Lag Screw Cut-out Research Articles

Failure of femoral head fixation: a cadaveric analysis of lag screw cut-out with the gamma locking nail and AO dynamic hip screw

The most commonly reported failure mode of sliding hip screws in published literature is cut-out of the lag screw. This study investigates the resistance to failure of the femoral head, with lag screws used in two types of sliding hip screws, the gamma locking nail (Howmedica) and the dynamic hip screw (DHS) (Synthes). The investigation consisted of biomechanical tests under static loading conditions on 12 pairs of cadaveric femoral heads, to establish the failure loads due to screw cut-out for the two implant lag screws. The gamma nail appeared to reduce the tendency to cut-out in the osteoporotic bone (soft) associated with elderly patients in whom these devices are commonly used (p<0.05). In high density bone (hard) the gamma lag screw also appeared to be stronger, because the DHS showed a tendency to bend. The larger diameter of the gamma nail lag screw resists bending and appears to reduce the risk of cut-out compared with the DHS.

An experimental study of the failure modes of the Gamma Locking Nail and AO Dynamic Hip Screw under static loading: a cadaveric study

The sliding compression screw is widely regarded as the optimum treatment for intertrochanteric fractures of the femur, allowing bone fragments to impact until a bony support has been established across the fracture site. This study carried out biomechanical, cadaveric tests to establish the influence of direct static loading situations on the modes of failure of the Gamma Nail compared with the Dynamic Hip Screw (DHS). Clinical studies report DHS failures of lag screws cutting-out, bending of the lag screws and cortical screws pulling out causing plate loosening. Gamma Nail failures include lag screw cut-out or fractures of the femoral shaft around the distal locking screws or nail tip. In this study each failure mode has been isolated, to establish the loads to failure under various fracture configurations. The biomechanical results indicated that the intramedullary Gamma Locking Nail can be recommended over a standard DHS in cases of subtrochanteric fracture or conditions of very poor bone quality.