Scapular deformity in obstetric brachial plexus palsy: a new finding

Abstract

While most obstetric brachial plexus palsy patients recover arm and hand function, the residual nerve weakness leads to muscle imbalances about the shoulder which may cause bony deformities. In this paper we describe abnormalities in the developing scapula and the glenohumeral joint. We introduce a classification for the deformity which we term Scapular Hypoplasia, Elevation and Rotation. Multiple anatomic parameters were measured in bilateral CT images and three-dimensional CT reconstruction of the shoulder girdle of 30 obstetric brachial plexus palsy patients (age range 10 months-10.6 years). The affected scapulae were found to be hypoplastic by an average of 14% while the ratio of the height to the width of the body of scapula (excluding acromion) were not significantly changed, the acromion was significantly elongated by an average of 19%. These parameters as well as subluxation of the humeral head (average 14%) and downward rotation in the scapular plane were found to correlate with the area of scapula visible over the clavicle. This finding provides a classification tool for diagnosis and objective evaluation of the bony deformity and its severity in obstetric brachial plexus palsy patients.

Fig. 1

At rest the child is noted to exhibit an internal rotation posture at the shoulder with elbow flexion and pronation of the forearm. There is apparent shortening of the arm

Fig. 2

Measurement of the different scapular variables. a The width is assessed in the posterior scapular view (left) along the axis of the scapular spine. The total width (W) is calculated as the length from the end of the acromion to the most medial aspect of the scapula. The scapular body width (w) is calculated as the distance from the mid glenoid to the most medial aspect of the scapula. The acromion length (acr) is also calculated on this view. The height (H) is measured along the medial border of the scapula in the medial scapular view (right). b Lines are drawn from the center of the glenoid cavity perpendicular to the vertebral axis line on the posterior trunk view. Superior displacement = A/H. Downward/upward rotation around an axis perpendicular to the scapular plane is defined as the difference between the angles α defined by the vertebral axis and the extension of the lines connecting the center of the glenoid cavity and the medial end of the spine of the scapula. c In the anterior trunk view three lines are drawn: Line 1 is the line between the sternoclavicular joint and the center of the acromio-clavicular joint, line 2 is the line between the center of the acromio-clavicular joint and the inferior angle of the scapula, line 3 is the vertebral axis. The superior scapular angle γ is the angle defined between lines 1 and 2 and the inferior scapular angle δ is the angle between lines 2 and 3. d In the superior outlet view the anterior/posterior rotation is calculated as the angle ϕ between the line connecting the acromio-clavicular joint to the superomedial angle and the line between the sterno-clavicular joint and the center of the acromio-clavicular joint (clavicular axis). e Schematic drawing showing the method of calculating glenoscapular angle (glenoid version θ), posterior subluxation of the humeral head and spinoscapular angle (ζ). The scapular line that connects the medial aspect of the scapula and the mid glenoid is drawn. A second line is drawn connecting the posterior and anterior margins of the glenoid. 90° are subtracted from the angle of the posterior medial quadrant defined by these lines to determine the glenoid version θ. A line perpendicular to the scapular line is drawn and the percentage of posterior subluxation is defined as the ratio of the distance from the scapular line to the anterior portion of the head to the diameter of the humeral head (LM/LN × 100). The spinoscapular angle (ζ) is measured as the angle between the scapular line and the medial plane

Fig. 3

The different SHEAR stages of scapular deformity as determined by three dimensional computer tomography. In SHEAR Grade 0 less than 2% of the scapula, less than 20% of the superior border and less than 6.5% of the medial border are visible above the clavicle. In SHEAR Grade 1 2–3.6% of the scapular area, 20–45% of the superior border and 6.5–16.5% of the medial border are visible over the clavicle. In SHEAR Grade 2 3.6–20% of the scapular area, 45–58% of the superior border and 16.5–28% of the medial border are visible above the clavicle. In SHEAR Grade 3 20–45% of the scapula, 58–68% of the superior border and 28–50% of the medial border are visible over the scapula. In SHEAR Grade 4 more than 42% of the area of the scapula, more than 68.5% of the superior border and more than 50% of the medial border are visible over the scapula