Bilateral Hip Implants, Spinal Hardware, and a Single Evaluable Vertebra
A 71-year-old woman (155 cm, 82 kg) is referred for DXA. She had a right total hip arthroplasty in 2014 and a left total hip arthroplasty in 2018, and a posterior spinal fusion from L2 to L5 with pedicle screws and rods in 2019. She walks with a cane and has fallen twice in the past year, once resulting in a wrist fracture treated conservatively. On the spine scan, only L1 is free of hardware and artifact; its BMD is 0.860 g/cm² (T −2.2). Neither hip can be scanned because of the implants. The technologist is unsure whether any result can be reported and considers scanning the forearm. The referring physician has asked simply: "Does she have osteoporosis, and can we monitor her?" The patient is right-handed and has no fracture or hardware in either forearm.
1. Which sites are valid for diagnosis in this patient, and what rules govern that choice?
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Neither the hip nor the spine can carry a diagnostic T-score here.
- Hips: bilateral arthroplasties make both hip regions unmeasurable. Implant artifact and altered geometry preclude a valid femoral neck or total hip value; do not attempt to scan around the hardware.
- Spine: a diagnostic spine T-score requires at least two evaluable vertebrae. Only L1 is free of hardware, so the spine cannot be used for classification. The L1 value can be reported as informational - it is real data - but it must be labeled as not usable for diagnosis and not used to monitor treatment.
That leaves the 33% radius of the non-dominant forearm, which ISCD accepts as a diagnostic site when the hip and spine cannot be measured or are not interpretable. Measure the non-dominant forearm; if it had a fracture, hardware, or artifact, measure the dominant side and document the substitution. In this patient the right (non-dominant) forearm is clean, so scan it. Use the 33% site, not the ultra-distal site, for diagnostic classification.
2. The 33% radius scan returns BMD 0.470 g/cm² (T −3.3). What does that mean diagnostically, and what caveats belong in the report?
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A T-score of −3.3 at the 33% radius, in a patient whose hip and spine cannot be evaluated, meets the WHO threshold of −2.5 or below and supports a classification of osteoporosis. That classification is consistent with her low-trauma wrist fracture and her fall history.
Caveats that must accompany the number:
- Site rationale. State that the forearm was used because bilateral hip implants and spinal hardware left no valid hip or spine site; a reader who does not see this will assume the technologist chose the forearm arbitrarily.
- Which forearm and which site. Non-dominant, 33% radius. Do not substitute the ultra-distal region for diagnosis.
- Monitoring limitation. The 33% radius is predominantly cortical bone and responds less to treatment than the spine or hip; it is acceptable for diagnosis here but is a poor monitoring site. If spine or hip ever becomes measurable, switch to it.
- The isolated L1 value. Report it as not valid for diagnosis, with the reason.
Avoid softening the result: this is osteoporosis by criteria, not osteopenia, and the report should say so plainly.
3. The physician asks how to monitor this patient. What do you recommend, and what non-DXA information should be part of the answer?
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Monitoring: the 33% radius can be repeated on the same densitometer, with the same technologist and analysis, and compared in g/cm² against a forearm-specific least significant change - the facility must establish that precision separately, since spine precision does not transfer to the forearm. Intervals of 1–2 years are appropriate; shorter intervals on a cortical site will mostly produce noise. If the patient ever becomes eligible for spine or hip scanning, that becomes the preferred monitoring site and the forearm series should be replaced, not blended with it.
Non-DXA information that should be part of the answer:
- She has had a low-trauma fracture and two falls in a year. Falls risk, vision, gait and balance, home hazards, sedating medications, and vitamin D status are integral to management, and a DXA result alone will not capture them.
- Bilateral hip arthroplasty and a multilevel spinal fusion are themselves markers of skeletal fragility in an older woman and belong in the clinical risk picture.
- Vertebral fracture assessment or lateral spine imaging is worth considering for the thoracic spine, since the fused lumbar segments cannot be assessed but the thoracic vertebrae can.
The technologist's contribution is to certify what was measured, why that site was chosen, and what can and cannot be tracked over time; treatment and falls interventions are the physician's call.