Bone Pathology
Review of Normal Structure:
Mature/Secondary/Lamellar Bone
- slowly produced & highly organized
- Remember – anything other than lamellar bone in the adult skeleton is abnormal
- HISTO
Ø few osteocytes, parallel arrangement of type I collagen fibers, uniform osteocytes
Immature/Primary/Woven Bone
- rapidly produced & ill-arranged
- low tensile strength
- HISTO
Ø irregular arrangement of type I collagen fibers, numerous osteocytes, variation in osteocytes
- normally found in embryonic development
Hereditary Disorders – Osteopetrosis, Classic achondroplasia, osteogenesis imperfecta
Osteopetrosis (Albers-Schonberg Disease)
- group of rare diseases that are due to osteoclast dysfunction
- you get a overgrowth and sclerosis of bone (the cortex thickens and the marrow cavity narrows)
- brittle bones therefore prone to fractures
- There are 4 different types depending on inheritance and clinical findings
Ø autosomal recessive is most severe
- Characteristic sign on XR = Erlenmeyer flask widening of the metaphyses to the diaphyses
Classic Achondroplasia
- most common cause of non-lethal dwarfisms
- can be auto dom or new mutation
- the pathology lies in a disorder of the epiphyseal bone plate
- the bone is normal – but the epiphyses ossifies abnormally, thus sealing off the growth plate
- Big head, trunk — short limbs
Osteogenesis Imperfecta
- deficiency in Type I collagen
- results in too little bone
- very brittle bones
- deformities usually result due to numerous fractures
- other effects
Ø Blue sclerae
Ø Abnormal joints, ligaments, teeth, skin
Ø Deafness
- There are 2 major clinical groups
1) OI congenita
Ø severe neonatal form
Ø high mortality
Ø multiple fractures in utero
2) OI tarda
Ø milder form
Ø infant normal at birth
Ø autosomal dominant
Paget’s Disease (Osteitis Deformans)
- DISORDERED BONE REMODELLING
- First you get increased bone resorption then you get excessive disorganized bone formation; lytic and sclerotic areas exist in the bone
- Characterized by abnormal bony architecture caused by increases in both osteoblastic and osteoclastic activity
- Net effect – increased bone mass (new bone is disordered and abnormal)
- Begins in the 5th decade
- Involves: axial skeleton (pelvis, spine, skull) or proximal femur in 80% of cases
- Unknown etiology
- XR: irregular thickening of cortical and trabecular bone.
Pathology
- Three morphological phases
1) osteolytic phase – large osteoclasts in Howship’s lacunae; osteoclast resorption predominates
2) Mixed osteoblastic and osteolytic phase – new bone formation leads to the mosaic pattern
3) Late phase – increased bone density, thick trabeculae, mosaic pattern is prominent
- Histological hallmark – mosaic pattern produced when the new bone separates from the old bone forming irregular cement lines
- eventually you get to an inactive stage.
Clinical Findings
- variable depending on the site and extent of disease
- most are mild and asymptomatic
- most common symptom – pain due to microfractures and bone overgrowth compressing spinal and cranial nerve roots
- other: “leonine” facies, anterior bowing of femur and tibia, kyphosis
- associated with an increased risk of developing bone tumors
Osteonecrosis (Avascular Necrosis)
Causes
1) mechanical vascular interruption (fractures)
2) thrombosis/embolism
3) vessel injury
4) Increased interosseous presure with vascular compression
5) Venous HTN
6) Most common cause: idiopathic, fracture, steroids
Morphology
- subchondral infarcts
Ø triangular wedge-shaped necrotic segment
Ø NO OSTEOCYTES IN LACUNAE
Bone Fractures
- Different types
Ø complete, incomplete, comminuted, compression, transverse, closed, open, pathologic
- Healing of Fractures
Ø 3 phases
1) Inflammatory phase
- hematoma forms and fills fracture gap
- there is an influx of inflammatory cells and ingrowth of fibroblasts and capillary buds
- organization of the hematoma into soft tissue usually occurs by the end of the first week
- this provides the framework for anchorage of the ends of the fractures bones
- no structural rigidity
2) Reparative Phase
- periosteal osteoblasts deposit new woven bone
- mesenchymal cells differentiate into chondroblasts which results in the formation of cartilage at fracture site (envelops around it)
- at 2nd to 3rd week the tissue repair is the greatest
- still not strong enough for weight bearing
3) Remodeling Phase
- the newly formed cartilage ossifies
- bony callus bridges the ends of the bones
- further mineralization
- now solid enough for weight bearing
Osteomyelitis
- this is an inflammation of bone and bone marrow
- most commonly due to pyogenic bacteria and mycobacteria
- how do they get there?
Ø hematogenously
Ø extension
Ø direct implantation
Pyogenic Osteomyelitis
- Causative organisms
Ø S. Aureus (80-90% of time)
Ø E. coli, Pseudomonas, Klebsiella – IV drug users, GU infections
Ø H. influenza, Group B Streptococcus – neonates
Ø Salmonella – sickle cell disease
- Locations
Ø influenced by vascular circulation
neonates – metaphysis and epiphysis, or both
Children – metaphyseal location
Adults – epiphysis and subchondral regions
- Morphology
- bone necrosis due to release of toxins and enzymes
- osteoclastic bone resorption
- ingrowth of fibrous tissue and deposition of new bone
- X-Ray appearance
Ø lytic focus of bone destruction; zone of sclerosis surrounds
Tuberculous Osteomyelitis
- 2o to tuberculous infection elsewhere
- in US – older adults and immunosuppressed
- in developing countries – adolescents and young adults
- usually hematogenous
- focal usually; multifocal in AIDS
- most common sites – spine (1), knees (2), hips (3)
- vertebral collapse can lead to spinal deformity
Osteoporosis
- you get a proportional decrease in organic osteoid and mineralization
- results in a decreased bone mass density
- pronness to fractures
- can be localized or generalized (most commonly)
- can result in kyphosis, spinal fractures, shortened stature
Types of Generalized Osteoporosis
1) 1o – most commonly seen in post-meopausal women
2) 2o – there are defined causes (endocrine dysfunction, Vit C and D deficiency, steroids)
Contributing factors
Ø genetics
Ø reduced activity
Ø estrogen deficiency
Ø environmental factors (smoking)
Ø Aging
Ø Hypercorticism
Ø Hyperthyroidism
Ø Calcium deficiency
Osteomalacia and Rickets
- both have inadequate calcification/mineralization of newly formed bone matrix
- rickets – childhood form
- osteomalacia – adult form
- Causes
Ø Vitamin D deficiency
Ø Hypophosphatemia
Ø Defects in mineralization process
Clinical Presentation
- depends on a # of factors (severity, duration, and age of onset)
- Rickets (childhood form)
Ø deformities at sites of rapid growth
Ø craniotabes = thinning of skull (leads to frontal bossing)
Ø rachitic rosary
Ø enlarged wrists and ankles
Ø pigeon breast deformity
Ø lumbar lordosis, femur bowing
- Osteomalacia (adult form)
Ø non-specific aches
Ø bone pain
Ø NO SKELETAL DEFORMITIES
XR
- Looser’s zones/Milkman’s fractures
Ø represent inadequately healed stress fractures or mechanical erosion by penetrating nutrient arteries
- loss of bone density and cortical thickness
Histology
- Rickets (childhood form)
Ø lots of non-mineralized bone (osteoid)
Ø lack of calcified cartilage
- Osteomalacia
Ø increase in amount of osteoid
Ø loss of bone density and cortical thickness
Tags: achondroplasia, Albers-Schonberg Disease, Avascular Necrosis, Blue sclerae, Osteitis Deformans, osteogenesis imperfecta, osteomyelitis, Osteonecrosis, Osteopetrosis, Paget's disease, Pyogenic Osteomyelitis, Salmonella, Tuberculous Osteomyelitis
