Bone Fractures (Week 1--Metten and Schwartz) Flashcards
Do bones scar when they heal?
No!
Bone can completely regenerate without scar formation
Involves complex biologic cascade that is mediated by a variety of bioactive cells and proteins
Two types of fracture healing
Secondary fracture healing: cartilaginous intermediate like endochondral ossification; most common (no surgery)
Primary fracture healing: repair through periosteum like intramembranous ossification; require surgery
Endochondral ossification (secondary fracture healing)
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
4 stages of endochondral ossification
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
Fourth step of endochondral ossification
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
Do adults (post-puberty) have woven bone?
No, not unless something went wrong (fracture or tumor)
Physis (growth plate) Zones
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
Articular cartilage
Cartilage on end of physis that stays to become articular cartilage
What causes longitudinal growth at physis to stop?
Chondrocytes stop mitosis so no more cartilage platform to initiate the 4-step endochondral ossification process
Salter Harris fracture
Fracture into physis (growth plate)
Children can get these fractures
Blood supply to bone
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
3 phases of secondary (endochondral) fracture healing
1) Inflammatory phase (48 hours): acute inflammatory reaction
2) Reparative phase (2 months): bone callus formed
3) Remodeling (variable)
Inflammatory phase of secondary fracture healing
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
Reparative phase of secondary fracture healing
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!
Remodeling phase of secondary fracture healing
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
Primary (intramembranous) fracture healing
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
Does primary fracture healing (intramembranous ossification) happen in development?
Yes, but only in flat bones of the skull (and in the scapula?)
At what point during secondary fracture healing can you manipulate the bone if it’s not healing the way you want it to?
Reparative phase when you have the soft callus
Delayed healing
Fracture that has not healed after 16-20 weeks (4-6 months)
Nonunion
Fracture that has not healed after 9 months
Risk factors for nonunion
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!)
Fractures that have high incidence of nonunion because of problems with blood supply
Femoral neck fractures
Fractures of scaphoid bone in wrist
Fractures of talus in the foot
Fractures of the dens of the axis (C2) vertebra
What other diseases in older people could predispose them to getting fractures
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
Location of fracture
Intra-articular: fracture line crosses articular cartilage and enters joint
Metaphyseal
Diaphyseal (proximal or distal)
Epiphyseal (Salter-Harris)
Simple fracture
No break in the skin, only 2 pieces
Closed fracture
No break in the skin
Compound (open) fracture
Break in the skin
Bacteria can enter and cause infection (osteomyelitis)
(gunshot wound is open)
Nondisplaced fracture
Fracture segments in anatomical alignment
Displaced fracture
Fracture segments are malaligned
Comminuted fracture
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
More severe compared to less severe fractures
More severe: displaced, comminuted, compound (open)
Less severe: non-displaced, simple, closed
Fractures described by fracture lines
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
In general, are fractures in children complicated?
Usually no, because periosteum in children is thicker and more vascular so fractures are completely healed
Exception is when fracture occurs in physis
Why do children get physis fractures?
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
Fractures in children
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
Why are physis fractures in children complicated?
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
Salter-Harris Classification of physis fractures
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
Management of fractures
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
