The influence of sagittal angle of posterior malleolus fracture on ankle joint stability：a retrospective study of 87 cases

Background: Previous studies have studied more factors on the ankle stability of the posterior ankle fracture, which is related to a stereostructure of the fracture fragment. Previous studies have shown that the ankle stability may be affected by the sagittal surface of the fracture block, with less research in this field. The aim of this study was to explore the influence of the sagittal angle(SA) on ankle joint stability by scanning and reconstructing three types of posterior malleolus fractures(PMFs) with different sagittal angle (SA).MethodsThe CT data of 87 patients with PMFs were collected retrospectively and reconstructed. PMFs were divided into three types: posterolateral-oblique type (type I), medial-extension type (type II) and small-shell type (type III).The collected sagittal angle data were statistically analyzed with the posterior fragment area, fragment area ratio (FAR), fragment transverse diameter ratio (FWR), fragment length ratio (FLR), fragment height (FH), and contact area (CA).Results(1)SA was positively correlated with posterior fragment area(r = 0.804,P < 0.01),with regression equation s = 0.085*SA + 0.34;(2)SA was positively correlated with FAR(r = 0.392,P < 0.01),with regression equation FAR = 0.004*SA + 0.092;(3)SA was positively correlated with FWR(r = 0.261,P < 0.05), with regression equation FWR = 0.03*SA + 0.4624;(4)SA was positively correlated with FLR(r = 0.481,P < 0.01), with regression equation FLR = 0.05*SA + 0.209;(5) SA was positively correlated with CA (r = 0.474, P < 0.01),with regression equation CA = 7.942*SA + 160.866;(6)SA was positively correlated with FH(r = 0.474,P < 0.01), with regression equation FH = 0.046*SA + 1.406.ConclusionThe sagittal angle was positively correlated with posterolateral-oblique type (type I) of Posterior malleolus fractures, and SA could be considered to reflect the ankle joint stability of PMFs.Level of evidence: Level III, retrospective comparative study.