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Bone

Non-neoplastic or metabolic disease

Fracture


Reviewers: Dariusz Borys, M.D. (see Reviewers page)
Revised: 7 June 2012, last major update June 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

See sections below for Stress fractures, Subchondral insufficiency fractures

General
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● Break in continuity of bone, often with severance of blood vessels, periosteum or muscle
● Complete (bone broken completely) vs. incomplete
● Closed (intact overlying tissue, also called simple) vs. compound (fracture site communicates with skin surface)
● Displaced (ends of bone not aligned)
● Comminuted (many fragments)
● Pathologic (due to diseased bone) or traumatic
● Fractures often due to weakened bone (osteoporosis, tumor, infection) or falls in elderly and children

Types of fractures:
● Spiral configuration through cortex is typical
● Transverse fractures (like breaking chalk) are associated with Pagetís disease, osteopetrosis or other severe bone disturbances
● Stress or insufficiency fractures - see below
● Avulsion fractures are associated with trauma at ligamentous and tendinous insertions, often in pelvis or distal thigh

Osgood-Schlatterís disease:
● Avulsion fractures of tibial tubercle causing fragmentation, in children
● Most common causes of knee pain in adolescents, pain in children and young athletes usually between the ages of 10 and 15
● Occurs due to rapid bone growth plus high level of sporting activity; associated with overuse injury
● Can be quite painful, but usually resolves itself within 12 to 24 months (SportsInjuryClinic.net)

Primary callus:
● Exuberant cartilage and disorderly membranous bone may resemble osteosarcoma
● Increased callus is present in unstable areas

Pseudoarthrosis:
● False joint developing after chronic nonunion of a fracture

Congenital Pseudoarthrosis:
● Rare; equally in girls and boys
● Almost always unilateral
● Fractures occur during first 2 yrs of life, usually shortly after birth
● Associated with anterolateral bowing and neurofibromatosis (Orthop Traumatol Surg Res 2011;97:750)

Healing process
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● Hematoma forms between two ends of bone, creates fibrin mesh which seals fracture site
● Young capillaries enter hematoma
● Dead bone reabsorption begins at 3 days
● Periosteal inner layer promotes intramembranous bone growth on each side of fracture, which meets at fracture site to form a primary callus, which anchors ends but doesnít support weight bearing
● This is resorbed and replaced by secondary callus, composed of mature lamellar bone
● New bone is laid down along lines of stress
● In children, marked bone remodeling occurs, even with gross deformities or shortening of a long bone
● Open reduction and internal fixation of fractures is usually not needed
● Movement along fracture line creates lining of synovial cells and pseudoarthritis
● Soft tissue must be removed and bone stabilized to promote healing
● Fractures may not heal due to improper immobilization, devascularization of bone fragments, persistent infection or interposition of soft tissue between ends of bone
● Noncorrosive nails are isolated from bone substance by fibrous tissue; do not elicit foreign body giant cell reaction

Case reports
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● 52 year old man with sarcoma developing 35 years after uncomplicated fracture (Arch Pathol Lab Med 2003;127:e186)

Micro description
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● Varies with type of injury
A few days - acute tissue damage and hemorrhage, necrotic bone [empty lacunae, poorly staining bone matrix] at fracture, may be more extensive in patella, femoral neck, carpal scaphoid
1-2 weeks - hypercellular, hypervascular tissue, often with brisk mitotic activity, resembles sarcoma but without atypia or atypical mitotic figures; reduced callus in midshaft of tibia or other poorly vascularized areas
● Callus reduced if rigid internal or external surgical fixation

Micro images
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Remodeling in metaphysis


Stress fractures

General
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● Also called fatigue or insufficiency fractures
● Due to physical activity (ballet dancing, long distance running, military training) or metabolic bone disease
● Usually lower limbs, especially femoral neck in those with metabolic disease, tibial shaft in joggers or dancers, second or third metatarsal bones in military trainees
● May require serial parallel cuts to find evidence of stress fractures

Gross description
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● White-gray with linear notched zone paralleling subchondral bone end plate

Micro description
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● Zonal with necrotic, reparative (fracture callus, granulation tissue) and viable tissue

Differential diagnosis
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● Aseptic bone necrosis: younger patients, wedge shaped infarct, total necrosis of bone trabeculae and bone marrow


Subchondral insufficiency fractures of femoral head

General
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● Relatively common in elderly osteoporotic women or renal transplant recipients (Joint Bone Spine 2004;71:131, Am J Surg Pathol 2000;24:464)
● Usually resolves after conservative therapy, without surgery
● May cause acute onset of hip pain

Radiology description
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● Bone marrow edema by MRI

Treatment
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● Immobilization, no NSAIDs

Micro description
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● Fracture callus and granulation tissue growing along both edges of fracture line

End of Bone > Non-neoplastic or metabolic disease > Fracture


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