MSK: Bone (Anatomy)

Why do bones have a good capacity for healing?

They are highly vascularized and thus regenerative

What are 5 key characteristics about bones?

skeletal CT with solidified matrix, **highly vascularized**, **regenerative**, mineralized, and resilient

What are the main functions of bone? (5)

protect organs, supports body, provides leverage for movement, stores salts like calcium, and creates new blood cells

How many bones are in the human skeleton? Appendicular? Axial?

206, 126, 80

What are the cells of bone?

osteocytes (mature), osteoblasts (builders), osteoclasts (break down bone)

Osteocytes

**bone maintenance**, mature bone cells

Osteoblasts

**bone formation** cells

Osteoclasts

**breaks down** bone matrix, good for bone remodeling

In the extracellular matrix, what gives bone its hardness?

salts

Qualities of bone extracellular matrix

Salts for bone hardness, 20% water, **collagen for tensile strength**, mucopolysaccharides organize and mineralize, osteoid (part of matrix not calcified yet)

Where is periosteum NOT on bones?

**Not on the articular surfaces**

What happens if bone loses its periosteum?

Bone is subject to necrosis, painful

What are the 2 types of bone?

Compact/Cortical surrounding Trabecular/Spongy/Cancellous

Which type of bone withstands **torsional** stress?

Compact/Cortical bone

Trabecular/Spongy/Cancellous bone

Meshwork of trabeculae, has intercommunicating marrow spaces in between

Which bone type dissipates **compressive** forces?

Trabecular/Spongy/Cancellous

In bones, what is disposed along lines of greatest compression and stress? What rule does this follow?

Trabeculae, Wolff’s Law

Ward’s triangle

an area of weakness in the proximal femur where there are 3 areas of a lot of stress nearby but not strong forces in the triangle, thus that bone is less adapted for stress

Principal compressive group in proximal femur (supporting bundle)

runs from head of femur to inferior neck, **STRONGEST** for WB in hip, sends stress from hip joint to the shaft of femur

Secondary compressive group in proximal femur (Trochanteric bundle)

lesser to greater trochanter, for stabilizing trochanteric forces

Principal tensile group in proximal femur (Arcuate bundle)

inferior greater trochanter to femoral head, resisting tensile forces from muscles and joint attachment

What are the structural classifications of bones?

long bone, short bone, flat bones, irregular bones, sesamoid bones

Long Bones (shape, type, importance, example)

Elongated shape, thick compact bone cylinder with little trabecular bone, expanded articular ends called epiphyses, ex) femur, humerus

Short Bones (shape, type, importance, example)

small geometric shapes, thin cortex of compact bone, mostly trabecular bone, for compressive forces, ex) tarsals and carpals (navicular, cuboid)

Flat bones (shape, type, importance, example)

flat in shape, thin compact bone surrounding trabecular bone, for protection, ex) scapula, skull

Irregular Bones (shape, type, importance, example)

odd shapes, thick trabecular and thick compact bone depending on where torsional and compressional forces are being applied, ex) **vertebrae, mandible, zygomatic bones**

Sesamoid Bones (shape, type, importance, example)

small and round, located in tendons, for mechanical advantage in pull of muscles, ex) patella

What are two functions of bony prominences?

site for mm attachment and alters the line of pull of mm

Endochondral ossification

start with hyaline cartilage model → replaced by bone (later in prenatal life)

Intramembranous ossification

direct ossification from condensed mesenchyme (early in prenatal life)

How many ossification centers do short bones have?

One center site, ossification from center out

Most bones have ___ ossification centers

several (primary and secondary centers)

Where are primary ossification centers located?

start at center and ossify towards bone ends

Where are secondary centers of ossification located?

at cartilaginous ends of long bones (the growth plates), can be multiple in one bone

What structure in bone helps you to grow taller?

Secondary centers of ossification

Appositional Bone Growth

new layers of bone on already made bone, THICKENS bone (increase diameter)

Which bone growth allows us to get taller?

Interstitial

Interstitial Bone Growth

LENGTHENING of bone near growth plates

What are the components of a long bone?

diaphysis, epiphysis, epiphyseal plate, metaphysis, and apophysis

Diaphysis (location, ossification development, function)

shaft of bone, from primary center of ossification (appositional), for mechanical support and housing bone marrow

Epiphysis (location, ossification development, function)

expanded end of bone with cartilage, from secondary center of ossification (interstitial), for supporting joint movement

Epiphyseal plate (location, ossification development, function)

hyaline cartilage growth plate at epiphysis, adding length to bone until fusion, only present during + the site of bone growth (interstitial)

What name does a fracture have when the epiphyseal plate of a child is involved?

Salter-Harris fracture

Metaphysis (location, ossification development, function)

between the diaphysis and epiphysis, interstitial growth, actively growing (in length) part of diaphysis

Apophysis (location, function, example)

bony projection, attachment site for ligaments and tendons, ex) greater trochanter

How do long bones get nutrients?

**pretty vascular**, 1 or 2 diaphyseal nutrient arteries **transmitted through nutrient foramina in diaphysis** for bone healing/growth + epiphyseal and metaphyseal nutrient arteries at bone ends

Short and flat bones blood supply

from the periosteum

Large irregular bones blood supply

blood supply from periosteum + nutrient arteries penetrating trabecular bones

Nerve supply to bone?

numerous nerves

Risser's Sign

grading system for iliac epiphysis (iliac crest) for sign of spinal maturity, ranging from 1-5 (25%, 50%, 75%, 100%, fusion), from ASIS→PSIS

At what age does acetabulum ossification commence and **fuse**?

12yrs and **16yrs**

When does the head of the femur commence and fuse?

1 yr and 18yrs

Fracture

disruption in the continuity of bone that is painful because of periosteal nerve irritation, many types based on why it broke (traumatic, pathologic, periprosthetic, stress fracture), did the skin break, displaced or non-displaced, and how many pieces it broke into

Osteoporosis

decrease in bone mass and density

Osteosarcoma blastic lesion

increases in bone formation from tumor induced osteoid production

Osteosarcoma lytic lesion

bone destruction, part of bone fully eaten away

Multiple Myeloma

malignant condition with many small “punch out regions” from increased bone resorption

What type of fracture has a break part-way across the bone?

Incomplete (greenstick fracture)