A single number has defined osteoporosis diagnosis for more than three decades: the T-score, a measure of bone mineral density taken from a DEXA scan and codified by the World Health Organization. It is still the standard insurers use to decide who qualifies for treatment. But according to Paul Anderson, MD, an orthopedic surgeon at the University of Wisconsin School of Medicine and Public Health in Madison, that standard is missing most of the patients who are actually at risk.
A 2020 study from the University of Wisconsin’s Osteoporosis Clinical Research Program, published in 2020 in Neurosurgical Focus, evaluated 104 patients undergoing bone health optimization ahead of spine surgery. Researchers classified each patient’s bone status two ways: first using the WHO’s density-only criteria, then using the broader National Osteoporosis Foundation criteria, which accounts for risk factors beyond density alone. Under the WHO criteria, 32.1% of patients qualified as osteoporotic. Under NOF criteria, that number was 81.6%.
“Bone mineral density is not the only factor that results in fractures or risk of fractures,” Dr. Anderson said. The gap between those two figures, he said, is the clearest evidence that the field’s default diagnostic threshold is too narrow.
Why 1 number isn’t enough
What the WHO’s T-score does not capture, according to Dr. Anderson, is the structural integrity of the bone itself.
He compared it to the Champlain Towers South collapse in Surfside, Fla., in 2021.
“They had all the quantity of bone material there, but the microstructure was all degraded away from all the things, and that’s why it fell down,” he said. “It was a structural problem, not a quantity problem.”
He calls this microarchitecture damage: internal degradation of bone structure that a DEXA scan does not detect.
The University of Wisconsin study’s patient profile helps explain why measuring density alone falls short, Dr. Anderson said. Patients had a mean historical height loss of 5.6 cm — a common marker of undiagnosed vertebral compression fractures — and 54% had a documented history of fracture. Secondary osteoporosis linked to chronic renal failure, inflammatory arthritis, diabetes, and steroid use was present in 51% of the group. None of those risk factors show up in a T-score, but they all affect real fracture risk, Dr. Anderson said, adding that turnover rate — how quickly bone is being broken down and rebuilt biologically — and collagen structure, which can be altered by conditions such as diabetes, compound the problem.
The study also incorporated FRAX, a tool that calculates a patient’s 10-year fracture risk using age, prior fracture history and other clinical variables, alongside bone density scores measured at three sites: the femoral neck, lumbar spine and distal radius. The researchers found the T-scores across those three sites differed significantly from one another within the same patients, underscoring Dr. Anderson’s assertion that a single density measurement at a single site may not reliably capture a patient’s overall fracture risk.
Dr. Anderson noted that the Wisconsin cohort was not a general surgical population. The 104 patients had already been selected based on surgeon-identified risk factors and suspected compromised bone health, which is part of why its NOF-eligible rate ran as high as 81.6%. A less pre-screened population would likely show a smaller gap in absolute terms. But he said the underlying pattern — NOF criteria identifying substantially more at-risk patients than the WHO’s density-only threshold — is the more important takeaway.
Why insurers haven’t caught up
Despite the clinical case for a broader definition, Dr. Anderson said insurance companies continue to rely on the WHO standard, a classification system he describes as “10 years back” relative to where the diagnostic conversation has moved.
The incentive, as he sees it, is straightforward. Insurers are “interested in not paying out money,” he said, and a narrower diagnostic threshold means fewer patients qualify for treatment and reimbursement. Broadening the criteria to include microarchitectural damage, fracture risk scoring and fracture history would substantially expand the population eligible for coverage.
That disconnect matters beyond individual patient care, Dr. Anderson said, because it shapes how bone health gets prioritized ahead of orthopedic surgery. If the diagnostic bar insurers recognize is set too low to capture real risk, the preoperative screening and treatment pathways built around that bar will keep missing patients who may go on to have preventable complications.
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