ObjectiveTo investigate the factors affecting rehabilitation outcomes in children with congenital muscular torticollis (CMT).MethodsWe retrospectively reviewed the medical records of 347 patients who were clinically suspected as having CMT and performed neck ultrasonography to measure sternocleidomastoid (SCM) muscle thickness. Fifty-four patients met the inclusion criteria. Included were demographic characteristics as well as measurements of cervical range of motion (ROM), SCM muscle thickness, and the abnormal/normal (A/N) ratio, defined as the ratio of SCM muscle thickness on the affected to the unaffected side.ResultsSubjects were divided into three groups depending on degree of cervical ROM (group 1A: ROM>60, n=12; group 1B: 60≥ROM>30, n=31; group 1C: ROM≤30, n=11), the SCM muscle thickness (Th) (group 2A: Th<1.2 cm, n=23; group 2B: 1.2≤Th<1.4 cm, n=18; group 2C: Th≥1.4 cm, n=13), and the A/N ratio (R) (group 3A: R<2.2, n=19; group 3B: 2.2≤R<2.8, n=20; group 3C: R≥2.8, n=15). We found that more limited cervical ROM corresponded to longer treatment duration. The average treatment duration was 4.55 months in group 1A, 5.87 months in group 1B, and 6.50 months in group 1C. SCM muscle thickness and the A/N ratio were not correlated with treatment duration.ConclusionInfants with CMT who were diagnosed earlier and had an earlier intervention had a shorter duration of rehabilitation. Initial cervical ROM is an important prognostic factor for predicting the rehabilitation outcome of patients with CMT.