Retraction Note to four articles published in World Journal of Orthopaedics:(1)Iwamoto J,Sato Y,Takeda T,Matsumoto H.Return to sports activity by athletes after treatment of spondylolysis.World J Orthop 2010;1(1):26-30 PMID:22474624 DOI:10.5312/wjo.v1.i1.26;(2)Iwamoto J,Sato Y,Takeda T,Matsumoto H.Effectiveness of exercise for osteoarthritis of the knee:A review of the literature.World J Orthop 2011;2(5):37-42 PMID:22474634 DOI:10.5312/wjo.v2.i5.37;(3)Iwamoto J,Sato Y,Takeda T,Matsumoto H.Analysis of stress fractures in athletes based on our clinical experience.World J Orthop 2011;2(1):7-12 PMID:22474626 DOI:10.5312/wjo.v2.i1.7;and(4)Iwamoto J,Takada T,Sato Y,Matsumoto H.Effect of risedronate on speed of sound in postmenopausal women with osteoporosis.World J Orthop 2013;4(4):316-322 PMID:24147269 DOI:10.5312/wjo.v4.i4.316.These articles[1-4]have been retracted at the request of the Editors-in-Chief as misconduct over authorship of the paper was detected and confirmed.