Pathophysiology of Bone + OA Flashcards
What are the functions of bone?
Structural = support, protection + movement
Mineral storage = calcium + phosphate
Lipid storage
Blood cell formation
What are the different types of bones?
Long bone
Short bone
Flat bone
Irregular bone
Describe a long bone
Long shaft + 2 distinct ends
Compact bone on exterior with spongey inner bone marrow
What is an example of a long bone?
Humerus, femur
Describe a short bone
Roughly cube-like
Thin compact bone layer surrounding spongy bone mass
What is an example of a short bone?
Carpal + tarsal bones
Describe a flat bone
Thin, flattened + usually curved
Parallel layer compact bone with spongy layer between
What is an example of a flat bone?
Sternum, skull, ribs
Describe an irregular bone
Complicated shapes
Consist of spongy bone with thin layer of compact
What are the 2 major types of bone?
Compact bone = stronger, dense, NOT porous
Cancellous bone = spongy
Describe a compact bone
Mechanical + protective
Dense bone tissue on outside of bone
Enclosed + covered by periosteum
Describe a cancellous bone
Interior = fibres + lamellae
Metabolic Ca regulation
Storage
Stem cells
LEARN long bone gross anatomy
LOOK AT LECTURE
What does red bone marrow do?
Supplies nutrients to osteoclasts
Forms red + white blood cells
What does yellow bone marrow do?
Stores fat
What are the 4 main types of bone cells?
Osteoprogenitor
Osteoblasts
Osteocytes
Osteoclasts
What is the function of osteoprogenitor?
Develop into osteoblasts
What is the function of osteoblasts?
Bone building
Differentiate into osteocytes
What is the function of osteocytes?
Form osteoblasts
What is the function of osteoclasts?
Bone crushing
What is the mechanism of bone remodelling?
Response of osteocytes to microdamage
Signalled by growth hormones/cytokines
Bone surface populated with osteoclast precursors
Osteoclast + osteoblasts recruited
Osteoclasts mature + remove mineralised bone
Osteoclast numbers decline + replaced by osteoprogenitor cells
Osteoprogenitor = osteoblasts = collagen = mineralisation
Describe the method of osteoclast resorption
Osteoclast adheres to bone = secretes HCl + proteases
What is osteoarthritis?
Degenerative disorder of joints, causes significant pain + disability
Where is osteoarthritis usually located?
Knee
Hip
Spine
Small joints of hand
What are the risk factors for OA?
Obesity
Increasing age
What is the cause of primary OA?
Idiopathic
What is the cause of secondary OA?
Previous injury to joint
Inflammatory arthritis (gout/RA)
What is the pathophysiology of OA?
Imbalance between joint repair + destruction
Joints subjected to large load/impact = cartilage + bone strain + damage
Rate of damage > rate of repair
Cartilage progressively destroyed
= narrowing of joint space + overgrowth of bone
= inflammation of synovial lining + swelling of joint
What is OA characterised by?
Breakdown of articular cartilage + proliferative changes of surrounding bones
What are the risk factors of OA?
> 50
Female
BMI >25
Previous injury
Laxity of joint ligaments
Occupational/recreational use of affected joint
Family history
What happens with OA?
Thinned cartilage = bone ends rub together
What is the diagnosis of OA?
No validated diagnostic tool
Pain symptoms with physical joint findings in patients with risk factors
OA features can be seen on a x-ray
What OA features can be seen on a x-ray?
Space narrowing
Bone spurs
Subchondral sclerosis
Subchondral cysts
What are Heberden’s nodes?
Hard bony swelling on distal interphalangeal joints at end of fingers
What are Bouchard’s nodes?
Hard bony cysts occurring on proximal interphalangeal joints
What is the most common location of OA?
Knee joint
Describe the pain with OA in knee
Activity-related
Worse at end of day
Symptoms may be episodic + vary in severity
What is the second most common location of OA?
Hip
What are the risk factors for hip OA?
Obesity
Employment with lifting heavy objects
Physical work
Sport - eg. running
What is common in patients with hip OA?
Difficulty moving hip joints
= putting shoes + socks on
= getting in + out of car
= going up + down stairs
What is the molecular pathophysiology of OA?
Chondrocytes generate matrix degradation products + proinflammatory mediators for repair
= stimulate chondrocyte + proliferation
= increased vascularity + vascular invasion
= increased bone turnover + subchondral bone marrow lesions
Osteophytes form at joint margins
Describe the symptoms of OA
Pain
Morning stiffness
Joint swelling
Reduced range of motion + muscle weakness
Crepitus of joints
Joint instability
Fatigue
Pain-related psychological stress
Describe treatment of OA
1st line = paracetamol/topical NSAID
Adjuncts = capsaicin cream/intra-articular corticosteroids
Ineffective = add in OR substitute
Add in/substitute = NSAID + PPI
