Table of Contents

Component Description

Users of the 2013-2014 dual-energy X-ray absorptiometry vertebral fracture assessment data (DXXVFA_H) are encouraged to read the documentation before accessing the data file.

Vertebral Fracture Assessment (VFA) is obtained using dual energy x-ray absorptiometry (DXA) to perform a lateral scan of the thoraco-lumbar spine. The image resolution of lateral spine scans obtained with DXA is close to the image resolution of a standard radiograph, but the DXA scan produces much lower radiation exposure (Lewiecki 2006, Genant 2000). Several studies have found that the accuracy of detecting moderate-to-severe vertebral fracture (as defined by the semiquantitative criteria of Genant (1993), is similar between DXA VFA and standard radiographs (Schousboe 2006, Hospers 2009, Fuerst 2009, Damiano 2006, Ferrar 2008, Vokes 2008). In 2013-2014, lateral DXA scans of the thoraco-lumbar spine were administered in the NHANES mobile examination center (MEC).

The Instant Vertebral Assessment (IVA) lateral spine scans provide vertebral fracture information for 13 individual vertebrae from T4-L4.

Eligible Sample

DXA scans were administered to eligible survey participants 40 years of age and older. Pregnant females were ineligible for the DXA examination. Participants who were excluded from the DXA examination for reasons other than pregnancy were considered to be eligible nonrespondents. Reasons for exclusion from the DXA examination were as follows:

  • Pregnancy (positive urine pregnancy test and/or self-report at the time of the DXA examination).
  • Self-reported history of radiographic contrast material (barium) use in past 7 days.
  • Self-reported weight over 450 pounds (DXA table limitation).

Participants were excluded from all spine scans if they reported a Harrington Rod in the spine for scoliosis.

The variable DXDLSPST indicates the examination status for the IVA lateral spine scan. The codes for DXDLSPST are as follows:

DXDLSPST – lateral spine scan examination status variable
1 = IVA lateral spine scan completed, all vertebra are valid
2 = IVA lateral spine scan completed, but one or more vertebrae is invalid
3 = IVA lateral spine not scanned, pregnancy
4 = IVA lateral spine not scanned, weight > 450 lbs
5 = IVA lateral spine not scanned, other reason

The main reasons for completed, but invalid, IVA lateral spine scans (code 2) were an insufficient scan area or partial scan, degenerative disease/severe scoliosis, sclerotic spine/spinal fusion/laminectomy and poor image quality due to morbid obesity. The “Not scanned, other reason” (code 5) includes no time to complete the examination, pregnancy test not completed, and participant refusal, as well as exclusion for reasons other than pregnancy, such as a medical test.

Protocol and Procedure

The IVA lateral spine scans were acquired on Hologic Discovery model A densitometers (Hologic, Inc., Bedford, Massachusetts), using software version Apex 3.2. The radiation exposure from DXA for the IVA lateral spine scan is extremely low at less than 20 uSv. All scans in the DXXVFA_H file were analyzed by Optasia Spinalizer software using Genant’s semiquantitative (SQ) technique (Genant 1993).

The DXA examinations were administered by trained and certified radiology technologists. Further details of the DXA examination protocol are documented in the Body Composition Procedures Manual located on the NHANES website: https://www.cdc.gov/nchs/nhanes/index.htm.

Quality Assurance & Quality Control

A high level of quality control was maintained throughout the DXA data collection and scan analysis, including a rigorous phantom scanning schedule.

Monitoring of Field Staff and Densitometers
Staff from the National Center for Health Statistics (NCHS) and the NHANES data collection contractor (Westat) monitored technologist acquisition performance through in-person observations in the field. Retraining sessions were conducted with the technologists annually and as needed to reinforce correct techniques and appropriate protocol. In addition, technologist performance codes were recorded by the NHANES quality control center at the University of California, San Francisco (UCSF), Department of Radiology during review of participant scans. The codes documented when the technologist had deviated from acquisition procedures and where scan quality could have been improved. The performance codes were tracked for each technologist individually and a summary was reported to NCHS on a quarterly basis. Additional feedback on technologist performance was provided by the UCSF when problems were noted during review of the scans. Ongoing communication was maintained throughout the year among the UCSF, the NCHS, and the data collection contractor regarding any issues that arose.

Hologic service engineers performed all routine densitometer maintenance and repairs. Copies of all reports completed by the manufacturer’s service engineers were sent to the UCSF when the scanners were serviced or repaired so any changes in measurement as a result of the work could be assessed.

Scan Analysis
Each participant scan and phantom scan was reviewed and analyzed by the UCSF using standard radiologic techniques and study-specific protocols developed for NHANES. The IVA lateral spine images were analyzed using a semiquantitative scoring system to identify vertebral deformities. The IVA AP spine image were used with the lateral spine images to more accurately define the deformities. The deformities were assessed by Optasia Spinalizer software using Genant’s semiquantitative (SQ) technique (Genant 1993) which is the standard for vertebral facture assessment and is recommended by the International Society of Clinical Densitometry (Schousboe 2008).

VFA images were read by a single reader at the UCSF QC center, who was trained by Dr. Harry Genant. Scans of all participants, who were coded as having a vertebral deformity on any vertebrae by the UCSF reader, were re-read by Dr. Genant to confirm fracture status. Dr. Genant’s readings were assigned as the final scores for these participants.

Invalidity Codes
Invalidity codes were applied by the UCSF to indicate the reasons spine regions of interest (ROI) could not be analyzed accurately. The invalidity codes are provided in the data file (see Data Processing and Editing section for a more detailed description of the invalidity codes).

Quality Control Scans
The quality control phantoms were scanned according to a predetermined schedule. The Hologic Anthropomorphic Spine Phantom that traveled with each MEC was scanned daily as required by the manufacturer to ensure accurate calibration of the densitometer. A Hologic Spine (HSP-Q96) Phantom and a Hologic Block Phantom circulated among the MECs and were scanned at the start of operations at each survey site.

The complete phantom scanning schedule is described in the Body Composition Procedures Manual located on the NHANES website.

In 2013-2014, longitudinal monitoring was conducted through daily spine phantom scans as required by the manufacturer in order to correct any scanner-related changes in participant data. The circulating HSP-Q96 and block phantoms, which were scanned at the start of operations at each site, provided additional data for use in longitudinal monitoring and cross calibration, as well as to monitoring the vertebrae dimension measurement.

A number of data quality issues were addressed through the quality control program. Direct feedback given to the technologists regarding acquisition problems affecting the quality of the scans and yearly refresher training resulted in improved technologist performance. The rigorous schedule of quality control scans provided continuous monitoring of machine performance. The expert review procedures helped to ensure that scan analysis was accurate and consistent.

Data Processing and Editing

During the editing process, data were reviewed for completeness, consistency, and outliers. Back-end edits of the data were performed when errors were identified.

Invalidity Codes
Invalidity codes were included in the data file to indicate the reasons and spine regions of interest (ROI) could not be analyzed accurately. Invalidity codes were applicable to completed scans only (DXDLSPST = 1 or 2). If a participant was not scanned, all invalidity codes are missing.

The invalidity codes are provided in the data file as follows:

Values for invalidity codes DXXT4CC, DXXT5CC, DXXT6CC, DXXT7CC, DXXT8CC, DXXT9CC, DXXT10CC, DXXT11CC, DXXT12CC, DXXL1CC, DXXL2CC, DXXL3CC and DXXL4CC

  • 0 = Valid data
  • 1 = Objects not removed
  • 2 = Non-removable objects such as implants
  • 3 = Excessive x-ray noise due to morbid obesity
  • 4 = Insufficient scan area
  • 5 = Movement
  • 6 = Other (degenerative diseases, spinal fusion, fractures)

Values for fracture scores (Genant semiquantitative criteria) DXXT4FX DXXT5FX DXXT6FX DXXT7FX DXXT8FX DXXT9FX DXXT10FX DXXT11FX DXXT12FX DXXL1FX DXXL2FX DXXL3FX and DXXL4FX

  • 0= Normal (Grade 0)
  • 1= Mild deformity (Grade 1)
  • 2= Moderate deformity (Grade 2)
  • 3= Severe deformity (Grade 3)

Analytic Notes

The NHANES examination sample weights should be used for any analyses using the DXXVFA_H data. Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial for further details on the use of sample weights and other analytic issues. Both of these are available on the NHANES website https://www.cdc.gov/nchs/nhanes/index.htm.

References

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:
SEQN
SAS Label:
Respondent sequence number
English Text:
Respondent sequence number.
Target:
Both males and females 40 YEARS - 150 YEARS

DXDLSPST - IVA Lateral Spine scan status

Variable Name:
DXDLSPST
SAS Label:
IVA Lateral Spine scan status
English Text:
Instant Vertebral Assessment (IVA) Lateral Spine scan status
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 IVA Lateral Spine scan completed, all vertebra are valid 2875 2875
2 IVA Lateral Spine scan completed, but one or more vertebrae are invalid 455 3330
3 IVA Lateral Spine not scanned, pregnancy 3 3333
4 IVA Lateral Spine not scanned, weight > 450 lbs 1 3334
5 IVA Lateral Spine not scanned, other reason 374 3708
. Missing 0 3708

DXXT4CC - T4 fracture invalidity code

Variable Name:
DXXT4CC
SAS Label:
T4 fracture invalidity code
English Text:
T4 fracture invalidity code
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Valid data 2987 2987
1 Objects not removed 1 2988
2 Non-removable objects such as implants 0 2988
3 Excessive x-ray noise due to morbid obesity 64 3052
4 Insufficient scan area 78 3130
5 Movement 0 3130
6 Other (degenerative diseases, spinal fusion, fractures) 200 3330
. Missing 378 3708

DXXT5CC - T5 fracture invalidity code

Variable Name:
DXXT5CC
SAS Label:
T5 fracture invalidity code
English Text:
T5 fracture invalidity code
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Valid data 3103 3103
1 Objects not removed 1 3104
2 Non-removable objects such as implants 0 3104
3 Excessive x-ray noise due to morbid obesity 57 3161
4 Insufficient scan area 15 3176
5 Movement 0 3176
6 Other (degenerative diseases, spinal fusion, fractures) 154 3330
. Missing 378 3708

DXXT6CC - T6 fracture invalidity code

Variable Name:
DXXT6CC
SAS Label:
T6 fracture invalidity code
English Text:
T6 fracture invalidity code
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Valid data 3189 3189
1 Objects not removed 1 3190
2 Non-removable objects such as implants 0 3190
3 Excessive x-ray noise due to morbid obesity 39 3229
4 Insufficient scan area 2 3231
5 Movement 0 3231
6 Other (degenerative diseases, spinal fusion, fractures) 99 3330
. Missing 378 3708

DXXT7CC - T7 fracture invalidity code

Variable Name:
DXXT7CC
SAS Label:
T7 fracture invalidity code
English Text:
T7 fracture invalidity code
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Valid data 3237 3237
1 Objects not removed 1 3238
2 Non-removable objects such as implants 0 3238
3 Excessive x-ray noise due to morbid obesity 29 3267
4 Insufficient scan area 1 3268
5 Movement 0 3268
6 Other (degenerative diseases, spinal fusion, fractures) 62 3330
. Missing 378 3708

DXXT8CC - T8 fracture invalidity code

Variable Name:
DXXT8CC
SAS Label:
T8 fracture invalidity code
English Text:
T8 fracture invalidity code
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Valid data 3272 3272
1 Objects not removed 1 3273
2 Non-removable objects such as implants 0 3273
3 Excessive x-ray noise due to morbid obesity 20 3293
4 Insufficient scan area 0 3293
5 Movement 0 3293
6 Other (degenerative diseases, spinal fusion, fractures) 37 3330
. Missing 378 3708

DXXT9CC - T9 fracture invalidity code

Variable Name:
DXXT9CC
SAS Label:
T9 fracture invalidity code
English Text:
T9 fracture invalidity code
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Valid data 3291 3291
1 Objects not removed 0 3291
2 Non-removable objects such as implants 3 3294
3 Excessive x-ray noise due to morbid obesity 12 3306
4 Insufficient scan area 0 3306
5 Movement 0 3306
6 Other (degenerative diseases, spinal fusion, fractures) 24 3330
. Missing 378 3708

DXXT10CC - T10 fracture invalidity code

Variable Name:
DXXT10CC
SAS Label:
T10 fracture invalidity code
English Text:
T10 fracture invalidity code
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Valid data 3301 3301
1 Objects not removed 0 3301
2 Non-removable objects such as implants 0 3301
3 Excessive x-ray noise due to morbid obesity 11 3312
4 Insufficient scan area 0 3312
5 Movement 0 3312
6 Other (degenerative diseases, spinal fusion, fractures) 18 3330
. Missing 378 3708

DXXT11CC - T11 fracture invalidity code

Variable Name:
DXXT11CC
SAS Label:
T11 fracture invalidity code
English Text:
T11 fracture invalidity code
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Valid data 3298 3298
1 Objects not removed 0 3298
2 Non-removable objects such as implants 0 3298
3 Excessive x-ray noise due to morbid obesity 12 3310
4 Insufficient scan area 0 3310
5 Movement 0 3310
6 Other (degenerative diseases, spinal fusion, fractures) 20 3330
. Missing 378 3708

DXXT12CC - T12 fracture invalidity code

Variable Name:
DXXT12CC
SAS Label:
T12 fracture invalidity code
English Text:
T12 fracture invalidity code
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Valid data 3291 3291
1 Objects not removed 0 3291
2 Non-removable objects such as implants 1 3292
3 Excessive x-ray noise due to morbid obesity 17 3309
4 Insufficient scan area 1 3310
5 Movement 1 3311
6 Other (degenerative diseases, spinal fusion, fractures) 19 3330
. Missing 378 3708

DXXL1CC - L1 fracture invalidity code

Variable Name:
DXXL1CC
SAS Label:
L1 fracture invalidity code
English Text:
L1 fracture invalidity code
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Valid data 3291 3291
1 Objects not removed 0 3291
2 Non-removable objects such as implants 2 3293
3 Excessive x-ray noise due to morbid obesity 20 3313
4 Insufficient scan area 3 3316
5 Movement 1 3317
6 Other (degenerative diseases, spinal fusion, fractures) 13 3330
. Missing 378 3708

DXXL2CC - L2 fracture invalidity code

Variable Name:
DXXL2CC
SAS Label:
L2 fracture invalidity code
English Text:
L2 fracture invalidity code
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Valid data 3281 3281
1 Objects not removed 0 3281
2 Non-removable objects such as implants 2 3283
3 Excessive x-ray noise due to morbid obesity 24 3307
4 Insufficient scan area 5 3312
5 Movement 1 3313
6 Other (degenerative diseases, spinal fusion, fractures) 17 3330
. Missing 378 3708

DXXL3CC - L3 fracture invalidity code

Variable Name:
DXXL3CC
SAS Label:
L3 fracture invalidity code
English Text:
L3 fracture invalidity code
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Valid data 3263 3263
1 Objects not removed 0 3263
2 Non-removable objects such as implants 14 3277
3 Excessive x-ray noise due to morbid obesity 26 3303
4 Insufficient scan area 6 3309
5 Movement 1 3310
6 Other (degenerative diseases, spinal fusion, fractures) 20 3330
. Missing 378 3708

DXXL4CC - L4 fracture invalidity code

Variable Name:
DXXL4CC
SAS Label:
L4 fracture invalidity code
English Text:
L4 fracture invalidity code
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Valid data 3241 3241
1 Objects not removed 0 3241
2 Non-removable objects such as implants 22 3263
3 Excessive x-ray noise due to morbid obesity 27 3290
4 Insufficient scan area 12 3302
5 Movement 1 3303
6 Other (degenerative diseases, spinal fusion, fractures) 27 3330
. Missing 378 3708

DXXVFAST - Vertebral fracture status summary

Variable Name:
DXXVFAST
SAS Label:
Vertebral fracture status summary
English Text:
Vertebral fracture status summary
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Normal (No fracture in T4-L4 and there are no more than one un-evaluable vertebrae in T7 to L4) 3038 3038
2 Fractured (Mild, moderate or severe fracture at any level inT4-L4) 186 3224
3 Un-interpretable (No fracture and more than one un-evaluable vertebrae in T7-L4) 106 3330
. Missing 378 3708

DXXT4FX - T4 fracture score

Variable Name:
DXXT4FX
SAS Label:
T4 fracture score
English Text:
T4 fracture score
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Normal (Grade 0) 2981 2981
1 Mild deformity (Grade 1) 4 2985
2 Moderate deformity (Grade 2) 2 2987
3 Severe deformity (Grade 3) 0 2987
. Missing 721 3708

DXXT5FX - T5 fracture score

Variable Name:
DXXT5FX
SAS Label:
T5 fracture score
English Text:
T5 fracture score
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Normal (Grade 0) 3093 3093
1 Mild deformity (Grade 1) 6 3099
2 Moderate deformity (Grade 2) 4 3103
3 Severe deformity (Grade 3) 0 3103
. Missing 605 3708

DXXT6FX - T6 fracture score

Variable Name:
DXXT6FX
SAS Label:
T6 fracture score
English Text:
T6 fracture score
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Normal (Grade 0) 3168 3168
1 Mild deformity (Grade 1) 12 3180
2 Moderate deformity (Grade 2) 9 3189
3 Severe deformity (Grade 3) 0 3189
. Missing 519 3708

DXXT7FX - T7 fracture score

Variable Name:
DXXT7FX
SAS Label:
T7 fracture score
English Text:
T7 fracture score
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Normal (Grade 0) 3209 3209
1 Mild deformity (Grade 1) 19 3228
2 Moderate deformity (Grade 2) 9 3237
3 Severe deformity (Grade 3) 0 3237
. Missing 471 3708

DXXT8FX - T8 fracture score

Variable Name:
DXXT8FX
SAS Label:
T8 fracture score
English Text:
T8 fracture score
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Normal (Grade 0) 3244 3244
1 Mild deformity (Grade 1) 16 3260
2 Moderate deformity (Grade 2) 10 3270
3 Severe deformity (Grade 3) 2 3272
. Missing 436 3708

DXXT9FX - T9 fracture score

Variable Name:
DXXT9FX
SAS Label:
T9 fracture score
English Text:
T9 fracture score
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Normal (Grade 0) 3276 3276
1 Mild deformity (Grade 1) 13 3289
2 Moderate deformity (Grade 2) 2 3291
3 Severe deformity (Grade 3) 0 3291
. Missing 417 3708

DXXT10FX - T10 fracture score

Variable Name:
DXXT10FX
SAS Label:
T10 fracture score
English Text:
T10 fracture score
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Normal (Grade 0) 3287 3287
1 Mild deformity (Grade 1) 7 3294
2 Moderate deformity (Grade 2) 6 3300
3 Severe deformity (Grade 3) 1 3301
. Missing 407 3708

DXXT11FX - T11 fracture score

Variable Name:
DXXT11FX
SAS Label:
T11 fracture score
English Text:
T11 fracture score
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Normal (Grade 0) 3257 3257
1 Mild deformity (Grade 1) 26 3283
2 Moderate deformity (Grade 2) 14 3297
3 Severe deformity (Grade 3) 1 3298
. Missing 410 3708

DXXT12FX - T12 fracture score

Variable Name:
DXXT12FX
SAS Label:
T12 fracture score
English Text:
T12 fracture score
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Normal (Grade 0) 3247 3247
1 Mild deformity (Grade 1) 11 3258
2 Moderate deformity (Grade 2) 27 3285
3 Severe deformity (Grade 3) 7 3292
. Missing 416 3708

DXXL1FX - L1 fracture score

Variable Name:
DXXL1FX
SAS Label:
L1 fracture score
English Text:
L1 fracture score
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Normal (Grade 0) 3257 3257
1 Mild deformity (Grade 1) 4 3261
2 Moderate deformity (Grade 2) 24 3285
3 Severe deformity (Grade 3) 6 3291
. Missing 417 3708

DXXL2FX - L2 fracture score

Variable Name:
DXXL2FX
SAS Label:
L2 fracture score
English Text:
L2 fracture score
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Normal (Grade 0) 3265 3265
1 Mild deformity (Grade 1) 6 3271
2 Moderate deformity (Grade 2) 9 3280
3 Severe deformity (Grade 3) 1 3281
. Missing 427 3708

DXXL3FX - L3 fracture score

Variable Name:
DXXL3FX
SAS Label:
L3 fracture score
English Text:
L3 fracture score
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Normal (Grade 0) 3252 3252
1 Mild deformity (Grade 1) 3 3255
2 Moderate deformity (Grade 2) 7 3262
3 Severe deformity (Grade 3) 1 3263
. Missing 445 3708

DXXL4FX - L4 fracture score

Variable Name:
DXXL4FX
SAS Label:
L4 fracture score
English Text:
L4 fracture score
Target:
Both males and females 40 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 Normal (Grade 0) 3228 3228
1 Mild deformity (Grade 1) 6 3234
2 Moderate deformity (Grade 2) 6 3240
3 Severe deformity (Grade 3) 1 3241
. Missing 467 3708