Effects of Aging on Patellofemoral Joint Stress During Stair Negotiation on Challenging Surfaces
Authors: Hunt Nicholas Lynn 
Published: December 2022

Introduction: Patellofemoral pain is an incessant lower limb musculoskeletal disorder that may be underreported
in older adults. During common locomotor activities, such as when negotiating stairs, older adults (over the age of 65 years)
adopt knee biomechanics reported to increase patellofemoral pain. Negotiating stairs with a challenging surface, such as uneven
or slick, may place greater demand on the knee and further exacerbate joint biomechanics related to PFJ stress. Yet, it is unknown
if older adults exhibit increases in patellofemoral joint (PFJ) stress when negotiating stairs with challenging surfaces. Purpose: The
purpose of this study was to examine the effect of age (young and older adults) and surface (normal, slick, and uneven) on the magnitude
and temporal waveform of patellofemoral joint stress during stair ascent and descent tasks. Methods: Two cohorts (12 young: ages
18-25 years; 12 older: over 65 years) had knee biomechanics quantified after they ascended and descended 18.5 cm stairs on normal, slick, and
uneven surfaces at a self-selected speed. Statistical Analysis: Peak of stance (0-100%) PFJ stress and associated components
(including PFJ reaction force and contact area, and knee flexion angle and moment) were submitted to a two-way RM ANOVA to test the main effects
of and interaction between age (young vs old) and surface (normal, slick, and uneven). A statistical parametric mapping two-way ANOVA was used
to determine main effects of and interaction between age and surface for the PFJ stress waveform. Results: During the stair ascent,
older adults exhibited greater PFJ stress from 56 to 84% of stance (p < 0.001), which may be attributed to the greater PFJ stress-time
integral (p = 0.004) and later peak PFJ stress (p = 0.024) compared to young adults. Additionally, a significant age by surface interaction
was observed for time of peak PFJ stress (p = 0.041) during stair ascent, where older adults exhibited a later peak PFJ stress compared to
young adults (p = 0.008), and later peak PFJ stress compared to normal and slick surface (both: p = 0.014). Surface impacted PFJ stress
waveform (all: p < 0.001), but not magnitude (p > 0.05) during both stair ascent and descent. During stair ascent on the uneven
surface, participants exhibited smaller PFJ stress from 8 to 25% of stance compared to normal surface, but greater PFJ stress from 57
to 90% and 49 to 77% of stance compared to the normal and slick surfaces (all: p < 0.001). On the uneven surface, participants exhibited
a greater PFJ stress-time integral (both: p = 0.010) compared to the normal and slick surfaces. During stair descent, on the uneven surface,
participants only exhibited greater PFJ stress-time integral (p = 0.017) compared to slick surface, while PFJ stress was smaller from
5 to 18% of stance, but greater stress from 92 to 99% of stance (both: p < 0.001) on the slick compared to the normal
surface. Conclusion: Older adults are more likely to exhibit knee biomechanics related to PFJ pain development when
navigating stairs. Specifically, the larger, later PFJ stress exhibited by older adults when ascending, but not descending the
stairs may increase loading of the joint’s articular cartilage and increase risk of developing PFJ pain. Yet, all participants
exhibited alterations in knee biomechanics that may lead to greater PFJ stress when negotiating stairs with slick and uneven surfaces.