Factors that predict a poor outcome 5-8 years after the diagnosis of patellofemoral pain: a multicentre observational analysis

Background Patellofemoral pain (PFP) has traditionally been viewed as self-limiting, but recent studies show that a large proportion of patients report chronic knee pain at long-term follow-up. We identified those patients with an unfavourable recovery ('moderate improvement' to 'worse than ever' measured on a Likert scale) and examined whether there is an association between PFP and osteoarthritis (OA) at 5-8-year follow-up. Methods Long-term follow-up data were derived from 2 randomised controlled trials (n=179, n=131). Patient-reported measures were obtained at baseline. Pain severity (100 mm visual analogue scale (VAS)), function (Anterior Knee Pain Scale (AKPS)) and self-reported recovery were measured 5-8 years later, along with knee radiographs. Multivariate backward stepwise linear regression analyses were used to evaluate the prognostic ability of baseline pain duration, pain VAS and AKPS on outcomes of pain VAS and AKPS at 5-8 years. Results 60 (19.3%) participants completed the questionnaires at 5-8-year follow-up (45 women, mean age at baseline 26 years) and 50 underwent knee radiographs. No differences were observed between responders and non-responders regarding baseline demographics, and 3-month and 12-month pain severity and recovery. 34 (57%) reported unfavourable recovery at 5-8 years. 48 out of 50 participants (98%) had no signs of radiographic knee OA. Multivariate models revealed that baseline PFP duration (>12 months; R-2=0.22) and lower AKPS (R-2=0.196) were significant predictors of poor prognosis at 5-8 years on measures of worst pain VAS and AKPS, respectively. Summary and conclusion More than half of participants with PFP reported an unfavourable recovery 5-8 years after recruitment, but did not have radiographic knee OA. Longer PFP duration and worse AKPS score at baseline predict poor PFP prognosis. Education of health practitioners and the general public will provide patients with more realistic expectations regarding prognosis.