Longitudinal Fibular Deficiency: A Cross-Sectional Study Comparing Lower Limb Function of Children and Young People with That of Unaffected Peers

: Longitudinal fibular deficiency (LFD), or fibular hemimelia, is congenital partial or complete absence of the fibula. We aimed to compare the lower limb function of children and young people with LFD to that of unaffected peers. A cross-sectional study of Australian children and young people with LFD, and of unaffected peers, was undertaken. Twenty-three (12 males) children and young people with LFD (74% of those eligible) and 213 unaffected peers, all aged 7⁻21 years were subject to the Knee Osteoarthritis Outcome Score (KOOS/KOOS-Child) and the Cumberland Ankle Instability Tool (CAIT/CAIT-Youth). Linear regression models compared affected children and young people to unaffected peers. Participants with LFD scored lower in both outcomes (adjusted p < 0.05). The difference between participants with LFD and unaffected peers was significantly greater among younger participants than older participants for KOOS activities and sports domain scores (adjusted p ≤ 0.01). Differences in the other KOOS domains (pain/symptoms/quality of life) and ankle function (CAIT scores) were not affected by age (adjusted p ≥ 0.08). Children and young people with LFD on average report reduced lower limb function compared to unaffected peers. Knee-related activities and sports domains appear to be worse in younger children with LFD, and scores in these domains become closer to those of unaffected peers as they become older.