Spine-hip discordance and fracture risk assessment: a physician-friendly FRAX enhancement.
The FRAX® tool estimates a 10-year probability of fracture based upon multiple clinical risk factors and an optional bone mineral density (BMD) measurement obtained from the femoral neck. We describe a simple procedure for using lumbar spine BMD to enhance fracture risk assessment under the FRAX system.


BACKGROUND
Discordance between lumbar spine (LS) and femoral neck (FN) T-scores is common and a source of clinical confusion since the LS measurement is not an input variable for the FRAX algorithm. The purpose of this study is to develop a procedure for adjusting FRAX probability based upon the T-score difference between the LS and FN (termed offset).


METHODS
The Manitoba BMD database was used to identify baseline LS and FN dual-energy X-ray absorptiometry examinations (33,850 women and 2,518 men age 50 and older) with FRAX estimates for a major osteoporotic fracture categorized as low (<10%), moderate (10-20%), and high (>20%). Fracture outcomes were assessed from population-based administrative data. An approach was developed and internally validated using a split-cohort design.


RESULTS
The offset was found to significantly affect fracture risk [HR, 1.12 (95% CI, 1.06-1.18) per SD LS below FN] independent of the FRAX probability. The following rule was formulated: "Increase/decrease FRAX estimate for a major fracture by one tenth for each rounded T-score difference between LS and FN." In the validation subgroup, there was a significant improvement in the fracture prediction using FRAX with the proposed offset adjustment for major osteoporotic (P = 0.007) and vertebral fracture prediction (P < 0.001). For those at moderate risk under FRAX, 12.6% showed reclassification using the offset to a risk level that more accurately reflected their observed risk (25.2% reclassification for moderate risk discordant cases).


CONCLUSIONS
A simple procedure that incorporates the offset between the LS and FN T-scores can enhance fracture risk prediction under the FRAX system.
Department of Medicine, University of Manitoba, Winnipeg, Canada. bleslie@sbgh.mb.ca
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Leslie
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Johansson
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Oden
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McCloskey
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Kanis
D015502:Absorptiometry, Photon; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D015519:Bone Density; D005260:Female; D005272:Femur Neck / Q000000981:diagnostic imaging*; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging*; D008297:Male; D008350:Manitoba / Q000453:epidemiology; D008875:Middle Aged; D058866:Osteoporotic Fractures / Q000453:epidemiology*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D016103:Spinal Fractures / Q000453:epidemiology*