RESUMO
Objective:To compare the biomechanical characteristics of screw only spatial weaving fixation and calcaneal plate fixation in calcaneal fractures.Methods:Sanders type III calcaneus fracture model was established by using calcaneus model specimens: the physiological model group were the normal calcaneal models; the steel plate group were conventional steel plate fixation fracture models; the metal screw group were fracture models with only metal screw weaving fixation; seven and nine absorbable screw spatial weaving groups (seven absorbable screw group, nine absorbable screw group) were used to weave and fix fracture models with seven and nine absorbable screws. Cyclic test and mechanical compression test were carried out, and load-displacement curves were recorded. The material properties of metal screw spatial weaving and calcaneal anatomical plate system were replicated, finite element fracture models were established, and the calcaneal internal fixation models of plate screw group and spatial weaving screw group were completed by reverse processing. The changes of biomechanical characteristics of calcaneal bone in human (70 kg) standing on one foot were simulated, and the distribution of structural strength was analyzed by Von Mises equivalent stress cloud diagram and displacement cloud diagram.Results:In the cyclic test of 20-200 N load, the physiological model group, the plate group, the metal screw group, the absorbable 7 screw group, the absorbable 9 screw group were 0.87±0.22, 0.82±0.08, 0.70±0.12, 1.04±0.13 and 0.83±1.76 mm, the difference in model gap was statistically significant ( F=3.16, P=0.037). Among them, the absorbable 7 screws group was larger than the metal screws group ( t=4.28, P=0.003), and the other pin-two comparisons were not statistically significant ( P>0.05). The deformation of the five groups was 0.37±0.06, 0.38±0.07, 0.38±0.06, 0.52±0.07 and 0.42±0.07 mm, and the difference was statistically significant ( F=4.39, P=0.010). The deformation of absorbable 7 screws group was greater than that of physiological model group, the plate group and metal screw group ( t=3.69, P=0.006; t=3.25, P=0.012; t=3.51, P=0.008). In static test, compression displacement was 7.14±0.79, 7.30±0.66, 6.95±0.28, 8.19±0.61 and 7.16±0.55 mm, the difference was statistically significant ( F=3.28, P=0.032). The displacement of the absorbable 7 screws group was greater than that of the metal screws group ( t=4.13, P=0.003). The stiffness changes were 570.60±122.62, 512.86±80.77, 497.40±66.50, 456.21±58.19 and 560.39±94.40 N/mm, respectively, with no statistical significance ( F=1.44, P=0.258). The results of finite element analysis showed that under 3 500 N axial pressure load, the maximum compression displacement and stiffness of the plate and screw set were 6.47 mm, 540.96 N/mm, and the Von Mises equivalent stress peaks were 450.31 and 353.15 MPa, respectively. The maximum compression displacement and stiffness of the braided screw group were 5.25 mm, 666.67 N/mm, and the peak Von Mises equivalent stress of the screw was 396.20 MPa. Conclusion:Compared with lateral plate fixation, spatial weaving fixation can provide sufficient biomechanical stability for calcaneal healing and is superior to plate fixation in terms of structural stability, which may help to improve the effectiveness of calcaneal fracture fixation.
RESUMO
Objective:To evaluate the clinical significance of the coincidence test with 3D mirror image of unaffected side in the treatment of contralateral calcaneal fracture.Methods:A retrospective analysis was performed of the 35 patients who had been treated for single calcaneal fracture by coincidence test with 3D mirror image of unaffected side from January 2016 to June 2018 at Department of Trauma Orthopedics, The Sixth Hospital of Ningbo. They were 29 males and 6 females with an average age of 44 years (from 18 to 71 years). By Sanders classification, 19 cases were type Ⅱ and 16 cases type Ⅲ. CT scan and reconstruction of both calcaneuses was performed. The image of unaffected calcaneus was mirrored by Mimics software to guide virtual treatment of contralateral calcaneal fracture. Preoperatively the virtual bilateral calcaneuses and the reduced calcaneus were 3D printed to guide the actual operation. The coincidence test with 3D mirror image of unaffected side was used to evaluate fracture reduction after operation. Postoperative parameters such as B?hler Angle, Gissane Angle, calcaneal width, and coincidence of the affected calcaneal bone were recorded at 12 months after surgery. The clinical outcomes were assessed by American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot score and visual analogue scale (VAS) score.Results:In this cohort, operation time averaged 43.9 min (from 30 to 55 min), time from admission to operation 3.6 d (from 0 to 14 d), and hospital stay 6.3 d (from 3 to 11 d). The patients were followed up for an average of 18.8 months (from 13 to 24 months). All patients achieved bone union after an average of 17 weeks (from 12 to 26 weeks). Re-collapse of subtalar articular surface, talocalcaneal joint fusion, loss of calcaneal height or length, and calcaneal width increase were observed in none of the patients. The VAS scores averaged 2 (from 0 to 4), and the AOFAS scores 93.3 (from 76 to 98). The total coincidence was 95.2%±3.5%. Spearman test indicated a positive correlation between postoperative total coincidence and AOFAS score ( ρ=0.588, P<0.05). Conclusion:The coincidence test with 3D mirror image of unaffected side can be used to treat contralateral calcaneal fracture, with advantages of reduced surgical time, increased surgical accuracy and fine clinical outcomes.