Effect of marker misplacement on 3D Instrumented Gait Analysis kinematic measurements

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Introduction and aim: Marker misplacement is recognized as one of the main sources of error on 3D Instrumented Gait Analysis (3DGA) [1]. Most of current widespread 3DGA multisegmental rigid body models use standardized protocols based on the localization of anatomic landmarks by palpation in order to determine joint axes [2]. Although the professionals involved in the test are well trained to avoid a lack of reliability in lab measures, there is little evidence about the quantitative changes expected in 3D kinematic measurements due to marker misplacement and joint axes malalignment. The aimof this studywas to evaluate the changes on kinematic measurements during a typical 3DGA session inducing controlled marker misplacement (CMM). Patients/materials and methods: 5 healthy subjects (mean 20.6 years)were testedduringnormalwalking, usingCODAmotiom cx1 system with two cameras (Charnwood Dynamics Ltd, Leicester, UK), by an experienced operator. 5 gait cycles fromeach subject were recorded to serve as the referencedata. 5 gait cycles for eachof the 20 CMM that we studied were also recorded. The CMM studied were selected based on what was found on specialized literature and the researchers experience of themarkermisplacementsmore likely to happen. Data processingwas blind. Statistical analysiswas performed using the generalized linear model, with a level of significance of 5%. Results: Almost every CMM from the 20 studied produced statistically significant (p<0.05) changes in the graphs of the three planes of motion, and in joints different from the one directly involved in the misplacement. A 10◦ external deviation from the original position of the femoral wand, produced 15◦ more internal rotation in the knee, increased knee flexion and inverted the varus/valgus plot during swing phase. A 1 cm upward misplacement of the fibular malleolus marker caused a 10◦ decrease in the knee flexion during loading response, and increased both ankle pronation and ankle external rotation during stance.