Prospective Predictors of Patellofemoral Pain Syndrome

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.