Does the position of the scapula in relation to the glenopolar angle change the preferred treatment of extra-articular fractures?

Abstract

Objective: To analyse the glenopolar angle (GPA) at different inclinations of the scapula using 3D CT, to test the hypothesis that the result could change the indication from conservative treatment to surgery.

Materials and methods: Analysis of 30 3D CT images of patients' scapulae, measuring the GPA. The GPA was measured with scapulae at 0^° and at 20^° and 30^° of internal and external rotation. Angles were compared by age, sex and examiner for the different angles of rotation of the scapulae.

Results: The GPA of scapulae in rotation tended to be smaller than the GPA without rotation, and the larger the degree of rotation, the more the angle was underestimated. Additionally, for the same degree of rotation, internal rotation was associated with greater underestimation of the GPA than external rotation. Two different examiners achieved an excellent level of agreement between angle measurements. The GPA with the scapula at 0^° was significantly higher among elderly patients. The variation in GPA with the scapula in rotation (20^° and 30^°) in relation to the GPA without rotation was significantly greater for female patients.

Conclusions: As the rotation of the scapula was displaced from the scapula in the coronal position (GPA 0^°), both in internal rotation and in external rotation, the GPA reduced. Therefore, rotational displacement may lead to an error in GPA measurement, resulting in incorrect indication of treatment. It is recommended that whenever possible, GPA measurements should be taken in neutral rotation, with the scapula in a neutral position at 0^°.

Keywords: 3D CT; 3D computed tomography; Glenopolar angle; Scapula.