SNOWBOARDER'S FRACTURE: CHANGING JOINT MECHANICS BY FOOT POSITION DURING A SIMULATED LANDING TASK

Abstract

A high proportion of fractures to the lateral process of the talus (LPT) has been reported in snowboarding, which accounted for 34% of all ankle fractures (Kirkpatrick et al., 1998). A fracture to the LPT is an injury unique to snowboarders and is often misdiagnosed by physicians as an anterolateral ankle sprain. LPT fractures often involve the articular surface of the subtalar joint and it has been shown that misdiagnosis may lead to severe degeneration of the ankle joint and long term morbidity (Boon et aI., 1999). The mechanism of this injury has been studied intensively. LPT fractures are high impact injuries, landing after aerial manoeuvres is thought to be the major cause of LPT fractures (Boon et aI., 1999). In a cadaver study no fractures to the LPT were recorded under purely dorsalflexed conditions but in six of the eight specimens fractures occurred with the addition of 20° external rotation. An axial load of 2200 -8900 N was required to produce a fracture (LPT) in this position. It was proposed by Boon and colleagues tr.at the subsequent 'opening' of the ankle joint seen with heel inversion and external rotation of the talus results in the lateral process shifting upwards on the posterior articular process of the calcaneus. The purpose of this study was to simulate a snowboard landing in the laboratory with using an inverse dynamics approach to calculate effective joint loading for different binding alignments. It was hypothesised that the 'stance' chosen will affect loading and that an optimum foot alignment will help to minimise joint load.