Background: For the robot-assisted fracture reduction, due to the complex fracture musculoskeletal environment, it is necessary to consider the influence of soft tissue traction on preoperative reduction path planning.Method: An improved 3D A* algorithm is adopted to plan the fracture reduction path. The distal fragment point clouds are updated to avoid the collision, and the end point coordinates of the muscles are updated to calculate muscular lengths during the path search.Results: 3D reduction path of long-bone fracture is planned, effectively avoiding the fracture fragments collision and ensuring the length of the corresponding muscle is always less than the allowable maximum muscle length after elongation.
Conclusion:The proposed method can effectively avoid the collision between the distal fragment and the proximal fragment during the fracture reduction, can avoid secondary injury of the muscles around the femoral bone caused by overdistraction, and effectively improve the safety of robot reduction operation.
Robot-assisted reduction of pelvic fracture, the bone traction needles need to be inserted into the iliac bone of the affected pelvis, and the clamping instrument of the robot is connected to the bone traction needle. The biomechanical characteristics of the pelvic musculoskeletal tissues are different with the different spatial position and orientation of the bone traction needle. In this paper, a new PA-MTM model considering the pinnate angle of skeletal muscle is proposed to analyze the muscle force of skeletal muscle. According to the planned reduction path, reduction force during the reduction process is calculated. Based on the pelvic CT scan data and the muscle distribution of the pelvis, the musculoskeletal model of the fractured pelvis is reconstructed. Then, the finite element model of the pelvic musculoskeletal tissue with bone traction needle is established. The maximum reduction force is applied on the bone traction needles, and the stress distribution of the pelvic musculoskeletal tissue with the needles in different spatial position and orientation is comparatively studied. The results show that the suitable force point on bone traction needle is S1 point. When the bone traction needle is inserted into the iliac crest and the anterior inferior iliac spine, the pelvis is in a good stress state.
To present the ligament effects on sacroiliac joint (SIJ) stability and human pelvis biomechanical characteristics in two different positions by using three-dimensional (3D) finite element (FE) models of pelvis. Based on the computed tomography (CT) data of human pelvis, three-dimensional FE models of human pelvis in sitting and standing positions were established, which include the bone (sacrum, ilium, and coccyx) and six ligaments (sacroiliac, sacrospinous, sacrotuberous, inguinal, superior pubic, and arcuate pubic ligaments). 600 N vertical load was applied at the upper surface of sacrum to analyze the stress and displacement distribution of pelvis and SIJ. The simulation results demonstrated that the maximum stresses of sacrum and ilium on SIJ contact surface were 5.63 MPa and 7.40 MPa in standing position and 7.44 MPa and 7.95 MPa in sitting position. The stresses of ligament dysfunction group were higher than that of health group, which increased by 22.6% and 35.7% in standing position and 25.2% and 43.6% in sitting position in sacrum and ilium. The maximum displacements located on the upper surface of sacrum, which were 0.13 mm and 1.04 mm in standing and sitting positions. Ligaments dysfunction group increased 30.7% and 9.6% than health group in standing and sitting positions. The integral displacement of pelvis was greater in sitting position. The location of stress concentration and displacement distribution of pelvic bone are closely resembled previous research results in two different positions. The simulation results may provide beneficial information and theoretical models for clinical research of pelvic fracture, joint movement, and ligament functional injuries, and so on.
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