Prognostic value of the Haraguchi classification in posterior malleolar fractures in A0 44-C type ankle fractures.

BACKGROUND AND PURPOSE:Incidence of posterior malleolar fractures (PMFs) associated with ankle fractures is historically based on plain radiographs. Several classification systems for PMF are currently in use, but the reliability of the Haraguchi classification is not reported. The aim of this diagnostic cohort study was to assess incidence of PMF in patients with AO 44-C fractures, and test the reliability of the Haraguchi fracture classification based on CT. In addition, to evaluate the clinical outcome in patients with PMF. METHODS:210 patients with an AO 44-C type fracture treated with syndesmotic fixation between 2011 and 2017 were included. Presence of PMF was registered, morphology was assessed and classified according to the Haraguchi classification. Interobserver agreement for the Haraguchi classification was evaluated. Patient assessment was conducted at 6 weeks, 6 months, 1 and 2 years. The American Orthopaedic Foot & Ankle Society Ankle-Hindfoot Score (AOFAS) was the primary outcome measure. Secondary outcome measures included presence of osteoarthritis. RESULTS:125 of 210 patients (60%) had a PMF. 34% of the PMFs were missed on plain radiographs compared to CT. The interobserver agreement was 0.797, (95% CI: 0.705 to 0.889, p < 0.001), for the Haraguchi classification. The 2-year follow-up rate was 86%. Haraguchi type II fractures had a lower AOFAS compared with the no-fracture group at 6 weeks (mean difference -7.5 (95% CI; -15.0 to -0.2), p = 0.04) and 6 months (mean difference -8.4 (95% CI; -15.3 to -1.5), p = 0.01). Presence of osteoarthritis was higher in patients with Haraguchi type II PMF compared to the no PMF group, this finding was not significant (relative risk (RR) 1.6(95% CI 1.1 to 2.4, p = 0.059)). CONCLUSIONS:Plain radiographs underestimated PMF. Patients with a Haraguchi type II fracture had a poorer outcome measured by the AOFAS score compared to no PMF up until 6 months. Classification of PMF according to the Haraguchi classification was reliable.