The screw-plate interface of stainless steel implants is susceptible to fretting corrosion. Fretting has been evaluated by stereomicroscopy. Although non locking screw apparatus have been investigated, little is known about the locking screw-plate interface after implantation. Thirty seven explanted TPLO locking plates were evaluated for contact damages consistent with an alteration of the polish, presence of crevice and depositions using high definition digital stereo-microscopy. A score from 0 to 5 was attributed to each holes, the lower score describing the least visible damages. Each scores was assigned to locking and non locking groups. Only the locking holes used in combination with a locking screw were assigned to the locking group. The distributions were compared with a Kolmogorov-Smirnov test. Locking holes had significantly lower scores (p<0.001). Various locking screw holes designs were available. The pattern of wear was specific to each locking hole and the least damages were noticed in the AO round and SOP screw holes. All plates used with non locking screws demonstrated fretting corrosion. The implants history, the screw and their insertion torque were unavailable, the screws and plates may be issued from different manufacturers with possible different tolerances in the screw head or thread, the load on each hole may be different due to the plate configuration. The light microscopic evaluation may underestimate the extend of the surface damages. The locking screw-plate interface seems to remain mechanically stable after implantation in TPLO plates. This configuration may provide more biologically compatible properties than non locking screw holes.
