The effect of glenohumeral plane of elevation on supraspinatus subacromial proximity

Abstract

Shoulder pain is a common clinical problem affecting most individuals in their lifetime. Despite the high prevalence of rotator cuff pathology in these individuals, the pathogenesis of rotator cuff disease remains unclear. Position and motion related mechanisms of rotator cuff disease are often proposed, but poorly understood. The purpose of this study was to determine the impact of systematically altering glenohumeral plane on subacromial proximities across arm elevation as measures of tendon compression risk. Three-dimensional models of the humerus, scapula, coracoacromial ligament, and supraspinatus were reconstructed from MRIs in 20 subjects. Glenohumeral elevation was imposed on the humeral and supraspinatus tendon models for three glenohumeral planes, which were chosen to represent flexion, scapular plane abduction, and abduction based on average values from a previous study of asymptomatic individuals. Subacromial proximity was quantified as the minimum distance between the supraspinatus tendon and coracoacromial arch (acromion and coracoacromial ligament), the surface area of the supraspinatus tendon within 2 mm proximity to the coracoacromial arch, and the volume of intersection between the supraspinatus tendon and coracoacromial arch. The lowest modeled subacromial supraspinatus compression measures occurred during flexion at lower angles of elevation. This finding was consistent across all three measures of subacromial proximity. Knowledge of this range of reduced risk may be useful to inform future studies related to patient education and ergonomic design to prevent the development of shoulder pain and dysfunction.

Keywords: Glenohumeral; Impingement; Kinematics; Supraspinatus; subacromial proximity.

FIGURE 1:

Example of a subject-specific anatomical model reconstructed from MR images. Black area on the distal supraspinatus denotes the tendon region from which subacromial proximities were measured.

FIGURE 2:

Angular constraint during calculation of the minimum distance vector. The two red lines represent the unconstrained minimum distance vectors between two pairwise sets of vertices. The four solid lines represent the vertex normal vectors. When the opposition angle between pairwise vertex normals was <150° (e.g. α), the minimum distance vector is considered invalid because the surface of the supraspinatus tendon is not oriented towards the coracoacromial arch surface and therefore would not be compressed by it. When the opposition angle between pairwise vertex normals was ≥150° (e.g. β), the minimum distance vector was retained.

FIGURE 3:

The effect of glenohumeral plane across angles of elevation on the minimum distance between the supraspinatus tendon and coracoacromial arch for both groups. The lines illustrate the predicted average minimum distance for each glenohumeral plane with shaded 95% confidence intervals. Abbreviations: ABD = abduction, FLEX = flexion, SAB = scapular plane abduction.

FIGURE 4:

The effect of glenohumeral plane across angles of elevation on the surface area of the supraspinatus tendon within 2 mm of the coracoacromial arch for both groups. The lines illustrate the predicted average surface areas for each glenohumeral plane with shaded 95% confidence intervals. Abbreviations: ABD = abduction, FLEX = flexion, SAB = scapular plane abduction.

FIGURE 5:

The effect of glenohumeral plane across angles of elevation on the volume of the supraspinatus tendon intersecting with coracoacromial arch for both groups. The lines illustrate the predicted average intersecting volume for each glenohumeral plane with shaded 95% confidence intervals. Abbreviations: ABD = abduction, FLEX = flexion, SAB = scapular plane abduction.

FIGURE 6:

Individual subject volume of intersection between the supraspinatus tendon and coracoacromial arch during glenohumeral elevation: A) flexion, B) scapular plane abduction, and C) abduction. Data for some subjects are not visible due to very small magnitudes of intersections and the scale of the y-axis.

FIGURE 7:

Proximity maps of a representative subject at 0° glenohumeral elevation in each plane from superior transverse plane view. The acromion, coracoacromial ligament, and humerus are made semi-transparent to better visualize the supraspinatus tendon (in color). The black ‘x’ in the image denotes the locations on the coracoacromial arch and the supraspinatus tendon in closest proximity (i.e. endpoints of the overall minimum distance vector). A more posterior and lateral position of the supraspinatus tendon during flexion helps shift the tendon away from under the anterolateral acromion resulting in a reduced proximity. Abbreviations: SAB = scapular plane abduction, CA = coracoacromial.

FIGURE 8:

Surface plots demonstrating the average surface area (mm²) of the supraspinatus tendon within 2 mm proximity of the coracoacromial arch as a function of glenohumeral plane and elevation. Altering glenohumeral elevation (x-axis) has a larger effect on the magnitude of the surface area than altering glenohumeral plane (y-axis). The protective effect of flexion at lower angles can also be seen as less warm colors compared abduction and scapular plane abduction. Abbreviations: ABD = abduction, FLEX = flexion, SAB = scapular plane abduction.