The advantages of treatment by open reduction and internal fixation for intertrochanteric fractures of the proximal femur have been well known for several decades. Failure of fixation can result in revision surgery, prolonged inpatient stay and has major socio-economic consequences. There are many new devices on the market to help deal with this problem. Expandable hip screw (EHS) is one such device, which is an expanding bolt that may offer superior fixation in osteoporotic bone compared to the standard dynamic hip screw (DHS) type device. Static axial compression tests with elastic deformation of the specimens were performed with a crosshead speed of 10 mm/min to determine stiffness of testing was performed with 3 cycles from 0 N to 250 N, 3 cycles from 0 N to 500 N, 3 cycles from 0 N to 750 N and 3 cycles from 0 N to 1000 N with a holding time of 10 s per test cycle. Displacement control was apply the pullout strength with a velocity of 1mm/sec. The ability to resist rotation about the axis of a lag screw is of critical importance particularly when the fracture line is perpendicular, or nearly perpendicular, to the femoral neck. Implants were subjected to a rotation of 1 degree/sec and peak torque values were recorded.Background
Methods
Basic engineering principles dictate that unplugged screw holes serve as sites of the concentration of stress and the initiation and growth of cracks (1,2). The idea of filling the holes were tested previously in the literature showing promising results (3). However there's either adverse results which might be a design mistake (4). The purpose of this study was to determine if the use of specially designed screw hole inserts in empty locking screw holes improves the strength and failure characteristics of locking plates. Forty two 7-hole locking LC/DCP plates were mounted on cylindric UHMW Polyethylene blocks with a 1-cm gap between blocks, simulating a fracture with comminution and bone loss. 21 plates had a screw hole insert placed in the center hole (centered over the simulated fracture), while 21 of the plates remained empty in the center hole. The plate–block constructs were placed in a mechanical testing machine and subjected to a series of loading conditions. The axial, bending and torsional stiffness and displacements needed for failure of each plate-block construct was calculated. The Statistical analysis was performed by Mann Whitney-U test for independent variables. All plates were then loaded to failure. There were significant difference in the axial load to failure (p=0.017), bending load to failure (p<0.01) and bending diplacements (p<0.01) of the test groups favoring the screw hole insert group as a higher mechanical strength. In conclusion the study demonstrates that the addition of the specially designed locking screw hole insert does significantly change the stength of the locking LC/DCP plates and might be suggested in the clinical application.
