Objective To investigate the validity of improving the femur’s mechanical characteristics by implanting calcium phosphate ceramic screws after removing dynamic hip screw (DHS). Methods The three dimensional finite element model of the femur was built based on the CT scanning of a normal male volunteer. Then the models of the femur with and without DHS were established. According to calcium phosphate ceramic screws with porosity and apparent elastic modulus, 80% and 0.1 GPa were set as group A, 50% and 1.0 GPa as group B, and 30% and 1.5 GPa as group C. Von Mises stress distribution and maximum stress were recorded when the joint was maximally loaded in a gait cycle. Results The Von Mises in normal femoral shaft was uniform; no phenomena of stress concentration was observed and the maximum stress located at the joint load-bearing site of the proximal femur. The stress concentration was observed in the femur without DHS, and the maximum stress located at the distal femur around the screw hole. By comparing several different calcium phosphate ceramic screws, the stress distribution of group B was similar to normal femur model, and the maximum stress located at the joint load-bearing site. The other screws of groups A and C showed varying degrees of stress concentration. Conclusion Implanting calcium phosphate ceramic screw can improve the mechanical characteristics of the femur after removing dynamic hip screw, and the calcium phosphate ceramic screw with 50% porosity and 1.0 GPa apparent elastic modulus is suitable for implanting.
Objective To investigate the effectiveness of dorsal perforator flap of cross-finger proper digital artery in the treatment of finger soft tissue defect caused by high-pressure injection injury. MethodsBetween July 2011 and June 2020, 14 cases of finger soft tissue defect caused by high-pressure injection injury were repaired with dorsal perforator flap of cross-finger proper digital artery. All patients were male, with a mean age of 36 years (range, 22-56 years). The defects were located on the index finger in 8 cases, middle finger in 4 cases, and ring finger in 2 cases. The causes of injury include 8 cases of emulsion paint injection, 4 cases of oil paint injection, and 2 cases of cement injection. The time from injury to debridement was 2-8 hours, with a mean time of 4.5 hours. The soft tissue defects sized from 4.0 cm×1.2 cm to 6.0 cm×2.0 cm. The flaps sized from 4.5 cm×1.5 cm to 6.5 cm×2.5 cm. The donor site of the flap was repaired with skin graft. The pedicle was cut off at 3 weeks after operation, and followed by functional exercise. ResultsAll flaps and skin grafts at donor sites survived, and the wounds healed by first intention. Twelve patients were followed-up 16-38 months (mean, 22.6 months). The texture and appearance of all flaps were satisfactory. The color and texture of the flaps were similar to those of the surrounding tissues. The two-point discrimination of the flap was 10-12 mm, with a mean of 11.5 mm. There were different degrees of cold intolerance at the end of the affected fingers. At last follow-up, the finger function was evaluated according to the Upper Extremity Functional Evaluation Standard set up by Hand Surgery Branch of Chinese Medical Association, 3 cases were excellent, 8 cases were good, and 1 case was poor. Conclusion The dorsal perforator flap of cross-finger proper digital artery can effectively repair finger soft tissue defect caused by high-pressure injection injury. The operation was simple, and the appearance and function of the finger recover well.