In this retrospective study (NCT04523415), the data of patients diagnosed with proximal humerus fractures and people without fractures were evaluated in one orthopaedics centre from 2015.1-2019.12, and the last 95 CT scans of proximal humeral surgical neck fractures were collected to illustrate the fracture distribution. Thirty-eight normal people with intact proximal humerus were enrolled to measure cortical thickness. All anonymous data were evaluated. Ethical approval was obtained from the Regional Ethics Committee of the Third Hospital of Hebei Medical University, and the study was conducted in accordance with the Declaration of Helsinki. Informed consent was obtained from all patients enrolled in the study.
The inclusion criteria were as follows: (i) clear records of demographic data; (ii) complete initial X-ray and CT imaging data; and (iii) patients older than 18 years. The exclusion criteria for the study were as follows: (i) patients with the presence of neurological disease (syringomyelia) and (ii) open or pathological fractures (tumour , etc.).
Participants were scanned in the clinical while-body multidetector computerized tomography machine (120 kV, 170 mAs, ≤ 1 mm reconstructed slice thickness, and Siemens SOMATATION sensation 64). The subjects were divided into two different groups (males and females).
Proximal humeral templates
The series of DICOM images were received in our hospital via PACS (ICZ, Brno, Czech Rep.) and were subsequently reconstructed to identify the fracture pattern. The CT scan DICOM data were imported into Mimics 20.0 (Materialise, Leuven, Belgium), and thresholding function was conducted with the software package predetermined cortical bone window value. In this research, Hounsfield units of 226 (minimum) and 1600 (maximum) were used as the threshold of the bone tissue.
Lateral images of the 3D proximal humerus were exported from the Mimics medical workstation. Using Mimic with B30 CT data, the 3D construction was then exported directly to 3 Matic 12.0 (Materialise, Leuven, Belgium). The wall thickness analysis tool was used to analyse the cortical thickness. The minimum threshold was set at 0.33 mm (the smallest possible pixel size), and the maximum thickness was set at 10 mm. Then, the cortical thickness images (2D) were imported into Adobe Illustrator and identified as the templates for the surgical neck fracture model.
Fracture distribution in cortical thickness map
Thirty-four men (47.2 ± 17.6 years) and 61 women (62.0 ± 14.5 years) who were diagnosed with proximal humeral surgical neck fractures in the clinic were enrolled. The 3D reconstruction images were obtained using the Radioant DICOM reviewer, and the fracture line was observed clearly.
The fracture lines were simulated and transcribed freehand onto the templates to illustrate the surgical neck fractures in the established template. For ease of analysis, small areas of relatively high comminution fractures were simplified as single fracture lines. To optimize the accuracy of this procedure, the transcriptions were performed by the first and second authors and were reassessed by an additional two trauma surgeons. Any discrepancies between the reviewers were reassessed, and the final results were identified by experienced surgeons after a comprehensive evaluation.
The local cortical thickness can be observed from the cortical thickness map in each normal person, and the relationship with the surgical neck region is illustrated in the template.
Cortical thickness measurement
Normal people without fractures, including 23 men (46.1±11.1 years) and 15 women (50.8 ±18.1 years), were enrolled to measure the cortical thickness of the greater tuberosity, surgical neck region and diaphysis.
Ⅰ. The line located under the lesser tuberosity was chosen as the plane to measure the cortical thickness of the surgical neck region. Three points were selected adjacent to the bicipital groove (anterolateral), middle of the greater tuberosity and posterolateral point. Ⅱ. The line located at the top of the lesser tuberosity was chosen as the plane to measure the cortical thickness of the surgical neck region. Three points were selected adjacent to the bicipital groove (anterolateral), middle of the greater tuberosity and posterolateral point. III. The line that was parallel and had the same distance from the above line to the first line was chosen as the plane to measure the cortical thickness of the diaphysis (Figure 1). Finally, the average value of three locations was used as the final measurement result. Furthermore, the width (the distance between the proximal and distal directions) of this surgical neck region was measured and illustrated (Figure 2).
Statistical analysis
Continuous data are presented as the means with standard deviation. Mann-Whitney U tests were conducted for comparisons between the 2 independent groups, and Kruskal-Wallis H tests were used to conduct comparisons among 3 independent groups. In addition, x2 tests were used to evaluate categorical variables. Homogeneity of variance for continuous variables was evaluated using the Levene test for equality of variances. For all analyses in this research, significance was set at the P < 0.05 level. Before data analysis, statistical significance was set at P = 0.05. All analyses were conducted using SPSS Version 22.0 (IBM Corp, Armonk, NY).