Objective:To compare the biomechanical parameters of Ortho-Bridge system (OBS) and locking compression plate+locking attachment plate (LCP+LAP) in the fixation of femoral periprosthetic type B1 fracture.Methods:The same periprosthetic type B1 fracture of human femur were made, including simple fracture model and comminuted fracture model, 12 in each. And the simple fracture models were randomly divided into 6 pieces of OBS system fixation group and 6 pieces of LCP+LAP system fixation group, and the complex fracture models were also randomly divided into 6 pieces of OBS system fixation group and 6 pieces of LCP + LAP system fixation group. Then the four groups of models were tested by axial compression and torsion tests, and the stiffness of the models under axial compression and torsion angle of the models under torsion test were collected. The axial compression failure test was carried out to collect the vertical load of the ultimate failure test. The axial stiffness, torsion angle and axial failure load of OBS and LCP+LAP fixed simple and comminuted fractures were statistically analyzed by t test. Results:For the test of fixed simple fracture, there was no significant difference ( t=0.535, P=0.522) in the axial stiffness between the OBS group (868.87±157.14 N) and the LCP+LAP group (904.53±44.76 N), whereas the results of torsion test showed that the LCP+LAP group had a higher torsion angle 7.17°±0.52° than the OBS group 5.45°±0.44° ( t=5.616, P<0.001); When fixing comminuted fractures, the OBS group had a higher axial stiffness (145.33±10.34 N) than the LCP+LAP group (84.15±8.94 N) ( t=10.961, P<0.001), but the LCP+LAP group had a higher torsion angle 7.75°±1.17° than the OBS group 5.23°±0.31° ( t=4.652, P=0.001). Ultimate failure test data showed that the failure pressure of OBS fixed group (4 967.49±132.88 N) was higher than LCP+LAP group (3 967.41±145.16 N) ( t=12.447, P<0.001). In the LCP+LAP group, there was destruction of the contact cortex at the fracture site, while in the OBS group, there was destruction of the contact cortex at the fracture site as well as fractures around the proximal fixation screw. Conclusion:OBS group has similar axial compression resistance to LCP+LAP group, but better torsion resistance than LCP+LAP group when it is used to fix B1 simple fracture around femoral prosthesis. When comminuted fracture is fixed, the axial compression resistance and torsion resistance of OBS group are better than LCP+LAP group. The stress is dispersed during OBS fixation, which can better avoid the failure of internal fixation during early functional exercise.

Objective:To introduce the surgical method of Ortho-Bridge system (OBS) in the treatment of distal femoral fractures in elderly patients and investigate its clinical effect.Methods:From January 2018 to July 2021, 24 elderly patients who suffered distal femoral fractures were treated with bilateral OBS. There were 8 males and 16 females aging from 62 to 87 years, with an average age of 72.6 years. It included 15 cases of simple distal femoral fractures. According to AO classification, there were one case of A1, two of A2, five of A3, two of C1, three of C2 and two of C3. Nine cases of femoral periprosthetic fractures after total knee arthroplasty (TKA) were classified as type II according to rorabeck's classification. After operation, all patients were guided to perform knee joint functional exercise and to measure the range of motion of the knee joint. Then imaging examinations were used to evaluate the fracture healing and measure the femoral-tibial and femoral angles. The American Hospital for Special Surgery (HSS) knee joint scoring system was used to evaluate the knee function.Results:All 24 patients successfully completed the operation. The operation time was 84-115 min, with an average of 96.6 min; the intraoperative blood loss was 150-335 ml, with an average of 240 ml. All patients were followed up for 8-17 months, with an average of 13.6 months. Except for 1 case of nonunion due to few primary bone grafts, which required secondary bone grafting, the other 23 cases achieved bone union. The healing time was 3.5-6 months, with an average of 4.6 months. At 1, 3, and 6 months after operation and at the last follow-up, the flexion angles of knee were 92.2°±10.2°, 98.6°±13.3°, 106.4°±13.7°, 115.7°±15.3°, and the extension angles were -4.7°±4.1°, -1.2°±4.2°, 0.7°±4.5°, 1.8°±4.6°, respectively; and all differences were statistically significant ( F=17.03 and 12.68, P<0.001). The knee flexion and extension angles at the last follow-up were greater than 1, 3, and 6 months after operation, and the differences were statistically significant ( P<0.001). The femoral-tibial angle was 171.2°±2.4° and 170.7°±3.2°, and the femoral angle was 80.3°±1.7° and 79.6°±2.1°, respectively, at the immediate postoperative and last follow-up, with no significant difference. The HSS scores at 1, 3, 6 months after operation and at the last follow-up were 71.5±7.5, 74.6± 9.3, 78.9±10.4 and 84.7±9.4 respectively, with significant difference ( F=9.17, P<0.001). At the last follow-up, the HSS score was higher than that at 1, 3, and 6 months after the operation, and the differences were statistically significant ( P<0.001), and the knee function was evaluated according to the HSS scoring system: excellent in 12 cases, good in 9, fair in 3, with an excellent and good rate of 88% (21/24). There was no OBS crack or fixation failure in all patients, and no prosthetic loosening and instability occurred in patients with periprosthetic femoral fractures after TKA. Statistical analysis of the data at the last follow-up between the distal femoral fracture group and the periprosthetic femoral fracture group after TKA showed that the knee flexion function and HSS score of the periprosthetic femoral fracture group after TKA (126.8°±3.7°, 92.2±4.1) were both better than the simple distal femur fracture group (108.9°±15.7°, 80.2±8.8). The difference was statistically significant ( t=4.22, 4.52, P<0.05). One patient had incision fat liquefaction and healed after debridement; bone nonunion occurred in 1 case, which healed after iliac bone grafting. Conclusion:Double OBS has a good clinical effect in the treatment of distal femoral fractures in the elderly, especially in patients with periprosthetic femoral fractures after TKA.