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 two 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 one NVF. The overall NVF incidence rate was 91.8 (95% confidence interval [CI]: 62.4-130.3) per 10 000 person-years, representing a rate more than five 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 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 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 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 one year before first NVF, including 6-min walking distance (6MWD), 10-m walking test time (10mWT), and time from supine to standing (TSS), were significantly worse compared to those without NVF. Specifically, 6MWD was shorter (p = .007), while 10mWT and TSS were longer (p = .025 and p = .020, respectively). Receiver operating characteristic (ROC) curves indicated that a 6MWD of 248.2 m and a 10mWT of 9.85 s were optimal cut-off values for predicting the onset of first NVF, suggesting that a decline in 6MWD to approximately 250 m and an increase in 10mWT to approximately 10 s may serve as early warning indicators.