Morphological analysis of posterior malleolar fractures with intra-articular impacted fragment in computed tomography scans

BACKGROUND: Intraarticular impacted fragment (IAIF) of posterior malleolar fractures has been reported by a few studies. However its location, morphology, and the correlation of posterior malleolar fractures have not been described in detail. The aim of this study was to describe the morphology of IAIF in posterior malleolar fractures, to analyze the related factors between IAIF and posterior malleolar fragments, and explore the treatment of IAIF. MATERIALS AND METHODS: Between January 2013 and December 2018, 108 consecutive patients with unilateral posterior malleolar fractures were managed in our hospital. Basic demographic and computed tomography (CT) data were collected and classified by Lauge–Hansen, OTA/AO, Haraguchi, and Mason classification. Additional radiographic data, including the length and area of posterior malleolar fragment, IAIF, and stable tibial plafond were measured. The location of IAIF was described, and involvement of the fibular notch and medial malleolus was also observed. Statistics were analyzed based on univariate analysis (Chi-square test, t-test, Mann–Whitney U test, Fisher’s test) and Spearman’s correlation test. RESULTS: Among the 108 cases of posterior malleolar fractures, 75 (69.4%) were with IAIF and 33 (30.6%) cases were without. There were 74 (68.5%) females and 34 (31.5%) males, and the average age of the patients was 49 years (18–89 years). The average L(IFN)/(L(IFN) + L(SFN)) [length of involving fibular notch/(length of involving fibular + length of stable notch fibular notch)] was 32.9% (11.6–64.9%). The A(PMF)/(A(PMF) + A(STP) + A(IAIF)) [area of posterior malleolar fragment/(area of posterior malleolar fragment + area of IAIF + area of stable tibial plafond)] and A(IAIF)/A(PMF) (area of IAIF/area of posterior malleolar fragment) were 13.1% (0.8–39.7%) and 52.6% (1.2–235.4%), respectively. Involvement of medial malleolus (fracture line extended to medial malleolus, P = 0.022), involvement of fibular notch (P = 0.021), L(IFN)/(L(IFN) + L(SFN)) (P = 0.037), L(MPMF) (P = 0.004), and A(PMF) were significantly related to the occurrence of IAIF. CONCLUSION: Our research indicates a high incidence of IAIF in posterior malleolar fractures. All IAIFs were found in posterior malleolar, and the most common location was within the lateral area A. Posterior malleolar fracture lines that extend to medial malleolus or fibular notch herald the incidence of IAIF. L(IFN)/(L(IFN) + L(SFN)), L(MPMF) and A(PMF) are also associated with the incidence of IAIF. CT scans are useful for posterior malleolar fractures to determine the occurrence of IAIF and make operational plans. Operation approach selection should be based on the morphology of posterior malleolar fragments and the location of IAIF. LEVEL OF EVIDENCE: Level III, retrospective case analysis.