BACKGROUND: When treating knee osteoarthritis (KOA), rehabilitation exercise is often combined with low-level (LLLT) or high-intensity laser therapy (HILT). However, the effectiveness of these combinations is still uncertain. OBJECTIVE: To examine the effects of LLLT or HILT combined with rehabilitation exercise (LLLT plus E or HILT plus E) on pain, stiffness and function in KOA. DATA SOURCES: Five databases (PubMed, Web of Science, CINAHL, PEDro and SPORTDiscus) were searched for relevant studies published up to 31 December 2019. STUDY SELECTION: KOA randomised controlled trials, LLLT plus E or HILTand E against exercise alone with or without placebo laser, reported clinical outcomes, human studies and English language. DATA SYNTHESIS: Methodological quality was assessed by the PEDro and Cochrane risk-of-bias scales, and the meta-analysis was undertaken using RevMan 5.3. RESULTS: Of the 10 retrieved studies, six investigated LLLT plus E, three on HILT plus E, and one evaluated both. All the studies had high PEDro scores. However, as most of the studies employed a single type of laser therapy, only indirect comparison of LLLT plus E and HILTand E was possible. This study found all treatment modalities were effective in reducing KOA symptoms. Interestingly, relative to control, the meta-analysis showed significant improvements in knee pain, stiffness and function for the HILT plus E. CONCLUSION: Both LLLT and HILT are beneficial as adjuncts to rehabilitation exercise in the management of KOA. Based on an indirect comparison, the HILTand E seems to have higher efficacy in reducing knee pain and stiffness, and in increasing function. To confirm this finding, a direct comparative investigation of the two types of laser therapy may be necessary. SYSTEMATIC REVIEW REGISTRATION: PROSPERO ID CRD42020206228.

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