The Impact of Radiographic Patellofemoral Osteoarthritis on Symptomatic, Physical and Psychosocial Features in Individuals with Persistent Patellofemoral Pain

Purpose: Patellofemoral pain (PFP) is a common, burdensome condition across the lifespan, that often starts in adolescence and persists into adulthood. There is increasing suggestion that persistent PFP may be related to patellofemoral osteoarthritis (PFOA). Understanding the characteristics of people with persistent PFP, and how these relate to the presence of radiographic PFOA, may help us develop targeted treatments to improve patient outcomes. The aim of this study was to explore how symptomatic, psychosocial and physical characteristics differ in those with persistent PFP based on the presence or absence of radiographic PFOA. Methods: 84 participants with persistent PFP were recruited from the community in Melbourne, Australia (aged 26-50 years; antero- or retro-patellar knee pain aggravated by at least two activities that load the PF joint; knee pain severity of at least 30mm on a 100mm visual analogue scale during aggravating activities; pain during these activities on most days of the preceding month; duration of knee pain at least 3 months). Participants completed a battery of patient-reported outcome measures and physical measures. Posteroanterior, lateral and skyline radiographs were acquired of the study knee, and graded for osteoarthritis features by a musculoskeletal radiologist, using the Kellgren & Lawrence (KL) scale. Descriptive statistics were used to compare individuals with and without radiographic PFOA (classified as KL grade 2-4), with reference to the minimal important difference for patient-reported outcome measures. Results: Knee radiographs were available for 83 participants. Radiographic PFOA was present in 20 participants (15 [75%] women, median [IQR] age 38.5 [11] years, body mass index [BMI] 26.6 [9.3] kg/m2). Those without PFOA (n=63, 38 [60%] women) had a median [IQR] age of 33 [8] years and BMI of 24.7 [4.2] kg/m2. Participants with PFOA reported greater pain severity on visual analogue scales for average pain with movement (median difference 17.5mm), pain with walking (18.7mm), pain walking up and down stairs (23.8mm), pain with squatting (17.8mm) and pain with running (20.1mm), which exceeded the minimal important difference (15mm). Clinically meaningful differences were also found on the Knee injury and Osteoarthritis Score (KOOS), with PFOA participants reporting worse scores for subscales of pain (median difference 8.4) and quality of life (21.9). On physical tests, participants with PFOA had lower hip internal rotation torque (median difference 0.06 Nm/kg), lower hip external rotation torque (0.05 Nm/kg), and better performance on the one-leg rise test (8.5 repetitions). The groups were not different on the remaining KOOS subscales, Kujala Patellofemoral Score, EQ-5D, Tampa Scale for Kinesiophobia, Arthritis Self-Efficacy Scale, Pain Self-Efficacy Scale, Hospital Anxiety and Depression Scale, measures of ankle dorsiflexion and foot mobility, Beighton score, side bridge test, and pain provocation tests (step up, step down, squat). Conclusions: In young and middle-aged adults with persistent PFP, the presence of radiographic PFOA was associated with worse pain severity and knee-related quality of life. This suggests that radiographic features of structural PFOA in this population should not be considered a benign, incidental finding, as suggested in other musculoskeletal conditions. The cross-sectional nature of this study precludes conclusions regarding whether findings of lower hip muscle strength are a cause or consequence of PFOA, although may indicate a potential treatment target for individuals with persistent PFP and PFOA. Further studies are required to determine the temporal relationship between PFP and PFOA, as well as modifiable factors that may predict the development of PFOA in individuals with persistent PFP.