Comparing the mechanical strength of hip spica cast between a conventional and a new method of application

PURPOSE The current technique of hip spica application is mostly based on a publication by Kumar (J Pediatr Orthop 1(1):97-99, 1981). We modified the technique of hip spica application in order to reduce the rate of breakage across the hip joint and designed this study to compare the strength between hip spica applied according to Kumar's technique and the new technique. METHODS We created 12 hip spica casts with 24 hips according to Kumar's technique, and another 12 casts according to a new technique. The two types of spica were tested with a mechanical testing machine (Instron 3365 series) by using compression loading to failure in flexion, extension, abduction and adduction. Data were analysed in SPSS version 20.0. Comparison of means was done with an independent T test for normally distributed data and the Mann-Whitney test for skewed data. RESULTS The new technique involved the creation of three slabs, instead of 14 slabs as described by Kumar. The loads to failure for hip spica cast applied according to the new technique were higher than those applied according to Kumar's technique, and the differences were statistically significant. The stiffness was also higher in spica casts applied with the new technique; the difference was not statistically significant under extension force. CONCLUSION Hip spica applied with the new technique was stronger than that applied according to Kumar's technique based on load to failure testing. The new technique of application would potentially reduce the risk of cast breakage during the management of developmental dysplasia of the hip (DDH) and femur fracture in children.