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OBJECTIVE To evaluate the effectiveness of an additional rim plate [3.5-mm precontoured locking compression plate (LCP)] for stabilizing the posterolateral fragment in lateral tibial plateau fractures. METHODS Standard lateral locking plates [either a proximal tibial plate (PTP) or a proximal tibial locking plate (PTLP)] were applied to 40 matched pair knees from 20 fresh-frozen cadavers followed by the application of a secondary rim plate [variable angle LCP (VALCP)] posterior laterally. RESULTS The mean ratio of supported articular surface in the PTP group was 0.692, whereas that in the PTLP group was 0.569. This difference was statistically significant (P < 0.001). Additional rim plating with a VALCP could only be performed for 27 of 40 knees; 8 of 20 knees in the PTP group and 5 of 20 knees in the PTLP group could not be fitted with a VALCP due to anatomic limitations. For the total standard plating group alone, the mean ratio of supported articular surface was 0.596, whereas the mean ratio of supported articular surface with additional rim plating was 0.798 (P < 0.001). In contrast, additional rim plating was possible for more knees that received a PTLP than a PTP. Ultimately, there was no significant difference in the ratio of supported articular surface after additional rim plating between the 2 different types of standard plates (P = 0.087). CONCLUSION Our results identified a bare area in the posterolateral corner of the lateral plateau that was unsupported by rafting screws following conventional, 3.5-mm, precontoured LCP plating. Thus, additional rim plating may be useful for treating plateau fractures with a posterolateral fragment.