MSK 3a: bones and joints Flashcards
Fibrous joint types? (tough fibrous tissue, no synovial cavity, for strength)
- Syndesmoses: slightly movable. E.g. middle radioulnar and middle tibiofibular joints
- Gomphoses: immovable, teeth articulating with maxillae or mandible
- Sutures: immovable, only in flat bones of the skull. Not fixed in early life so skull can slightly deform to pass through birth canal
Catilaginous joint types? (fibro- or hyaline. No synovial cavity. Act as shock absorbers)
- Synchondroses: hyaline cartilage. Immovable to slightly moveable. E.g. the joint between the diaphysis and epiphysis of a growing long bone
- Symphyses: fibro- or hyaline cartilage. Slightly moveable e.g. pubic symphysis
What is a joint?
An articulation (arthrosis) between neighbouring bones/cartilage and bone/teeth and bone
What is a synarthrosis?
An immoveable joint
E.g. suture, synchondrosis
What is an amphiarthrosis?
A slightly moveable joint
E.g. syndesmosis, symphysis
What is a diarthrosis?
A freely-moveable joint
All types of synovial joint
What is a synovial joint?
Filled with synovial fluid, usually fully-moveable
The main joint type of the body
Planar synovial joint?
Gliding movement
E.g. sternoclavicular joint
Articulating surfaces flat/slight curve, non-axial movement (side to side or back and forth)
Hinge synovial joint?
Monoaxial
Convex surface of one bone fits into concave surface of another
Movements: flexion, extension
E.g. knee, elbow, ankle
Pivot synovial joint?
Monoaxial. Rotation may occur
Rounded or point of one bone articulates within a ring partly formed by a ligament
E.g. proximal radio-ulnar joint
Condyloid (aka ellipsoidal) joint?
Biaxial: flexion, extension, abduction, adduction, circumduction
Oval-shaped condyle of one bone rests in elliptical cavity of another
E.g. wrist, MCPJ and MTPJ
Saddle synovial joint?
Biaxial, more freedom than condyloid
Articular surface of one bone is saddle shaped and that of another resembles the legs of a rider in a saddle
E.g. between trapezium and base of 1st metacarpal
Ball and socket synovial joint?
Multi-axial: the 4 angular movements plus rotation
A rounded surface of one bone rests against a cuplike depression of another
E.g. shoulder, hip
What is a bursa?
Sac lined with synovial membrane and filled with synovial fluid
Can communicate with joint cavity
Purpose is friction reduction
What is a tendon sheath?
An elongated bursa that is wrapped around a tendon
Double sheet but doesn’t completely enclose
Permits free gliding of tendons by reducing friction
Describe articular cartilage of synovial joints
Allows smooth, low-friction movement and resists compression
Hyaline (except acromioclavicular, sternoclavicular and temporomandibular which are fibrocartilage)
Describe the fibrous capsule of synovial joints
Collagen-longitudinal and interweaving bundles
Encloses joint except where interrupted by synovial protrusions
Stabilises joint
Structure of the synovial membrane
Thin and very vascular
Does not cover articular cartilage or menisci
Lines capsule, covers exposed bony surfaces, tendon sheaths and bursae
Produces synovial fluid
Composition of synovial fluid?
Hyaluronic acid
Proteinase
Lubricin
Collagenase
Function of synovial fluid?
Reduced friction
Shock absorption
Nutrient and waste transport
Blood supply to synovial joints?
Periarticular arterial plexus around most
Cartilage avasular
Fibrous capsule and ligaments poor supply
So depends on diffusion through synovial fluid
General functions of the skeleton?
Support Protection Movement Storage Haematopoeisis
Bone classification?
FLAT-curved, protect organs. E.g. frontal bone (skull)
SHORT-equal in length and width. E.g. carpal bones
SESAMOID-embedded within a tendon or muscle. E.g. patella
SUTURAL-within a cranial structure
IRREGULAR: e.g. vertebrae
LONG-longer than wide, muscles act on them as rigid levers. E.g. femur
Structure of long bones?
Mainly compact bone
Some spongy at extremities
Epiphysis at distal and proximal ends, metaphysis in between the epiphysis and diaphysis on each end, diaphysis (shaft) middle part
Covered in endosteum which is covered in periosteum
Nutrient arteries within
Structure of short, flat and sesamoid bones?
Mainly spongy
Thin layer of periosteum-covered compact bone on outside
Bone marrow between trabeculae
No epiphyses or diaphysis
What is avascular necrosis?
Loss of blood supply causing death of bone
Cause: fracture, dislocation, steroids, radiation, decompression sickness
Effects: collapse of the necrotic section and secondary osteoarthritis
What contributes to stability of a joint?
Structure and shape of articulatory bones Strength and tension of ligaments Arrangement and tone of muscles arround Apposition of neighbouring soft tissue Hormones Disuse of joint
Effects of ageing on joints?
Decreased synovial fluid production
Thinning of articular cartilage
Shortened ligaments and decreased flexibility
Degenerative changes
Theory on why joints crack?
Bones pulled away from each other
Synovial cavity expands but fluid volume remains constant
Partial vacuum results
Gases dissolved in synovial fluid are pulled out of solution, causing popping sound
Osteoarthritis summary?
Cause: heavy use of joints over many years which wears away articular cartilage and underlying bone (usually joints tht support full body weight: hips and knee)
Effect: decreased capacity as a shock absorber, roughened edges cause further damage and repeated friction causes the symptoms
Rheumatoid arthritis summary?
Cause: autoantibodies attack synovium causing inflammation
Effect: joint erosion and deformity. Also can damage eyes, skin, lungs, heart etc
X ray features: bones still in union but incorrect orientation. Narrowing of joint space, periarticular osteopenia, subluxation and gross deformity
Osteoporosis summary?
Cause: decreased bone density or atrophy of skeletal muscle. Osteoclast activity exceeds osteoblast activity
Effect: bones become brittle, lose their elasticity, fracture easily
Risk factors: age, female as decreased oestrogen after menopause, ethnicity, smoking, immobility, dietary insufficiencies of Vit D and Ca2+
Osteomalacia summary?
Vitamin D/Ca2+ deficiency in adults
Problem with bone remodelling causing softening of the bones
Osteoid laid down by osteoblasts is poorly mineralised, so bones are weakened
Rickets summary?
Vitamin D/Ca2+ deficiency in children.
Osteoid is poorly mineralised and remains pliable
Epiphyseal growth plates can then become distorted under the weight of the body, causing skeletal deformities.
Presents often with bowing of the legs, knock knees, etc
Paget’s disease of bone?
Increased bone turnover in focal areas
Increased abnormal osteoclast activity
Increased no. osteoblasts due to the loss of bone
New bone is disorganised and mechanically weaker
