ABSTRACT
Objective To study biomechanical effects of cannulated screws at different fixation angles on posterior malleolus fracture based on finite element method, so as to determine the best fixation method of cannulatedscrew. Methods The finite element model of ankle joint, including tibia, fibula, astragalus, corresponding cartilage and ligaments was reconstructed using CT images, and 1 / 2 posterior malleolus fracture model was established on the basis of verifying its validity. The biomechanical effects of cannulated screw fixation on posterior malleolus fracture fixation model were analyzed. Results Compared with 0°,5°,10°,20° fixation model, the 15° fixation model had the smallest displacement. The screw stress of 15° fixation model was lower than that of 5°, 10°, 20° fixation model, and higher than that of 0° fixation model. But when the screw fixation angle was 0°, the peak contact pressure of ankle joint was much larger than that of normal ankle joint, which was easy to cause traumatic osteoarthritis. Conclusions Cannulated screw is safe and effective for treating posterior malleolus fracture which is less than 1 / 2 fragment size. The displacement and stress of the model are different at different fixation angles of screws. When the fixation angle of screw is 15°, the biomechanical stability is the best, which can be used to guide clinical operation.
ABSTRACT
Objective To investigate the feasibility of absorbable magnesium alloy screws in atlantoaxial dislocation fixation. Methods Four kinds of screws with triangular, rectangular, trapezoidal and zigzag thread were designed with WE43 magnesium alloy. The finite element simulation analyses were performed on the screw- polyurethane model and atlantoaxial fixation system model. The stress and displacement distributions on the models were obtained. Results The pull-out force simulations were carried out on four kinds of magnesium alloy screws according to ASTM F543 standard specification. The stresses of screws with triangular, rectangular, trapezoidal and zigzag thread were 146.20, 185.22,194.98, 264.55 MPa, respectively. The pull-out strength of the screw with triangular thread was the largest, and the peak stress was the smallest. The magnesium alloy screw with triangular thread used for atlantoaxial fixation could meet the strength requirements of flexion/extension, rotation and bending of the neck. The peak stress of the screw was reduced by 17.16 MPa after adding hydroxyapatite (HA) coating on the surface, and the stress on the screw was within the range of bonding strength between coating and magnesium alloy substrate. Conclusions Under the same loading condition, the screw with triangular thread has good stability and the best pull-out force performance. After heat treatment, the strength of magnesium alloy screw with triangular thread meets the load-bearing requirements for atlantoaxial dislocation fixation. HA coating on screw surface can optimize mechanical properties of the screw, and there exits good bonding strength between the coating and the screw.
ABSTRACT
Objective To evaluate the effect of locking compression plate for treatment in the osteoporotic of unstable distal radius fractures.Methods 48 cases of osteoporotic of unstable distal radius fractures were treated with open reduction and LCP fixation through volar approach.They were 8 men and 40 women aged from 58 to 77 years (range,63.7 years).They were all diagnosed by dual energy X ray absorptiometry before operation.According to AO/OTA criterion,there were 12 patients with type B2 fractures,10 cases with type B3,8 cases with type C1,13 cases with type C2,5 cases with type C3.All patients were performed locking plate fixations through volar approach and no bone graf.All patients were assessed from time of fracture healing,palmar tilt,radiographic measurements of ulnar inclination,radial height,and range of motion after 18 months,to evaluate the effect of clinical results and postopera-tive functional recovery.Results The patients were followed up for average 17.8 months (range,12 -24 months). All fratures united within 6 months (3 to 7 months),no infection in all patients,reduction loss in 2 cases after operation,traumatic arthritis in three.According to the Cooney criterion,the result was excellent in 35 pateints,good in 9 cases,fair in 3 cases and poor in 1 case,and the excellence rate was 92%.Conclusion The valor approach with locking compression plate can provide firm fixation and allow early functional exercise and so is suitable for unstable distal radius fracture especially in the osteoporotic of unstable distal radius fractures.