Factors determining loss of reduction in paediatric supracondylar humerus fractures treated by closed reduction and percutaneous pinning

Closed reduction and percutaneous pinning is the preferred surgical intervention for paediatric supracondylar humerus fractures (SCHF). Loss of reduction (LOR) is one of the infrequent complications associated with percutaneous pinning. We aim to analyse the various factors that could lead to LOR. We retrospectively reviewed records of all children with Gartland's type III and IV SCHF who were operated at our institution between 2014 and 2016. A defined set of radiologic indices were measured on postoperative and follow-up radiographs. Correlation between LOR (as defined by Skaggs) and radiologic indices, was calculated. In total 187 children who satisfied the inclusion criteria were included in the study. Major LOR was present in 8 patients (4.28%), mild LOR was seen in 21 patients (11.22%), and there was no LOR in 158 patients (84.49%). A pin-spread fracture width ratio of 0.37 had maximum sensitivity and specificity for predicting LOR. The convergent pin configuration had the highest rate of LOR of 15%, whereas it was about 3% in the crossed pin and lateral divergent pinning group. The incidence of iatrogenic ulnar nerve injury in our series was 4.76%, and all were in the cross pinning group. Pin-spread fracture width ratio is the most crucial factor determining LOR, and a ratio of less than 0.37 has a significantly higher rate of LOR. As the incidence of LOR is not significantly different between the lateral-only and crossed pin groups, a medial pin should be used judiciously to avert the risk of ulnar nerve injury. Level of evidence: Level IV.