Bone density

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A scanner used to measure bone density using dual energy X-ray absorptiometry Bone density scanner.jpg
A scanner used to measure bone density using dual energy X-ray absorptiometry

Bone density, or bone mineral density, is the amount of bone mineral in bone tissue. The concept is of mass of mineral per volume of bone (relating to density in the physics sense), although clinically it is measured by proxy according to optical density per square centimetre of bone surface upon imaging. [1] Bone density measurement is used in clinical medicine as an indirect indicator of osteoporosis and fracture risk. It is measured by a procedure called densitometry, often performed in the radiology or nuclear medicine departments of hospitals or clinics. The measurement is painless and non-invasive and involves low radiation exposure. Measurements are most commonly made over the lumbar spine and over the upper part of the hip. [2] The forearm may be scanned if the hip and lumbar spine are not accessible.

Contents

There is a statistical association between poor bone density and higher probability of fracture. Fractures of the legs and pelvis due to falls are a significant public health problem, especially in elderly women, leading to substantial medical costs, inability to live independently and even risk of death. [3] Bone density measurements are used to screen people for osteoporosis risk and to identify those who might benefit from measures to improve bone strength.

Testing

A bone density test may detect osteoporosis or osteopenia. [4] The usual response to either of these indications is consultation with a physician. [4] Bone density tests are not recommended for people without risk factors for weak bones, [5] [4] which is more likely to result in unnecessary treatment rather than discovery of a weakness. [4]

Indications for testing

The risk factors for low bone density and primary considerations for a bone density test include:

Other considerations that are related to risk of low bone density and the need for a test include smoking habits, drinking habits, the long-term use of corticosteroid drugs, and a vitamin D deficiency. [4]

Test result terms

Results of the test are reported in three forms:

Types of tests

Illustration of Bone Densitometry Scan Blausen 0095 BoneDensitometryScan.png
Illustration of Bone Densitometry Scan

While there are many types of bone mineral density tests, all are non-invasive. The tests differ according to which bones are measured to determine the test result.

These tests include:

DXA is the most commonly used testing method as of 2016. [7] The DXA test works by measuring a specific bone or bones, usually the spine, hip, and wrist. The density of these bones is then compared with an average index based on age, sex, and size. The resulting comparison is used to determine the risk for fractures and the stage of osteoporosis (if any) in an individual.

Quantitative ultrasound (QUS) has been described as a more cost-effective approach for measuring bone density, as compared to DXA. [8]

Average bone mineral density = BMC / W [g/cm2]

Interpretation

Results are generally scored by two measures, the T-score and the Z-score. Scores indicate the amount one's bone mineral density varies from the mean. Negative scores indicate lower bone density, and positive scores indicate higher.

Less than 0.5% of patients who underwent DXA-scanning were found to have a T- or Z-score of more than +4.0, often the cause of an unusually high bone mass (HBM) and associated with mild skeletal dysplasia and the inability to float in water. [9]

T-score

The T-score is the relevant measure when screening for osteoporosis. It is the bone mineral density at the site when compared to the "young normal reference mean". It is a comparison of a patient's bone mineral density to that of a healthy 30-year-old. [10] The US standard is to use data for a 30-year-old of the same sex and ethnicity, but the WHO recommends using data for a 30-year-old white female for everyone. [11] Values for 30-year-olds are used in post-menopausal women and men over age 50 because they better predict risk of future fracture. [12] The criteria of the World Health Organization are: [13]

  • Normal is a T-score of −1.0 or higher [14]
  • Osteopenia is defined as between −1.0 and −2.5
  • Osteoporosis is defined as −2.5 or lower, meaning a bone density that is two and a half standard deviations below the mean of a 30-year-old man/woman.
Hip fractures per 1000 patient-years [15]
WHO categoryAge 50–64Age > 64Overall
Normal5.39.46.6
Osteopenia 11.419.615.7
Osteoporosis 22.446.640.6

Z-score

The Z-score for bone density is the comparison to the "age-matched normal" and is usually used in cases of severe osteoporosis. This is the standard score or number of standard deviations a patient's bone mineral density differs from the average for their age, sex, and ethnicity. This value is used in premenopausal women, men under the age of 50, and in children and adolescents. [12] [16] It is most useful when the score is less than 2 standard deviations below this normal. In this setting, it is helpful to scrutinize for coexisting illnesses or treatments that may contribute to osteoporosis such as glucocorticoid therapy, hyperparathyroidism, or alcoholism.

Prevention

To prevent low bone density it is recommended to have sufficient calcium and vitamin D. [17] [18] Sufficient calcium is defined as 1,000 mg per day, increasing to 1,200 mg for women above 50 and men above 70. [18] Sufficient vitamin D is defined as 600 IUs per day for adults 19 to 70, increasing to 800 IUs per day for those over 71. [18] Exercise, especially weight-bearing and resistance exercises are most effective for building bone. Weight-bearing exercise includes walking, jogging, dancing, and hiking. Resistance exercise is often accomplished through lifting weights. [19] Other therapies, such as estrogens (e.g., estradiol, conjugated estrogens), selective estrogen receptor modulators (e.g., raloxifene, bazedoxifene), and bisphosphonates (e.g., alendronic acid, risedronic acid), can also be used to improve or maintain bone density. Tobacco use and excessive alcohol consumption have detrimental effects on bone density. [20] [18] Excessive alcohol consumption is defined as more than one standard-sized alcoholic beverage per day for women, and drinking two or more alcoholic beverages per day for men. [18]

Genetics

Bone mineral density is highly variable between individuals. While there are many environmental factors that affect bone mineral density, genetic factors play the largest role. [7] [21] Bone mineral density variation has been estimated to have 0.6-0.8 heritability factor, meaning that 60-80% of its variation is inherited from parents. [22] Because of the heritability of bone mineral density, family history of fractures is considered as a risk factor for osteoporosis. [23] Bone mineral density is polygenic and many of the genetic mechanisms remain poorly understood. [21]

Genetic diseases associated with bone mineral density

There are several rare genetic diseases that have been associated with pathologic changes in bone mineral density. The table summarizes these diseases: [24] [23]

DiseaseGene AffectedInheritanceSource
Osteogenesis Imperfecta COLIA1Autosomal Recessive [24] [23]
Osteogenesis Imperfecta COLIA2Autosomal Recessive [24] [23]
Osteoporosis Pseudoglioma Syndrome LRP5Autosomal Recessive [23]
Osteopetrosis TCIRGIAutosomal Recessive [23]
Camurati-Engelmann Disease TGFβ-1Autosomal Recessive [23]
Van Buchem Disease SOSTAutosomal Recessive [23]
Severe Infantile OsteopetrosisCLCN7Autosomal Recessive [23]

Related Research Articles

<span class="mw-page-title-main">Osteoporosis</span> Skeletal disorder

Osteoporosis is a systemic skeletal disorder characterized by low bone mass, micro-architectural deterioration of bone tissue leading to bone sterility, and consequent increase in fracture risk. It is the most common reason for a broken bone among the elderly. Bones that commonly break include the vertebrae in the spine, the bones of the forearm, the wrist, and the hip. Until a broken bone occurs there are typically no symptoms. Bones may weaken to such a degree that a break may occur with minor stress or spontaneously. After the broken bone heals, the person may have chronic pain and a decreased ability to carry out normal activities.

<span class="mw-page-title-main">Dual-energy X-ray absorptiometry</span> Diagnostic test for bone mineral density testing

Dual-energy X-ray absorptiometry is a means of measuring bone mineral density (BMD) using spectral imaging. Two X-ray beams, with different energy levels, are aimed at the patient's bones. When soft tissue absorption is subtracted out, the bone mineral density (BMD) can be determined from the absorption of each beam by bone. Dual-energy X-ray absorptiometry is the most widely used and most thoroughly studied bone density measurement technology.

<span class="mw-page-title-main">Teriparatide</span> Pharmaceutical drug for treating osteoporosis

Teriparatide, sold under the brand name Forteo, is a form of parathyroid hormone (PTH) consisting of the first (N-terminus) 34 amino acids, which is the bioactive portion of the hormone. It is an effective anabolic agent used in the treatment of some forms of osteoporosis. Teriparatide is a recombinant human parathyroid hormone analog. It has an identical sequence to the 34 N-terminal amino acids of the 84-amino acid human parathyroid hormone.

<span class="mw-page-title-main">Alendronic acid</span> Chemical compound

Alendronic acid, sold under the brand name Fosamax among others, is a bisphosphonate medication used to treat osteoporosis and Paget's disease of bone. It is taken by mouth. Use is often recommended together with vitamin D, calcium supplementation, and lifestyle changes.

Kallmann syndrome (KS) is a genetic disorder that prevents a person from starting or fully completing puberty. Kallmann syndrome is a form of a group of conditions termed hypogonadotropic hypogonadism. To distinguish it from other forms of hypogonadotropic hypogonadism, Kallmann syndrome has the additional symptom of a total lack of sense of smell (anosmia) or a reduced sense of smell. If left untreated, people will have poorly defined secondary sexual characteristics, show signs of hypogonadism, almost invariably are infertile and are at increased risk of developing osteoporosis. A range of other physical symptoms affecting the face, hands and skeletal system can also occur.

<span class="mw-page-title-main">Osteopenia</span> Medical condition

Osteopenia, known as "low bone mass" or "low bone density", is a condition in which bone mineral density is low. Because their bones are weaker, people with osteopenia may have a higher risk of fractures, and some people may go on to develop osteoporosis. In 2010, 43 million older adults in the US had osteopenia. Unlike osteoporosis, osteopenia does not usually cause symptoms, and losing bone density in itself does not cause pain.

Renal osteodystrophy is currently defined as an alteration of bone morphology in patients with chronic kidney disease (CKD). It is one measure of the skeletal component of the systemic disorder of chronic kidney disease-mineral and bone disorder (CKD-MBD). The term "renal osteodystrophy" was coined in 1943, 60 years after an association was identified between bone disease and kidney failure.

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<span class="mw-page-title-main">Quantitative computed tomography</span>

Quantitative computed tomography (QCT) is a medical technique that measures bone mineral density (BMD) using a standard X-ray computed tomography (CT) scanner with a calibration standard to convert Hounsfield units (HU) of the CT image to bone mineral density values. Quantitative CT scans are primarily used to evaluate bone mineral density at the lumbar spine and hip.

<span class="mw-page-title-main">Relative energy deficiency in sport</span> Syndrome of disordered eating, oligomenorrhoea and osteopenia

Relative energy deficiency in sport (RED-S) is a syndrome in which disordered eating, amenorrhoea/oligomenorrhoea, and decreased bone mineral density are present. It is caused by eating too little food to support the amount of energy being expended by an athlete, often at the urging of a coach or other authority figure who believes that athletes are more likely to win competitions when they have an extremely lean body type. RED-S is a serious illness with lifelong health consequences and can potentially be fatal.

<span class="mw-page-title-main">Denosumab</span> Human monoclonal antibody

Denosumab is a human monoclonal antibody for the treatment of osteoporosis, treatment-induced bone loss, metastases to bone, and giant cell tumor of bone.

Senile osteoporosis has been recently recognized as a geriatric syndrome with a particular pathophysiology. There are different classification of osteoporosis: primary, in which bone loss is a result of aging and secondary, in which bone loss occurs from various clinical and lifestyle factors. Primary, or involuntary osteoporosis, can further be classified into Type I or Type II. Type I refers to postmenopausal osteoporosis and is caused by the deficiency of estrogen. While senile osteoporosis is categorized as an involuntary, Type II, and primary osteoporosis, which affects both men and women over the age of 70 years. It is accompanied by vitamin D deficiency, body's failure to absorb calcium, and increased parathyroid hormone.

Digital X-ray radiogrammetry is a method for measuring bone mineral density (BMD). Digital X-ray radiogrammetry is based on the old technique of radiogrammetry. In DXR, the cortical thickness of the three middle metacarpal bones of the hand is measured in a digital X-ray image. Through a geometrical operation the thickness is converted to bone mineral density. The BMD is corrected for porosity of the bone, estimated by a texture analysis performed on the cortical part of the bone.

Steroid-induced osteoporosis is osteoporosis arising from the use of glucocorticoids analogous to Cushing's syndrome but involving mainly the axial skeleton. The synthetic glucocorticoid prescription drug prednisone is a main candidate after prolonged intake. Bisphosphonates are beneficial in reducing the risk of vertebral fractures. Some professional guidelines recommend prophylactic calcium and vitamin D supplementation in patients who take the equivalent of more than 30 mg hydrocortisone, especially when this is in excess of three months. The use of thiazide diuretics, and gonadal hormone replacement has also been recommended, with the use of calcitonin, bisphosphonates, sodium fluoride or anabolic steroids also suggested in refractory cases. Alternate day use may not prevent this complication.

<span class="mw-page-title-main">Medication-related osteonecrosis of the jaw</span> Medical condition

Medication-related osteonecrosis of the jaw is progressive death of the jawbone in a person exposed to a medication known to increase the risk of disease, in the absence of a previous radiation treatment. It may lead to surgical complication in the form of impaired wound healing following oral and maxillofacial surgery, periodontal surgery, or endodontic therapy.

FRAX is a diagnostic tool used to evaluate the 10-year probability of bone fracture risk. It was developed by the University of Sheffield. FRAX integrates clinical risk factors and bone mineral density at the femoral neck to calculate the 10-year probability of hip fracture and the 10-year probability of a major osteoporotic fracture. The models used to develop the FRAX diagnostic tool were derived from studying patient populations in North America, Europe, Latin America, Asia and Australia.

The trabecular bone score is a measure of bone texture correlated with bone microarchitecture and a marker for the risk of osteoporosis. Introduced in 2008, its main projected use is alongside measures of bone density in better predicting fracture risk in people with metabolic bone problems.

Dual X-ray absorptiometry and laser technique (DXL) in the area of bone density studies for osteoporosis assessment is an improvement to the DXA Technique, adding an exact laser measurement of the thickness of the region scanned. The addition of object thickness adds a third input to the two x-ray energies used by DXA, better solving the equation for bone and excluding more efficiently these soft tissues components.

Single photon absorptiometry is a measuring method for bone density invented by John R. Cameron and James A. Sorenson in 1963.

<span class="mw-page-title-main">Radiofrequency Echographic Multi Spectrometry</span> Medical diagnostic

Radiofrequency Echographic Multi Spectrometry (REMS) is a non-ionizing technology for osteoporosis diagnosis and for fracture risk assessment. REMS processes the raw, unfiltered ultrasound signals acquired during an echographic scan of the axial sites, femur and spine. The analysis is performed in the frequency domain. Bone mineral density (BMD) is estimated by comparing the results against reference models.

References

  1. ↑ Bone+Density at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
  2. ↑ Cole RE (June 2008). "Improving clinical decisions for women at risk of osteoporosis: dual-femur bone mineral density testing". J Am Osteopath Assoc. 108 (6): 289–95. PMID   18587077.
  3. ↑ "Preventing Falls and Related Fractures | NIH Osteoporosis and Related Bone Diseases National Resource Center". www.bones.nih.gov. Retrieved 2021-03-12.
  4. 1 2 3 4 5 6 7 8 9 10 11 Consumer Reports; American Academy of Family Physicians (May 2012), "Bone-density tests: When you need them – and when you don't" (PDF), Choosing Wisely: an initiative of the ABIM Foundation , Consumer Reports, archived from the original (PDF) on March 4, 2016, retrieved August 14, 2012
  5. ↑ American Academy of Family Physicians, presented by ABIM Foundation, "Five Things Physicians and Patients Should Question" (PDF), Choosing Wisely: an initiative of the ABIM Foundation , American Academy of Family Physicians, archived from the original (PDF) on June 24, 2012, retrieved August 14, 2012
  6. 1 2 3 4 5 "Bone Mass Measurement". NOF. Archived from the original on 2008-03-07. Retrieved 2008-03-20.
  7. 1 2 Goolsby, Marci A.; Boniquit, Nicole (2016-11-30). "Bone Health in Athletes". Sports Health. 9 (2): 108–117. doi:10.1177/1941738116677732. ISSN   1941-7381. PMC   5349390 . PMID   27821574.
  8. ↑ "Bone densitometry" . Retrieved 2008-09-02.
  9. ↑ Gregson CL, Steel SA, O'Rourke KP, et al.: 'Sink or swim': an evaluation of the clinical characteristics of individuals with high bone mass. Journal Osteoporos Int./ Osteoporosis Int., 2012 Feb; 23(2): 643–654. Published online 2011 Apr 1. doi: 10.1007/s00198-011-1603-4. PMCID: PMC3261396. PMID   21455762
  10. ↑ "Bone Density Scan: MedlinePlus Medical Test". medlineplus.gov. Retrieved 2020-10-29.
  11. ↑ Unknown, Unknown (2011-07-29). "T and Z scores". University of Washington Bone Physics. Retrieved 2013-06-22.
  12. 1 2 Richmond, Bradford (2007-11-13). "Osteoporosis and bone mineral density". American College of Radiology. Archived from the original on 2008-09-17. Retrieved 2008-05-11.
  13. ↑ WHO Scientific Group on the Prevention and Management of Osteoporosis (2000 : Geneva, Switzerland) (2003). "Prevention and management of osteoporosis : report of a WHO scientific group" (PDF). Retrieved 2007-05-31.{{cite web}}: CS1 maint: numeric names: authors list (link)
  14. ↑ "Bone Mass Measurement: What the Numbers Mean | NIH Osteoporosis and Related Bone Diseases National Resource Center". www.bones.nih.gov. Retrieved 2021-03-12.
  15. ↑ Cranney A, Jamal SA, Tsang JF, Josse RG, Leslie WD (2007). "Low bone mineral density and fracture burden in postmenopausal women". Canadian Medical Association Journal. 177 (6): 575–80. doi:10.1503/cmaj.070234. PMC   1963365 . PMID   17846439.
  16. ↑ Bachrach LK (February 2005). "Assessing bone health in children: who to test and what does it mean?". Pediatr Endocrinol Rev. 2 (Suppl 3): 332–6. PMID   16456501.
  17. ↑ Lawrence, Jean. "Building Stronger Bones". WebMD. Retrieved 2020-04-20.
  18. 1 2 3 4 5 "How to keep your bones healthy". Mayo Clinic. Retrieved 2020-04-20.
  19. ↑ "Exercise for Your Bone Health | NIH Osteoporosis and Related Bone Diseases National Resource Center". www.bones.nih.gov. Retrieved 2020-11-09.
  20. ↑ "Smoking and Bone Health | NIH Osteoporosis and Related Bone Diseases National Resource Center". www.bones.nih.gov. Retrieved 2022-09-19.
  21. 1 2 Yang, Tie-Lin; Shen, Hui; Liu, Anqi; Dong, Shan-Shan; Zhang, Lei; Deng, Fei-Yan; Zhao, Qi; Deng, Hong-Wen (February 2020). "A road map for understanding molecular and genetic determinants of osteoporosis". Nature Reviews Endocrinology. 16 (2): 91–103. doi:10.1038/s41574-019-0282-7. ISSN   1759-5037. PMC   6980376 . PMID   31792439.
  22. ↑ Peacock, Munro; Turner, Charles H.; Econs, Michael J.; Foroud, Tatiana (2002-06-01). "Genetics of Osteoporosis". Endocrine Reviews. 23 (3): 303–326. doi: 10.1210/edrv.23.3.0464 . ISSN   0163-769X. PMID   12050122.
  23. 1 2 3 4 5 6 7 8 9 Huang, Qing-Yang; Kung, Annie Wai Chee (2006-08-01). "Genetics of osteoporosis". Molecular Genetics and Metabolism. 88 (4): 295–306. doi:10.1016/j.ymgme.2006.04.009. ISSN   1096-7192. PMID   16762578.
  24. 1 2 3 Marom, Ronit; Rabenhorst, Brien M.; Morello, Roy (2020-10-01). "Management of Endocrine Disease: Osteogenesis imperfecta: an update on clinical features and therapies". European Journal of Endocrinology. 183 (4): R95–R106. doi:10.1530/EJE-20-0299. ISSN   0804-4643. PMC   7694877 . PMID   32621590.
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