Minimum toe clearance adaptations to floor surface irregularity and gait speed

Abstract

Toe speed during gait generally nears its maximum while its height reaches a local minima approximately halfway through swing phase. Trips are thought to frequently occur at these local minima (minimum toe clearance or MTC events) and trip risk has been quantified using the minimum distance between the toe and ground here (MTC). This study investigated MTC on floor surfaces with and without multiple small obstacles. After shoes and floor surfaces were digitized, 14 unimpaired subjects (half women) each traversed a 4.88 m walkway 4 times at slow, preferred, and fast speeds across surfaces with no obstacles, visible obstacles, and hidden obstacles. Both surfaces with obstacles had the same random obstacle configuration. Shoe and body segment motions were tracked using passive markers and MTC and joint kinematics calculated. All MTC and kinematic variables tested significantly increased with faster instructed gait speed except the likelihood of MTC event occurrence (local minima in minimum toe clearance trajectory when foot is in upper quartile of speed). MTC events were less frequent for swing phases on surfaces with obstacles (80% vs. 98% for no obstacles). MTC values, when present, were doubled by the presence of visible obstacles (22.2 ± 7.3mm vs. 11.1 ± 5.7 mm) and further increased to 26.8 ± 7.1mm when these obstacles were hidden from view (all comparisons p ≤ 0.0003). These substantial floor surface-related changes in MTC event occurrences and values resulted from alterations in toe- and heel-clearance trajectories caused by subtle but significant changes in joint kinematics that did not exceed 10% each joint's swing phase range of motion.

Active dorsiflexing prostheses may reduce trip-related fall risk in people with transtibial amputation

“…Thus, it is possible that differences in MTC may be attributed to differences in foot design that are independent of inertial differences [51][52]. Finally, many of the steps in the ProprioFoot condition did not include a local minimum in the toe trajectory, and these steps often resulted in MTC values much greater than reported in any study to date [12][13][14]22,41]. For example, approximately 5 percent of all steps in the ProprioFoot condition were greater than 50 mm, (although more than 90% of these steps were taken by two subjects and occurred across multiple conditions).…”

“…Two major assumptions underlying these curves are that they represent the likelihood of tripping given that (1) an obstacle is present at the time of MTC and (2) the obstacle is unseen. If an obstacle is seen, subjects will increase MTC to avoid contacting it [22]. Although it may seem unreasonable that an individual would trip over an obstacle of only several millimeters, it seems more likely that a smaller obstacle would go unnoticed, and smaller obstacles may be more common than larger ones [42].…”

“…For example, approximately 5 percent of all steps in the ProprioFoot condition were greater than 50 mm, (although more than 90% of these steps were taken by two subjects and occurred across multiple conditions). Whereas previous researchers have opted to disregard steps lacking a true "MTC event" [22] and these extreme MTC values could bias the likelihood of tripping curves, even so, the larger values are less meaningful when interpreting the curves.…”

“…In addition to inclined walking, increasing or decreasing walking speed may also alter the likelihood of tripping. For nondisabled individuals, decreased walking speed can decrease MTC [22] and faster walking speeds can increase the likelihood of a failed recovery (i.e., a fall) following a laboratory-induced trip [23]. The extent to which speed affects MTC in people with amputation is unknown.…”

Restricting ankle motion via orthotic bracing reduces toe clearance when walking over obstacles

“…However, the importance of swing phase ankle motion itself in achieving clearance has not been directly researched. Instead it is often simply mentioned that ankle dorsiflexion during swing assists the proximal joints in attaining/increasing clearance [2][3][4]14,17].…”