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The North Star ambulatory assessment (NSAA) is a functional motor outcome measure in Duchenne muscular dystrophy (DMD), widely used in clinical trials and natural history studies, as well as in clinical practice. However, little has been reported on the minimal clinically important difference (MCID) of the NSAA. The lack of established MCID estimates for NSAA presents challenges in interpreting the significance of the results of this outcome measure in clinical trials, natural history studies and clinical practice. Combining statistical approaches and patient perspectives, this study estimated MCID for NSAA using distribution-based estimates of 1/3 standard deviation (SD) and standard error of measurement (SEM), an anchor-based approach, with six-minute walk distance (6MWD) as the anchor, and evaluation of patient and parent perception using participant-tailored questionnaires. The MCID for NSAA in boys with DMD aged 7 to 10 years based on 1/3 SD ranged from 2.3–2.9 points, and that on SEM ranged from 2.9–3.5 points. Anchored on the 6MWD, the MCID for NSAA was estimated as 3.5 points. When the impact on functional abilities was considered using participant response questionnaires, patients and parent perceived a complete loss of function in a single item or deterioration of function in one to two items of the assessment as an important change. Our study examines MCID estimates for total NSAA scores using multiple approaches, including the impact of patient and parent perspective on within scale changes in items based on complete loss of function and deterioration of function, and provides new insight on evaluation of differences in these widely used outcome measure in DMD.

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M=43) patients were treated. Mean age at follow-up was 87.5 months (range 18-157 m). 42 cases were bilateral and thus 117 feet were treated. 45 (60%) were idiopathic and 30 (40%) nonidiopathic.Of the 75 patients, 50 (67%) underwent tenotomy under local anaesthetic in clinic. Tenotomy rates were higher in nonidiopathic vs idiopathic patients (83% vs 56%)(P<0.002)Mean dorsiflexion (knee extended) in affected feet was 14°. In unilateral cases mean dorsiflexion (knee extended) in unaffected foot vs affected foot was 17°vs 12°. All idiopathic feet were plantigrade.Abnormal evertor function was seen in 3 of 66 (5%) idiopathic feet versus 22 of 51 non-idiopathic feet (43%) (p<0.0001).Calf circumference discrepancy was higher in unilateral cases versus bilateral (mean 1.3 cm versus 0.6 cm respectively). Unilateral cases undergoing tenotomy had a greater mean circumference difference (1.5 cm) versus those managed without tenotomy (0.7 cm).43 idiopathic patients were suitable for OXFORD scoring at time of last review (i.e. older than 5 years old). The overall median OxFAQ was 96% with points lost only in the physical scale. Function in non-idiopathic cases was determined by their overall condition. Conclusion The idiopathic club foot is well treated by a physiotherapy-delivered Ponseti technique with excellent outcomes at 5 yr follow-up both subjectively and objectively.