Bone Fractures (Week 1--Metten and Schwartz)

Question 1

Do bones scar when they heal?

Answer 1

No!

Bone can completely regenerate without scar formation

Involves complex biologic cascade that is mediated by a variety of bioactive cells and proteins

Question 2

Two types of fracture healing

Answer 2

Secondary fracture healing: cartilaginous intermediate like endochondral ossification; most common (no surgery)

Primary fracture healing: repair through periosteum like intramembranous ossification; require surgery

Question 3

Endochondral ossification (secondary fracture healing)

Answer 3

Most bones develop by endochondral ossification

Hyaline cartilage model of what bone is going to look like is how development starts out (all skeletal structure is formed by hyaline cartilage)

Initiating process is primary ossification center in diaphysis –> blood vessels enter diaphysis –> bony collar laid down under periosteum and around diaphysis to make cortex of shaft, and width increases as bony collar grows

Secondary ossification centers in epiphyses (after birth) –> bone growth stops over the edge of epiphysis and becomes articular cartilage (this cartilage generated during development and can’t regenerate more over your life!)

Physis or growth plate on each end is a line of cartilage where process of endochondral ossification continues until puberty at which point physis ossifies and get no more length growth

Question 4

4 stages of endochondral ossification

Answer 4

1) Resting cartilage: hyaline mitosis, cartilage cells divide and replenish
2) Hypertrophic cartilage
3) Mineralized cartilage: scaffolding created when cells mineralized and die
4) Ossification: osteoid –> woven bone –> lamellar bone

Question 5

Fourth step of endochondral ossification

Answer 5

Ossification

Osteoblasts lay down osteoid (unmineralized matrix) –> woven bone (not very strong; immature) on top of mineralized cartilage scaffold becomes mineralized –> osteoclasts remove composite –> osteoblasts produce lamellar bone (stronger; mature) by making osteoid in layers

Question 6

Do adults (post-puberty) have woven bone?

Answer 6

No, not unless something went wrong (fracture or tumor)

Question 7

Physis (growth plate) Zones

Answer 7

Process of endochondral ossification occurs in the physis (stimulated by hormones), so have a zone for each step

1) Resting zone
2) Hypertrophic cargilage zone
3) Mineralized cartilage zone
4) Ossification zone

Question 8

Articular cartilage

Answer 8

Cartilage on end of physis that stays to become articular cartilage

Question 9

What causes longitudinal growth at physis to stop?

Answer 9

Chondrocytes stop mitosis so no more cartilage platform to initiate the 4-step endochondral ossification process

Question 10

Salter Harris fracture

Answer 10

Fracture into physis (growth plate)

Children can get these fractures

Question 11

Blood supply to bone

Answer 11

Main nutrient artery enters diaphysis

Epiphyseal artery at each end

If you get a fracture, broken piece can become separated from blood supply and become necrotic

Question 12

3 phases of secondary (endochondral) fracture healing

Answer 12

1) Inflammatory phase (48 hours): acute inflammatory reaction
2) Reparative phase (2 months): bone callus formed
3) Remodeling (variable)

Question 13

Inflammatory phase of secondary fracture healing

Answer 13

Rupture of blood vessels in periosteum and muscle/soft tissue

(can have necrosis of bone at fracture site)

Within hours, blood vessels constrict to stop bleeding

In 2-5 days, get hematoma from extravascular blood at injury site which seals fracture site and provides fibrin mesh

Neutrophils and macrophages recruited by cytokines which also activate osteoprogenitor cells in adjacent periosteum and endosteum

Macrophages clean up debris of neutrophils and initiate repair process

Question 14

Reparative phase of secondary fracture healing

Answer 14

Begins in second week and extends for about 2 months

Repair proceeds from periosteum toward center of fracture site

Neovascularization

Differentiation of pluripotent cells from periosteum into fibroblasts, chondroblasts, osteoblasts

Granulation tissue formed and tissue becomes denser and hyaline cartilage forms in parts of it

Hematoma is organized and cartilage (collagen type II) between ends of bones forms soft tissue callus (unmineralized)

Cartilage matrix becomes mineralized, osteoclasts resorb to form spicules of mineralized cartilage, then osteoblasts deposit woven bone, then osteoclasts remove so osteoblasts replace spicules with lamellar bone

End of reparative phase, fractured ends are bridged by bony callus/collar (~6 weeks) which is NOT normal looking yet!

Question 15

Remodeling phase of secondary fracture healing

Answer 15

Cutting cones consist of osteoclasts removing bone and osteoblasts following to produce new bone

Bony callus reduced in size to restore normal shape and outline of fractured bone

Medullary cavity also restored

Question 16

Primary (intramembranous) fracture healing

Answer 16

You surgically fixate two ends of the bone together, usually using compression plating/screws

No intermediate cartilaginous callus forms! Bone formed directly from membrane

Osteoprogenitor cells from periosteum form membrane of cells that differentiate into osteoblasts

Osteoblasts deposit woven bone spicules, removed by osteoclasts and replaced with lamellar bone

Periosteum also contributes blood vessels for healing

Cutting cones help integrate new bone directly into normal structure

Question 17

Does primary fracture healing (intramembranous ossification) happen in development?

Answer 17

Yes, but only in flat bones of the skull (and in the scapula?)

Question 18

At what point during secondary fracture healing can you manipulate the bone if it’s not healing the way you want it to?

Answer 18

Reparative phase when you have the soft callus

Question 19

Delayed healing

Answer 19

Fracture that has not healed after 16-20 weeks (4-6 months)

Question 20

Nonunion

Answer 20

Fracture that has not healed after 9 months

Question 21

Risk factors for nonunion

Answer 21

Smoking

Infection (osteomyelitis) or other bone pathology (osteoporosis, tumors, avascular conditions)

Inadequate immobilization

Malnutrition (alcoholism and drug abuse)

Use of NSAIDs during inflammatory phase (need inflammation to heal!)

Question 22

Fractures that have high incidence of nonunion because of problems with blood supply

Answer 22

Femoral neck fractures

Fractures of scaphoid bone in wrist

Fractures of talus in the foot

Fractures of the dens of the axis (C2) vertebra

Question 23

What other diseases in older people could predispose them to getting fractures

Answer 23

Osteoporosis

Osteomalacia

Bone tumors (primary or secondary)

In these older patients, repair is less optimal and often requires mechanical methods of immobilization to facilitate healing

Question 24

Location of fracture

Answer 24

Intra-articular: fracture line crosses articular cartilage and enters joint

Metaphyseal

Diaphyseal (proximal or distal)

Epiphyseal (Salter-Harris)

Question 25

Simple fracture

Answer 25

No break in the skin, only 2 pieces

Question 26

Closed fracture

Answer 26

No break in the skin

Question 27

Compound (open) fracture

Answer 27

Break in the skin

Bacteria can enter and cause infection (osteomyelitis)

(gunshot wound is open)

Question 28

Nondisplaced fracture

Answer 28

Fracture segments in anatomical alignment

Question 29

Displaced fracture

Answer 29

Fracture segments are malaligned

Question 30

Comminuted fracture

Answer 30

More than two fracture segments

(ex: butterfly fracture)

Usually implies high-energy mechanism of injury but can also be from low-energy injury if bone already weakened by disease

Question 31

More severe compared to less severe fractures

Answer 31

More severe: displaced, comminuted, compound (open)

Less severe: non-displaced, simple, closed

Question 32

Fractures described by fracture lines

Answer 32

Transverse: at an angle perpendicular to shaft of bone

Oblique: crosses bone diagonally from one cortex to the other (angulated)

Longitudinal

Spiral: due to twisting force; complex fracture line

Compression: end to end force causes bone to collapse upon itself

Avulsion: when injury causes ligament or tendon to tear off (avulse) a small piece of bone to which it is attached

Segmental: separate segment of bone bordered by fracture lines (broken at two places)

Stress: repetitive injury (ex: shin splints)

Pathologic: fracture through bone weakened by disease or tumor (occurs from normal stress on bone)

Greenstick: break through one cortex but not the other (happens in children bc have more malleable bone)

Torus (buckle): bone bends but doesn’t break

Pearls: fat pad sign; fat in joint aspirate indicates intra-articular fracture

Question 33

In general, are fractures in children complicated?

Answer 33

Usually no, because periosteum in children is thicker and more vascular so fractures are completely healed

Exception is when fracture occurs in physis

Question 34

Why do children get physis fractures?

Answer 34

18 - 30% of all fractures in children involve the physis

Physis is made of cartilage and is injured easier than bone

In children, ligaments attached to physes are stronger than physis itself so forces that in adult would lead to ligament injury cause physis fracture in children

Question 35

Fractures in children

Answer 35

Bowing fracture: bone bent without noticeable fracture line

Torus fracture (buckle fracture): due to axial compression of bone at metaphyseal-diaphyseal junction; stable and heal in 2-3 weeks without mobilization

Greenstick fracture: bone angulated beyond its limits but force did not cause complete fracture; fracture on tension side and intact cortex and periosteum on compression side

Question 36

Why are physis fractures in children complicated?

Answer 36

1) Sometimes fracture is invisible on radiograph because doesn’t extend into epiphysis or metaphysis
2) Can cause growth disturbance: if one area damaged and other not, get angular deformity; if large area of damage growth may cease altogether

Question 37

Salter-Harris Classification of physis fractures

Answer 37

Type I: fracture extends only through the physis (best prognosis)

Type II: fracture extends through most of physis and small part of metaphysis (50% of all growth plate fractures)

Type III: fracture extends through part of physis and part of epiphysis

Type IV: fracture extends through part of metaphysis, physis, and part of epiphysis

Type V: compression injury to physis without fracture of epiphysis or metaphysis

Question 38

Management of fractures

Answer 38

Ranges from doing nothing to surgical repair, just want to optimize speed of healing and recovery of function with least risk of complications

1) In situ, not moving it
2) Reduction, put back in place
3) Electrical stimulation to enhance healing
4) Diet and general health can affect healing
5) Weight bearing can affect healing of lower extremity fractures