Subacromial impingement syndrome: the role of posture and muscle imbalance.

Changes in upper body posture, colloquially termed forward head posture (FHP), are considered to be an etiologic factor in the pathogenesis of subacromial impingement syndrome (SIS). The literature suggests that postural deviations associated with FHP follow distinct patterns involving an increase in the thoracic kyphosis angle and a downwardly rotated, anteriorly tilted, and protracted scapula, which in turn leads to increased compression in the subacromial space. These postural changes are thought to occur concurrently with an imbalance of the musculature, and conservative rehabilitation commonly involves addressing both posture and muscle imbalance. There is a paucity of evidence supporting the hypothesis that posture and muscle imbalance are involved in the etiology of SIS. The purpose of this study was to investigate whether FHP was associated with an increased thoracic kyphosis, an altered position of the scapula; and a reduction in glenohumeral elevation range. Selected sagittal and frontal plane postural measurements were made in 60 asymptomatic subjects and 60 subjects with SIS. The findings suggested that upper body posture does not follow the set patterns described in the literature, and further research is required to determine whether upper body and scapular posture and muscle imbalance are involved in the pathogenesis of SIS.