Subjects
This was a retrospective study, with ethical permission by the ethical committee of Beijing Friendship Hospital (No. 2020-P2-153-01). The data came from the department of radiology. CT Digital Imaging was screened from December 2018 to February 2020. Patients had shoulder CT examination because of shoulder pain or injuries around shoulder. Inclusion criteria were that CT showed normal structure of GT and humeral head, and age of 18-50, both left and right shoulders. Patients selected for this study were not older than 50 years, because patients older than 50 years may develop osteophytes, which may interfere with the measurement results. Exclusion criteria were proximal humeral fracture, arthritis around the greater tuberosity which interfere with the measurement of the morphology, or a humerus shaft was not perpendicular to the scanning plane which had a tilt angle more than 18° on the surview (Fig 1).
CTTechnique
All shoulder CT scans were performed on a 128/DE CT Scanner (Ingenuity CT, Philips Medical Systems, Cleveland, USA). The scanning parameters were as follows: helical scan type, tube voltage 120 KV, tube current 401 mA, scanning layer thickness and layer spacing 0.5 mm, matrix 512×512, pixels field of view (FOV) 32.9 cm×29.3 cm and exposure 3.4 s. Due to MPR allows for more accurate identification of bone structure and accurate measurements of size, so we choose it rather than 3D-CT for this study. When examine the shoulder radiograph, the humerus should be placed in the correct direction, that is, the axis perpendicular to the scanning plane (deviation ≤ 18°, bias < 5%, cos18°=0.95106, cos19°=0.94552), achieving most standard sagittal and coronal plane (Fig 1). In a pilot study, on cadaver humerus, we placed a metal marker on the insertion of the teres minor muscle to locate the precise position (Fig 2), due to it was a key point of MPR analysis[8,6,12].
Measurement of Parameters
Images from the initial axial CT data were reconstructed at a 0.5 mm slice thickness in MPR (Fig 3). On the sagittal planes A, find the one which shows the most prominent tip of the lesser tuberosity. On the chosen sagittal plane, reconstruct the horizontal plane that perpendicular to the shaft through the tip of the lesser tuberosity. On the horizontal plane B, draw a circle that most match the humeral head. And then draw a line (line a) which connect the center of the circle and the middle point of the cortex of greater tuberosity. Then we reconstruct 30 sagittal planes perpendicular to line a containing the greater tuberosity, with 0.5mm interval. Among these sagittal planes, find the one which shows the prominent teres minor insertion (image C). On image C, draw two lines through the medial and lateral margin of the greater tuberosity respectively which is parallel to the shaft (line b and line c). Then draw a line perpendicular to the shaft through teres minor insertion (line d). Draw a line e through most prominent tip of the greater tuberosity to line d and perpendicular to line d. Then we reconstruct a coronal plane through line e (image D). On image D, line f was in the center of the shaft. Line g was parallel to line f, and it went through the medial margin of the humeral head. Line h was parallel to line f and went through the lateral margin of the greater tuberosity. Line i was parallel to line f and went through the boundary of humeral head and greater tuberosity.
GT width was defined as the distance between the anterior (the posterior wall of the bicipital groove) and posterior margin (insertion of the teres minor muscle), as shown in Fig. 3C between line c and line d. GT Height was defined as the distance between tip of the GT and teres minor insertion, as shown in Fig. 3C between line e and line d. GT thickness was defined as the distance between lateral cortex and articular margin, as shown in Fig. 3D between line h and line I. The thickness of proximal humerus (PH) was defined as the distance between lateral cortex and articular margin, as shown in Fig. 3D between line h and line g. All distances were recorded using an electronic caliper in millimeters by 2 trained, independent radiologists.
Statistical analysis
Statistical analysis was performed with SPSS version 17.0 (IBM Corp, Armonk, NY, USA). All results are expressed as means with 95% confidence intervals (CIs) (lower bound to upper bound). The ICC was calculated to determine the amount of concordance [13]. An ICC of 0.01 was considered poor agreement, 0.01 to 0.2 was considered slight agreement, 0.21 to 0.4 was considered fair agreement, 0.41 to 0.6 was considered moderate agreement, 0.61 to 0.8 was considered substantial agreement, and 0.8 to 1.0 was considered almost perfect agreement. The difference between two observers was analyzed with paired-samples T test. The difference between male and female cases was analyzed with Analysis of Variance (ANOVA). P < 0.05 was considered significant.