Table 1

Eligibility criteria

Patellofemoral OA (n=15)	Controls (n=15)
Inclusion
Aged ≥40 years.	Aged ≥40 years.
Peri- or retro-patellar knee pain.	Asymptomatic for >1 year.
Pain aggravated by ≥1 activity that increases patellofemoral joint load (eg, squatting).
Pain rated ≥3/10 on numeric pain rating scale.
Pain on most days of previous month.
At least doubtful patellofemoral osteophytes on skyline or lateral view radiographs, confirmed by a musculoskeletal radiologist (ie, KL Grade ≥1).
Exclusion
Pain elsewhere in the knee, hips, ankles, feet, or lumbar spine.	Any lower-limb symptoms in the past year.
Knee or hip arthroplasty, osteotomy, reconstruction, meniscectomy, fracture; history of major traumatic knee injury requiring non-weightbearing for ≥24 hour (eg, dislocation, complete ligament rupture).	Knee or hip arthroplasty, osteotomy, reconstruction, meniscectomy, fracture; history of major traumatic knee injury requiring non-weightbearing for ≥24 hour (eg, dislocation, complete ligament rupture).
BMI ≥35 kg/m².	BMI ≥35 kg/m².
Planned lower-limb surgery in the following 6 months.	Planned lower-limb surgery in the following 6 months.
Knee injections in the past 3 months.	Knee injections in the past 3 months.
Contraindications to imaging.	Contraindications to imaging.
Inability to understand written and spoken English.	Inability to understand written and spoken English.
Tibiofemoral joint OA severity of KL grade 3 or 4, or worse OA severity at the tibiofemoral joint than the patellofemoral joint.

Controls were individually matched to patellofemoral OA cases on age, sex, ethnicity, BMI, and current physical activity level.
BMI, Body mass index; KL, Kellgren and Lawrence; OA, Osteoarthritis; OA classification criteria.