ABSTRACT
OBJECTIVE@#To establish a new mechanical model of distal humerus in children with epiphysial cartilage, stimulate supracondylar humerus fracture and perform three dimensional finite elements, and study effect of pins numbers, pin tract, outlet height and pin configurations on stability of fixation.@*METHODS@#Three dimensional computed tomography (CT) data of 6-year-old boy with distal humerus was downloaded from picture archiving and communications systems software (PACS), the data of picture was imported into Simpleware and SolidWorks 2016 software to establish distal humerus fracture in children contained ossific nucleus of the capitellum (ONC) and distal cartilage. Normal extense supracondylar humerus fracture model was established to stimulate configurations of crossed and lateral pinning fixation, 30 N was added on the direction of flexion extension and varus valgus, while 50 N was added on the direction of internal and external turning. Stability was analyzed by displacement degree of distal fracture.@*RESULTS@#Among 2-pin configurations, 2-crossed pins were more stable against rotation forces which could resist rotation stress over 2 585 Nmm/ °, while low position through ONC of 2-divergent lateral pins were more stable, which could resist stress of 45 N /mm and 190 N /mm during the test of resistant strains and varus-valgus stress. The third pins was added into the more stable lateral 2-pins, the stability in all directions were increased obviously, and 3 crossed pins is the most stable, stress of flexion-extension, varus-valgus and internal-external turning were 198 N /mm, 395 N /mm and 6 251 Nmm/ °.@*CONCLUSION@#Two-divergent lateral pins could provide enough stability for supracondylar humerus fracture in children. In two-crossed pins, the upper border of MDJ could provide the best stability. Three-crossed pins could offer the best stability against both translation and rotation forces.
Subject(s)
Child , Humans , Male , Biomechanical Phenomena , Bone Wires , Finite Element Analysis , Fracture Fixation, Internal , HumerusABSTRACT
<p><b>OBJECTIVES</b>To evaluate the mid-term outcome after Salter innominate osteotomy in developmental dysplasia of the hip (DDH), and to observe the developmental characteristics of the hip after operation and the relationships between the mid-term outcome and radiographic parameters as well as age at operation.</p><p><b>METHODS</b>: Forty-four patients with 61 treated hips were selected. The patients were treated with Salter innominate osteotomy and followed-up for at least three years with intact serial radiographs. Radiographs taken before operation, 6 weeks, 1 year and 2 - 3 years after operation and in the latest follow-up were selected. Acetabular index (AI), Sharp acetabular angle (SAA) and center-edge angle of Wiberg (CEA) were measured and Severin classification was done according to radiographs taken in the latest follow-up.</p><p><b>RESULTS</b>The average correction of AI was 14° postoperatively. The acetabulum remodels best at 2-3 years after operation when the average AI became very close to normal. In the latest follow-up the SAA was 41° which could be regarded as normal. Postoperative CEA was on average 23° which increased to 25° 2-3 years later. In the latest follow-up, the average CEA was 26°. The ratio of excellent and good outcomes (Severin I, II) was 84%, while the ratio of moderate and poor outcomes (Severin III, IV, V, VI) was 16%. Age at operation had a negative effect on outcomes. Although 70% patients operated after age 6 had satisfactory outcomes. The Severin I, II group showed no difference in AI from III, IV, V, VI group 6 weeks after operation, but the AI of the former obviously improved 2-3 years after operation while that of the latter deteriorated. Significant difference in SAA and the CEA could be observed in the latest follow-up.</p><p><b>CONCLUSIONS</b>Salter innominate osteotomy focuses on normalizing the abnormal acetabular direction in DDH children as well as stimulating the remodeling of the acetabulum, which provides a satisfactory middle-term outcome. The acetabulum remodels rapidly during the first three years after operation when AI and CEA develops into normal. Interference should be adopted if these changes have not appeared in the first three years.</p>