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Flashcards in MSK Mod 1A Deck (39):

Classification of bone types (4)

1. Long bones
a. ex: humerus, femur, tibia, etc..
2. Short bones
a. Tend to be equal in both dimension…cuboidal shape
b. ex: carpals of wrist, tarsals of foot
3. Flat bones
a. protective function
b. ex: skull
4. Irregular bones
a. ex: vertebrae, facial bones


Characteristics of Long Bone (4)

A. Diaphysis
1. primary ossification center
2. body of bone
B. Metaphysis
1. flattened portion of the diaphysis
C. Epiphysis
1. secondary ossification center (develop after birth)
D. Epiphyseal Plate
1. cartilagenous growth plate between diaphysis and epiphysis


2 Types of Bone

compact (cortical) and spongy (cancellous, trabecular)


Cortical – “compact” bone

1. Forms 80% of the human skeleton
2. Slow turn over rate
3. Dense, tightly packed osteons with haversian canal system
4. Haversian system (aka Osteon)
a. Haversian canal (central canal) – each canal contains blood vessel and nerve that communicate with perisoteum
b. Concentric layers of bone surround the canal – lamelle
c. Osteocytes found within concentric layers
d. Volkman’s canal – “horizontal” canal system connecting to periosteum


Cancellous bone – trabecular or spongy bone

1. 20% of skeletal mass
2. Less dense but “large” surface area
3. Higher turnover rate
4. Undergoes remodeling according to line of stress
5. Wolff’s Law = increased mechanical stress will increase bone density



A. Thin, double-layered, tough fibrous membrane that surrounds the bone
B. Surrounds all of bone except at ligament or tendon insertion sites


Periosteum Outer and Inner Layer

C. Outer layer contains…
1. Capillaries and nerves

D. Inner layer contains…
1. Sharpey’s fibers anchor periosteum (as well as tendons and ligaments) to the cortical bone
2. Difficult to separate the periosteum from the bone
3. If active bone formation then:
a. inner layer contains osteoblasts
4. If inactive bone formation then:
a. the inner layer contains fibroblasts that can become osteoblasts if new growth needed


Bone Marrow Consists of? (6)

1. Blood vessels
2. Nerves
3. Mononuclear phagocytes
4. Stem cells
5. Blood cells in various stages of differentiation
6. Fatty tissue


2 Types of Bone Marrow in adults

1. Red (active) bone marrow
a. Not all bones have active marrow
b. Pelvic bones, vertebrae, cranium and mandible, sternum and ribs, proximal femur and humerus
c. Found in trabecular or spongy bone regions

2. Yellow (inactive) bone marrow
a. Yellow represents more of fatty cells
b. Found in medullary cavity of long bone


Blood Supply to Bone

A. Nutrient arteries are primary source of blood
1. Usually enter middle of diaphysis
B. Epiphysiseal and metaphyseal arteries

C. Periosteal capillaries

D. Clinical: Blood supply is critical for fracture repair and to maintain bone health


Bone Remodeling

A. General healthy remodeling occurs in both cortical and cancellous bone
B. Occurs throughout life
C. Balance between osteoblasts and osteoclasts
D. osteoporosis = osteoblast activity < osteoclastic activty


5 Phases of Remodeling

1. Activation

2. Resorption

3. Reversal:

4. Formation

5. Quiescence:


Phase 1 of Bone Remodeling

1. Activation
a. Stimulus: hormone, drug, or physical stimulus
b. Action: stimulus activate resting osteoblasts to signal activation of osteoclastic activity


Phase 2 of Bone Remodeling

2. Resorption
a. Action: osteoclasts break down bone, create a resorption cavity
• Compact bone: resorption cavity follows longitudinal axis of Haversian’s canals
• Cancellous bone: resorption cavity follow surface of trabeculae


Phase 3 of Bone Remodeling

a. Action: macrophages “clean-up” the site and prepare it for laying down new bone


Phase 4 of Bone Remodeling

a. Action: osteoblasts lay down new bone in resorption cavity
b. Compact bone:
• Bone is laid down in concentric layers until small canal is formed (haversian’s canal)
• Haversion systems are constantly broken down with new ones being formed
c. Cancellous bone:
• Trabeculae are broken down and new ones formed


Phase 5 of Bone Remodeling

5. Quiescence:
a. Action: osteoblasts “rest” and are now “bone lining cells” on the newly formed bone surface


Three basic etiological classifications of fractures

a. Sudden traumatic fracture
• Single episode of excessive force
b. Stress or fatigue fracture
• Repetitive episodes of “normal” force
c. Pathological fracture
• “Normal” force on abnormal bone


Condition of the Soft Tissue with Fractures (2)

a. Closed fracture
• fx not exposed to the external environment
b. Open fracture
• fx exposed to the external environment


Deformities of the Fracture

a. Displacement (translation) - describes the position of the distal fragment
• Ant/post, medial/lateral
b. Rotation – IR/ER with observation
c. Shortening of the fracture – ends of the fx overlap
d. Angulation – direction in which the distal fragment “points”
• Ex: lateral/medial “angulation”


Fracture classifications…many “systems” of description

Anatomical Location of the Bone
Region of the Bone
Direction of the Fracture Line
Condition of the bone
Condition of the Soft Tissue
Deformities of the Fracture


Condition of the Bone

a. Comminuted – fx with 3 or more fragments
b. Pathological – fx in area of pre-existing bone disease
c. Incomplete – fx does not span entire cross section of bone, bone is not broken into separate segments
d. Segmental – fx middle fragment of bone surrounded by proximal and distal segments
e. Butterfly segment – similar to segmental except fx doesn’t span the entire cross section of bone
f. Stress fracture – small fx caused by repetitive loading of bone
g. Avulsion fracture


Avulsion Fx

portion of bone is separated from bone, caused from pulling of tendon or ligament at the insertion site


3 Phases of Bone Healing

Inflammatory Phase
Reparative Phase
Remodeling Phase


Inflammatory Phase of Bone Healing

(days up to 1- 2 weeks)
• Increased blood flow into area after acute response to fracture
• Hematoma forms
• Osteoclastic activity removes damaged bone
• Growth factors stimulate fibroblasts, osteoblasts at site
• X-ray : fracture line becomes more visible as necrotic tissue is “removed”


Reparative Phase of Bone Healing

(up to several months)
• Soft fibrous callus forms initially followed by a hard callus
(i) Osteoblasts are responsible for mineralizing soft callus causing...hard callus to form
(ii) Hard callus is considered immature bone…stable compared to soft callus but weak compared to mature bone
(iii) X-ray: fracture line begins to disappear


Remodeling Phase of Bone Healing

(months to years)
• Immature bone is replaced by organized mature bone
• Fracture line disappears
• Process begins during reparative phase


5 Goals of Fracture Management

1. Achieve anatomic reduction
2. Restore stability
3. Create environment conducive to fracture healing
4. Return patient to pre-injury function
5. Achieve acceptable cosmesis


Criteria for Determining When a Fx has Healed

1. Not an “absolute science” in orthopedic practice
2. Balance between fracture healing vs. negative consequences of immobilization
3. Criteria…
a. Clinical judgment
• Patient’s pain, etc….
b. Radiographic appearance
• Callus formation with disappearance of fx line
c. Anatomical location of fracture and device
• Different bones tend to heal at different rates
(i) Ex: distal radial fx approximately 6 – 8 weeks vs mid-diaphyseal fx approximately 3 months


Healing Time

will vary with age, location and type/severity of fracture…very general example
a. Kids: 4 – 6 weeks
b. Adolescents: 4 – 8 weeks
c. Adults: 10 – 18 weeks


Immobilization of Fractures (7)

1. Cast: secondary healing with periosteal callus formation
2. Intramedullary rods/nails: secondary healing with periosteal callus formation
3. Pins, wire, screws: secondary healing with periosteal callus formation
4. Compression plate: primary bone healing, NO periosteal callus formation
a. Primary healing is slower thus longer period of non-wt bearing
5. External fixator – either primary or secondary healing will occur
a. If less rigid fixation – callus formation, secondary healing
b. If very rigid - no callus formation, primary bone healing
6. Closed Reduction
a. Manual manipulation of the extremity to align the fracture fragments
7. Open Reduction
a. Surgical reduction of extremity to align the fracture fragments
• Ex: “ORIF” – open reduction and internal fixation


Potential secondary complications of fractures

1. potential growth impairments in children
2. long term disuse can have significant impact on elderly
3. cardiopulmonary complications due to immobilization
4. bone – localized osteoporosis
5. transient muscle atrophy


Healing Complications of Fractures

1. Delayed or non-union
2. Avascular necrosis
a. Femur head & scaphoid are common examples
3. Infection


Salter Harris fractures in developing bone

1. Type 1 – disruption of the growth plate…distraction or slip injury
2. Type 2 – fracture line through growth plate and metaphysis
3. Type 3 – fracture line through growth plate and epiphysis
4. Type 4 – fracture through metaphysis, growth plate, epiphysis
5. Type 5 – compression injury of the growth plate


4 Stages of intramembranous ossification

• Stage 1
(i) Cluster of osteoblasts form ossification center within fibrous connective tissue membrane
• Stage 2
(i) Osteoblast secretes bony matrix in surrounding fibrous membrane
(ii) Matrix is then calcified – osteoblast are now osteocytes “trapped” within matrix
Stages of intramembranous ossification (cont.)
• Stage 3
(i) Formation of trabeculae - osteoid form around invaginating blood vessels
(ii) Periosteum forms from mesenchymel cells
• Stage 4
(i) Bone collar of compact bone forms
(ii) red marrow is now formed within trabeculae


Endochondral ossification

Cartilage model”
b. Bone replaces cartilage (cartilage is NOT converted into bone)
c. Responsible for
• Longitudinal bone growth during development
• Appositional growth (“widening”) during early development


3 Layers of the Physis

1. Reserve zone
a. early stages of cartilage cell
2. Proliferative zone
a. mature cartilage cell
3. Hypertrophic zone
a. Cartilage cell hypertrophies, accumulate calcium and then dies….osteoblasts then enter and form new bone


2 cartilagenous growth zones exist in immature long bone

• Spherical zone around the end of the epiphysis
(i) Allows for growth of the epiphysis
• Physis (epiphyseal plate)
(i) Between metaphysis and epiphysis
1. Classically referred to as “growth plate”
2. Allows for longitudinal growth


Bone Maturation

1. Epiphyseal plates typically fuse between ages 14 – 21 years of age
2. Occurs earlier in females vs males (d/t earlier puberty of females)
3. Skeletal development
a. Growth of spine: 80% of full growth by age 8
b. Extremities grow a faster rate throughout childhood than axial skeleton
• Premature closure of lower extremity growth plates will influence ht more than spine