Pathogenesis and bone tissue changes
The human skeleton is constantly renewing itself: about 10% of bone tissue is remodeled annually. Two groups of cells are responsible for this process: osteoblasts (build new bone) and osteoclasts (break down old bone).
Normally, their work is balanced, but with age or under the influence of various factors, osteoblast activity decreases. Osteoclasts begin to dominate, and the rate of resorption exceeds the rate of bone formation. At the microscopic level, the bone tissue itself remains normal, but there is less of it: trabeculae become thinner, and porosity increases. Because of this, the bone loses mechanical strength, resembling perforated paper that easily tears even under slight stress.
Diagnostics: Densitometry and criteria
Conventional radiography has low efficacy for early diagnosis, as changes on X-rays become visible only after a loss of about 50% of bone mass.
The gold standard for diagnosis is dual-energy X-ray absorptiometry (DEXA or densitometry). The examination is performed in the proximal femur and lumbar spine regions.
Results are evaluated using two parameters:
- T-score (T-score): compares the patient's bone density with the peak bone mass of a young, healthy adult.
- Normal: > -1.0 SD
- Osteopenia: from -1.0 to -2.5 SD
- Osteoporosis: ≤ -2.5 SD
- Z-score (Z-score): compares density with the age-matched normal value. A low Z-score indicates secondary causes of bone mass loss.
Risk factors and prevention
Maximum skeletal strength (peak bone mass) is achieved by approximately 30 years of age, after which a gradual decline begins. In women, this process accelerates sharply during menopause.
Highest risk group: underweight postmenopausal Caucasian or Asian women. In men, decreased bone density is more often secondary (associated with smoking, alcoholism, low testosterone, or glucocorticoid intake).
Basic preventive measures:
- Adequate intake of calcium (at least 1200 mg/day) and vitamin D (800–2000 IU/day).
- Weight-bearing physical exercises.
- Smoking cessation and limitation of excess alcohol.
- Fall prevention (improving balance, safe home environment).
Briefly: answers to topical questions
What are the main differences between the T-score and Z-score in densitometry?
The main differences lie in the baseline used to compare bone mineral density and the clinical purpose of the parameters.
| Characteristic | T-score (T-score) | Z-score (Z-score) |
|---|---|---|
| Comparison baseline | Average peak bone mass of a young healthy adult | Age-matched cohort of people |
| Indication | Diagnosis of osteoporosis | Search for secondary causes of bone mass loss |
What are the main indications for bone mineral density screening?
The main indications for bone mineral density screening are age and anamnestic factors in women. Screening for osteoporosis is indicated for the following patient groups:
- Age factor — all women aged over 65 years.
- burdened history — women of any age with risk factors for osteoporosis.
Class and exam questions
What is the difference between osteopenia and osteoporosis?
The difference lies in the degree of bone mineral density loss according to densitometry data. Osteopenia is a T-score from -1.0 to -2.5, and osteoporosis is less than -2.5.
Why is osteoporosis called a "silent" disease?
Because the decrease in bone mass is asymptomatic. The patient often remains unaware of the problem until the first low-energy fracture occurs (for example, from a standing height fall).
Why are calcium, vitamin D, and PTH blood tests prescribed for fractures?
These tests are necessary to exclude secondary osteoporosis. In primary (age-related or postmenopausal) osteoporosis, routine laboratory parameters usually remain within normal limits.
What else to study on this topic
- Typical fractures in osteoporosis (Colles' fracture, hip fracture, vertebral fracture) and their age peaks
- Secondary osteoporosis: differential diagnosis and causes (Z-score)
- Pharmacotherapy of osteoporosis: bisphosphonates, RANK ligand inhibitors, and anabolics
- Clinical presentation of late stages (kyphosis, height loss)
- Indications for DEXA densitometry according to guidelines
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