Biomechanical Comparison Between Distal Locking And Non-locking Of PFNA In Treating Intertrochanteric Fracture (A1/A2)

Objective：Biomechanical study is conducted to compare the differences betweendistal locking and non-locking of PFNA in treating intertrochanteric fracture(A1/A2).。The study is designed to explore the femoral biomechanics distribution,displacement of the femoral head when intertrochanteric fractures (A1/A2) are treatedwith non-locking PFNA, and whether the stress concentration is smaller whenintertrochanteric fractures (A1/A2) are treated with non-locking PFNA, aiming atproviding some references for PFNA distal screw applications in clinical surgery.Methods:4anticorrosive cadavers are chosen (within six months), of which2aremale and2are female at an average age of50(44-56).8limb specimens areavailable, the attached soft tissue is removed. With X-ray taken to exclude skeletalinjuries and diseases, the inside diameter of femoral canal has been measured in orderto choose the right type of internal fixation. The eight femoral specimens wererandomly divided into A, B groups. Group A is made as an intertrochanteric fracturemodel of A1while group B, by contrast, as an intertrochanteric fracture model ofA2.All of them were fixed with PFNA（distal non-locking)。Postoperative radiographswere taken to make sure the PFNA securely fixed. Simulate the model of single footstanding, osteotomy were conducted above the femur condyle, ensuring femur lengthat30cm after osteotomy, then embedding the end of the femur. Three strain gaugeswere furnished at the lateral of femoral,and another three strain gauges were furnishedat the medial of femoral. Dial indicator were furnished at the femoral head to measurethe vertical arrangement and horizontal displacement of the femoral head. Themechanical model were fixed on the multifunctional mechanical experimentalinstrument and the wire of strain gauges were connected to the static resistance straingauges, then reconcile the balance. Pre-loaded100N three times to remove the time changing impacts with bone relaxation and creep before the formal experiment, toimprove the measurement accuracy of the experiment. The vertical pressure wereloaded on the femoral head from0N to1200N, at1.80mm/min loading rate,recording femoral strain in the lateral and medial, displacement of the femoral head.Complete the test and record relative data and then install the distal locking screw,then load the vertical stress in accordance with the method described above andrecord corresponding strain values and the corresponding dial indicator readings.Analyze the results by the method of ANOVA randomized block design.Results: With the load on the femoral head from0N to1200N,the value of all thepoints of strain tended to increase, the load strain is linear correlated,and thecorrelation coefficients were greater than0.985. In the experiment, three test points inthe lateral femoral cortex strain values are positive, bearing the tension, another threetest points in the medial femoral cortex strain values are negative, bearing the pressure.The maximum strain were located at the distal locking hole of femoral cortex,regardless of the distal locking or non-locking. Comparing the strain values at distallocking hole of femoral cortex (B、E point)，distal locking was greater thannon-locking (P values are0.00).the stress of distal locking is more concentrated. Inthe loading process, the strain values at the proximal femoral cortex (A、D point)，type A2intertrochanteric fractures were smaller than the A1intertrochanteric fractures(P values are0.00). The strain values at the Nail ends(C、F point) have no statisticaldifference between distal locking and non-locking.(P value was0.740,0.506). Withthe load on the femoral head from0N to1200N, the horizontal displacement andvertical displacement of the femoral head in two test specimens showed an increasingtrend. the horizontal displacement and vertical displacement of the femoral head intype A2intertrochanteric fractures were greater than the A1intertrochanteric fractures(P values are0.00), while has nothing to do with the distal locking or not.Conclusion: Through this experiment we discover that for A1/A2intertrochantericfractures, whether the distal locking screw locks or not, stress always concentratesnear the distal locking hole of femoral cortex, and stress of distal locking is moreconcentrated than that of non-locking. The stability of intertrochanteric fractures (A1/A2) have no different between distal locking and non-locking of PFNA whenloading vertical stress.