5.6 Hip DXA Interpretation & Bilateral Comparison
Key Takeaways
At the hip, use the femoral neck and total hip for adult densitometric diagnosis. Ward’s area and isolated trochanter measurements do not qualify.
When both hips were scanned, use the lowest valid diagnostic score from the left or right neck or total hip. Do not average diagnostic scores.
When both hips were scanned on repeat studies, compare mean bilateral total hip BMD against the applicable facility LSC. If only one hip is comparable, match the side, region and applicable unilateral LSC.
Use valid sites for the diagnostic decision
The International Society for Clinical Densitometry (ISCD) permits measurement of either hip and regards bilateral acquisition as appropriate. First review the image and region of interest (ROI) for technical validity. A hip replacement, fixation hardware, local pathology or an unreliable projection can make a hip result unsuitable. Consider the opposite hip if it can be measured. If the hip or spine cannot be measured or interpreted, the one-third radius can be indicated.
At the hip, the two sites used for adult densitometric classification are the femoral neck and total hip. In postmenopausal women and men aged 50 or older, choose the lower valid T-score from those sites. If both hips were acquired, consider the valid neck and total hip results from both sides. Do not average scores or substitute Ward's area or an isolated trochanter measurement. In an adult population where Z-scores are appropriate, apply the corresponding ISCD score-selection guidance and interpret the age comparison in context. A low Z-score is not a substitute for a T-score osteoporosis classification.
| Question | Measurement | Interpretation |
|---|---|---|
| What hip result supports adult densitometric classification? | Lowest valid femoral neck or total hip T-score from the side or sides scanned | Compare with the diagnostic thresholds where applicable. Include other valid skeletal sites when assigning the overall category. |
| What hip BMD can go into standard FRAX? | A valid femoral neck measurement, if supplying BMD | Use the calculator's model and reference requirements. A total hip result is not a substitute. |
| What hip measurement should be compared over time if both hips were scanned on both tests? | Mean of left and right total hip BMD for each time point | Apply the facility's appropriate precision and least significant change (LSC) for the measurement. |
| What if one prior scan includes only one hip? | Matched valid side and ROI, if comparable | Do not compare the unilateral result to a bilateral mean or the opposite hip. |
Worked bilateral interpretation
A 70-year-old postmenopausal woman has left femoral neck T-score −2.6, left total hip −1.8, right femoral neck −2.1, and right total hip −1.7. All measurements are valid. The lowest hip score is −2.6 at the left femoral neck, which meets the densitometric osteoporosis threshold. The average score is irrelevant to the classification. An isolated trochanteric score of −2.9 would not change the decision.
The patient's comparable total hip BMD measurements are as follows. Both sides were acquired at both visits and the illustrative facility LSC for the bilateral total hip mean is 0.025 g/cm².
| Study | Left total hip BMD (g/cm²) | Right total hip BMD (g/cm²) | Mean total hip BMD (g/cm²) |
|---|---|---|---|
| Prior | 0.760 | 0.800 | 0.780 |
| Follow-up | 0.790 | 0.830 | 0.810 |
The increase in mean BMD is 0.030 g/cm², or about 3.85% of the prior mean. This reaches the applicable LSC. The serial report describes a significant increase in mean bilateral total hip BMD. The comparison is distinct from the diagnostic impression, which uses the lowest valid diagnostic score rather than the average.
Now suppose a left hip replacement prevents a valid left hip measurement at follow-up. Recheck the prior images and confirm that the right total hip was positioned and analyzed comparably on both studies. Compare the prior right total hip BMD of 0.800 g/cm² with the follow-up right total hip BMD of 0.830 g/cm². The difference is 0.030 g/cm², or 3.75% of the prior right hip value. With an illustrative LSC of 0.035 g/cm² for this unilateral total hip comparison, report no statistically significant change at the right total hip. Identify the right-sided comparison and document why the left side was excluded. The bilateral mean and its LSC apply only to the original comparison.
Explain asymmetry in context
Meaningful side differences warrant an image review for rotation, placement, surgery, and focal conditions. In a patient with a unilateral prosthesis, report the native hip if technically valid. The prosthetic side cannot enter the bilateral mean used in the worked comparison. Differences in habitual loading, such as after a stroke or prolonged immobilization, can contribute to genuine asymmetry. A fixed difference between left and right does not by itself establish a focal diagnosis. Document the measured sites and the technical or clinical reason for excluding an unreliable result. Include one overall diagnostic category based on the valid sites.
ISCD Adult Official Positions · ISCD U.S. Adult DXA Sample Report · FRAXplus FAQ · ISCD Precision Assessment FAQ · International DXA practice guideline
Which hip regions can establish a DXA densitometric classification of osteoporosis in a postmenopausal woman?
Femoral neck and total hip.
Femoral neck, total hip and Ward’s area.
Total hip, isolated trochanter and Ward’s area.
Greater trochanter and intertrochanteric crest only.
Both hips were validly scanned at baseline and follow-up. The lowest T-score was at the left femoral neck. Which measurement should be used for serial hip monitoring?
Mean of the four hip T-scores at each time point.
The lowest hip T-score at each time point even if its side differs.
Mean bilateral total hip BMD at each time point, with the applicable LSC.
Mean bilateral femoral neck T-score without an LSC.
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