How should hip T-score be managed in patients with bilateral hip replacement?

Hip T-Score Measurement in Patients with Bilateral Hip Replacement

In patients with bilateral hip replacements, hip T-scores cannot be measured and alternative skeletal sites such as the lumbar spine and forearm should be used for bone mineral density assessment.

Alternative Measurement Sites

When hip T-scores cannot be obtained due to bilateral hip replacements, the following alternative sites should be used:

Primary Alternative: Lumbar Spine

• The American College of Radiology (ACR) Appropriateness Criteria rates DXA lumbar spine as "usually appropriate" (rating 9/9) for BMD screening and follow-up 1
• Patient positioning: supine with hips and knees flexed to 90° to reduce lumbar lordosis 1
• Measurement includes vertebrae L1-L4
• Caveat: Degenerative changes, compression fractures, or surgical implants may affect accuracy

Secondary Alternative: Forearm (Distal 1/3 Radius)

• Indicated when lumbar spine cannot be measured or interpreted 1
• ACR rates DXA distal forearm as "may be appropriate" (rating 5/9) for initial screening 1
• ACR rates DXA distal forearm as "usually appropriate" (rating 8/9) for certain populations including those where hip/spine cannot be measured 1
• Non-dominant arm should be measured
• Particularly useful when:
  • Spine has significant degenerative changes
  • Patient exceeds weight limit of scanner table
  • Patient has hyperparathyroidism

Measurement Protocol

1. Lumbar spine measurement:

   • Position patient supine with legs straight and feet uncrossed
   • Flex hips and knees to 90° using positioning blocks
   • Ensure spine is in neutral position with arms at sides

2. Forearm measurement:

   • Use non-dominant arm
   • Position forearm with radius and ulna parallel to short axis of scanning table
   • Ensure no hardware, fusion, osteoarthritis, or fractures are present

Interpretation and Follow-up

• For diagnostic classification, use T-scores for postmenopausal women and men over 50 years; Z-scores for younger individuals 1
• The lowest T-score from available measurement sites should be used for diagnostic classification
• Follow-up BMD testing is recommended every 2-3 years to assess treatment efficacy 2

Common Pitfalls to Avoid

1. Do not attempt to measure hip BMD through prosthetic components

   • Metal implants create artifacts that invalidate measurements

2. Avoid using only one measurement site

   • Using multiple sites (spine and forearm) provides more comprehensive assessment

3. Beware of overestimating bone density in lumbar spine

   • Degenerative changes can artificially elevate BMD measurements
   • Consider forearm measurements when spine shows significant arthritis

4. Ensure consistent positioning for follow-up scans

   • Reproducible positioning is critical for accurate longitudinal assessment

5. Don't overlook Trabecular Bone Score (TBS)

   • TBS of lumbar spine can provide additional fracture risk information
   • ACR notes TBS "may be appropriate" (rating 4/9) as an adjunct to DXA 1

By following these guidelines, clinicians can effectively monitor bone health in patients with bilateral hip replacements despite the inability to obtain hip T-scores.