Bone Remodeling and Structure

• Bone dynamically modifies itself according to internal and external stresses and can regenerate
• A new skeleton replaces the old one every 7-10 years via constant remodeling
• Younger animals have a faster bone turnover rate than older animals
• Older dogs' bones have poor blood supply and are prone to non-union fractures, like radius-ulna fractures
• Bone is dense connective tissue with high mineral content, mainly calcium in the form of hydroxyapatite, providing rigidity
• High collagen content, especially type 1 collagen, is organized to support bone strength and structure
• Osteoprogenitors are precursor cells that turn into osteoblasts
• Neutrophils and macrophages produce growth factors that are released locally (paracrine) and are needed for healing.
• Blood clot cells stimulate growth factor production in osteoprogenitors
• Osteoblasts build new bone by secreting bone matrix and facilitating mineralization
• Synthesized components of bone by osteoblasts include collagen for the bone framework, osteocalcin, and osteopontin for mineralization, which play a role in osteon formation
• Alkaline phosphatase is an enzyme secreted by osteoblasts, playing a key role in hydroxyapatite formation
• Mature osteoblasts become osteocytes
• Osteocytes maintain the bone matrix, communicate with other bone cells and occupy lacunae (empty space) within the bone
• Osteoclasts are derived from monocytes and break down/resorb bone tissue to help remodel and maintain bone health
• Tartrate Resistant Acid Phosphatase (TRAP) is an enzyme used by osteoclasts to digest bone matrix, mainly collagen and proteoglycans
• TRAP facilitates bone resorption by breaking down bone matrix proteins, enabling osteoclasts to remove hydroxyapatite
• Howships lacuna is a cavity created by osteoclasts during bone breakdown
• Mechanical loading produces stress and strain distributions within tissue
• Biological systems are plastic, such that all loads cause damage and require continual repair/remodeling
• The stress-strain graph has four regions:

Stress-Strain Graph Regions

• Toe Region: Initial stretch with minimal resistance where the material is "getting settled"
• Isometric contraction in the Toe Region loads the bone more as seen with weight bearing
• Elastic Region: Predictable material stretching where the material returns to original shape once force is gone, for example while walking
• Plastic Region: Permanent material deformation where the material does not break, for example microfractures from jumping or galloping
• Failure Point: Material breaks/fractures and can no longer perform its original function, for example bone fracture
• Adaptation refers to the ability of tissues to maintain properties like stiffness and strength required for their specific function
• When bone is regularly stressed, collagen production increases, strengthening ECM and adding minerals (calcium) to make it stiffer
• The bone adapts to microfractures making it denser and stronger
• Bone ECM adjusts to handle more weight when regularly stressed
• Physiologic response to tissue includes bone formation and remodeling during growth/fracture healing
• Pathologic adaptation includes thickening and fibrosis/ossification of joint capsule in response to chronic joint instability which can cause pain/reduced range of motion
• A bone's mineral component (hydroxyapatite) provides high stiffness and strength, resisting compressive forces
• Tensile strength comes from the bones organic component
• Collagen fibers, the main organic component of bone, help resist tensile (stretching) forces
• The bone matrix's collagen fibril configuration creates varied bone forms
• Cortical bone has a highly organized layered pattern which is found in the diaphysis and can handle compressive forces
• Woven/cancellous bone, found in healing fracture areas, is loosely organized and has a higher density which means it is more elastic and can absorb forces better

Cancellous Type and Function

• Spongy bone absorbs shock and handles forces from various directions due to its increased surface area
• Bone is strongest in compression, weaker in shear (translation), and weakest in tension
• Mineral component (hydroxyapatite), organic component (collagen), and structure (cortical, woven, spongey) determine bone strength
• Hydroxyapatite keeps bones rigid and strong in compression thereby keeping bone rigid
• With tensile forces, think of the bow (tension) along with compression tensile sides

Wolff's Law

• Wolff's Law the ability of bone to remodel adaptively in response to load applied to the bone
• Bones need tension to hypertrophy
• When bones bear weight from compressive forces, the bone is resorbed in areas of compression
• Resorption prevents weakening and fracturing
• The bone then replaces the resorbed material with stronger bone better able to handle the force if bone is regularly stressed
• Overtraining causes damage to accumulate, microfractures, and stress fractures
• Bone is the rate-limiting system for training horses since it adapts and repairs slowly
• A horse's bone strength and density affects how much exercise the horse can take, and will prevent the horse from progressing in training if bones cannot take the force or stress

New Growth Factors

• Death of osteocytes stimulates the bone remodeling unit but only when that tissue is mineralized
• The bone remodeling unit is a team of osteoclasts and osteoblasts working together to create a complete osteon
• Osteoclasts resorb bone, creating a resorption pit; and osteoblasts fill it in with new bone
• Training trumps hormonal and metabolic stimuli
• Overload followed by over repair yields balance
• Otherwise injury from training happens
• New bone forms via bone microdamage sensed by osteocytes
• Osteocytes signal growth factors and cytokines to bone lining cells which recruit osteoclasts
• Osteoclasts resorb bone which recruits osteoblasts to lay new bone

Stronger Bones

• For bones to become stronger and more resistant they need to be exposed to tension
• Increased volume (and shape), mainly improving resistance to bending because bigger bones can resist more load
• One limitation is that bones cannot continue to get bigger once they are grown if they are an adult
• Increased density happens when the bone can handle more load, and leads to better bone health
• Overtraining symptoms include avoidance of work, and lameness

Bone Fractures

• Stress fractures are small bone cracks from repeated mechanical stress or overuse, rather than a single traumatic incident
• Fractures can result from a single traumatic incident or hit by a car
• Also, fractures can stem from degradation possibility for degradation then failure
• A fracture may be the result of abnormalities in bone
• Force can overcome the strength of the bone or be applied to the bone rapidly thereby having no time to deform

Bone Fracture Types

• Bending occurs from force applied at two points (the bone bends & puts the inside under compression with tension outside)
• Compression fractures are from compressive squeezes where the bones compress and squeezes
• Fibers Compress/Fibers withstand.
• Shearing injuries are from two parts of the bone that slide and are in opposite directions
• Tension Bone occurs when it is pulled apart from stretching
• Torsion happens when a force twists the bone

Characterizing Features of Bone Fractures

• fractures are characterized by which bone it is a, what anatomic location it is in and what is its severity
• Location is articular, metaphyseal/Diaphyseal fractures
• The metaphyseal location is between the epiphysis and diaphysis which occurs in growth plates
• Severity is that it is partial or complete if both cortices are broken

Bone Fracture Patterns

• Transverse fracture: break that is perpendicular
• Oblique Fracture: a short or long angle

Other Bone Fracture Classifications

• Displacement refers to cases where the bone has been moved
• Contamination refers to indications that the bone has broken skin. Look for indicators in xrays

Treating Bone Fractures

• treatment involves reducing movement and preserving blood supply, along with giving a correct diet
• Open reduction is where an incision is made that will be used to realign the bone with internal fixation

Healing an Open Fracture

The fracture Pierces the Dermis and there is a Risk of Infection

• Determine which factors take place for the form of fracture
• Take into account (size of gap and reduction of fracture), and the biology surrounding it.
• Biological environment of surrounding bone
• Cutting cones form because osteoclasts resorb the damaged bone near to the facture site
• Osteoclasts generate long tunnels to remove dead areas that are then filled with bone from osteoblasts
• bridge will form throughout the longitudinal osteons as they lengthen.

Gap Healing stages

• Inflammatory stage which occur for 2 weeks
• There will be blood clot and other white blood cells surrounding.
• The repair stage will begin next to allow for growth in 6 weeks, as well as angiogenesis and secretion of protein
• This will allow for growth of lamellar
• The Remodelling begins to begin collagen and become an bone that has recovered its physical properties
• Bone less 0.01 mm apart will have formation from contact, with bone formed between, which reduces a callus
• In Gap Healing when Bone 0.01 or an mm apart, fibrin will allow new bone structure

Secondary Bone Healing

• gap is large between bones and less training
• Haematosis and fibrin begin form together and start the healing cascade.
• Bone begins cartilage and start to from a new hard structure
• The bones are replaced and remodel with support from osteoblasts and the bones begin to become functional again
• Law of wolf supports placement.

Bone Treatment Devices

• Stress protection refers to bone being kept stable for healing and reduce strain. Pros are an idea environment and the cons are that bone isn’t adapting to force being placed
• bones fail to heal when they do not touch. They mal union as deformity.

Identifying Fracture

• We will check cortisol continuity as well as where the callus forming and it can be seen that it is visibly lost
• All animals can have Angular Limb but it will cause to be limp.
• Flexural happen in animal
• Cerviail occur in animals and people -Osteoneconidris can move and should be removed

Bone Infections

Cartilage has no vessels however bone has many This would be a Multifactorial infection and can be helped from nutrition if a joint cap has ruptured and infection spreads and this could lead to iatrogenic bacteria.

• In long bones infection can kill and the remains are known a sequestrum.

Density

The infection can be cause from cast around the area or cause in that region. JOINT

• Can be synarthrosis or Synstosis if a fuse happen.
• The synovial contains bone and tissue which produces cartilage
• The joint capsule protects with the layers of fiber
• Bones don’t die because of cartilage has no way
• collagen

Forces and Properties

Water will help protect with compression and there will be a release.

• 4 players to decrease stressor
• Damage to membrane result of cytokines
• Involment
• Synial
• Hyelertince - less lubration

Cartilage Degradation Phases

• The collagen becomes harder
• Can't get through this To fix joints,
• They don't get fixed most the time
• It is better deep to heal

More Notes

• Tendons connect muscle to bone they have very small about of macrophages, and high levels of injury.
• There made in type 1 but type 3 is in the collagen