Postural variability of clinical parameters evaluated in orthostatic position in idiopathic scoliosis

Background. In the last 10-15 years many devices have been developed for objectively quantifying the clinical examination. Nevertheless to date the source and size of potential errors in patients examined in standing position (orthostatic posture) has not been established. Therefore the aim of this work is to assess the variability of the parameters usually collected in orthostatic posture during clinical assessment of scoliotic patients. Methods. In a consecutive group of patients affected by adolescential idiopathic scoliosis, we made repeated measurements of various clinical parameters using an optoelectronic device. The adoption of an optoelectronic measurement device (AUtomatic SColiosis ANalyzer, AUSCAN) allowed the replication of the clinical process for obtaining data in orthostatic posture from some surface anatomical landmarks. The source error due to the measurement device was quantified by assessing 4 dummies, with 50 measurements each. Two consecutive groups of patients were examined after a first acquisition: group A (N=86) after 24 sec, group B (N=31) after 6 sec and 167 sec (the last measurement after performing some movements of the trunk). Results. The weight of the measuring system errors is less than 1 mm. Two in vivo source error due to posture have been identified: postural adjustments (between 2.59 and 20.14 mm, according to the considered parameter) and postural positioning (between 4.38 and 22.95 mm). Conclusions. The findings of this study sustain the hypothesis that posture is the major source of variability in repeated clinical measures on the human being. These variations are inherent the clinical evaluation, but presumably they are involved in any other measure collected in orthostatic posture.