Objective To compare the biomechanical characteristics between S2 alar-iliac (S2AI) screw and sacroiliac joint screw in treating unilateral type C sacroiliac joint dislocation. Methods A 25 year-old healthy male adult agreed to take computed tomography scan of the pelvis. The pelvic floor thickness was 1 mm and the image data were saved in DCOM format. A three dimensional finite element model of intact pelvis was reconstructed by Mimics, Geomagic, SolidWorks, and Abaqus softwares. A finite element model of type C unilateral sacroiliac dislocation was established. One S1 vertebral sacroiliac screw of 6.5 mm in diameter (S1 group), one S2AI screw (S2AI group) and one Si vertebra sacroiliac screw + one S2 vertebra sacroiliac screw (S1+S2 group) were placed in the model, respectively. The500 N vertical load on the upper surface of the sacrum was simulated. The displacement value of sacroiliac joint, the displacement of sacrum, the stress value of the internal fixation and surrounding bone, and the stress distribution cloud map were recorded and analyzed. Results The displacement data showed that displacement distribution in the three groups had a consistent trend. In terms of the absolute value of displacement the result was S, group＞S 2AI group＞S1+ S2 group, of which the maximum displacement of sacroiliac joint in S1 groups was 0.87 mm and that of sacrum was 1.6 mm; the maximum displacement of sacroiliac joint in S2 AI group was 0.22 mm, and that of sacrum was 0.24 mm; the maximum displacement of the sacroiliac joint in S1 + S2 group was 0.06 mm, and that of sacrum was0.16 mm. Stress data showed that the stress in the internal fixation was mainly distributed at the sacroiliac joint, and the stress result was S2AI group＞S, group＞S, + S2 group, of which the maximum stress value was 52.8 MPa in S1 group, 62.1 MPa in S2AI group, and 38.2 MPa in S1 + S2 group. The stress around the screws was also concentrated at the sacroiliac joint, and the stress result was S1 group＞S2AI group＞S1 + S2 group, of which the maximum stress value was 56.8 MPa in S1 group, 11.2 MPa in S2AI group, and 5.8 MPa in S1 + S2 group. Conclusions Single S1 screw, single S2 AI screw and S, screws combined S2 screws can be used for the treatment of unilateral C type sacroiliac joint dislocation. Early weight bearing of single S1 screw might lead to the risks of increased sacroiliac joint displacement and internal fixation failure. S2 AI screw fixation and S1 + S2 screw fixation have similar biomechanical strength, allowing early weight-bearing and contributing to better postoperative rehabilitation.

Objective:To investigate the clinical efficacy of extracorporeal shock wave (ESWT) combined with stretching training in the treatment of chronic plantar fasciitis.Methods:A prospective case-control study was conducted to include the patients with chronic plantar fasciitis who had been admitted to Department of Orthopaedic Trauma, Nanfang Hospital, Southern Medical University from June 2021 to June 2022. A SPSS random number generator was used to randomize the patients into an experimental group (receiving treatment with ESWT combined with stretching training) and a control group (receiving stretching training only). Shear wave elastography (SWE) was used to quantitatively evaluate the elastic modulus of the plantar fascia. The 2 groups were compared in terms of visual analogue scale (VAS) pain score, plantar fascia thickness, and elastic modulus of the plantar fascia in the patients at 12 weeks after treatment; the correlation between VAS pain score and elastic modulus of the plantar fascia was examined using Spearman analysis in the patients at 12 weeks after treatment.Results:This study included a total of 41 patients (52 feet), 20 males and 21 females with an age of (49.9±8.2) years. There were 16 left sides, 14 right sides and 11 bilateral sides affected. The course of the disease was 7.0 (6.0, 12.0) months. The 2 groups were comparable because there were no significant differences in the general data before treatment between them ( P>0.05). The VAS pain score at 12 weeks after treatment for the experimental group was 1.0 (1.0, 2.0) points, significantly lower than that for the control group [3.0 (2.0, 3.0) points] ( P<0.05). The elastic modulus of the plantar fascia at 12 weeks after treatment for the experimental group was (79.48 ± 17.65) kPa, significantly higher than that for the control group [(57.08 ± 14.16) kPa] ( P<0.05). However, there was no statistically significant difference between the 2 groups in the thickness of the plantar fascia at 12 weeks after treatment ( P>0.05). There was a significant correlation between VAS pain score and elastic modulus of the plantar fascia after 12 weeks of treatment ( r = -0.708, P<0.001). Conclusion:In the treatment of chronic plantar fasciitis, combination of ESWT and stretching training is more effective than stretching training only.