Mind your step: Target walking task reveals gait disturbance in individuals with incomplete spinal cord injury

Abstract

Background: Walking over obstacles requires precise foot placement while maintaining balance control of the center of mass (CoM) and the flexibility to adapt the gait patterns. Most individuals with incomplete spinal cord injury (iSCI) are capable of overground walking on level ground; however, gait stability and adaptation may be compromised. CoM control was investigated during a challenging target walking (TW) task in individuals with iSCI compared to healthy controls. The hypothesis was that individuals with iSCI, when challenged with TW, show a lack of gait pattern adaptability which is reflected by an impaired adaptation of CoM movement compared to healthy controls.

Methods: A single-center controlled diagnostic clinical trial with thirteen participants with iSCI (0.3-24 years post injury; one subacute and twelve chronic) and twelve healthy controls was conducted where foot and pelvis kinematics were acquired during two conditions: normal treadmill walking (NW) and visually guided target walking (TW) with handrail support, during which participants stepped onto projected virtual targets synchronized with the moving treadmill surface. Approximated CoM was calculated from pelvis markers and used to calculate CoM trajectory length and mean CoM Euclidean distance TW-NW (primary outcome). Nonparametric statistics, including spearman rank correlations, were performed to evaluate the relationship between clinical parameter, outdoor mobility score, performance, and CoM parameters (secondary outcome).

Results: Healthy controls adapted to TW by decreasing anterior-posterior and vertical CoM trajectory length (p < 0.001), whereas participants with iSCI reduced CoM trajectory length only in the vertical direction (p = 0.002). Mean CoM Euclidean distance TW-NW correlated with participants' neurological level of injury (R = 0.76, p = 0.002) and CoM trajectory length (during TW) correlated with outdoor mobility score (R = - 0.64, p = 0.026).

Conclusions: This study demonstrated that reduction of CoM movement is a common strategy to cope with TW challenge in controls, but it is impaired in individuals with iSCI. In the iSCI group, the ability to cope with gait challenges worsened the more rostral the level of injury. Thus, the TW task could be used as a gait challenge paradigm in ambulatory iSCI individuals. Trial registration Registry number/ ClinicalTrials.gov Identifier: NCT03343132, date of registration 2017/11/17.

Keywords: Balance control; Center of mass; Gait; Locomotion; Motor control; Spinal cord injury; Visually guided walking.

Conflict of interest statement

The authors declare that they have no competing interest.

© 2022. The Author(s).

Figures

Fig. 1

Target walking task. Schematic view of Motek GRAIL system. A Participants were asked to step onto moving white circular targets (10 cm diameter, here pink) projected on the black treadmill with their self-selected walking speed. B Aerial view of treadmill: participants had to change step length and width based on a variability of 40–80% of 0.8 m and 40–80% of 0.25 m, respectively, in order to step onto the targets. Accuracy was assessed in the anterior–posterior (AP) and medio-lateral (ML) direction monitored by a reflective marker placed on the second toe, the metatarsal 2 (MT2). Handrails and harness that were worn for safety are not shown in this schematic figure. This figure shows whole-body kinematics but for this study foot and pelvis markers were used

Fig. 2

Center of Mass trajectories. A CoM 3-D and 2-D trajectories in TW are reduced in participants with iSCI (top, right) and controls (top, left); however, the reduction is more pronounced in controls (top, left). Arrows indicate movement direction. B Reductions may be caused primarily by TW CoM trajectories in AP and V directions (middle) in participants with iSCI (middle, right) and controls (middle, left). Differences between NW and TW are significant at, and following HS and TO for participants and for controls throughout almost the entire CoM trajectory. TW induced alterations of CoM trajectory are assumed to subserve an increase of inertial stability of CoM and further to optimize CoM movement for accurate foot placement. For redundancy reasons, only differences in CoM trajectory lengths are shown and omitted for CoM 3-D and 2-D trajectories. Gray dashed lines depict time of TO. C CoM trajectory length is reduced most consistently in the V direction in controls and participants with iSCI. Participants with iSCI show on average less reduction of CoM trajectory length and more variability in AP, ML, and V when performing TW. Dots and triangles represent single participants. *p < 0.05; **p < 0.01; ***p < 0.001. CoM center of mass, TW target walking, NW normal walking, AP anterior–posterior, ML medio-lateral, V vertical, iSCI incomplete spinal cord injury, HS heel strike, TO toe off

Fig. 3

Relationship between CoM and clinical parameter and outdoor mobility score. A Ability of participants with iSCI to reduce 3-D CoM movement during TW is related to their lesion level (as well as 1-D AP trajectory and 2-D trajectories, see “Results”), as depicted by the mean Euclidean distance between TW and NW. B Mean SCIM outdoor mobility score is inversely correlated to the length of 3-D CoM trajectory length (also AP 1-D trajectory, and ML-AP 2-D trajectory, see “Results”) when participants with iSCI perform TW suggesting a relation with their lack of adaptability to adjust to the task. Dots represent single participants and their ID. CoM center of mass, TW target walking, NW normal walking, AP anterior–posterior, ML medio-lateral, V vertical, SCIM outdoor spinal cord independence measure outdoor mobility, iSCI incomplete spinal cord injury

Fig. 4

CoM trajectory length is related to preferred walking speed in controls and participants with iSCI. The relationship between preferred walking speed and CoM 3-D trajectory length is changed during TW (red dots) in participants with iSCI (A) and controls (gray triangles) (B) while the latter shows more decline and greater reduction than the former. In participants with iSCI, more variation of walking speed is obtained. Some participants, e.g., P01, P02, P07, and P15 prefer lower walking speeds during both NW and TW (A). The clear separation of TW and NW CoM 3-D trajectory length found in both participants and controls at similar walking speeds may be seen as an indication that reduction of CoM 3-D trajectory length is a common strategy to cope with TW independent of pathology and independent of preferred walking speed. Gray colored dotted lines connect NW and TW for each participant. Dots and triangles represent single participants and their ID. AP anterior–posterior, ML medio-lateral, V vertical, TW target walking, NW normal walking