MSK Pathophysiology Flashcards
What are some of the functions of bones?
- Stability
- Mobility
- Hematopoiesis
- Buffer calcium
concentrations - Protection to vital organs
Layers of the Bone
- Periosteum: Outer layer, contains vessels,
nerves, cells for repair - Cortex: Hard outer (Compact) bone
layer - Cancellous bone: Soft (Spongy or trabecular) inner bone
- Endosteum: Inner layer
Salt deposits are primarily ____ and ____ (Hydroxyapatite)
Caᐩ; PO4
What makes up the Tough organic matrix (30%) of bone ?
– (30%) Organic matrix is made up of collagen fibers (90-95%) and
ground substance
* Collagen fibers extend along lines of tensional force
– This gives the bones their tensile strength
* Ground substance- proteoglycans (connective tissue) and cells
Osteoblasts function
- Secrete collagen and ground substance
- Leads to formation of osteoids
- Collagen fibers (Osteoids) then bind to calcium salts→ mineralization
- Secrete tissue-nonspecific alkaline phosphatase (TNAP) which inhibits
pyrophosphate - Pyrophosphate inhibits hydroxyapatite crystallization→ ie. inhibits
bone mineralization
Osteoclasts tunnel through
bone for several weeks, than
are replaced by osteoblasts
which fill in the tunnel, until
just a blood vessel is left. This
remnant is called a ______
haversian canal
Osteocytes function
Osteoblasts become entrapped in osteoid, and they become osteocytes
Osteoclasts function
- Large phagocytic, multinucleated cells
- Stimulated by parathyroid hormone (PTH) indirectly
- PTH binds to osteoblasts
- Osteoblasts signal osteoclast precursors→ become mature osteoclasts
Recall what happens to bone in hyperparathyroidism?
PTH stimulates osteoclast activity and formation of osteoclasts, recruiting CA and phosphate from the bone
Calcitonin is the opposite of PTH and decreases osteoclast activity and inhibits the formation of osteoclasts
The mechanism of bone resorption
- Osteoclasts work by tunneling through bone
- Osteoclasts secrete proteolytic enzymes and acids
- Enzymes digest or dissolve the organic matrix
- Acids dissolve the bone salts
End of the bone
Epiphysis
Bone growth, highly vascular
Physis
Narrowed section before
growth plate
Metaphysis
Central shaft, cortical bone
Diaphysis
Fibrous band of connective tissue, holding bone to bone, or bone to cartilage
Ligament
Long bundles of collagen holding muscle to bone. Surrounded by a synovial membrane (Tendon sheath)
Tendon
Cartilage function
- Ends of the bones
- Covers the area of the epiphysis
- Provides smooth gliding surface
Fibrous joints
have minimal movement
Cartilaginous joints
have Fibrocartilaginous
segments, minimal movement
Synovial joints
– Most common, allows free movement
– Joint cavity, synovial membrane (lining)
Myofibrils contain _____
myosin and actin
I bands contain
actin
A bands contain
myosin and the tips of the actin
Z disk contains
ends of the actin filaments
sarcomere
the area of a Myofibril between Z disks
Cross Bridge
myosin filament protrusions that
interact with actin filament
Go over the process of muscle contraction
- Action potential moves along muscle motor neuron.
- Acetylcholine (ACh) is released and causes opening of ACh gated channels.
- Naᐩ is allowed to flow into muscle membrane causing depolarization. Kᐩ flows out
- Action potential travels along muscle fiber causing sarcoplasmic reticulum to release Caᐩ.
- Caᐩ ions initiate cross-bridge action between the myosin and actin filaments. Requires ATP to slide.
- Contraction ceases when Caᐩ are pumped back into the sarcoplasmic reticulum.
Characteristics of slow muscle fibers?
(Red Muscle)
1. Prolonged muscle activity
2. Smaller
3. Greater blood supply → more
oxygen
4. More mitochondria→ more
metabolism
5. Contains more myoglobin which
allows for increased oxygen
transport to mitochondria. Also
contains more Fe giving a red color
Isometric vs. isotonic
- Isometric: the muscle does not shorten
- Isotonic: the muscle shortens
Characteristics of fast muscle fibers
- Powerful muscle contractions
- Extensive sarcoplasmic reticulum for
rapid release of Caᐩ - Large amount of glycolytic enzymes
for fast release of energy - Less extensive blood supply as less
oxidative metabolism is needed - Fewer mitochondria
Muscle action is balanced by these four factors
- Agonist- movement occurs
- Antagonist- opposes movement
- Synergist- aide movement
- Stabilizer- restrict unnecessary
movement
Hypertrophy
– Increased muscle mass
– Increased number actin and myosin filaments, not increase in
muscle fibers
Atrophy
– Decrease in muscle mass
– Degradation of actin & myosin is greater than replacement
Denervation Atrophy
- Loss of nerve supply to a muscle
- Rapid atrophy occurs
- Degenerative changes occur in the muscle fiber within months
- Without return of innervation, chances of functional recovery become less and less, with no return possible in 1-2 years.
- Muscle fibers are replaced by fibrous fatty tissue
- Can lead to muscle contractures- important for PT
Forces Applied to cause a
fracture
- Compression
- Tension
- Shearing
- Torque
When the stress applied overcomes
the elastic region, then the tissues will
_____
begin to fail
3 Phases of healing an orthopedic injury
- Hematoma and inflammation
- Repair and proliferation
- Maturation and remodeling
Hematoma and inflammation phase of healing
- Bleeding to the area causes a hematoma formation
- Migration of bioactive cells. Phagocytosis of necrotic debri
Repair and proliferation phase of healing
- New blood vessels form
- Soft cartilaginous bridging callus forms and is then mineralized
by osteoblasts and is converted to immature bone
Maturation and remodeling phase of healing
- Can continue for months
- Immature (woven) bone is replaced by cancellous bone
Callus Formation
Periosteal and intraosseous reactions recruit osteoblasts formed from
osteoprogenitor cells to the area followed by deposition of calcium salts
→ The hematoma forms into a callus
What is Nonunion?
Fractures that do not unite
– Poor stability or reduction, atrophic, consider indolent infection, smoking, NSAID
– May require revision surgery and bone graft
What is Malunion?
Fractures that heal with unacceptable alignment and/or poor reduction
– May require revision, based on progress of healing, becomes a more
challenging surgery
Avascular necrosis of bone
delayed complication of interrupted blood
supply. eg. scaphoid, femoral head
Previously referred to as a
“compound” fracture
open fracture
Bowing Fracture
- Occurs in long bones
- Often in children
- Bent bone without
cortical disruption - May require completion
of the fracture
Torus/ Buckle Fracture
- Typically forearm
- Occurs in children
- Younger elastic
bones - Likely simple cast
and protection
Greenstick fracture
- An incomplete fracture
with an angular deformity - Fracture to one cortex
- Occurs in children as the
bones are more elastic - Possible need for reduction
Transverse Fracture
- Fracture perpendicular to bone shaft
- Typically long bones
- Fracture extends through the bone
- Be alert to displacement, rotation,
and shortening
Oblique Fracture
- Typically long bones
- Angulated fracture line
- Be alert to displacement,
rotation, and shortening
Spiral Fracture
- Long bones
- Multiplanar long bone fracture
- Occurs from a rotational force
- High risk of displacement
Longitudinal Fracture
- Fracture along axis of the bone
- Be alert for extension towards
the articular surface
Comminuted Fracture
- A multi-part fracture with
multiple fragments - The bone has been crushed
- Likely will require ORIF
Avulsion Fracture
- Occurs in numerous
locations - Fragment of bone breaks
away, often at attachment
point of tendon or ligament - Essentially the bone breaks
instead of the tendon or
ligament
Segmental Fracture
- Long bones
- Fracture with an
isolated free segment - Usually unstable
- May need surgery
Intra Articular Fracture
- Fracture that extends into a joint
- Higher chance of disruption of
the joint - Can lead to chronic pain and
degenerative changes, may f/u
with CT or MRI
Pathologic Fracture
Fracture occurring at a weak point in
the bone
- Eg. Malignant or benign tumor,
osteoporosis, poor bone health and
quality, advanced age, etc.
Diagnosis and treatment of a pathologic fracture
- X-ray and/or f/u with MRI or CT
- Biopsy (eg. Bone lesion)
- DEXA scan (eg. Osteoporosis)
- Tx based on underlying etiology
Are fractures more common in adults or children?
Children
Growth plate fractures are more
worrisome for ______
growth disturbance. (eg. growth arrest)
Think surgery consult for these types of fractures:
- Open, displaced, angulated, or unstable fractures that cannot be reduced or don’t stay reduced with splinting and/or casting.
- Compartment Syndrome
- Remember your IV Antibiotics for open
fractures
What is a Strain?
● Injury to a muscle or
musculotendinous junction
● Muscle undergoes a forced
eccentric load (eg.forced
lengthening)
● eg. gastrocnemius,
hamstring
● With age brings decreased
elasticity
What is a Sprain?
● An injury to a ligament
● Failure occurs when they
are stretched beyond
capacity
● eg. Ankle is a common
example
● Uncommon in kids because
the physis is weaker than
the ligament
Vascular or neurologic compromise can
occur for several reasons:
- Neurovascular bundle gets “kinked”
around a dislocation - Blood supply is interrupted by vascular
injury (eg. compression or disrupted)
What should you assess every time if you are concerned about Compromised Neurovascular injuries?
peripheral nerve function
Examples of injuries highly associated with
vascular compromise
- Dislocation of the knee→(Routine arteriography)
- Fracture-dislocation of the ankle
- Displaced supracondylar fracture of the
elbow in children
Compartment Syndrome
- Intracompartmental pressure exceeds vascular perfusion pressure
- Leads to ischemia of muscles, nerves, vessels
- Compartment Syndrome defined
Possible causes of compartment syndrome
- Anything that has caused bleeding or edema in closed nonelastic muscle
compartment surrounded by fascia & bone - High energy injuries (fractures and/or severe soft tissue injuries)
- Crush injuries- most common
- Burns, coagulopathy, gunshot wounds
- Snake Bite
- Prolonged limb compression (“Tight cast”- A commonly feared complication)
- Spontaneous- Rare
- Chronic Exertional Compartment Syndrome- Sudden ↑ in activity or workout
6 Ps of compartment syndrome presentation
- Pain (esp. with stretch)- Most specific. “Pain out of proportion”
- Pink skin or pallor
- Paresthesias
- Poikilothermia- Cold skin distally
(misnomer in this case) - Pulselessness- Very Late
- Paralysis or paresis- Very Late
Diagnosis of Compartment Syndrome
– “6 Ps”
– Measured intracompartmental pressure
Normal tissue pressure vs. compartment syndrome
Normal tissue < 10 mmHg
* Consultation with Orthopedist at > 30 mmHg or simply suspect clinically
Diagnostic
1. Mean pressure of > 30 mmHg
2. ΔP < 30 mm Hg
a. (Diastolic - Compartment
pressure = ΔP )
Compartment Syndrome management
- Position affected limb at heart level
- Maintain ankle in neutral position if leg is affected
- Immediate fasciotomy recommended for
– Clinical or suspected diagnosis or elevated intracompartmental
pressure
– Absolute compartment pressure >30 mm Hg
– Perfusion pressure (diastolic blood pressure - compartment pressure)
< 30 mm Hg (Some references say 20 mmHg eg. AAOS 5th ed.)
How long does it take for muscle necrosis to begin?
Interrupted arterial circulation to an
extremity > 4-6 hours
Rheumatism is derived from a greek word implying ____
an influx of fluid to the joints
Rheum- meaning body fluid
Rheumatologic Pathophysiology
- Localized and systemic musculoskeletal inflammation and
damage to internal organs, loss of immune homeostasis - Dysregulated immunity rather then Immunodeficiency
Stages of Rheumatologic Pathophysiology
- Initiation
- Propagation
- Flare
* Acute vs Chronic
* Symptoms vary between
diseases based mechanism,
and target tissues affected
Chronic rheumatologic Disease
– Propagation when the body creates an autoimmune response →
self-amplifying cycle of damage
* Also described as an auto-amplifying loop
* Loss of T cell and B cell immune response checkpoints
Antibodies against self antigens
- Inflammatory response normally balanced
- Apoptosis and cell damage liberates secretory granules and mediators from inflammatory cells
- Normally these are cleared
- With autoimmune diseases these released products in
large amounts can become “self antigens”
Rheumatoid Arthritis
- Autoimmune- chronic inflammation of
synovial joints, genetic w/ environmental
trigger - Attacks the synovial lining of joints
– Can affect other tissues eg. lung, skin, vessels - Synovial thickening, cartilage damage, bone
erosions
– Typically symmetrical joints
