Syndesmotic malreduction may decrease fixation stability: a biomechanical study

BACKGROUND: This study aims to investigate the malreduction of syndesmosis and its effects on stability. METHODS: The biomechanical tests, including the three-dimensional (3D) displacement of the syndesmotic incisura, fibular rotation angle, and torque resistance, were performed on six cadaver legs. These specimens were first tested intact (intact group), then cut all the syndesmotic ligaments and fixed in anatomical position (anatomical model group) and test again. After that, syndesmosis was fixed in 1 cm malreduction (anterior and posterior displacement group) to do the same test. RESULTS: In internal or external load, there were significant differences in torque resistance and fibular rotation angle (internal t = 2.412, P = 0.036; external t = 2.412, P = 0.039) between the intact and post-malreduction groups. In internal rotation load, there were significant differences in sagittal displacement between the intact and post-malreduction groups (P = 0.011), and between the anatomical and post-malreduction groups (P = 0.020). In external rotation load, significant differences existed between the intact and ant-malreduction group (P = 0.034) in sagittal (anterior-posterior) displacement. Significant differences also existed between the intact and post-malreduction groups (P = 0.013), and between the anatomical and post-malreduction groups (P = 0.038) in coronal (medial-lateral) displacement. CONCLUSIONS: Malreduction in different conditions does affect the stability of the syndesmotic fixation. The result of the study may reveal the biomechanical mechanism of poor clinical outcome in syndesmosis malreduction patients and pathological displacement patterns of the ankle under syndesmotic malreduction conditions. LEVEL OF EVIDENCE: III