Effects of Aging on Patellofemoral Joint Stress during Stair Negotiation on Challenging Surfaces

This study examined the effect of age and surface on patellofemoral joint (PFJ) stress magnitude and waveform during stair ascent and descent tasks. A total of 12 young and 12 older adults had knee biomechanics quantified while they ascended and descended stairs on normal, slick, and uneven surfaces. The peak of stance (0-100%) PFJ stress and associated components were submitted to a two-way repeated measures ANOVA, while the PFJ stress waveform was submitted to statistical parametric mapping two-way ANOVA. During stair ascent, older adults exhibited greater PFJ stress waveforms, from 55 to 59% and 74 to 84% of stance (<i>p</i> < 0.001) as well as greater PFJ stress-time integral across stance (<i>p</i> = 0.003), and later peak PFJ stress, than young adults (<i>p</i> = 0.002). When ascending on the uneven surface, participants exhibited smaller PFJ stress from 9 to 24% of stance compared to the normal surface, but greater PFJ stress from 75 to 88% and from 63 to 68% of stance (<i>p</i> < 0.001) as well as greater PFJ stress-time integrals compared to normal and slick surfaces (<i>p</i> < 0.032). During stair descent, older adults exhibited a smaller PFJ contact area range (<i>p</i> = 0.034) and peak knee flexion angle (<i>p</i> = 0.022) than young adults. When descending on the slick surface, participants exhibited smaller PFJ stress from 5 to 18% of stance, but greater stress, from 92 to 98% of stance (both: <i>p</i> < 0.001), compared to the normal surface. Negotiating slick and uneven stairs may produce knee biomechanics that increase PFJ stress, and the larger, later PFJ stress exhibited by older adults may further increase their risk of PFJ pain.