BMD Flashcards
What is osteoporosis?
A progressive systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue.
What is osteopenia?
A clinical term used to describe a decrease in bone mineral density (BMD) below normal reference.
Why is osteoporosis more common in women?
Woman have a lower peak bone mass
Hormonal changes at menopause - loss of oestrogen
Longer life expectancy
What are cortical bones?
Outer envelope of all bones and shafts of long bones
What are trabecular bones?
Inner parts of bones (spongy insides)
Describe the bone remodelling process and its function in the skeletal system?
It is the resorption of old or damaged bone by Osteoclast, followed by the deposition of new bone material by Osteoblast.
This process protects the structural integrity of the skeletal system and contributes to the body’s balance of calcium and phosphorus.
What are some unmodifiable risk factors of osteoporosis?
Age - Elderlies
Poor health/Frailty
Height loss of more than 2cm over 3 years
History of fracture in a first degree relative
Low body weight
Personal history of previous fragility fracture as an adult
Female esp. elderly female.
What are some modifiable risk factors of osteoporosis? (lifestyle)
Current cigarette smoking
Alcohol abuse
Low calcium intake
Lack of regular physical activity
Prolonged immobilisation (sedentary lifestyle)
What are some secondary risk factors of osteoporosis?
Drugs
Ongoing disease conditions (esp. endocrine)
Early natural or surgical menopause before age 45 years.
Other conditions that can affect bone density
Paget’s disease (increase BMD)
Osteogenesis Imperfecta
Osteomalacia
Rickets
Neoplams
Autoimmune disorders
Fibrous dysplasia
What is DXA?
Dual Energy X-ray Absorptiometry (DXA)
Uses dual (high and low peak) energy to differentiate soft tissue and bones
Primarily assess the central and peripheral skeleton.
What is a commonly practised way to produce dual energies in Singapore?
Voltage Switching (Switching X-ray)
- 70 and 140 kV
Manufactured by Hologic (company)
Explain the differential absorption by bone and soft tissues using dual energies?
Low energy (30 - 50keV)
- Bone attenuation greater than soft tissue attenuation
High energy (>70keV)
- Bone attenuation similar to soft tissue attenuation
- Suppress impact of overlying soft tissue.
What is the measurement unit of BMD?
g/cm2
Which is the prevalent dataset in Singapore for reference?
Hologic Singapore Reference Dataset
What do central DXA measures?
Spine and Hip
What do peripheral DXA measures?
Forearm
Where is the primary measurement site for BMD Screening?
Lumbar Spine, L1 - L4
(with an exclusion allowance of up to 2 vertebrae in cases of structural abnormality or artifact)
Why is Lumbar Spine used as primary measurement site for BMD Screening?
Due to the lack of rib obstruction and more consistent visual uniformity
What are the positioning key areas to note (hologic)
- Shoulders positioned directly under the upper lateral indicator lines
- Legs to be raised to achieve a 90 degree bend at the hips with legs supported with provided spine cushion
- Positioning laser centred at umbillicus
- Patient to remain still during the scan
What are the contraindications to BMD Scans?
Pregnancy
Obstructions to GI tract (Contrast media, calcium/iron pills)
Unable to lie supine
Unable to keep still
Full spine/Hip instrumentation
Apart from Spinal measurement, what is another routine procedure done using BMD?
Proximal Femur (Hip Scan).
What is T-Score and what is it used for?
It is the primary diagnostic value used for postmenopausal osteoporosis.
To compare bone density measurement to a young adult reference population, presumably at peak bone mass.
T-score more or equal to -1 SD = Diagnosis?
Normal
-1 > T-score> -2.5 SD = Diagnosis?
Low bone mass/Osteopenia
T-score lesser or equal to -2.5 = Diagnosis?
Osteoporosis
What is Z-scores used for?
To diagnose low bone mass in children, premenopausal women and men less than 50 years of age.
Used to compare bone density measure to an age-matched reference population.
What is the purpose of Whole Body Composition?
To estimate the proportion of fat mass to fat-free mass (bone and muscle)
Usually used for nutritional assessment and research purposes.
