Menzies Health Institute Queensland An alternative marker set to accurately and reliably quantify joint kinematics during load carriage Gavin Lenton1,2, Tim Doyle, PhD3, Dan Billing, PhD2, David Lloyd, PhD1 1Centre for Musculoskeletal Research, Griffith University, Gold Coast, Australia 2Land Division, Defence Science and Technology Group, Melbourne, Australia 3Faculty of Medicine and Health Sciences, Macquarie University, Sydney, Australia Background & Aims Determine the accuracy and repeatability of joint kinematics with and without body armour Compare the accuracy and repeatability of our new marker set against a conventional marker set Conclusions Virtual method provides a viable alternative for researchers to reliably measure joint kinematics when equipment (e.g., body armour) obscures marker placement Kinematics involves the measurement of the position and time components of human motion. Camera systems track markers placed over anatomical landmarks and reconstruct the three- dimensional position and orientation of body segments in space1. Body armour, however, occludes bony landmarks at the torso and pelvis, preventing direct marker placement Previous studies using body armour simplified the kinematic model2, modified the equipment3, or placed markers over the armour4. However, these methods may not accurately derive joint kinematics from the trunk and pelvis. This study proposed a new marker set to use when body armour (or other equipment) occludes markers at the pelvis and torso. New marker set showed good accuracy and repeatability compared with conventional marker set without armour New marker set superior to placing markers over armour in both accuracy and repeatability Cannot reliably obtain joint kinematics with markers placed over armour Results compare well with previous repeatability studies7 Consistent marker placement remains critical for collecting reliable kinematics Results (n= 8) Physical marker set Virtual marker set Sagittal Frontal Transverse No Armour   Within-day CMC Hip 0.99 (0.01) 0.94 (0.03) 0.92 (0.06) Pelvis 0.74 (0.10) 0.95 (0.04) 0.84 (0.05)* 0.90 (0.14) Trunk 0.81 (0.08) 0.98 (0.01) 0.87 (0.06) 0.97 (0.01)* Between-day CMC 0.97 (0.03) 0.97 (0.02) 0.87 (0.09) 0.97 (0.04) 0.81 (0.16) 0.47 (0.27) 0.95 (0.05) 0.89 (0.17) 0.49 (0.22) 0.93 (0.07) 0.84 (0.14) 0.58 (0.29) 0.97 (0.07) 0.43 (0.30) 0.92 (0.07) 0.90 (0.09) Armour 0.89 (0.09) 0.91 (0.07) 0.71 (0.09) 0.89 (0.08) 0.76 (0.16) 0.85 (0.12) 0.68 (0.14) 0.82 (0.09)* 0.96 (0.03) 0.96 (0.04) 0.78 (0.19) 0.96 (0.02) 0.77 (0.20) 0.28 (0.12) 0.86 (0.14) 0.42 (0.13) 0.88 (0.10) 0.73 (0.20) 0.41 (0.09) 0.83 (0.15) 0.51 (0.16) 0.81 (0.21) 0.91 (0.09) Methods   z x y X O Y Z o s2 s3 s1 3-D printed a custom-designed sacral cluster that defined the position of virtual pelvis marker 11-camera motion capture system (Vicon, Oxford, UK) collected three-dimensional kinematic (100Hz) data as participants walked on a treadmill (AMTI, Watertown, USA) Virtual marker set Physical marker set   Marker position Physical marker set Virtual marker set Suprasternal notch Marker Pointer 7th Cervical vertebra Cluster 8th Thoracic vertebra 1st Sacral vertebra Anterior superior iliac spine Posterior superior iliac spine Bland-Altman analysis compared the accuracy between marker sets, The coefficient of multiple correlations6 determined within- and between- session repeatability (> 0.80 indicates good repeatability), and inter-protocol kinematic similarities Results (n = 8) Inter-protocol CMC Sagittal Frontal Transverse No Armour   Hip 0.99 (0.01) 0.97 (0.03) 0.79 (0.22) Pelvis 0.63 (0.14) 0.97 (0.02) 0.81 (0.14) Trunk 0.74 (0.11) 0.96 (0.04) 0.90 (0.09) Armour 0.96 (0.03) 0.95 (0.02) 0.70 (0.07) 0.08 (0.21) 0.91 (0.04) 0.65 (0.34) 0.16 (0.31) 0.89 (0.06) 0.81 (0.22) (n = 7) Hip   Pelvis Trunk Mean d (SD) 95% LOA No Armour Joint ROM Sagittal 46.7 –2.6 (4.9) –12.1 → 7.0 4.4 –1.2 (2.2) –5.4 → 3.1 4.8 –3.1 (1.3) –0.5 → 5.7 Frontal 17.5 –2.3 (3.0) –8.2 → 3.6 11.4 –1.0 (2.1) –5.0 → 3.1 13.6 –1.5 (2.6) –3.6 → 6.5 Transverse 15.6 1.3 (1.3) –5.3 → 7.8 10.9 1.9 (1.9) –1.1 → 5.0 17.2 2.3 (2.7) –7.6 → 2.9 Armour 47.4 –1.9 (3.2) –8.2 → 4.3 4.3 –2.6 (2.2) –7.0 → 1.8 5.0 –2.3 (2.5) –7.3 → 2.7 15.8 –1.5 (1.2) –3.9 → 0.8 9.8 –1.9 (1.3) –4.6 → 0.7 10.8 –1.2 (2.9) –6.9 → 4.5 18.1 –0.9 (3.8) –8.4 → 6.6 10.7 0.0 (1.8) –3.5 → 3.5 14.5 –0.4 (2.6) –5.6 → 4.7 References Leardini, Chiari, Croce, & Cappozzo. 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Mean, mean of both methods; d (SD), mean difference (standard deviation of difference) between the marker sets (physical – virtual); 95% LOA, lower and upper limits of agreement at ± 1.96 SD Menzies Health Institute Queensland menzies.griffith.edu.au Centre for Musculoskeletal Research, School of Allied Health Science, Griffith University