FAILURE OF FEMORAL-HEAD FIXATION - A CADAVERIC ANALYSIS OF LAG SCREW CUTOUT WITH THE GAMMA-LOCKING NAIL AND AO DYNAMIC HIP SCREW

The most commonly reported failure mode of sliding hip screws in publi shed literature is cut-out of the lag screw. This study investigates t he resistance to failure of the femoral head, with lag screws used in two types of sliding hip screws, the gamma locking nail (Howmedica) an d the dynamic hip screw (DHS) (Synthes). The investigation consisted o f biomechanical tests under static loading conditions on 12 pairs of c adaveric femoral heads, to establish the failure lends due to screw cu t-out for the two implant lag screws. The gamma nail appeared to reduc e the tendency to cut-out in the osteoporotic bone (soft) associated w ith 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 s tronger, because the DHS showed a tendency to bend. The larger diamete r of the gamma nail lag screw resists bending and appeals to reduce th e risk of cut-out compared with the DHS. (C) 1997 Elsevier Science Ltd .