Specific scapular kinematic patterns to differentiate two forms of dynamic scapular winging

Dynamic scapular winging (DSW) is a rare and misdiagnosed disorder causing considerable disability due to reduced scapular stability and abnormal motion. Two common causes are long thoracic nerve lesions resulting in serratus anterior muscle palsy and spinal accessory nerve lesions resulting in trapezius muscle palsy. The aim of this study was to analyse 3D scapular kinematic patterns in patients with DSW due to long thoracic (LTNL) or spinal accessory nerve lesions (SANL).

3D scapular kinematics were assessed using a non invasive method involving an electromagnetic device during arm elevation in the frontal and sagittal planes in 9 patients (4 with SANL and 5 with LTNL) with unilateral DSW confirmed by electrical evidence. Within subject affected-unaffected differences were measured and compared between pathological groups (Mann-Whitney).

Differences between affected and unaffected shoulders were significantly greater for scapular posterior tilt (at rest and 30° for sagittal arm elevation, at rest, 30° and 60° for frontal arm elevation) in the LTNL compared to the SANL group. Differences between affected and unaffected shoulders were significantly greater for scapular protraction (at rest and 60° of sagittal arm elevation, at rest, 30° and 60° of frontal arm elevation) and scapular lateral rotation at 60° for frontal arm elevation in the SANL compared to the LTNL group.

These kinematic findings show two different scapular patterns that are specific to the neurological lesion. Moreover our kinematic data relate to specific clinical signs and the functional roles of the muscles involved.