Functional calibration techniques have been proposed as an alternative to regression equations for estimating the position of the hip within the pelvic co-ordinate system for clinical gait analysis. So far validation of such techniques has focussed on healthy adults. This study evaluated a range of techniques based on regression equations or functional calibration procedures techniques in 46 children representative of those attending a major clinical gait analysis service against previously validated 3-D ultrasound techniques for determining the hip joint centre. Best agreement with ultrasound for the position of the hip within the pelvic coordinate system was found for the Harrington equations (mean 14 mm, sd 8 mm). Sphere fitting (mean≈22 mm, sd 11 mm) performed better than transformational techniques applied locally (mean≈33 mm, sd 12 mm) or globally (mean=30 mm, sd 14 mm). The participants with cerebral palsy showed reduced range of movement compared with healthy adults. Differences between these results and studies modelling the effects of simulated noise on functional techniques can probably be attributed to differences between that noise and the soft tissue displacements that are actually occurring.
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