Osteoporosis other imaging findings

Osteoporosis Microchapters
Home
Patient Information
Overview
Historical Perspective
Classification
Pathophysiology
Causes
Differentiating Osteoporosis from other Diseases
Epidemiology and Demographics
Risk Factors
Screening
Natural History, Complications and Prognosis
Diagnosis
History and Symptoms
Physical Examination
Laboratory Findings
Electrocardiogram
X-ray
CT
MRI
Echocardiography or Ultrasound
Other Imaging Findings
Other Diagnostic Studies
Treatment
Medical Therapy Life Style Modification Pharmacotherapy
Surgery
Primary Prevention
Secondary Prevention
Cost-Effectiveness of Therapy
Future or Investigational Therapies
Case Studies
Case #1
Osteoporosis other imaging findings On the Web
Most recent articles
Most cited articles
Review articles
CME Programs
Powerpoint slides
Images
American Roentgen Ray Society Images of Osteoporosis other imaging findings All Images X-rays Echo & Ultrasound CT Images MRI
Ongoing Trials at Clinical Trials.gov
US National Guidelines Clearinghouse
NICE Guidance
FDA on Osteoporosis other imaging findings
CDC on Osteoporosis other imaging findings
Osteoporosis other imaging findings in the news
Blogs on Osteoporosis other imaging findings
Directions to Hospitals Treating Osteoporosis
Risk calculators and risk factors for Osteoporosis other imaging findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Eiman Ghaffarpasand, M.D. [2]

Overview

The most important modality for measuring bone mineral density (BMD), on which every osteoporosis diagnostic and therapeutic decision is based on, is dual energy X-ray absorptiometry (DEXA). DEXA is a 2-dimensional image of a 3-dimensional subject, mainly depends on the size of the bone which is studied. DEXA is the gold standard for the diagnosis of osteoporosis and fracture risk assessment. Finite element modeling (FEM) is an engineering computer-based simulation software that typically simulates the physical loading effects on materials. The effects may be strain or compression, while the subject is determined as net-like elements connected to each other. BMD is focused on density and does not imply for microstructure or architecture of bones. One of the most powerful methods to determine the microstructure is trabecular bone score (TBS) as a complementary method for DEXA.

Other imaging findings

Osteopenia with forearm measurement - Case courtesy of Dr Henry Knipe, Radiopaedia.org, rID 45996

Osteoporosis - Case courtesy of Dr Henry Knipe, Radiopaedia.org, rID 45997

Dual energy X-ray absorptiometery (DEXA, DXA)

• The most important modality for measuring bone mineral density (BMD), on which every osteoporosis diagnostic and therapeutic decision is based on, is dual energy X-ray absorptiometry (DEXA). DEXA is a 2-dimensional image of a 3-dimensional subject, mainly dependent on the size of the bone which is studied; therefore, explaining the variety of BMD seen among different sexes, body weights, and also ethnicity.
• Considering the effect of bone size on the 2-dimensional image of DEXA, the measured BMD is not reflecting the exact BMD; however, the DEXA fracture prediction would be better than 3-dimensional images, because small bones fracture easily than large bones.
• DEXA is the choice modality because of the following factors:
  • Short duration of procedure
  • High validity in BMD measurement (accuracy)
  • High reliability in BMD measurement (reproducible)
  • High range of application (different bone sites)

• DEXA is the best predictor of osteoporosis and osteoporotic fractures by means of central BMD surveys.
• For adults, it has to be always two sites of BMD measurement; lumbar spine, and femoral neck. In case, if both are unavailable for evaluation, forearm can also be used.
• For children (less than 20 years old), femoral maturity level may be different among the population, leading to lack of unique reference measure; thus, just one site of measurement (i.e., lumbar spine) is considered.
• Upon the world health organization (WHO) report in 1994, using the T-score (standard deviations (SD) below or above the average of young Caucasian women), BMD measures are divided into three groups:
  • T-score greater than -1.0 SD assumed as normal BMD
  • T-score between -1.0 and -2.5 SD assumed as osteopenia
  • T-score less than -2.5 SD assumed as osteoporosis

• Z-score is the same as the T-score, but the target population is matched for age, sex, race, and also in some studies, for weight.
• DEXA in men, almost always show higher BMD levels. But regarding the effect of bone size on DEXA measured BMD levels, it seems that higher BMD levels may be due to larger bones in men. Surprisingly, after matching the BMD levels, it is concluded that volumetric BMD is even lower in men. However, their fracture risk is same as women's risk; thus, the women's reference range of BMD is assumed for men, too.
• Regarding the vast advantages of DEXA (low radiation exposure, high availability, and tremendous information related to fracture risk), it seems that DEXA will remain the masterpiece of fracture risk assessment and also osteoporosis diagnosis.

Indications for BMD testing

• Women of age 65 and older and men of age 70 and older, regardless of clinical risk factors.
• Younger postmenopausal women, women in the menopausal transition, and men of age 50 to 69 with clinical risk factors for fracture.
• Adults who have a fracture at or after age 50.
• Adults with any condition that can increase the risk for osteoporosis (e.g., rheumatoid arthritis) or taking a medication (e.g., glucocorticoids in a daily dose ≥5 mg prednisone or equivalent for ≥3 months) associated with low bone mass or bone loss

BMD in children and adolescent

• The preferred skeletal sites for DXA measurements in children are lumbar spine (L1–4) and total body, excluding the head. The cranium should be excluded from the total body scan analysis because the head constitutes a large portion of the total body bone mass but changes little with growth, activity, or disease; thus, the inclusion of the skull may potentially mask gains or losses at other skeletal sites.

• For children younger than 5 years old, the spine bone mineral content (BMC) and BMD can be measured; whole-body measurements are feasible only for those aged 3 years or older. DXA measurements of the hip region (total hip or femoral neck) are not as reliable in younger patients (<13 years) because of difficulties in identifying the bony landmarks for this region of interest.
• Scans of alternative regions of interest are recommended in special cases. DXA assessments of the lateral distal femur can be valuable in children with immobilization disorders and in those with contractures who cannot be positioned properly for spine or whole-body studies. The distal radius can be measured in patients who exceed the weight limit for the DXA table or those who cannot transfer onto the table because of a mobilization disorder. Scanning of these alternate skeletal sites also may be necessary for patients with metal hardware (eg, rodding for scoliosis) in the standard regions of interest.
• A vertebral fracture that occurs without major trauma is an important indication of abnormal bone fragility. Because these fractures can be asymptomatic, some type of imaging is needed to rule out vertebral fractures in patients with high risks, such as those receiving long-term glucocorticoid therapy. In the past, a lateral thoracolumbar radiograph has been used to assess for loss of vertebral height. Alternatively, vertebral fracture analysis (VFA) by DXA has been used with far less radiation than conventional radiography.

Finite element modeling (FEM)

• Finite element modeling (FEM) is basically an engineering computer-based simulation software. FEM typically simulates the physical loading effects on materials. The effects may be strain or compression, while the subject determined as net-like elements connected to each other.
• Currently, basic models for FEM is provided by vQCT scanners. Then, elastic properties of bone can be measured with bone mineral density (BMD). Finally, all of the anisotropic, non-homogeneous, and complex geometry of the bone is presented to determine the risk of fracture.
• Studies have shown that however osteoporotic vertebrae are capable of bearing daily stresses as same as normal bones, but the stress that is encountered by the osteoporotic bone during forward bending may be more severe.

Trabecular bone score (TBS)

• Fracture risk assessment is very important in osteoporosis. It is based on a couple of factors, including age, body weight, and some past medical histories (e.g., smoking or alcohol use); and is measured by means of BMD assessment through DEXA scans.
• The main limitation of using BMD as the identifier of osteoporosis is that the BMD is focused on density and does not imply for microstructure or architecture of bones, at all. One of the most powerful methods to determine the microstructure is the trabecular bone score (TBS) as a complementary method for DEXA.
• TBS is a texture identifier of bones, measured and extracted from DEXA scan findings. TBS findings are including:
  • Elevated levels of TBS reflect the better microstructure of bones.
  • Reduced levels of TBS is associated with higher risk of fracture.
• The literature supports the use of TBS along with BMD to predict the fracture risk more precisely.
• The major characteristics of TBS are as follow:
  • TBS is reduced in postmenopausal women
  • TBS is reduced in men with previous osteoporotic fractures
  • TBS is complimentary for lumbar spine DEXA
  • TBS is reduced in women who experienced osteoporotic fractures (in whom DEXA was normal)
  • TBS is the same as lumbar spine BMD in predicting fracture risk in postmenopausal women
  • TBS is associated with fractures induced by bone mass loss