To identify gait biomechanical characteristics associated with pain and cartilage damage in individuals with patellofemoral joint osteoarthritis (PFJ OA) during a stair descent activity.

Cross-sectional observational study.

University-based motion analysis laboratory and musculoskeletal imaging centre.

83 participants entered the study; 66 participants (41 female, 25 male) completed all components required for this analysis. Participants were recruited via electronic health records following clinical knee MRI. Inclusion criteria included MRI-confirmed patellofemoral cartilage lesions using Whole Organ MRI Score (WORMS) gradings (WORMS >1), pain during stair ambulation, body mass index (BMI) ≤35 and informed consent. Exclusion criteria were tibiofemoral abnormalities (WORMS >1), prior knee trauma, gait-altering conditions, MRI contraindications or pregnancy.

Primary outcomes included knee joint kinematics and during stair descent, assessed during three-dimensional motion capture, patient-reported outcomes from the Knee Injury and Osteoarthritis Outcome Score (KOOS) questionnaire and WORMS gradings to assess severity of cartilage abnormalities. Regression analyses were performed to examine correlations of biomechanics, age and BMI with pain and cartilage damage. Analyses were also performed on male and female participants separately.

Significant associations were found between biomechanical characteristics and KOOS scores (pain, symptoms and patellofemoral) as well as cartilage damage. For the whole cohort, greater knee flexion at late stance was linked to worse KOOS scores (β=0.53 to 0.71, p

Altered knee biomechanics during stair descent are linked to worse knee pain, function and cartilage damage in PFJ OA, with sex-specific differences emphasising the need for individualised interventions to address movement abnormalities.