Quantifying three-dimensional lumbar kinematics during gait using optoelectronic motion capture: A comparison of two kinematic models

Introduction: Adolescent Idiopathic Scoliosis (AIS) can result in visible deformity, pain, psychological morbidity, and can have a significantly impact on walking gait. Optoelectronic marker-based systems are the gold standard for gait analysis. However, conventional gait models are often used in scoliotic gait research that do not consider movement in the lumbar spine. Furthermore, placing markers on the spinous processes of lumbar vertebrae limits analysis in the sagittal and frontal plane. More recently, it has been proposed that a skin mounted 3D cluster attached over a spinous process can reduce relative error during the tracking of movement since the markers are in a fixed position1, 2. Objective: This preliminary study compared two kinematic modelling approaches that quantify three-dimensional movement (3D) in the lumbar region during gait, that could inform on clinical management strategies for people with AIS. Methods: After necessary ethical approval, ten male participants with no history of musculoskeletal impairments took part in this study. Marker coordinate data was recorded at 100 Hz using an eight-camera motion capture system (VICON, Oxford, UK). For model one3 individual markers were attached over the spinous processes of L1 and L5, in addition to two markers attached on to the back-surface either side of L1. For model two2 a 3D cluster was used, which consists of three markers positioned in a nonlinear configuration that are attached to a semirigid base and was attached over the spinous process of L3. Both kinematic models were constructed in Visual3D (C-Motion, Inc., Germantown, MD, USA) and segment angle data was processed using a low-pass Butterworth filter with a cut-off frequency of 6 Hz. Statistical parametric mapping analyses were applied to kinematic waveform data to compare angles in a time-domain4. Results and Discussion: While the kinematic waveform profiles of the two models were similar in all three planes of motion, a significant difference was noted in the transverse plane, with model two resulting in a greater range of motion compared to the model one. This is contrary to the notion of relative error, thus, greater range of motion reported for model two may relate to the structural design of the 3D cluster. The semi-rigid base plate was of an appropriate size to ensure the 3D cluster was less susceptible to excessive perturbation to discard the possibility of ‘wobble2, 5. Nevertheless, while the semi-rigid base plate conformed to the back surface, movement of the lateral sides of the base plate due the predisposed influence of para-spinal musculature, could have affected the estimation of axial rotation. While 3D clusters are a reliable technique when implemented in the same laboratory5, the 3D cluster used in the current study was handmade, which poses a challenge to accurately replicate in another gait laboratory. Therefore, to allow replication and for validation purposes, it is proposed that future comparative studies use a 3D printed cluster to remove the limitations of hand-built clusters and to provide a standardised structure6. Conclusion and Significance: The results of this study emphasise the usefulness of a 3D cluster approach to assess regional and localised range of motion. To facilitate this, it is recommended that future studies use a 3D printed cluster to provide a standardised structure to allow study replication and validation across gait laboratories. This will help in quantifying outcomes that will facilitate effective clinical management.