Scapular Motion Tracking Using Acromion Skin Marker Cluster: In Vitro Accuracy Assessment

Abstract

Several studies have recently investigated how the implementations of acromion marker clusters (AMCs) method and stereo-photogrammetry affect the estimates of scapula kinematics. However, in the large majority of these studies, the accuracy assessment of the scapular kinematics obtained with AMCs was carried out through a comparative evaluation using a scapula locator that is prone to error. The present study assesses AMC accuracy based on best practice recommendations, both with single and double anatomical calibration implementations, during several passive shoulder movements. Experiments were carried out on three cadaveric specimens. The scapula motion was acquired with a stereo-photogrammetric system using intra-cortical pins. When the scapula kinematics was estimated using an AMC combined with a single anatomical calibration, the accuracy was highly dependent on the specimen and the type of motion (maximum errors between -6.2°and 44.8°) and the scapular motion was generally overestimated. Moreover, with this implementation, scapular orientation errors increased for shoulder configurations distant from the reference shoulder configuration chosen for the calibration procedure. The double calibration implementation greatly improved the estimate of the scapular kinematics for all specimens and types of motion (maximum errors between -1.0°and 14.2°). The double anatomical calibration implementation should be preferred since it reduces the kinematics errors to levels which are acceptable in most clinical applications.

Measurement of scapular dyskinesis using wireless inertial and magnetic sensors: Importance of scapula calibration

“…We did not find a significant effect of double calibration for anterior tilt and lateral rotation, although increased lateral rotation was measured above 90°AB (10-14°, P 40.06). The different findings might be due to the study population (young healthy subjects with low variability (Brochard et al, 2011) and cadaveric specimen without shoulder damage (Cereatti et al, 2015) versus patients with shoulder pathology with high variability). Furthermore, in the set-up of (Brochard et al, 2011) and (Cereatti et al, 2015) the skin-fixed markers were placed on a different position on the scapula, i.e.…”

“…Brochard et al (2011) showed that when using optical markers for scapular kinematic measurement, double calibration with a scapula locator mainly affected the measure of anterior tilt and lateral rotation at high elevation angles. Also Cereatti et al (2015) showed that double calibration improved scapular kinematics (up to 14°). We did not find a significant effect of double calibration for anterior tilt and lateral rotation, although increased lateral rotation was measured above 90°AB (10-14°, P 40.06).…”

“…from the deltoid Veeger and van der Helm (2007)) causing movement artefacts. Cereatti et al used cadaveric specimen to evaluate double calibration during movement, however soft tissue artefacts during motion might have been less in comparison to living humans due to the lack of muscular contraction (Cereatti et al, 2015).…”

“…They modified the 3D positions of anatomical landmarks measured with optical markers between these two postures by linear interpolation in time (Cappello et al, 2005;Zhang, 2002). Recently, also Cereatti et al (2015) applied a double calibration technique (at start and end of the arm range of motion) in combination with an acromion skin marker cluster in cadaveric specimens. Both studies showed that double calibration improved the estimate of scapular kinematics, whereas single calibration resulted in errors at higher humeral elevation angles (Brochard et al, 2011;Cereatti et al, 2015) since it possibly only corrects for initial scapula angular offsets but not for soft tissue artefacts during the scapular motion.…”

“…Recently, also Cereatti et al (2015) applied a double calibration technique (at start and end of the arm range of motion) in combination with an acromion skin marker cluster in cadaveric specimens. Both studies showed that double calibration improved the estimate of scapular kinematics, whereas single calibration resulted in errors at higher humeral elevation angles (Brochard et al, 2011;Cereatti et al, 2015) since it possibly only corrects for initial scapula angular offsets but not for soft tissue artefacts during the scapular motion. Therefore, calibration with a scapula locator might correct for offset differences in retraction/protraction and anterior/posterior tilt as observed by van den Noort et al (van den Noort et al, 2014).…”