Background/Purpose: Patellofemoral joint (PFJ) osteoarthritis (OA) is a common source of pain and there is little evidence for rehabilitation treatment. Gait retraining treatments are effective in reducing pain in younger individuals with patellofemoral pain. Compared to self-selected step length, increased step length is related to increased PFJ stress. If step length affects PFJ stress, then individuals with a longer step length may be at increased risk of PFJ disease. The purpose of this study was to investigate the relation of step length to prevalent/worsening structural damage in the PFJ.

Methods: The Multicenter Osteoarthritis (MOST) Study is a NIH-funded cohort study of 3,026 individuals with or at risk for knee OA. Participants had MRI of their knee and two musculoskeletal radiologists assessed cartilage morphology and bone marrow lesions (BMLs) in the PFJ at the 60 and 84-month study visit. Spatial-temporal gait parameters were collected using the Gaitrite system at the 60-month visit. Step length was measured as the distance from heel center of footprint to heel center of previous footprint from the other foot. Step length was divided into quintiles and we determined the relation of step length to prevalent full-thickness cartilage loss and BMLs in PFJ subregions using logistic regression with generalized estimating equations, adjusting for age, sex, BMI and leg length (measured from long limb films from center of femoral head to center of talus). Because knee pain from structural damage could cause a person to shorten their step length and reduce PFJ stress, in order to examine causal effects of step length, we determined the relation of step length to incident cartilage loss and BMLs from 60 to 84-months in PFJ subregions without any cartilage loss or BMLs at 60-months. In secondary analyses we normalized step length by leg length and and also removed knees with frequent knee pain at 60 months.

Results: 4212 patellar and anterior femur subregions from 1132 knees were included. The mean age and BMI at the 60-month visit were 66.9 (±7.5) years and 29.6 (±4.7) kg/m², respectively, and 62% were female. While subregions in knees with the longest step length had the lowest prevalence of full-thickness cartilage loss, there was no association when adjusting for potential confounding variables. There was no association between step length and incident PFJ cartilage loss. Compared to subregions in knees with short step length, those with the longest step length were associated with 0.72 (0.52, 0.98) times the odds of prevalent BMLs in the PFJ (Table). There was no association between step length and incident BMLs. Similar results were seen in the secondary analysis.

Conclusion: Cartilage loss and BMLs were most common in knees with short step length but there was no relation of step length to worsening of cartilage or BMLs longitudinally. Individuals may shorten their step length to reduce PFJ stress.