Objectives: To describe the structure-pain and structure-function associations in isolated patellofemoral osteoarthritis (PF OA).
Design: Population-based study of 819 adults aged > or =50 years with knee pain. The severity of knee pain, stiffness and disability were measured using the Western Ontario and McMaster Osteoarthritis Index (WOMAC). Three radiographic views of the knee were obtained.
Results: Isolated PF OA was mild in 142 participants and moderate/severe in 44. Mean WOMAC scores for pain, stiffness and function were associated with radiographic severity of PF OA (F(2,389)=4.7, P=0.01; F(2,392)=4.5, P=0.012 and F(2,392)=6.1, P=0.002, respectively, adjusted for age, gender, and body mass index (BMI)). Post-hoc tests demonstrated statistically significant differences for mean pain, stiffness and function score between those with mild PF OA and those with normal X-rays. In task-specific items there was evidence of a stepped response, the proportion of participants with moderate/severe/extreme pain or difficulty in performing everyday tasks increasing with the severity of PF OA. The strongest association was observed for pain going up and down stairs (age-gender-BMI adjusted odds ratio (OR) 3.0; 95% confidence interval (CI) 1.4,6.6. Functional tasks most strongly related to radiographic severity were: descending stairs (OR 3.2; (CI 1.5,6.5)), getting in/out of the bath (3.2; 1.5,6.6), getting in/out of a car (3.0; 1.4,6.1).
Conclusions: Mild isolated PF OA is significantly associated with symptoms of pain, stiffness and functional limitation. Further research on its recognition in clinical practice and the development of targeted treatments to prevent or slow progression are warranted.