Bone Mineral Density Among Individuals With Residual Lower Limb Weakness After Polio

BACKGROUND: Literature indicates that individuals with long-term residual lower extremity (LE) weakness after polio have decreased bone mineral density (BMD) related to muscle weakness. Where weakness is asymmetrical, bone densitometry measured only on the stronger LE may misclassify BMD. OBJECTIVE: To determine (1) whether femoral neck BMD differed from side to side in individuals with asymmetrical LE muscle weakness, and (2) the proportion of individuals at risk for underdiagnosis of low bone density or osteoporosis given unilateral assessment of the femoral neck. DESIGN: Retrospective study. SETTING: Outpatient postpolio center. PARTICIPANTS: Patients >18 years old with complete relevant data. MAIN OUTCOME MEASURES: Bone densitometry T scores, BMD categories based on standard T-score ranges, and side of LE weakness determined by a strength score. RESULTS: Forty-three patients had at least 1 femoral neck T score and bilateral LE strength scores. Fourteen (32.5%) had bone densitometry only on their weaker LE and 14 (32.5%) had bone densitometry only on their stronger LE. Of the 15 patients with bone densitometry done on both femoral necks, T scores (mean [SD]) were lower in the weaker LE (-1.73 [1.09]) than the stronger LE (-0.88 [1.0]) (P = .001). Classification of low bone density or osteoporosis was more frequent based on T scores taken on a weaker LE (48.3% and 24.1%, respectively) than from T scores from a stronger LE (41.4% and 6.9%, respectively). CONCLUSIONS: In this small sample, using strong-limb T scores resulted in fewer individuals categorized as having low bone density or osteoporosis than when weak-limb T scores were used. Underestimating BMD loss may lead to undertreatment and increased risk of morbidity, mortality, and costs associated with femoral neck fractures in this high-fall-risk group. LEVEL OF EVIDENCE: III.