Objective To explore the effects of swan-like memory compressive connector(SMC) made of Ni-Ti shape memory alloy on stress shielding rate, struct ure and mechanical properties as well as the blood flow of cortical bone of expe rimental fracture healing. Methods Mid-shaft osteotomies of bilateral humerus we re performed in 56 rabbits. One side was randomly fixed with SMC, and the other side was plated with a 4-holes dynamic compressive plate (DCP). At 2, 4, 8, 12, 16,and 20 weeks after operations, the humeri in 8 rabbits were harvested. The st ress-shielding rate was measured using axial compressive test in situ samples. T he geometrical structure and bone density were examined by CT scans, and the mec hanical property was assessed by torsion tests. Blood flow was measured in real time using Laser-Doppler flowmetry. The cortical bone perfusion of 16 rabbits wa s measured at 10 time intervals (after periosteotomy, after fracture, instant af ter fixation, at 1, 3, and 7 days, and 2, 4, 8, and 12 weeks postoperatively). B lood flow was measured at outer and inner cortical bone beneath the fixation. Si multaneously, anteroposterior radiograph of the humerus was taken. Results The s tress-shielding rate in SMC group was significantly lower than that of DCP group (P

Objective To explore effect of swan-like memory connector (SMC) on bioelectric potential changes during the course of experimental fracture healing and its relation with fracture healing. Methods Bilateral humerus of 33 New Zealand rabbits were osteotomized in midshaft. One random side was fixed with SMC and the other one plated by the four-hole dynamic compression plate (DCP). The bioelectric potential changes of the fractured humerus in eight animals were determined using modified Friedenberg's technique,at eight time intervals (prefracture,postfracture,postfixation immediately,1, 2,4,8 and 12 weeks after surgery). The rabbits were killed at the 1st,2nd,4th,8th and 12th weeks respectively postoperatively and the humerus in 5 rabbits harvested for HE sections. Results The bioelectric potential of fracture site remained invariably negative all the time in the Group SMC. However,the bioelectric potential began to recover from the 2nd week after operation and reached the normal level of prefracture at the 4th week in the Group DCP,with a significant difference compared with the Group SMC ( P

Objective To discuss the complications following internal fixation of intra-articular calcaneal fractures and its prevention and treatment. Methods From January 1997 to July 2002, 59 sides of calcaneal fractures in 54 patients were treated with open reduction and Y-shaped plate fixation through lateral approach, most of them supplemented by autogenous bone grafting. According to Sanders classification, 20 sides were accounted for typeⅡ, 24 for type Ⅲ, 15 for type Ⅳ. During operation, lateral roentgenograms were made to assess Bler angle and Gissane angle, Broden view was made to evaluate congruency of the posterior facet. The wounds were drained underneath the lateral flap to prevent hematoma formation. Perioperative antibiotics were used routinely. All the cases were followed-up for an average of 17 months(range, 9 to 48 months). Results The clinical results were evaluated according to Maryland Foot Score, excellent results achieved in 30 cases, good in 21, fair in 6, poor in 2; excellent and good rate was 86.4%. Early complications were found in 4 cases(6.8%). Among them, 2 cases of wound necrosis were treated with suture after resection of necrotic tissue or covered with flap grafts, 1 case of wound infection recovered after dressing changes, 1 case of sural nerve injury recovered uncompletely without any special treatment. Late complications were found in 2 cases(3.4%) with obvious chronic pain, the patients were treated by subtalar arthrodesis and relieved from pain later. Conclusion The complications of internal fixation to fractures are related to anatomic features of calcaneus and their injury mechanism. Serious complications can be minimized in several ways as follows: optimal time for operation and preoperative design should be carefully considered, a full-thickness flap is recommended in avoidance of excessive distraction, bone grafting is needed to support intra-articular fracture fragments and to enhance the stability of internal fixation, the affected extremity should be immobilized by plaster and elevated, and perioperative use of antibiotics.The appropriate management should be taken in cases of complications.

Objective To investigate the effects of swan shaped memory connector(SMC) on the bone mineral density and mechanical properties of humeral fracture in rabbits in order to disclose the mechanism of SMC stimulating fracture healing. Methods Shafts of both humeri of 40 rabbits were osteotomized. One side was selected to fix with SMC, but the contralateral side was fixed with the 4 hole dynamic compression plate (DCP). Eight rabbits were sacrificed and the humeri were harvested respectively at 2, 4, 8, 12 and 16 weeks after operation. The bone mineral density(BMD) was examined by dual energy radiographic absorptiometry(DRA). The mechanical properties were assessed by mechanical traction test. Results From 4 to 16 weeks after operation, the BMD in SMC group was significantly higher than that in DCP group ( P

Objective:To quantitatively measure the blood flow of bone and muscle tissue by the radioactive microsphere techniques.Methods:The erythrocytes of hoptoad labelled with the 99m Tc were used as the radioactive microsperes.Each injection consisted of 10 6 microspheres.The blood flow of bone and muscle tissue of 10 rabbits were examined via injection of hoptoad erythrocytes labelled with the isotope; the blood flow of tissues were calculated according to the artery withdraw rate and radioactive counting of samples and reference blood.Results:The blood flow of femurs [(8.94?0.45) ml/(min?100 g)] was the highest among all the long bones,the blood flow of humeral metaphysis [(7.73?0.68) ml/(min?100 g)] was significantly higher than that of diaphysis and epiphysis ( P

BACKGROUND: The most frequently encountered problem that an orthopedic doctor encounters in treating humerus fracture is how to choose the exact direction and amount of load applied on humerus.OBJECTIVE: To explore the clinical significance of establishing a three-dimensional model and finite element analysis in treating humerus fracture and to provide theoretical basis for applying appropriate axial stress.DESIGN: The three dimensional model of humerus was reconstructed, on which compression from different directions was applied.SETTING: Orthopedic department of an affiliated hospital and life science laboratory of a university.MATERIALS: A humerus specimen received CT scanning and the trial was conducted in Shanghai Changhai Hospital and Life Science Laboratory of Tongji University from April 2002 to April 2004.METHODS: The three dimensional model of humerus was established and relevant calculation was completed with ANSYS 5.6 software. The humerus model was divided into 2 729 nodes and 49 041 units based on a three-dimensional ten-node tetrahedron as one unit. The distribution and intensity of axial compression on the fracture gap section were calculated and analyzed in the following conditions, i. e. when the humerus was fixed in X, Y and Z directions and the fracture gap section was 30°, 45°, 90° to Z axis.MAIN OUTCOME MEASURES: The axial pressure on the fracture gap section in different conditions to provide evidence for clinical treatment.RESULTS: The stress applied on the fracture gap was relatively concentrated and was 2 -3 times stronger than that in other areas, and it was generally symmetrically distributed within 10 mm around the fracture gap.CONCLUSION: The required load on humerus fracture should be calculated before a suitable implant is applied to accommodate the movement of humerus without compromising healing of the fracture.