Prospective Predictors of Patellofemoral Pain Syndrome: A Systematic Review With Meta-analysis

CONTEXT: Patellofemoral pain syndrome (PFPS) is one of the most common overuse injuries. OBJECTIVE: To assess the collective evidence of predisposing factors to PFPS. DATA SOURCES: MEDLINE (1960–June 2010), EMBASE (1980–June 2010), and CINAHL (1982–June 2010). STUDY SELECTION: Studies were included if patients were asymptomatic at baseline testing (free of PFPS) and were prospectively followed for the development of the disorder. Only studies that assessed at least 1 variable that can be measured at a typical clinic were included. After duplicates were removed, 973 studies were assessed from their titles or abstracts, 20 from the full text, and from these, 7 met the inclusion criteria. DATA EXTRACTION: Data were extracted for age, weight, height, sample size, patient type (military vs civilian), follow-up periods, diagnostic methods, and diagnostic criteria. Means and standard deviations were extracted for all outcome variables. RESULTS: Meta-analyses were performed for height, weight, leanness, Q angle, number of sit-ups, knee extension strength, and peak knee valgus angle during landing. Lower knee extension strength was the only variable that was predictive of PFPS (P < 0.01). Other variables that were identified as predictive of PFPS by single studies were vertical jump, push-ups, knee flexion and hip abduction strength, thumb-to-forearm flexibility, quadriceps and gastrocnemius flexibility, genu varum, navicular drop, knee valgus moment at initial contact during landing, social support, and palliative reaction. CONCLUSIONS: It appears that anthropometric variables are not associated with PFPS, while knee extension strength deficits appear to be predictors of PFPS.