• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Home
  • Online Consultation
  • About
  • Newsletter/Updates
  • Contact Us
  • Policies

Bone and Spine

Orthopedic health, conditions and treatment

  • General Ortho
  • Procedures
  • Spine
  • Upper Limb
  • Lower Limb
  • Pain
  • Trauma
  • Tumors

DEXA Scan or Dual-energy X-ray Absorptiometry

By Dr Arun Pal Singh

In this article
    • Indications For DEXA Scan
      • The Test
      • Interpretation
      • Related

DEXA [Now abbreviated as DXA] or dual-energy x-ray absorptiometry is a technique used to measure bone density.

Dexa scan involves passing two X-ray beams with different energy levels are aimed at the patient’s bones, and bone mineral density is determined from absorption of each bone after soft tissue absorption is subtracted out.

The test is also called bone density scanning or bone densitometry. Most commonly, the test is performed in hip and spine bones. However, in children and some adults, the whole body is sometimes may be scanned.

DEXA is the most widely used bone density measurement procedure.

A typical use of DEXA procedure is to diagnose and follow osteoporosis.

DEXA scan in use
DEXA scan in use

Indications For DEXA Scan

  • Females age 65 and above
  • Males age 70 and above
  • People over age 50 with previous bone fracture from trauma,  rheumatoid arthritis, low body weight or a parent with a hip fracture
  • Individuals with vertebral abnormalities.
  • Individuals receiving or planning to receive, long-term steroid therapy.
  •  Individuals with primary hyperparathyroidism.
  •  To assess the response or efficacy of an approved osteoporosis drug therapy.
  • Individuals with a history of eating disorders
  • A fracture following a minor fall or injury.
  • An early menopause (aged less than 45).

The Test

One should not have undergone any radionuclide stud 0r barium contrast studies for 2 weeks before undergoing the test. It takes less than 15 minutes to complete the test.

A DEXA scan uses low-energy X-rays. A machine sends X-rays from two different sources through the bone being tested. Bone blocks a certain amount of the X-rays with denser bone blocking more that lighter bone. Two x-ray sources improve accuracy over one.

The amount of X-rays that comes through the bone from each of the two X-ray sources is measured by a detector. This information is sent to a computer for calculation.

There are two different types of DEXA scanning devices:

  • Central DEXA devices are large machines that can measure bone density in the center of your skeleton, such as hip and spine.
  • Peripheral DEXA devices are smaller, portable machines that are used to measure bone density on the periphery of skeletons, such as your wrist, heel or finger.

Interpretation

The images can be used to evaluate bone mineral content [calcium] of the bone. The amount of calcium correlates with bony content and with bone strength. In clinical practice, bone mineral density measurements are widely used to diagnose osteoporosis. This is done by calculating T and Z scores.

Instead, T score is calculated which is the difference between the measured bone mineral density and the mean value of young adults, expressed in standard deviations (SD) for a normal population of the same gender and ethnicity.

According to WHO diagnostic criteria for osteoporosis

  • T-score below 2.5 – osteoporosis
  • T-score is between -2.5 and -1 – osteopenia

T-score

T score is calculated as

T Score =(patient’s BMD – young normal mean)/SD of young normal.

For example, if a patient has a BMD of 0.700 g/cm , the young normal mean is 1.000 g/cm², and the young normal standard deviation is 0.100 g/cm² then

T-score = (0.700 – 1.000)/0.100  = –0.300/0.100 =  –3.0 and has osteoporosis.

Z-score

Z score is the DXA reports also provide Z-scores, which are calculated similarly to the T-score, except that the patient’s BMD is compared with an age-matched (and race- and gender-matched) mean as comparing all patients to young adult data may lead to overdiagnosis of osteoporosis.

In children, comparing the bone mineral density of children to the reference data of adults ( T-score) would lead to an over-diagnosis of osteopenia for children. To avoid an overestimation of bone mineral deficits, Z score is calculated by comparing the patient to reference data for the same gender and age.

Because DEXA calculates BMD using area, it is not an accurate measurement of true bone mineral density, which is mass divided by a volume.

However, it is still a fairly accurate measure of bone mineral content and is, by far, the most widely used technique for bone measurements.

It is cheap, accessible, easy to use, and able to provide a fair estimation of bone mineral density in adults.

Image Credit: Wikipedia

Related

Spread the Knowledge
9
Shares
 
9
Shares
18   

Filed Under: Imaging

About Dr Arun Pal Singh

Arun Pal Singh is an orthopedic and trauma surgeon, founder and chief editor of this website. He works in Kanwar Bone and Spine Clinic, Dasuya, Hoshiarpur, Punjab.

This website is an effort to educate and support people and medical personnel on orthopedic issues and musculoskeletal health.

You can follow him on Facebook, Linkedin and Twitter

Primary Sidebar

Browse Articles

bone island xray

Bone Island or Enostosis

A bone island or enostosis is a common benign bone lesion. It is asymptomatic and does not require treatment. It is usually seen as an incidental finding on x-ray, computed tomogram and MRI. A bone island is a focus of mature cortical bone within the cancellous bone.  Pelvis, femur, and other long bones are the […]

Diagram of Risser sign

Risser Sign and Its Use in Scoliosis

The Risser sign, also called Risser index or Risser classification is a system used to assess and grade skeletal maturity based on the level of ossification and fusion of the iliac crest apophyses. The apophyses (singular: apophysis) are the normal bony outgrowths which have separate ossification centers and eventually fuse with the bone in time. Iliac […]

freiberg disease

Freiberg Disease or Osteochondrosis of Metatarsal Head

Freiberg disease is an uncommon condition which was described by Alfred H. Freiberg in 1914. Freiberg disease or infraction is a painful collapse of the articular surface of the metatarsal head. Second or third metatarsal heads are most commonly involved. First and fifth metatarsals show least common involvements. Bilateral involvement has been reported to occur […]

Shanz proximal femoral osteotomy

Proximal femoral Osteotomy

Proximal femoral osteotomy is a joint-sparing procedure that relies on maintaining the biologic integrity of the femoral head. Once common for hip dysplasia and arthritis of the hip, proximal femoral osteotomies are performed less commonly now. But they are still used in the treatment of hip fracture nonunions and malunions and in cases of congenital […]

nail anatomy

Nail Anatomy and Funtions

The nail is an integral component of the digital tip. It is a unique hardened structure formed by keratinized squamous cells. Nail functions to protect the fingertip and provides a counterforce to tactile sensation and for aiding in the grip formed by fingertips [ as in pinching]. It is also involved in temperature control [thermoregulationion] which […]

Iliopsoas Tendinitis

Iliopsoas Tendonitis Presentation and Treatment

Iliopsoas tendonitis or tendinitis is an inflammation of the tendon or surrounding tissue caused mainly by acute trauma and overuse due to repetitive hip flexion. Iliopsoas tendinitis and iliopsoas bursitis are closely interrelated because inflammation of one inevitably causes inflammation of the other because of the proximity of two structures. These two conditions are also […]

Russel traction

Skin Traction – Indications, Uses and Complications

Skin traction is a type of traction that transmits the force via skin. Traction is a directional pull on the trunk or on an extremity. The main goals of the use of  skin traction are Control muscle spasms and pain resulting due to them Reduction of the fractures Prevention and correction of the deformity. Skin […]

© Copyright: BoneAndSpine.com
Manage Cookie Consent
The site uses cookies. Please accept cookies for a better visiting experience.
Functional Always active
The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network.
Preferences
The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user.
Statistics
The technical storage or access that is used exclusively for statistical purposes. The technical storage or access that is used exclusively for anonymous statistical purposes. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you.
Marketing
The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes.
Manage options Manage services Manage vendors Read more about these purposes
View preferences
{title} {title} {title}
 

Loading Comments...