#Measurement artifact meaning skin

#Measurement artifact meaning skin

Alternatively, it was proposed to adopt technical protocols where marker clusters are rigidly attached to plates that are fixed to the skin ( Cappozzo, Cappello, Croce, & Pensalfini, 1997 Cappozzo, Croce, Leardini, & Chiari, 2005). Gage 1991), the “IfB” Marker Set ( List, Gülay, Stoop, Lorenzetti, & Renate, 2013), the “OSSCA” ( Taylor et al., 2010). Several examples of such protocol design can be found in the literature, such as the Davis protocol (Davis, R.B. Examples of such points are the bone epicondyles that are easily palpable through the skin. Several methods to reduce the effect of STA were proposed: the easiest one consists in the specific design of marker protocols having marker landmarks where the STA is expected to be the minimum. The non-invasive markers attached to the skin remain therefore the most accepted method to record the motion. In order to completely avoid STA, motion capture markers should be rigidly fixed to the underlying bone by means of screws ( Blankevoort, Huiskes, & de Lange, 1990 Leardini et al., 2005), but this is a highly invasive procedure that cannot be adopted in the daily clinical routine. The STA represents the failure of the rigid body hypothesis due to the relative motion between the skin and the underlying layers (fat, muscles, bones) occurring when the subject moves and it may lead to a significant error on the estimation of the quantities of biomechanical interest, such as the joint kinematics. However it is well known that the marker measurements are affected by the soft tissue artifact (STA) ( Leardini, Chiari, Croce, & Cappozzo, 2005). the thigh or the shank) as rigid bodies ( Ancillao, 2018 Davis, Ounpuu, & Gage, 1991). Most of the anatomical protocols adopted for the quantification of kinematics and kinetics assume the anatomical segments (e.g. Such motion capture measurements are usually considered reliable for clinical purposes ( Ancillao et al., 2017 Ferrari et al., 2008 Kadaba et al., 1989 Stief, Böhm, Michel, Schwirtz, & Döderlein, 2013). Gait analysis is a typical example of a motion analysis examination commonly conducted in the clinical routine ( Baker et al., 2009). In clinical contexts, the motor performance of patients is commonly recorded by means of optoelectronic systems that record the position of passive markers attached on the skin of the subjects ( Ancillao, 2018). A high variability of results across subjects was observed. The estimation of the IHA was not reliable when based only on markers, having an estimation error of ~17 deg. The largest effect was ~16 mm and the lowest was ~4 mm. The local STA deformation affected differently the markers. The shank cluster was mainly affected during the swing phase (~7 deg. The largest rigid-motion STA effect was observed on the thigh cluster (~10 deg. In addition to previous studies, the instantaneous helical axis (IHA) of the knee was calculated and the effect of the STA on its calculation was assessed. Rigid STA motion and local STA deformation were studied separately. The stance and swing phases were considered separately. The STA was studied by comparing the results calculated on the marker sets with the results obtained from the fluoroscopy data. The motion of the knee was concurrently recorded by means of (i) fluoroscopy imaging and (ii) an optoelectronic system and redundant markers attached to the thigh and shank. The dataset was composed of six adult subjects with a total knee arthroplasty who underwent gait analysis trials. The aim of this study was to quantify the STA by exploiting a recently published gait analysis dataset. The soft tissue artifact (STA) is a phenomenon occurring when the motion of bones or anatomical segments is measured by means of skin markers: the biological tissues between the markers and the bone produce a relative motion bone-markers that leads to inaccuracies in the estimation of rigid body poses or kinematics.