1. The Musculoskeletal System
VETERINARY PHYSIOLOGY

2. Dog Skeleton

3. Horse Skeleton

4. 5 Functions of the Skeleton
 Support
 Protection
 Attachment
 Heamopoiesis
 Act as a reservoir

5. Arthritis – What is it?
Arthritis is a condition that affects the synovial joint: broken down it means joint (arth) inflammation (itis). It is the
most common form of lameness in dogs – 1 in 5 dogs are affected (20% of dogs over 1).
There are different types of arthritis…
 Degenerative (DJD)
 Septic
 Neoplastic
 Immune mediated
 Haemoarthritis
 Polyarthritis
 Traumatic
 Metabolic

6. Degenerative Arthritis (DJD)
DJD can be further divided into primary and secondary.
Osteoarthritis is a form of DJD and falls into the secondary division – that is, it is usually the result of a primary
problem such as hip dysplasia, trauma or even as the animal ages!
However, despite the name, it is classed as a non-inflammatory disease.
What symptoms will the owner notice?
 Stiffness after rest (SAR)
 Panting in pain
 Lameness
 Swelling in the joint area

7. Osteoarthritis – Diagnosing It
A physical exam can determine whether the patient is suffering from osteoarthritis and in more severe cases,
radiography may be carried out to rule out a more serious problem.
The vet may ask the owner to take the animal on a short walk so signs of stiffness and abnormal gaits can be noted.
Manipulation is also key as this allows for any signs of heat, swelling and crepitus to be felt. But even before all of
this takes place, if an animal has an unkempt appearance, it is likely because they are in too much pain to groom!

8. Pathophysiology of Arthritis
Chondrocytes become damaged
Collagen degradation, altering the
synthesis of new collagen
Nitric acid is released
Breaks down cartilage
Synovial membrane inflames
Synovial fluid decreases in viscosity so
chondrocytes get less oxygen and
nutrients
Bone becomes sclerotic and as this
process continues, the cartilage tears
Fibrosis of the joint leading to
reduced function & ankylosis

9. Risk Factors
 Working animals
 Athletic animals
 Obese animals
 Pre-exisiting conditions with affect collagen – Cushing’s disease, diabetes, hyperthyroidism
 Prolonged use of steroids
 Trauma
 Developmental disorders – elbow and hip dysplasia, osteochondrodysplasia

10. Treatment of Osteoarthritis
 Palliative treatment
 Pain relief, e.g. NSAIDs
 Weight and dietary management
 Hydrotherapy
 Controlled walking
 Laser therapy

11. Cruciate Rupture
It is usually the cranial cruciate ligament (CrCL) which ruptures. It occurs
when there is a sudden rotation of the stifle joint resulting in the cruciates
winding around each other, rubbing against the lateral femoral condyle. It
leads to hyperextension of the limb and 10/10 lameness – 25-30% of stifle
injuries in dogs are CrCL.
Why doesn’t the caudal cruciate rupture?
It is rare for the caudal ligament to rupture because it is protected by other
structures. If it does, it would be the result of severe trauma or dislocation.
To diagnose, the vet will usually radiograph the patient but can also perform
a cranial drawer which will be positive if the ligament is ruptured:
https://www.youtube.com/watch?v=yoY_iG4a-1Y

12. Bone Formation – Endochondral
Ossification
Embryonic
connective tissue
forms cartilage
template
Central area
dehydrates
Cartilage cells
degenerate (engulf,
die, calcify)
Primary ossification
centre appears in
diaphysis
Blood vessels bring
osteoblasts
The collar of the
bone is formed
around the shaft
within the
perichondrium
The periosteum
surrounds the collar
Bone collar is
supportive, creates a
tubular shaft for
cartilage
Blood vessels from
periosteum
penetrate the collar
so osteoblasts enter
the cartilage model
Osteoblasts line up
along diaphysis and
secrete new bone
Calcified cartilage is
absorbed
Secondary stage of
ossification begins
in the epiphysis

13. Growth in the Juvenile Animal
The cartilage that remains between the epiphysis and diaphysis is known as the epiphyseal plate and this grows –
lengthening of this cartilage means lengthening of the bone.
The gradual replacement of cartilage by bone thins this plate so the epiphysis and diaphysis eventually fuse
together.
Intramembranous ossification widens the bone

14. Nutrition and Bone Growth
Low Calcium Development of osteochondritis
High Phosphorus Decreased calcium absorption resulting in
poorly calcified bones
Vitamin D Deficiency Inadequate mineralisation of bone, no
calcification of growth plate
High Energy Weaker growth plates and bone
Copper Deficiency Impair bone metabolism
Zinc Deficiency Impaired growth and skeletal development

15. Fractures
If a force is applied that exceeds the strength and elasticity of the bone, a fracture will occur.
Causes:
 Indirect Trauma – a force is applied to a ‘weak line’ in the bone in a specific fashion, such as the violent
contraction of a muscle
 Direct Trauma (RTAs, falls)
 Pathological – due to an underlying bony or systemic disease, such as neoplasia, hyperparathyroidism

16. Classifying Fracture
How do we classify fractures?
 Severity of the fracture (complete or incomplete)
 Whether it communicates through the skin (open or closed)
 Shape of the fracture line
 Anatomical location

17. Classifying Fractures: Shape

18. Classifying Fractures: Open or Closed
OPEN
CLOSED

19. Classifying Fractures: Severity
Complete Fracture Incomplete Fracture
• Simple transverse
• Simple oblique
• Simple spiral
• Comminuted
• Multiple
• Compression
• Avulsion
• Greenstick
• Fissure
• Depression

20. Bone Healing: 4 Stages
Inflammatory Phase
Periosteum is torn
Haemorrhage
Vasodilation
Oedema
Osteocytes die
Phagocytosis removes
necrotic tissue
Proliferative Phase
Haematoma organised
Stem cells invade area
Granulation tissue and
cartilage replace
haematoma
New blood vessels
Soft callus
Modelling Phase
Hard callus formation
High proportion of
osteocytes
Callus envelopes bone ends
 stability
More cartilage and bone
replaces fibrous tissue
Clinical union (bone
fragments rigidly united by
callus)
Remodelling Phase
Scavenger cells
remove soft callus and
extra bone
Woven bone replaced
by strong lamellar
bone
Correct alignment of
fragments allows
restoration of original
shape

21. Healing Complications!
 Non-union
 Delayed union
 Malunion
 Osteoporosis
 Atrophy
 Joint stiffness
 Tissue adhesion
 Movement

22. Factors Influencing Healing
 Patients age (geriatrics are slower to heal)
 Damage to the soft tissue
 Osteomyelitis (inflammation of bone)
 Debilitation and systemic illness
 Stability of fracture
 Good blood supply
 Oblique fractures heal more rapidly than transverse due to having a larger surface area for tissue re-growth

23. Types of Muscle
Skeletal Smooth Cardiac
• Voluntary
• Striated
• Multiple nuclei
• Stimulated by attached nerve
fibres
• Walking, biting, tail wagging
• Involuntary
• Non-striated
• One nucleus
• Nerves regulate movement
• Peristalsis, vasoconstriction,
urination
• Involuntary
• Striated
• One nucleus
• Found only in the heart
• No nervous stimulation required

24. Sarcomere & Transverse (T) Tubule

25. Sliding Filament Model
When we move, calcium is released from the sarcoplasmic reticulum. The calcium binds to the troponin on actin,
moving the tropomyosin which exposes the binding site for the myosin myofilament. The myosin head binds to the
actin myofilament, causing ATP to split into ADP (because one phosphate group is lost during the process), creating
energy . This binding forms a cross bridge. The myosin filaments ratchet over the actin filaments and this is known
as the power stroke – the sarcomere is shortened because of this. If calcium is still present, the muscle will continue
to contract.

26. Dogs: Intramuscular Injections
E Trapezius Muscle
Triceps Muscle
Quadriceps
Muscle
Hamstring Group
• Biceps Femoris
• Semitendinous
• Semimembranous
Epaxial Muscles

27. Dogs: IM Injections
Injection Site (Muscle) Advantages Disadvantages
Trapezius Large muscle to aim for.
Can be done solo
Increased risk of being bitten
Epaxial Easily palpitated site May inadvertently hit important
structures such as spinal cord.
Difficult if animal is moving around
Quadriceps Muscle belly more defined in some
breeds
Muscle belly can be quite small in
others. Blood vessels and nerves run
in this area
Hamstring Large muscle group Can hit sciatic nerve
Triceps Muscle belly is easy to palpate Nerves and blood vessels which
could be hit. May need another
person for restraint

28. Horses: IM Injection
Trapezius Muscle Pectoral Muscle
• Becomes sore easily
Gluteal Muscle
• Only use in case of
prolonged treatment