Impact of knee marker misplacement on gait kinematics of children with cerebral palsy using the Conventional Gait Model—A sensitivity study

Abstract

Clinical gait analysis is widely used in clinical routine to assess the function of patients with motor disorders. The proper assessment of the patient's function relies greatly on the repeatability between the measurements. Marker misplacement has been reported as the largest source of variability between measurements and its impact on kinematics is not fully understood. Thus, the purpose of this study was: 1) to evaluate the impact of the misplacement of the lateral femoral epicondyle marker on lower limb kinematics, and 2) evaluate if such impact can be predicted. The kinematic data of 10 children with cerebral palsy and 10 aged-match typical developing children were included. The lateral femoral epicondyle marker was virtually misplaced around its measured position at different magnitudes and directions. The outcome to represent the impact of each marker misplacement on the lower limb was the root mean square deviations between the resultant kinematics from each simulated misplacement and the originally calculated kinematics. Correlation and regression equations were estimated between the root mean square deviation and the magnitude of the misplacement expressed in percentage of leg length. Results indicated that the lowerlimb kinematics is highly sensitive to the lateral femoral epicondyle marker misplacement in the anterior-posterior direction. The joint angles most impacted by the anterior-posterior misplacement were the hip internal-external rotation (5.3˚per 10 mm), the ankle internalexternal rotation (4.4˚per 10 mm) and the knee flexion-extension (4.2˚per 10 mm). Finally, it was observed that the lower the leg length, the higher the impact of misplacement on kinematics. This impact was predicted by regression equations using the magnitude of misplacement expressed in percentage of leg length. An error below 5˚on all joints requires a marker placement repeatability under 1.2% of the leg length. In conclusion, the placement of the lateral femoral epicondyle marker in the antero-posterior direction plays a crucial role on the reliability of gait measurements with the Conventional Gait Model.

The Conventional Gait Model’s Sensitivity to Lower-limb Marker Placement

“…Regarding displacements of individual markers, displacements of the thigh and tibia wands and the knee marker in the anterior-posterior axis had the largest calculated impact on kinematics, all with an RMSD angle of over 5° in the transversal plane (Figure 4). These ndings con rmed previous results demonstrating the knee marker's high impact in the anterior-posterior axis in the transversal plane but it's very low impact when displaced in the proximal-distal axis 12,13 . Even though some studies have reported improvements in calibration methods, such as the Knee Alignment Device, marker placement reproducibility and reliability remains the CGM's most signi cant limitation 17 .…”

“…The present sensitivity analysis used a procedure similar to that of a previous study 13 . All subjects were equipped with the CGM marker set 3 (14 mm) and walked barefoot at a self-selected speed along a 10 m walkway.…”

A Methodology for Assessing the Impact of Error Components in Gait Analysis Using Closed-Loop Testing on a Biomimetic Rig

“…Misplacement (e.g., due to different protocols / practices among physicians, obesity, subject's morphology / wounds / cooperation spirit) may account for an angle error exceeding the 5 o acceptance limit which is what a trained eye is likely to differentiate [1]. The study of 10 children with cerebral palsy against 10 agedmatched typical developing children, showed that anterior-posterior misplacement of the lateral epicondyle marker, led to hip internal-external rotation angle offsets of 5.3 o per 10mm of displacement [7]. Determination of the ankle's internal-external rotation angle, demonstrated a sensitivity of 4.4 o per 10mm offset.…”

“…Naturally, measurements tend to worsen according to the ratio of the misplacement to leg length: the smaller the length, the bigger the angle error. It was concluded that in order to achieve an error below the limit of 5 o on all joints, a physician needs a repeatability precision below 1.2% of the leg length when placing the markers [7].…”

An analytical model to quantify the impact of the propagation of uncertainty in knee joint angle computation

“…Reproducibility studies have been performed in the literature to evaluate different sources of variability in gait analysis (McGinley et al 2009 ; Wren et al 2011 ). Some studies have performed a sensitivity analysis on joint axes for a given type of joint motion (Della Croce et al 1999 ; Fonseca et al 2020 ). More specifically, knee joint kinematics is known to be prone to non-linear error propagation, which results in the well-known kinematic effect of cross-talk (Baudet et al 2014 ; Pothrat et al 2015 ).…”