Difference in Joint Stability Between Small Posterior Malleolar Fragments With Fixation and Those Without Fixation: A Biomechanical Cadaver Study

The indication for the surgical treatment of ankle fractures that involve a posterior malleolar fragment remains controversial. This cadaver study assessed the biomechanical results of rotation stiffness of Haraguchi type 1 posterior malleolar fragments with or without cannulated screw fixation. Twelve anatomic lower-extremity specimens from 6 cadavers were tested. Six right legs were subjected to posterior malleolus osteotomy (Haraguchi type I) followed with (group A; n = 3) or without (group B; n = 3) fixation using a cannulated screw. Ankle joint stability was measured under both external rotation force and axial loading, and the passive resistive torque was measured in both groups. The mean torque value in group A was 0.1093 Nm/º, while that in group B was 0.0537 Nm/º. There was a significant intergroup difference (p = .004). In group B, the torque value was further increased in the latter rotation period (about 40-60 degrees). Group A proved more stable under experimental conditions than group B. Fixation in type I posterior malleolar fragments produced improved stability in ankle rotation, even for posterior malleolar fragments involving <25% of the articular surface, and has been considered an effective aid in treatment.