following trauma or as a result of weakening of the bone due to neoplasia, dietary or hormone deficiencies. Can involve single or multiple breaks in the bone and may be open or closed. Open fractures have a wound break in the skin.

Slipped disc/intervertebral disc herniation: back problems are more common in dogs than cats - a slipped disc is the most common cause of paralysis in the dog. A slipped disc can happen in two ways

  1. Rupture - of a healthy disc can be caused by trauma such as RTA or falling from a height
  2. Degeneration - result of the a premature ageing process which causes thickening of the dorsal part of the annulus fibrosis which presses up on the spinal cord