Report on hip joint instability in patients with spinal muscular atrophy: a cross-sectional analysis (2024–2026)

Introduction. Literature regarding hip joint displacement in patients with spinal muscular atrophy (SMA) remains limited. Given its impact on clinical outcomes, this issue is increasingly important. Aim. To evaluate the epidemiology of hip joint displacement in a treated population of children and young adults with SMA and to identify potential risk factors. Material and methods. The study group comprised 131 patients (262 hip joints) aged 1–21 years (mean age: 6.3±4.3) with SMA type 1 (n = 46), type 2 (n = 36), type 3 (n = 36), and presymptomatic cases (n = 13). Available genetic data included 2 (n = 45), 3 (n = 68), or 4 (n = 15) SMN2 copies. Evaluation included AP pelvic radiographs (Reimers Migration Index [MI], neck-shaft angle [NSA]) and clinical status (scoliosis, 10-meter walk test, Hammersmith Functional Motor Scale [HFMS]). Statistical analysis was performed using Statistica 13, utilizing Shapiro-Wilk, Mann-Whitney U, Kruskal-Wallis with Dunn-Bonferroni post-hoc tests, and Spearman’s correlation (α = .05). Results. Significant differences in radiographic parameters were observed across SMA types (p < .001). The highest median values occurred in SMA 1 and 2 (MI: 43.0% and 34.5%; NSA: 163.0° and 161.5°), and the lowest in SMA 3 and presymptomatic cohorts (MI: 11.5% and 19.0%; NSA: 151.0° and 151.5°). SMN2 copy number correlated negatively with both the MI (R = –.311) and the NSA (Rs = –.28, p < .001), with the lowest values in the 4-copy subgroup. Significant negative correlations were found between HFMS scores and both the MI (R = –.632) and the NSA (R = –.422, p < .001). Non-ambulatory status tracked with significantly higher MI (41.0% vs 14.5%) and NSA (161.0° vs 155.0°, p < .001) values. The presence of scoliosis is also associated with significantly higher MI (34.5% vs 18.0%, p < .001) and NSA (160.0° vs 155.5°, p = .002) values. Conclusions. The MI and the NSA correlate significantly with the clinical and genetic severity of SMA. Higher HFMS scores, independent walking ability, and the absence of scoliosis are associated with lower MI and NSA values.