A top-of-flight stairway defect affects foot overhang on lower steps during stair descent

Falls during stair descent have been associated with non-uniformities in stair dimensions. A common stairway non-uniformity is the top-of-flight defect, where the rise and run dimensions of the uppermost step in a stairway differ from the subsequent lower steps. This defect has been described as hazardous, but its effect on foot placement and misstep risk in stair descent has not been studied. In this experimental study, we quantified foot overhang for adults (n = 27) descending a seven-step staircase with a top-of-flight defect compared to descending a uniform staircase. When the defect was present, an increase in foot overhang occurred on the third, fourth and fifth steps down the stairs (S3, S4, and S5; p < 0.05), two to four steps below the step containing the defect (S1). Given that increased foot overhang is associated with an increased risk of misstepping and falling, this finding provides a biomechanical explanation for falls that originate downstream from the defect and in a region of the stair where the geometry is uniform. Our findings provide support for requiring uniform stair geometry beginning at the upper landing, a common area where stair dimensions change in both new and existing construction and renovations.