The relationship between thoracic kyphosis and Q angle with balance and falls in patients with osteoporosis

Falls drive fragility fractures in postmenopausal osteoporosis, but integrated evidence linking thoracic kyphosis, quadriceps (Q) angle, and ultrasound-derived quadriceps size indexed to body mass index to balance and self-reported fall history remains limited. We hypothesized that greater thoracic kyphosis and higher Q angle would be associated with poorer balance performance and self-reported fall history.

In this cross-sectional study between May and August 2024, 100 postmenopausal women with osteoporosis were assessed. Thoracic kyphosis was measured on lateral radiographs using the Cobb angle, and the Q angle by standing goniometry. Quadriceps muscle thickness was measured by ultrasound, and the previously published Sonographic Thigh Adjustment Ratio was calculated as thickness/body mass index. Balance was assessed using the Berg Balance Scale and one-leg standing test. Fall history was defined as at least one self-reported fall in the previous year. Spearman correlation, between-group comparisons, exploratory multivariable logistic regression, multiple linear regression, and receiver operating characteristic analyses were performed.

Of 125 screened individuals, 100 were included (mean age 65.9 ± 7.9 years; 51 fallers). Thoracic kyphosis and mean Q angle were correlated (r = 0.700, p < 0.001), and both were associated with poorer balance and lower quadriceps measures (all p < 0.001). After adjustment for age, body mass index, 25-hydroxyvitamin D, mean Q angle, and Sonographic Thigh Adjustment Ratio, thoracic kyphosis remained associated with self-reported fall history in the exploratory model (odds ratio 1.444 per 1°; 95% confidence interval 1.143-1.824; p = 0.002), whereas the Sonographic Thigh Adjustment Ratio was inversely associated with falls (odds ratio 0.35 per 0.1-unit increase; 95% confidence interval 0.15-0.79; p = 0.011). In multiple linear regression, thoracic kyphosis, Q angle, and the Sonographic Thigh Adjustment Ratio were associated with Berg Balance Scale score (p ≤ 0.004).

In postmenopausal women with osteoporosis, greater thoracic kyphosis and lower ultrasound-derived quadriceps size indexed to body mass index were associated with self-reported fall history and poorer balance. Quadriceps angle was related to balance but not associated with self-reported fall history after adjustment. These findings are preliminary and hypothesis-generating; because of the cross-sectional design, self-reported fall history, and possible residual confounding, they do not establish causality, predictive utility, or clinical cut-off values.