Fatigue in the sternocleidomastoid muscle and hip dysplasia : a surface electromyographic assessment in adult women

Objective: The aim of this study is to assess a possible relationship between unilateral hip dysplasia and sternocleidomastoid muscle function during a fatiguing task. Methods: In this patient-control, cross-sectional study, 11 female patients (aged 37-63 years) with unilateral coxoarthrosis subsequent to hip dysplasia and 9 female control subjects matched for age were assessed. Surface electromyography of the right and left sternocleidomastoid muscles was measured in the women performing a standardized endurance test. The median power frequency was calculated at the beginning (T(0)) and at the end of the task (T(1), endurance time). For each subject and muscle, percentage decrements in the median power frequency were computed at T(1). Results: Endurance time ranged between 15 and 125 s (control group), and 10 and 200 s (patient group), without a significant difference between the 2 groups (Mann-Whitney test, P &rt; .05). In the patient group, no significant differences in the median power frequency between the ispilateral to coxoarthrosis and contralateral sides were found (Wilcoxon test, P &rt; .05). The percentage decrements of the median power frequency in the control (right and left side pooled) and patient group did not significantly differ either in the ispilateral to coxoarthrosis and contralateral sides (Mann-Whitney test, P &rt; .05). Conclusions: The lack of significant differences between the sternocleidomastoid muscles of healthy women and those of women with hip dysplasia does not support the presence of a common noxa causing both congenital muscular torticollis and hip joint alterations. Alternatively, the coexistence of the 2 alterations in infancy may disappear during adult life.