Analysis on the mechanical resistance of fixation of femoral neck fractures in synthetic bone, using the dynamic hip system and an anti-rotation screw☆☆☆

OBJECTIVE To statistically analyze the results obtained from biomechanical tests on fixation of femoral neck fractures of Pauwels III type, in synthetic bone, using the dynamic hip system with an anti-rotation screw, versus a control group. METHODS Ten synthetic bones from a Brazilian manufacturer (model C1010) were used and divided into two groups: test and control. In the test group, fixation of an osteotomy was performed with 70° of inclination at the level of the femoral neck, using DHS with an anti-rotation screw. The resistance of this fixation was evaluated, along with its rotational deviation at 5 mm of displacement (phase 1) and at 10 mm of displacement (phase 2), which was considered to be failure of synthesis. In the control group, the models were tested in their entirety until femoral neck fracturing occurred. RESULTS The test values in the test group (samples 1-5) in phase 1 were: 1512 N, 1439 N, 1205 N, 1251 N and 1273 N, respectively (mean = 1336 N; standard deviation [SD] = 132 N). The rotational deviations were: 4.90°, 3.27°, 2.62°, 0.66° and 0.66°, respectively (mean = 2.42°; SD = 1.81°). In phase 2, we obtained: 2064 N, 1895 N, 1682 N, 1713 N and 1354 N, respectively (mean = 1742 N; SD = 265 N). The failure loading values in the control group were: 1544 N, 1110 N, 1359 N, 1194 N and 1437 N, respectively (mean = 1329 N; SD = 177 N). The statistical analysis using the Mann-Whitney test showed that the test group presented maximum loading at a displacement of 10 mm, i.e. significantly greater than the failure loading of the control group (p = 0.047). CONCLUSION The mechanical resistance of the test group was significantly greater than that of the control group.