Predictors of Pain, Function, and Change in Patellofemoral Pain Alexandra Hott,* y MD, Jens Ivar Brox, z§ Prof., MD, PhD, Are Hugo Pripp, || PhD, Niels Gunnar Juel, § MD, PhD, and Sigurd Liavaag, { MD, PhD Investigation performed at the Department of Physical Medicine and Rehabilitation, Sørlandet Hospital Kristiansand, Kristiansand, Norway Background: Identification of factors predictive of outcome and change is important to improve treatment for patellofemoral pain (PFP). Few studies have examined the predictive value of psychological factors in PFP, although they have been reported to be important predictors in other musculoskeletal pain conditions. Purpose: To evaluate predictors of pain, function, and change 1 year after an exercise-based intervention in PFP. Study Design: Cohort study; Level of evidence, 3. Methods: In sum, 112 patients were recruited to a randomized controlled trial; 98 attended 1-year follow-up. There were no between-group differences in the trial; thus, the material was analyzed as 1 cohort. Nine baseline factors—sex, bilateral pain, worst pain, pain duration, Anterior Knee Pain Scale (AKPS), kinesiophobia, anxiety and depression, self-efficacy, and number of pain sites throughout the body—were investigated for their predictive ability on outcome at 1 year (AKPS, worst pain) and for change at 1 year (global change score, change in AKPS, and change in worst pain). Multivariable linear regression models with stepwise backward removal method were used to find predictors of poor outcome. Results: Number of pain sites at baseline was a significant predictor of worse outcome for AKPS (B = –2.7; 95% CI, –4.0 to –1.3; P \ .01), worst pain (B = 0.5; 95% CI, 0.2-0.8; P \ .01), global change (B = –0.8; 95% CI, –1.2 to –0.5; P \ .01), change in AKPS (B = –2.7; 95% CI, –4.0 to –1.3; P \ .01), and change in worst pain (B = 0.5, 95% CI, 0.2-0.8; P \ .01) at 1 year. Baseline scores for AKPS and worst pain predicted respective 1-year levels and change scores (P \ .01). Lower self-efficacy and male sex predicted less global change (P \ .01). Longer pain duration predicted final score and change score for worst pain (P \ .01). The predictive models had reasonable fit with adjusted R 2 from 0.22 to 0.35. Conclusion: Higher number of pain sites throughout the body was a consistent predictor of poor outcome and less change at 1 year. Baseline levels for AKPS and worst pain predicted respective final scores and change scores. Registration: NCT02114294 (ClinicalTrials.gov identifier). Keywords: knee; physiotherapy; patellofemoral pain; prognosis; widespread pain Patellofemoral pain (PFP) is defined as pain around or behind the patella that is provoked by activities loading the patellofemoral joint in the absence of other distinct pathology. 14 PFP is common, with annual prevalence esti- mates of 23% in the general population and 29% in adoles- cents. 40 Women are affected approximately twice as commonly as men. 40 Newer surveys suggest higher degrees of chronicity than previously thought, with the majority of patients still reporting pain at 2- to 8-year follow-up. 30,39,40 Previous studies have identified some factors predictive of poor outcome in patients with PFP. A recent systematic review found that longer pain duration (.4 months) was the most reported prognostic factor of a poor outcome. 34 In addition, more intense self-reported symptoms at baseline, as evidenced by low Anterior Knee Pain Scale (AKPS) score, was a consistent predictor of poor outcome in a recent long- term analysis. 30 Other factors have been shown to predict poorer outcome, but these predictors are not consistent among studies. 34,38,39 Generally, strength of the evidence *Address correspondence to Alexandra Hott, MD, Department of Physical Medicine and Rehabilitation, Sørlandet Hospital Kristiansand, PO Box 416, 4604 Kristiansand, Norway (emails: alexandra.hott@sshf.no). y Department of Physical Medicine and Rehabilitation, Sørlandet Hos- pital Kristiansand, Kristiansand, Norway. z Faculty of Medicine, University of Oslo, Oslo, Norway. § Department of Physical Medicine and Rehabilitation, Oslo University Hospital, Oslo, Norway. || Oslo Centre for Biostatistics and Epidemiology, Oslo University Hos- pital, Oslo, Norway. { Department of Orthopedic Surgery, Sørlandet Hospital Kristiansand, Kristiansand, Norway. One or more of the authors has declared the following potential con- flict of interest or source of funding: This study was funded by the Research Department of Sørlandet Hospital. AOSSM checks author dis- closures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto. The American Journal of Sports Medicine 1–8 DOI: 10.1177/0363546519889623 Ó 2019 The Author(s) 1