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Osteoarthritis (OA) of the knee joint results in chronic pain and functional decline among older adults. Hip muscle weakness has been observed in persons with knee OA and is claimed to increase the medial compartment loading on the knee joint. Although individual studies are available, no review has yet integrated the literature on the benefits of hip muscle strengthening for persons with knee OA. This review aims to systematically summarize the current evidence on the effectiveness of hip muscle strengthening on knee pain, lower extremity function, and biomechanical measures of the knee in persons with knee OA.An extensive electronic literature search was conducted in the databases PubMed, Scopus, Cumulative Index to Nursing and Allied Health (CINAHL), Cochrane Central Register of Controlled Trials (CENTRAL), and Physiotherapy Evidence Database (PEDro) to identify the published trials in the English language from January 1990 to August 2017. Randomized controlled trials that studied the effectiveness of hip muscle strengthening in persons with knee OA on knee pain, physical function, and biomechanical measures of the knee were considered for inclusion. The key word combinations were knee osteoarthritis, degenerative arthritis, arthralgia, muscle strengthening, and resistance training using the Boolean operators AND, OR. Two reviewers independently performed the study selection, and a third reviewer intervened when the consensus was not attained. Quality assessment of the included studies was carried out using the PEDro scale.The search produced 774 results, among which 81 full-text articles were studied. Five randomized controlled trials of good methodological quality, including 331 participants, were included in the review. The effectiveness of hip muscle strengthening was assessed in isolation, combination, and comparison with other lower extremity exercise. Overall, the studies reported clear benefits of hip muscle strengthening on knee pain, physical function, and hip muscle strength. However, hip muscle strengthening was ineffective in improving the biomechanical measures such as dynamic alignment and knee adduction (also known as valgus) moment.The current review identified strong, high-quality evidence to recommend hip muscle strengthening in the conservative management of persons with knee OA. Further research is needed to establish the underlying mechanisms for the clinical benefits.