Osteoporosis 1+2 W4 Flashcards
There are 2 main types of bone
Cortical bone
- 80%
- compact bone that forms the dense outer supporting structure
Trabecular bone
- 20%
- spongy bone that forms the inner supporting structure
- composed of a lattice or network of branching bone spicules or trabeculae and spaces filled with bone marrow
Bone
No a static tissue
Constantly undergoes renewal called remodelling where old bone is removed and replaced by new bone
Bone remodelling q
Complex interaction between:
- Bone resorbing cells called osteoclasts
- Bone forming cells called osteoblasts
Osteoblasts
▪ Fill in bony cavity with bone matrix
▪ Release cytokines to attract osteoclasts
Osteoclasts
Release proteases which:
▪ dissolve the bone mineral matrix and collagen
▪ clear damaged bone
▪ Release chemicals that attract osteoblasts
Control of Bone Remodelling
Bone remodelling is under the control of:
⚫ Systemic hormones
- Parathyroid hormone
- Sex hormones (Oestrogen Androgens)
⚫ Activated vitamin D
⚫ Cytokines
- Interleukin-1 and Interleukin-6
- Tumour necrosis factor (TNF-alpha)
- Granulocyte colony stimulating factor (GCSF).
⚫ External factors
Bone mass is determined by:
Peak bone mass that was attained at
around age 30 years
Rate of bone loss that commences in 4th
decade
Rate of bone loss is determined by
Genetic factors (approx 75%)
- More likely to have osteoporosis if strong family history
- Possible involvement of several genes investigated: (Vitamin D receptor gene, oestrogen receptor gene, Interleukin (IL)-6 gene)
Rate of bone loss is also determined by
Environmental factors = risk factors for osteoporosis:
1. Low calcium intake and/or absorption
2. Low vitamin D intake or lack of
exposure to sunlight
3. Physical inactivity
4. Alcohol
5. Smoking
6. Thin body type
Osteoporosis
is a common metabolic bone disease characterised by a reduction in bone mass per unit volume (thinning of the bones) that occurs with increasing age
Or
A systemic skeletal disease characterised by low bone mass and micro-architectural deterioration of bone tissue with a consequent increase in bone fragility and susceptibility to fracture
WHO Definition
WHO defines osteoporosis on the basis of bone
mineral density (BMD) related to age
T-score
number of standard deviations by
which the individual’s BMD (g/cm2) differs from
the mean peak BMD for young adults of the
same gender
Fracture risk
doubles for every standard
deviation below the mean
Normal T-score
Above -1
Osteopenia t-score
Low bone mass
Between -1 and -2.5
Osteoporosis t-score
-2.5 or less
Establish osteoporosis t-score
-2.5t or less and fracture
How common is osteoporosis
Risk of suffering an osteoporotic fracture in people over 50 years is:
One in two women
One in five men
Detection of Osteoporosis
Xray is not capable of detecting bone loss until at least 30% of bone mass is lost
Not sufficiently reliable to diagnose or quantify osteopenia or osteoporosis
Dual Energy X-ray Absorptiometry (DEXA) scan is used
Enables accurate and reproducible measurement of BMD
Primary osteoporosis
Most common form
Diagnosed when the patient has no other disorders known to cause osteoporosis present
Secondary Osteoporosis
Osteoporosis related to:
Another medical condition
- Anorexia nervosa
- IBD
- Endocrine: E.g. Type 1 DM, Cushing’s syndrome, hyperthyroidism
- RA
The use of drug therapy
- Most commonly steroid-induced
Corticosteroids
Most common cause of secondary
osteoporosis accounting for up to
13% of cases in males and 10% of
cases in females
Steroids:
- Decrease osteoblast activity and active life span
- Decrease calcium absorption from the intestine and increase renal calcium loss causing abnormal PTH and vitamin D activity
- Suppress sex hormone production
Fragility fracture
Fracture that occurs as a result of
mechanical forces that would not ordinarily
cause fracture
WHO quantifies this as a force equivalent to
a fall from a standing height or less
