Influencing factors and early warning indicators for nonvertebral fractures in patients with Duchenne muscular dystrophy.

Nonvertebral fractures (NVFs) in patients with Duchenne muscular dystrophy (DMD) are often associated with an unfavorable prognosis. However, the influencing factors and early warning indicators for NVFs remain unclear. To address this knowledge gap, a retrospective cohort study was conducted across 2 centers involving 295 DMD patients who were evaluated between August 2013 and February 2022. Data collection included telephone callback records and outpatient face-to-face assessments. Among the 295 patients, 30 (10.2%) had experienced at least 1 NVF. The overall NVF incidence rate was 91.8 (95% CI, 62.4-130.3) per 10 000 person-years, representing a rate more than 5 times higher than that of traumatic NVFs in boys aged 0-14 yr. This finding underscores the significant burden of NVFs in DMD patients. Subsequent analysis investigated the association between the occurrence of the first NVF and various factors, including ambulant status, glucocorticoid (GC) regimen, and dystrophin isoform expression. Multivariate analysis revealed that ambulation was a significant risk factor for the first NVF, with an increased risk of 29.2-fold (95% CI, 3.9-217.3, p < .001). In contrast, a longer GC-naïve duration exhibited a protective effect against the first NVF, reducing the risk to 0.804-fold per year (95% CI, 0.691-0.936, p = .005). In patients aged 8-13 yr, motor function parameters 1 yr before the first NVF, including the 6-min walking distance (6MWD), the 10-m walking test time (10mWT), and the time from supine to standing (TSS), were significantly worse compared with those without NVF. Specifically, the 6MWD was shorter (p = .007), while 10mWT and TSS were longer (p = .025 and p = .020, respectively). Receiver operating characteristic curves indicated that a 6MWD of 248.2 m and a 10mWT of 9.85 s were the optimal cut-off values for predicting the onset of the first NVF, suggesting that a decline in the 6MWD to ~250 m and an increase in the 10mWT to ~10 s may serve as early warning indicators.