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Canine and feline musculoskeletal system

The musculoskeletal system of dogs and cats is a complex, multi-part, multi-functioning system that gives animals their shape, size, health, flexibility and speed. It can be fed and protected to turn a dog or cat into a biological machine… or it can become painfully dysfunctional, affecting their health and quality of life.

The canine and feline musculoskeletal system and all their other bodily systems work together symbiotically to build and balance the animal’s health. In this article, we’ll explore the components of the musculoskeletal system, its various functions, and what happens when things go wrong with bones, joints, muscles, cartilage, tendons and ligaments. We’ll also give you some tips on how to protect and feed your pet’s musculoskeletal system from young to old.

Components of the musculoskeletal system

The canine and feline musculoskeletal system literally forms ‘the bones’ of your dog or cat, giving them their size, structure and ability to move. The musculoskeletal system consists not only of the muscles (musculo­-) and bones (-skeletal), but also the components that hold them together and give them their mobility.

Bones

The bones are the hard framework that give the dog or cat’s body its size and stature. The bones contain bone marrow, where red and white blood cells are made and where bone minerals (calcium and phosphorus) are stored and supplied when the body requires them. Bone marrow plays a vital role in the body’s lymphatic system and immune function.

Muscles

There are different kinds of muscles in the body: skeletal muscle, smooth muscle and cardiac muscle (the heart). In the musculoskeletal system, skeletal muscle is attached to the bones, and it provides pets with the power of posture and movement. Skeletal muscle is associated with voluntary movement like walking, sitting, jumping. Smooth muscle is associated with involuntary movement and is responsible for processes like digestion (moving food and liquids along the gastrointestinal tract), blood flow (moving blood through the arteries and veins), urination, dilation and constriction of the iris in the eye (among others).

Joints

Joints consist of bones, cartilage and ligaments. The joint complex connects bones together, either in a hinged manner such as at knees and ankles (which allows for bending and straightening) or in a ball-and-socket manner such as in the hips and shoulders (which allows for rotation of the limb).

Cartilage

Cartilage is the strong, spongey protective covering on the ends of the bones of every joint, which prevents fiction between bones when the joint is in use.

Tendons vs ligaments

  • Tendons are the strong, collagen-based bands of connective tissue that attach muscles to bones. They are tough, sheathed cords that allow movement, but the tendons themselves do not stretch.
  • Ligaments are also connective tissue made of strong collagen fibres. These are bands of tissue that connect the bones that make up joints, offering support and stabilisation of each joint.

The functions of the musculoskeletal system

The musculoskeletal system has a number of important functions in the body, including:

  • Support: It is the frame upon which the whole body of the animal is built. It gives the body structure, shape and size.
  • Motion: The musculoskeletal system allows the body to move. The brain instructs the muscles to move, and the muscles – connected to the bones of the musculoskeletal system – generate movement.
  • Protection: The musculoskeletal system provides a structure of protection for the vital organs inside the animal’s body.
  • Heat generation: Muscle contraction generates heat when the animal is in motion, but also through shivering, which is the involuntary contraction of skeletal muscles.
  • Immunity: Bones contain bone marrow, where red and white blood cells are made and supplied to the body when the immune system responds to invading pathogens.
  • Mineral storage and supply: Bones comprise calcium, phosphorus and other minerals, acting as a reservoir of these minerals, which the body can use when its systems and processes require them. The body’s bones are constantly being ‘remodelled’ – a process in which old bone tissue is replaced by new bone tissue – in order to stay dense, healthy and strong.

How does the musculoskeletal system work?

The musculoskeletal system of dogs and cats is made up of more than 300 bones, 300 joints and over 600 muscles, which work together and with other systems in pets’ bodies to keep them in balance. In this example, we’ll demonstrate this symbiosis between body systems: When a cat needs to escape danger, her sympathetic nervous system is triggered to prepare her for a fight, flight or freeze response to the threat. In flight, she will use her major skeletal muscles to run away and climb up a tree.

Since she has exerted energy and needs oxygen to bring her body back into balance, her cardiovascular system will accommodate her needs by increasing her heartrate and her respiratory system will work hard to circulate enough oxygen around her body and carry the carbon dioxide waste products back to her lungs to be exhaled.

When the threat is over, the cat’s parasympathetic nervous system will calm her down again, her digestive system will return to normal function and she will again use her muscles to descend from the tree. She takes a big leap from the middle of the tree and lands comfortably on the grass – her landing cushioned by healthy skeletal muscles, flexible joints and strong bones and cartilage absorbing the impact. Her vulnerable internal organs are protected by the structure of her musculoskeletal system. As she saunters back into the house, the dog is using his strong chest and back muscles, along with his shoulder, stifle (knee) and hock (ankle) joints to dig an exciting hole in the backyard because he has too much pent-up energy and his skeletal muscles are longing to be exercised!

Problems in the canine and feline musculoskeletal system

As one of the largest systems in the body, the canine and feline musculoskeletal system is also subject to many disorders and problems that can severely impact their movement and quality of life. Problems in other areas of the body can also manifest as symptoms in the musculoskeletal system, for example: erratic movement can be caused by neurological issues; tremors can indicate poisoning; muscle diseases can be congenital, toxic, infectious or caused by injury; hormonal and metabolic abnormalities; bone deformities can be caused by poor nutrition or a gastrointestinal issue that doesn’t allow for optimal nutrient absorption; and birth defects can affect the bones and joints in a severe way.

Let’s take a look at just some of the bone, joint, muscle, cartilage, ligament and tendon problems that can arise and cause abnormalities in the musculoskeletal system.

Bone problems

Dogs and cats can be born with congenital conditions that affect their bones. Some of these are:

  • Osteogenesis imperfecta – fragile bones that fracture easily.
  • Polydactyly, ectrodactyly or syndactyly – extra toes, split toes or fused toes, respectively.
  • Angular limb deformities – when a puppy or kitten’s growth plates are injured or they are born with a predisposition to irregular growth, their front legs can develop irregularly, causing them to twist. They can take on a particularly bow-legged stance; while bending their elbows is painful and it can even result in lameness. Corrective surgery may be necessary.
  • Hypertrophic osteodystrophy – bone growth disorder in large or giant breed puppies, which can cause deformity in extreme cases.
  • Scottish Fold osteodystrophy – genetic bone deformities in Scottish Fold cats, characterised by bony growths that cause deformities, particularly in the spine and feet of this breed.
  • Osteochondromatosis – a fairly rare disorder in young dogs and cats, characterised by the formation of bony growths on the long bones (femur, tibia, humerus, radius and ulna), spine and rib bones. Sometimes the affected animals show no symptoms, but if pain and lameness affect them, the growths can be surgically removed.
  • Panosteitis – caused when large and giant breed puppies grow too much too quickly and their bones become inflamed and painful. It only lasts during the puppies’ growth spurt, so treatment is aimed at pain relief, and the vet may recommend dietary changes.
  • Osteomyelitis – inflammation in the bones can be caused by bacterial and/or fungal infection, exacerbated by a lack of blood flow to the bones, or trauma, and infection spreading through the bloodstream. The vet will prescribe antibiotics and offer supportive treatment if there is tissue death and secondary infection. If the condition doesn’t heal or causes complications, it may be necessary to amputate the affected limb.
  • Nutritional deficiency – osteopathies can also be caused by a lack of essential nutrients for bone growth. So if a kitten or puppy does not get enough calcium and/or vitamin D, or they get too much vitamin A, it can damage their kidneys and also cause their bones to grow abnormally. Bone diseases caused by nutritional imbalance include rickets, rubber jaw syndrome, hypervitaminosis A and nutritional secondary hyperparathyroidism.
  • Fractures – usually caused by traumatic injury such as car accidents, falling, or fights. Fractures range in severity from simple to compound, fissure, incomplete and complicated fractures, and the extent of the damage can be exacerbated by any existing weakness in the bone.
  • Bone tumours – osteosarcoma is one of the most common bone tumours, and is mostly found in the long bones. Tumours can be benign or malignant and, depending on the age and health of the animal, can be treated by surgical removal, chemotherapy and/or radiation.

Muscle problems

Dogs and cats can experience problems and diseases with their muscles (myopathy) due to congenital issues, nutritional deficiencies, toxicity, metabolic syndromes, inflammation due to infection or autoimmune diseases (myositis), and muscle injury.

  • Steatitis – also called ‘yellow fat disease’, this disease in cats is characterised by fatty tissue that becomes inflamed. It is thought to be caused by a combination of excess unsaturated fatty acids and a deficiency in vitamin E and antioxidants. It is mostly seen in young, obese cats who subsist on a diet predominantly of fish. Their diets must be changed to include more antioxidants and less fat, and if they experience pain when touched, the vet can prescribe painkillers until it resolves.
  • Labrador retriever myopathy and Great Dane myopathy – both of these muscle-wasting diseases are limited to the specific breeds, although the cause it not known. Wasting, stunted growth, weakness and post-exercise tremors characterise the disease during puppyhood, but then the dog’s health usually stabilises upon maturity. The veterinary treatment is supportive until the symptoms reduce.
  • Fibrotic myopathy – progressive degeneration of the thigh muscles.
  • Myositis ossificans – bony growths occur in the muscle and connective tissue and can be related to Von Willebrand’s disease in Doberman pinschers.
  • Hypokalaemic polymyopathy – occurs when a deficiency in potassium causes muscle weakness in cats, resulting in abnormal posture, abnormal gait, overall weakness, muscle pain and reduced appetite.
  • Polymyositis and masticatory myositis – inflammatory muscle disorders in dogs that affect the whole body or mainly the head and jaw, respectively, which are thought to be caused by an auto-immune response. Treatment is with corticosteroids and immune suppressants.
  • Malignant hyperthermia – the metabolism increases suddenly and abnormally, usually due to stress or anaesthetic gas. Very muscled dogs (think greyhounds) are especially susceptible to the condition, which can cause rapid heart rate, muscle stiffness, fever and heart failure. It’s a medical emergency and needs immediate treatment and withdrawing of anaesthesia.
  • Rhabdomyolysis – usually occurs in working and racing dogs after extreme exertion. It is caused by a lack of blood flow (and oxygen and nutrient supply) to and from the muscles, skeletal muscle breakdown, dehydration, and therefore too much potassium and myoglobin in the bloodstream. Pain, inflammation, fast breathing, stiffness and even kidney failure may occur.

Cartilage and joint problems

Most dogs and cats will experience joint problems at some stage in their lives – very often due to wear and tear in old age. There are also some genetic and development issues that may arise.

  • Osteoarthritis – also called degenerative joint disease, this is one of the most common joint issues in pets. The supportive cartilage between joints wears away or degenerates, causing friction between the bones of the joints, and resulting in inflammation and pain. Can be managed with supplements and pain medication, although surgery is recommended in extreme cases.
  • Other types of arthritis – dogs and cats can also get septic arthritis (from a bacterial infection that spreads in the blood), immune-mediated arthritis (when the body attacks its own joints, causing inflammation), and cancerous arthritis (caused by a synovial cell sarcoma).
  • Hip and elbow dysplasia – occurs when there is abnormal development of the ball-and-socket joints of the hips, or of the complex joint of the elbow. Changes in gait and signs of pain and lameness may present. Both conditions are diagnosed with X-rays and joint laxity (range of motion) tests.
  • Osteochondrosis – occurs when a young dog is growing rapidly and the developing cartilage separates from the ends of the bone. It is suspended in the joint cavity, where it causes pain and inflammation, and inhibits the proper development of the joint. Surgery is necessary to remove cartilage fragments from the joint cavity as well as remove any loose cartilage flaps, and encourage new cartilage to form.
  • Legg-Calvé-Perthes Disease – may be congenital and is caused by a lack of blood supply to the head of the femur, which affects the hip joint. Treatment includes the surgical removal of the necrotising bone (ostectomy) and then physical therapy until the joint has stabilised.
  • Patellar luxation – also called slipped stifles or knee displacement, it occurs in dogs and cats. Luxating patella is caused when the patellar ligament (which connects the femur to the tibia and stabilises the kneecap), ‘pops’ out of the trochlear groove while the animal is walking or running. There are various grades of severity of patellar luxation, with only grades 3 and 4 needing potential surgical repair.
  • Joint trauma – aside from congenital defects and arthritis, dogs and cats can also experience joint trauma, in which they injure themselves while exercising or playing, jumping down from a vehicle or furniture, in an accident, fight, or due to wear and tear over time. Traumatic joint injuries can include fractures to hips, knees, elbows and ankles, dislocations of joints, or the common cranial cruciate ligament (CCL) tear found in giant breed dogs, specifically the Newfoundland. Hyperextension of the forelimbs when landing can tear the palmar carpal ligaments of the wrist and collapse the joint, which needs to be surgically repaired, but usually prognosis is good.

Diagnosing and treating problems in the musculoskeletal system

With so many possible areas of injury, disease and disorder, the musculoskeletal system presents veterinarians with a potentially difficult job in diagnosing a specific disorder located in the bones, joints, muscles, cartilage and ligaments of dogs and cats. A common examination the vet will do is the lameness examination, which includes taking the pet’s history, a physical examination, and noting any signs of fever, infection, swelling, etc. They will also look for limping, lop-sidedness, how the animal lies down or gets up, and what their gait reveals about the health of their limbs.

Is there a crackling sound from their joints? Do they have full range of motion? Is there any muscle wasting – especially in their hind legs? Do they protect a limb or are unable to bear weight on it? There are specific symptoms associated with specific musculoskeletal problems, which the vet will look for in order to confirm a diagnosis.

Part of the lameness examination will include X-rays and other imaging tests, if needed. These will reveal cartilage fragments, joint disorders, swelling, fractures and other problems with pets’ bones, muscles, joints and ligaments. Imaging can reveal traumatic injury, fluid in the joints, inflammation, tears, and other telltale signs.

Once the vet has confirmed a diagnosis, they will suggest the best form of treatment for the animal. If the pet’s musculoskeletal disease or injury is severe, the vet will discuss the surgical procedure required to correct the issue, as well as the healing process and how to ensure the pet recovers in the best way possible. Very often, bone and joint surgeries require longer periods of rest as well as pain medication and physical therapy to restore the use of the limb. It is vital that pet owners heed the vet’s recommendation and ensure their pets are given enough rest and isolation time, so that they do not reinjure themselves.

How to support your pet’s healthy musculoskeletal system

Some bone, muscle and joint conditions may be congenital – pets are born with them, so there is not much pet owners can do to avoid the condition. However, many problems with your pet’s musculoskeletal system can be mitigated with a conscious and careful approach to your pet’s health.

Nutrition

Your pet’s food is always the cornerstone to their good health, so make sure that you are feeding them the quality and amount of food that’s ideal for their individual health needs. If you have a large breed puppy, make sure they are not overfed during their speedy growth in the first five to 12 months of their life. Weight gain that happens too fast can place too much stress on their bones and joints. Also make sure that the nutrients they get are appropriate for their breed and age – do not over-supply protein, calcium and phosphorus, which could cause malformation of the skeleton and have a knock-on effect on the development of their joints. Kittens also need a balanced diet as they are growing rapidly, for the correct formation of their skeleton and muscles.

Healthy weight

Your pet’s musculoskeletal system is designed to carry their optimal healthy bodyweight. Anything more than that and much greater forces of pressure are placed on their bones and joints. This can lead to pain in the joints and spine, and a faster rate of wear and tear in their joints, exacerbating degenerative joint disease. Overweight pets are not happy pets because they struggle to express their natural behaviours when their limbs are in pain. If your pet has joint pain and they are overweight, ask the vet to recommend a weight management diet to reduce their weight, which will also help to relieve their pain.  

Physical activity

It is important for growing pets to get exercise to develop their lean muscle, strength and balance, and to exert their puppy and kitten energy, develop co-ordination, and just be happy and healthy.  However, growing puppies and kittens must not be over-exercised while their bones and joints are still forming, and they should preferably not be exercised on slippery floors. A coarse, uneven surface (like grass or sand) is best for exercising on, allowing for stable development of the joints and lowering the risk of slips and falls. Daily walks at an appropriate speed and distance on the pavement or a gravel road are ideal to develop a puppy’s muscles without compromising their bone and joint health. Ask the vet to recommend the right type and amount of exercise your young pet should be getting while they are rapidly growing.

Adult pets’ physical health should also be protected. If your giant breed dog has a high risk for cranial cruciate ligament rupture, don’t allow them to jump up or down from your car or furniture. Pet stairs can help to protect their ligaments. Also make sure they engage in activity and exercise where they are not making sudden stops and turns (such as games of catch or frisbee). Keep them fit and healthy with daily exercise, as strong thigh muscles help to reduce the load on their joints. Also maintain your dog’s optimal weight in order to not place too much load on the cruciate ligaments.

Nutritional supplements

If your pet has a risk of developing osteoarthritis or if they have been diagnosed with a bone, joint or muscle condition, a nutritional supplement can feed their body with the additional nutrients, antioxidants, vitamins and omega fatty acids they need. The onset of osteoarthritis can be mitigated or slowed by introducing a nutritional supplement containing glucosamine, chondroitin, green-lipped mussel extract and MSM, the combination of which reduces cartilage deterioration, inflammation and pain.

If your pet needs additional calcium or other minerals, these can also be supplemented, but only under the vet’s supervision. Excessive vitamins and minerals can have other health consequences, so only give your pet the supplements recommended by the vet.

Pet bedding and rest

Protect your pets’ musculoskeletal system with a high-quality, supportive pet bed, preferably with a memory foam mattress. The memory foam takes the form of your pet’s resting body and also retains and radiates their body heat, which will keep joints warm and supported.

Regular vet check-ups

It is vitally important to take your pets to the vet at least once a year for a check-up. This gives the vet the opportunity to fully examine their physical condition, and detect potential problems – especially if they are at risk of developing musculoskeletal disorders. If these health concerns are addressed early, it can save your pets from suffering unnecessary pain, medication or even surgical procedures to repair what could have been prevented in the first place.

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