Acetabular fractures with medial displacement patterns, particularly medial displacement of the quadrilateral surface, may be technically challenging to treat. Minimal bone stock, limited anatomic access, and difficulty in obtaining stable internal fixation in the true pelvis contribute to the surgical challenge of open reduction and internal fixation. Applying a medial buttress plate across the quadrilateral plate below the iliopectineal line in the true pelvis can be a helpful adjunct to internal fixation in these fractures. The quadrilateral plate is approached from the opposite side of the injury through a standard ilioinguinal approach or a modified Stoppa approach. An undercontoured plate is secured posteriorly along the sciatic buttress posterior to the joint and the quadrilateral plate and anteriorly on the posterior surface of the pubic ramus. By resisting medial secondary redisplacement, this technique adds to stable fixation for acetabular fractures involving medial displacement, particularly of the quadrilateral plate.