30 shoulders in 15 healthy men were examined. Mean age of the subjects was 31 (21–33) years. The Qualisys ProReflex System (Qualisys Medical AB, Gothenburg, Sweden) including 7 charge-coupled device cameras was used to analyze reflecting markers attached to bilateral epicondyles of the elbow, the lateral side of the acromion on both arms, and 4 sites of the trunk—including the C7 and T8 spinous processes, the xiphoid process, and the jugular notch of the sternum. Passive ranges were evaluated in each subject with a goniometer (). Both arms were moved symmetrically from the dependent position with neutral rotation to the maximum elevated position and vice versa, in 4 planes. Subjects were instructed to abduct the arms by referring to tapes attached to the floor, at regular intervals of 30˚ (0˚, 30˚, 60˚, and 90˚ anterior to coronal plane) to standardize the amount of horizontal abduction (Figure ). Each path was given a number from 1 to 4, starting with the coronal plane. The amount of pronation or supination of the forearm was not specified. One cycle of abduction required an average of 2.3 (2.1–2.4) seconds. Those motions were captured at 500 frames per second and 3D images were displayed and investigated on a computer screen using Qualisys Track Manager tracking software. Before each participant conducted a series of movements, calibration was performed to confirm that error remained within 2 mm.
Passive range of motion (degrees) for the left and right shoulders in 15 men. Values are mean (SD).
Figure 1 A. Both arms were moved symmetrically from the dependent position with neutral rotation to the maximum elevated position in 4 different planes, referring to tapes attached to the floor at regular intervals of 30°. B. Local thoracic and humeral (more ...)
The glenohumeral center was defined as the point located cranially from the marker on the acromion at a distance of 15% of the humeral length, as described elsewhere (Ebara et al. 1998
, Nakamura et al. 2004
). Local thoracic and humeral coordinate systems were defined with reference to the study by Meskers et al. (1998)
, as follows (Figure ). The local thoracic system (X, Y, Z): Y = ((JN + C7) / 2 – (XP + T8) / 2) /
((JN + C7) / 2 – (XP + T8) / 2)
, where X is perpendicular to the plane JN, C7, (XP + T8) / 2, Z is perpendicular to Y and X, XP and JN represent the xiphoid process and jugular notch of the sternum, respectively, and C7 and T8 are the spinous processes of the seventh cervical and eighth thoracic vertebrae, respectively. The local humeral coordinate system (x, y, z): y = (GH – (ME + LE) / 2) /
(GH – (ME + LE) / 2)
, where z is perpendicular to y and LE-ME, and x is perpendicular to y and z. GH is the center of the glenohumeral joint, and ME and LE are the medial and lateral epicondyles of the humerus. Rotation matrices of the humerus were decomposed into Euler angles. To determine whether the arm of each participant was abducted or adducted along different paths, angles of horizontal abduction and abduction were analyzed. To determine contributions of axial rotation to abduction along each path, relationships between angles of axial rotation and abduction were analyzed.
The shoulders of 8 other healthy men (mean age 28 (17–32) years) were studied using an open MRI system (Magnetom Open; Siemens, Germany) to evaluate the validity of data of the glenohumeral center. Shoulders with the arm neutrally rotated at the side and maximally elevated were scanned using a 3D gradient echo sequence (TR, 56 ms; TE, 25 ms; flip angle, 40˚) with a 2-mm section thickness. Images were digitized to a computer (O2; Silicon Graphics, CA) in which 3D images were constructed using 3D-Virtuoso software (Siemens). Head center and axis of the humeral bone were analyzed as previously described (Inui et al. 2002
). 2 cross sections of the humerus were obtained at 3 and 6 inches from the proximal end. The centers for these 2 cross sections of cortical bone were determined by fitting a circle, and the humeral axis was defined as the line passing through these centers. Using the data of Ianotti et al. (1992), showing correlations between size of the glenoid and the radius of curvature of the humeral head, each humeral radius was calculated as follows: radius (mm) = 24 × length of glenoidal long axis / 39 (where 24 is the average head radius and 39 is the average glenoidal long axis). The head was cut by the plane perpendicular to the humeral axis at the distance of the radius from the proximal end, and the center was determined by fitting a circle of the same radius, to be regarded as the head center. We investigated the extent to which the estimated glenohumeral joint center and humeral axis differed from the head center and axis of the humeral bone in each image.
Differences between measurements of each participant were evaluated using the Friedman test. When p-values derived with the Friedman test were significant, the Wilcoxon signed-rank test was used to determine which measurements differed statistically from the others. Values of p < 0.05 were considered statistically significant.