Purpose Avascular necrosis (AVN) may occur following treatment for developmental dysplasia of the hip (DDH). The primary aim of this study was to identify the incidence of AVN in a cohort of patients treated for DDH. Secondary aims were to classify AVN using available classification systems, analyze the correlation between the systems and investigate their relationship with the age at diagnosis of DDH. Methods An 11-year retrospective study was carried out at a single tertiary centre, using data from the clinical portal (patient records database) and IMPAX (system used to store plain radiographic images). Clinical details (patient demographics and outcomes) and plain radiographic images were used to identify cases of DDH and categorize cases of AVN using available classification systems: Tonnis and Kuhlmann, Kalamchi and McEwen, Bucholz and Ogden and Salter. Severin was used to assess final clinical outcome. Results In total, 405 (522 hips) cases of DDH were identified, of which 213 resolved without treatment, 93 were treated conservatively and 99 surgically. Only treated cases were included in the analysis (n = 192). AVN (45/99; 45.5%) was found to occur only postoperatively. A positive correlation was present between age at presentation and severity of AVN as classified according to Salter’s criteria (chi-squared p value < 0.01). Conclusion AVN incidence was 23.4% (45/192) and only occurred in surgically treated patients. Older age at diagnosis was associated with a higher incidence of AVN, as defined according to Salter’s criteria. The classification systems appeared to show no correlation amongst each other (p-value < 0.01). Level of evidence: III - Retrospective cohort study

We describe the case of an 8-year old female patient with an open pelvic fracture after being run over by a bus. Open pelvic injuries in pediatric patients are very rare and are associated with high mortality rates and long-term morbidity. In this case, a multidisciplinary surgical approach is described. The injuries include a complex pelvic ring fracture, which was treated with an internal external fixator, together with severe urogenital and soft-tissue injury. The internal external fixator, a surgical technique involving a temporary internal fixation device, is well described in adults, but has not been described in pediatric patients before. This case presentation shows the severity and complexity of the treatment of open pelvic fractures with severe associated injures. Albeit the treatment of her orthopaedic injuries has been successful so far, our patient unfortunately still suffers notable morbidity from her other injuries.