The Impact Of Thigh And Shank Marker Quantity On Lower Extremity Kinematics Using A Constrained Model

Musculoskeletal models are commonly used to quantify joint motions and loads during human motion. Constraining joint kinematics simplifies these models but the implications of the number of markers used during data acquisition remains unclear. The purpose of this study was to establish the effects of marker placement and quantity on kinematic fidelity when using a constrained-kinematic model. We hypothesized that a constrained-kinematic model would faithfully reproduce lower extremity kinematics regardless of the number of tracking markers removed from the thigh and shank. Healthy-young adults (N = 10) walked on a treadmill at slow, moderate, and fast speeds while skin-mounted markers were tracked using motion capture. Lower extremity kinematics were calculated for 256 combinations of leg and shank markers to establish the implications of marker placement and quantity on joint kinematics. Sagittal joint and hip coronal kinematics errors were smaller than documented errors caused by soft-tissue artifact, which tends to be approximately 5 degrees, when excluding thigh and shank markers. Joint angle and center kinematic errors negatively correlated with the number of markers included in the analyses (R2 > 0.97) and typically showed the greatest error reductions when two markers were included. Further, we demonstrated that a simplified marker set that included markers on the pelvis, lateral knee condyle, lateral malleolus, and shoes produced kinematics that strongly agreed with the traditional marker set. In conclusion, constrained-kinematic models are resilient to marker placement and quantity, which has implications on study design and post-processing workflows.\n\nEthics Approval and Consent to Participate this study was approved by the Institutional Review Board at the University of Pennsylvania (#824466). Subjects provided written-informed consent\n\nConsent to Publish this submission does not contain any individual data\n\nAvailability of Data and Materials the datasets analyzed in this study are available from the corresponding author on reasonable request.\n\nCompeting Interests one author (JB) is an associate editor for BMC Musculoskeletal Disorders. None of the other authors have any competing interests.\n\nFunding no funding has been provided for this research\n\nAuthors ContributionsAS, TH, and JB designed the experiment; AS and TH collected the data; AS and JB analyzed and interpreted the data; AS and JB drafted the manuscript; AS, TH, and JB revised the intellectual content of the manuscript; AS, TH, and JB approved the final version of the manuscript; and AS, TH, and JB agreed to be accountable for all aspects of the study.