Is hip strength a risk factor for patellofemoral pain? A systematic review and meta-analysis

Objective To evaluate and synthesise the literature on hip strength among patients with patellofemoral pain (PFP) to address the following: (1) differentiate between hip strength as a risk factor and associated deficit in PFP; (2) describe hip strength in men and women with PFP across different age ranges; (3) investigate the effects of hip strengthening on biomechanical knee variables associated with PFP development. Methods MEDLINE, CINAHL, Web of Science, SportDiscus and Google Scholar were searched in November 2013 for studies investigating hip strength among patients with PFP. Two reviewers independently assessed papers for inclusion and quality. Means and SDs were extracted from each included study to allow effect size calculations and comparisons of results. Results Moderate-to-strong evidence from prospective studies indicates no association between isometric hip strength and risk of developing PFP. Moderate evidence from cross-sectional studies indicates that men and women with PFP have lower isometric hip musculature strength compared to pain-free individuals. Limited evidence indicates that adolescents with PFP do not have the same strength deficits as adults with PFP. Conclusions This review highlights a possible discrepancy between prospective and cross-sectional research. Cross-sectional studies indicate that adult men and women with PFP appear to have lower hip strength compared to pain-free individuals. Contrary to this, a limited number of prospective studies indicate that there may be no association between isometric hip strength and risk of developing PFP. Therefore, reduced hip strength may be a result of PFP rather than the cause.