18 - Radiology of Metabolic Bone Disease Flashcards
Describe the balance of bone
Despite the static appearance of bone, it is a dynamic system, a constant balance of osteogenic and resorptive processes
Bone metabolism
- Cellular differentiation depending on metabolic state of bone
- Osteoblasts produce osteoid matrix an amorphous ground substance and collagen matrix
- Bone is made of ions having crystallized (hydroxyapatite) on the osteoid matrix forming the bone unit
Bone composition
- Water (8%)
- Organic substance (21%)
- Inorganic substance (71%)
If you’re looking at an image and wondering if it is an MRI or CT scan… In an MRI, the density is based on water content. There is very little water in cortical bone, so bone will be darker.
Osteogenesis
Making of bone
Process of osteogenesis
- Osteoblasts make osteoid from albumin, process is aided by vitamin A and C, estrogen and growth hormone
- Mineralization or calcification is triggered by the high affinity of osteoid matrix for hydroxyapatite
- Stimulated by a low oxygen tension and acidic environment
- Aided by a local alkaline environment
Bone making is stimualted by acidic and low oxygen, but it needs an alkaline environment to make bone - phosphate content creates this alkaline environment in the bone formation process
Osteolysis
Dissolution of bone
Process of osteolysis
- Osteoclasts and PTH hormone stimulate an acid phosphatase to proteolytic action on the osteoid crystals
- Osteoclasts are stimulated by high oxygen tension
- Aided by an acidic environment and a decrease in calcium and phosphate ions
Multi-system balance for bone health
- Normal functioning bone cells
- Adequate number of bone cells
- Nutritional balance
- Normal renal function
- Normal GI function
- Normal endocrine function
- Normal function stress-stimulations and nerve stimulations
If you’re going to do surgery on bone, you need to make sure your patient can heal and will be able to recover
Osteopenia
- A descriptive term for a loss of bone density observed RADIOGRAPHICALLY ***
- 50% bone loss is clinically significant
- 30% bone loss is RADIOGRAPHICALLY *** detectable
- Quantified by DEXA or ultrasound as T-scores and Z-scores
T- scores
WHO
- Normal = Bone density is within 1 SD (+1 or −1) of the young adult mean
- Low bone mass = Bone density is between 1 and 2.5 SD below the young adult mean (−1 to −2.5 SD).
- Osteoporosis = Bone density is 2.5 SD or more below the young adult mean (−2.5 SD or lower).
- Severe osteoporosis = Bone density is more than 2.5 SD below the young adult mean, and there have been one or more osteoporotic fractures
Osteopenia classifications
- Osteoporosis (generalized)
- Osteoporosis (localized)
- Osteomalacia/Rickets
- Endocrinopathies
- Marrow packing disorders
Generalized osteoporosis
- Definition: decrease in bone density (mass per unit volume) of mineralized bone
- Bone is normal, there’s just not enough of it
- Clinical and lab correlation required! You need to diagnose it!
Possible diagnoses for generalized osteoporosis
MOST COMMON
- Acquired (aging)
- Disuse (sedentary lifestyle)
Others
- Congenital (osteogenesis imperfecta)
- Deficiencies (vitamins, protein, calcium)
- Liver disease
- Hypoxemia
- Idiopathic
- Iatrogenic (steroid therapy, heparin therapy)
- Inborn errors
Radiographic findings in generalized osteoporosis
- Diminished bone density
- Cortical thinning with endosteal resorption
- Preferential resorption of transverse trabeculae
- Anterior wedging of the vertebral bodies
Scurvy (cause of generalized osteoporosis)
- Vitamin C deficiency (“orange peel” appearance of skin)
- Osteoblasts fail to produce osteoid
- Lack of mineralization
- Alcoholism/starvation
- Slow wound healing
- Hemorrhagic cutaneous lesions
The bone they have is normal, they just don’t have enough of it
Radiographic findings of Scurvy
- White line of scurvy
- Bone spicules at metaphyseal margins (Pelkin’s sign)
- Corner sign
- Trumifield zone
- Epiphyseal displacement (epiphyseal looks “washed out”)
- Ringed epiphysis
- Cortical deossification with ground glass appearance
Bone spicules are little sharp edges
Corner’s sign is when the sharp little spicules are washed out (gray inside)
Localized osteoporosis classifications
- Disuse atrophy
- Inflammatory (RA, osteomyelitis***)
- Tumores ***
- Sudeck’s atrophy (CRPS)
- Muscular paralysis
- Denervation or tendon section
Early radiographic findings of localized osteoporosis
Early: spotty loss of density with irregular rarefaction, loss of sharp outline of the articular cortex
Late radiographic findings of localized osteoporosis
Later: periarticular deossification
Final radiographic findings of localized osteoporosis
Final: uniform loss of density with a thin well-defined cortex
What do we call localized osteoporosis in tumors/infection?
In tumors and infection the process if referred to as lysis (lytic lesions)
Increased bone density around the outside with a central area of decreased bone density (the body is walling it off by forming bone around the outside)
Localized ostoporosis in Complex Regional Pain Syndrome (CRPS) Stages
- Stage I: Acute
- Stage II: Dystrophic
- Stage III: Atrophic
If the pain cycle hasn’t been broken in 6-8 weeks, they end up with an extremity with osteoporosis, called “Sudeck’s Atrophy”
Complex regional pain syndrome “Sudeck’s atrophy”
- Patchy osteoporosis
- Accentuated joints
- Subchondral bone resorption
- Ground-glass appearance
Osteopalacia and Rickets
- Defect in calcification with increased accumulation of uncalcified osteoid
- Vitamin D deficiency
- Renal tubular insufficiency
- Non-resorptive process *** (UNIQUE)
- HALLMARK FINDING = Skeletal deformity ***
Osteomalacia radiographic findings
- Generalized decrease in bone density
- Loss of trabecular detail
- Cortex may be thin and lack definition
- Skeletal deformities
- Looser’s lines (appear like a fracture, but are not actual fractures)
Rickets
- Widening of epiphyseal plate with a frayed appearance
Irregular zone of provisional calcification - Metaphyseal cupping
- Milkman’s fracture
BENDING of bones *** more so in children because
Endocrinopathies
- Hyperparathyroidism
- Hyperthyroidism
- Hyperadrenalism
- Diabetes
Radiographic features of endocrinopathies
- ***Subperiosteal resorption
- *** Generalized loss of bone density
- ***Terminal tuft resorption
- ***Brown tumors
- Soft tissue calcifications
Marrow packing disorders
- Thalassemia
- Multiple myeloma
- Leukemias
Radiographic disorders of marrow packing disorders
- *** Hyperplastic marrow response
- *** Expansile areas of lytic destruction
- Periosteal new bone formation
- Pathologic fracture
Osteosclerosis
Osteosclerosis: a descriptive term for an increase in bone density observed radiographically
Mechanism of osteosclerosis
- Failure of primary spongiosa to be absorbed in the metaphysis during enchondral bone formation
- Errors of internal modeling of compacta and spongiosa
- Stimulation of normal endogenous osteoblasts to form excessive new bone
Classification of osteosclerosis
“I’m not going to go through all of these, but if you see increased bone density, these are the things you can consider”
- Paget’s disease
- Osteopetrosis (Albers-Schonber)
- Myelofibrosis
- Fluorosis
- Bone healing
- Hypervitaminosis
- Insula compacta
- Neoplasm
- Osteopoikilosis
- Myositis ossificans
Paget’s disease
- Incidence: 5th decade
- Sites: skull, spine, pelvis and major long bones (my hat doesn’t fit anymore)
- Etiology: ? no idea
- Skeletal pain and deformity
- Alk Phosphatase, N-telopeptides and deoxypyridinoline
Radiographic findings in Paget’s disease
Lytic phase
- Destructive changes
- Flamed shaped-lesions
- Osteoporosis circumscripta
Sclerotic phase
- Bizarre new bone formation
Combined phase
- Malignant transformation where flame shaped lesions become malignant
Osteopetrosis
- Diagnosed as incidental or pathologic fracture
- Failure to absorb primary spongiosa
Two forms
- Bone deformity is rare
- No joint involvement
Radiographic findings of osteopetrosis
UNIFORM increase in bone density (can’t tell a difference, just more bone density all around)
- Uniform increase in bone density
- Loss of distinction between cortical and medullary bone
- Erlenmeyer flask appearance of tubular bones
- Bone within bone appearance
- Fractures are common
Osteopoikilosis
- Hereditary bone disorder
- Unknown etiology
- Incidental finding
Osteopoikilosis radiographic findings
- Multiple round/ovoid bone densities (“bone islands”)
- Few mm to several cm
- Non-progressive
- Metaphyseal and epiphyseal involvement in long bones
Myositis ossificans
- Heterotrophic soft tissue ossification
- Metaplasia
- Three variants
Radiographic findings of myositis ossificans
- Ill-defined calcifications
- Organization into bone
- Follows axis of muscle
- Adjacent periosteum may show changes
- Differentiate from sarcoma
Happens a lot in athletes - soft tissue is injured and bleeds, then heals as bone
Usually goes away on its own
Instead of a muscle or tendon healing normally, it heals as bone
