MSK 3a: bones and joints

Question 1

Fibrous joint types? (tough fibrous tissue, no synovial cavity, for strength)

Answer 1

1. Syndesmoses: slightly movable. E.g. middle radioulnar and middle tibiofibular joints
2. Gomphoses: immovable, teeth articulating with maxillae or mandible
3. Sutures: immovable, only in flat bones of the skull. Not fixed in early life so skull can slightly deform to pass through birth canal

Question 2

Catilaginous joint types? (fibro- or hyaline. No synovial cavity. Act as shock absorbers)

Answer 2

1. Synchondroses: hyaline cartilage. Immovable to slightly moveable. E.g. the joint between the diaphysis and epiphysis of a growing long bone
2. Symphyses: fibro- or hyaline cartilage. Slightly moveable e.g. pubic symphysis

Question 3

What is a joint?

Answer 3

An articulation (arthrosis) between neighbouring bones/cartilage and bone/teeth and bone

Question 4

What is a synarthrosis?

Answer 4

An immoveable joint

E.g. suture, synchondrosis

Question 5

What is an amphiarthrosis?

Answer 5

A slightly moveable joint

E.g. syndesmosis, symphysis

Question 6

What is a diarthrosis?

Answer 6

A freely-moveable joint

All types of synovial joint

Question 7

What is a synovial joint?

Answer 7

Filled with synovial fluid, usually fully-moveable

The main joint type of the body

Question 8

Planar synovial joint?

Answer 8

Gliding movement
E.g. sternoclavicular joint
Articulating surfaces flat/slight curve, non-axial movement (side to side or back and forth)

Question 9

Hinge synovial joint?

Answer 9

Monoaxial
Convex surface of one bone fits into concave surface of another
Movements: flexion, extension
E.g. knee, elbow, ankle

Question 10

Pivot synovial joint?

Answer 10

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

Question 11

Condyloid (aka ellipsoidal) joint?

Answer 11

Biaxial: flexion, extension, abduction, adduction, circumduction
Oval-shaped condyle of one bone rests in elliptical cavity of another
E.g. wrist, MCPJ and MTPJ

Question 12

Saddle synovial joint?

Answer 12

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

Question 13

Ball and socket synovial joint?

Answer 13

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

Question 14

What is a bursa?

Answer 14

Sac lined with synovial membrane and filled with synovial fluid
Can communicate with joint cavity
Purpose is friction reduction

Question 15

What is a tendon sheath?

Answer 15

An elongated bursa that is wrapped around a tendon
Double sheet but doesn’t completely enclose
Permits free gliding of tendons by reducing friction

Question 16

Describe articular cartilage of synovial joints

Answer 16

Allows smooth, low-friction movement and resists compression

Hyaline (except acromioclavicular, sternoclavicular and temporomandibular which are fibrocartilage)

Question 17

Describe the fibrous capsule of synovial joints

Answer 17

Collagen-longitudinal and interweaving bundles
Encloses joint except where interrupted by synovial protrusions
Stabilises joint

Question 18

Structure of the synovial membrane

Answer 18

Thin and very vascular
Does not cover articular cartilage or menisci
Lines capsule, covers exposed bony surfaces, tendon sheaths and bursae
Produces synovial fluid

Question 19

Composition of synovial fluid?

Answer 19

Hyaluronic acid
Proteinase
Lubricin
Collagenase

Question 20

Function of synovial fluid?

Answer 20

Reduced friction
Shock absorption
Nutrient and waste transport

Question 21

Blood supply to synovial joints?

Answer 21

Periarticular arterial plexus around most
Cartilage avasular
Fibrous capsule and ligaments poor supply
So depends on diffusion through synovial fluid

Question 22

General functions of the skeleton?

Answer 22

Support
Protection
Movement
Storage
Haematopoeisis

Question 23

Bone classification?

Answer 23

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

Question 24

Structure of long bones?

Answer 24

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

Question 25

Structure of short, flat and sesamoid bones?

Answer 25

Mainly spongy
Thin layer of periosteum-covered compact bone on outside
Bone marrow between trabeculae
No epiphyses or diaphysis

Question 26

What is avascular necrosis?

Answer 26

Loss of blood supply causing death of bone
Cause: fracture, dislocation, steroids, radiation, decompression sickness
Effects: collapse of the necrotic section and secondary osteoarthritis

Question 27

What contributes to stability of a joint?

Answer 27

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

Question 28

Effects of ageing on joints?

Answer 28

Decreased synovial fluid production
Thinning of articular cartilage
Shortened ligaments and decreased flexibility
Degenerative changes

Question 29

Theory on why joints crack?

Answer 29

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

Question 30

Osteoarthritis summary?

Answer 30

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

Question 31

Rheumatoid arthritis summary?

Answer 31

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

Question 32

Osteoporosis summary?

Answer 32

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+

Question 33

Osteomalacia summary?

Answer 33

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

Question 34

Rickets summary?

Answer 34

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

Question 35

Paget’s disease of bone?

Answer 35

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