The Biomechanical Study Of The Treatment In Osteoporotic Femoral Neck Fracture With " F "Technique

Objective:Present-day popular traditional methods of femoral neck fixation, which are performed by three cancellous screws, placed parallel to each other,are associated with poor results in20to42%when patient is under the conditions of osteoporosis. Orlin Filipov puts forward a new way of cannulated screws in2010,which was described "Biplane double-supported screw fixation".In A-P view,the projection of the distal screw crosses the projections of the other two screws, thus forming the letter F (F-technique). What is innovative about this method is that the three screws are laid in two planes, the middle and the proximal screws are placed first because they are perpendicular to the fracture surface which can make sure a repeated impaction of the fracture with an additional tightening up of the screws follows. The provision of two steady supporting points for the distal and the highly increased (obtuse) angle at which they are positioned allow the body weight to be transferred successfully from the head fragment onto the diaphysis. Although Orlin Filipov reports this technique can obtain88.64%good rate,but lack of the support of biomechanical study.This study was designed to compare the biomechanical characteristics of the two geometric configuration ("F " shaped and inverted triangle shaped)of three cannulated compression screws in the fixation for femoral neck fracture and to provide a theoretical foundation in the treatment of osteoporotic femoral neck fracture.Methods:Six matched pairs of human cadavers were obtained.The soft tissues were stripped,and the radiography was done to evacuate congenital abnormality,fracture and tumor.All specimens were evaluated with dual energy X-ray absorptiometry to determine the bone-mineral density.A swing saw was used to creat an osteotomy as the femoral neck fracture model and to remove at one-third of distal femur for being easily potted in dental cement. All the specimens were divided into2groups.The group A were fixed by the method of F-technique,while group B used inverted triangle shaped cannulated compression screws. The biomechanical test was divided into three steps. Axial compression test was conducted first.For this test,femoral was vertically loaded at the speed of20N/s, and the finally vertical loading was 600N.Displacement of femoral head was recorded at200N,400N,600N vertical loading.After compression strength test, Torsional test was carried out at the anticlockwise speed of0.2°/s and record the torque moments at2°,4°. At last,We took destructive axial loading test. The maximal vertical loading was measured with biomechanical meter till the failure of internal fixation.Data were dealt with SPSS17.0software and by the first author in this study. P value was set at0.05for the statistical difference and at0.01for the significant difference.Results:No statistically significant differences existed between the two groups in terms of bone mineral density.Compression strength test:The displacement of femoral head of the A group were0.349±0.106mm0.482±0.089mm、0.711±0.114mm at200N、400N、600N,while the B group was0.484±0.055mm、0.648±0.098mm、0.875±0.089mm.There was statistical difference between the two groups in compress-ion strength at the200N、400N、600N(P<0.05).Torsibility test:The torque-moments of the A group were3.551±0.582N.m、1.267±0.596N.m at°、4°torsibility,while the control group were4.495±0.696N.m、3.033±0.511N.m. There was Significant difference between the two groups(P<0.01). Axial compression damage test, measure the specimens’maximum load, group A maximum load was2411.7±413.2N, group B:1950±281N. The F-technique shaped screws showed better maximum vertical loading than the inverted triangle shaped ones with with a statistical difference (P<0.05).Conclsion:With the result we can get the conclsion:the"F"technique had better twisting resistance in the torsion test and also get the superiority in the load test and the destructive load test. Compared with the tradition method,The"F"technique can offer more stable fixation in the treatment of osteoporotic femoral neck fracture.Our study supply tthe use of the "F"technique,but Its actual effect needs further clinical evaluation.