title: Associations of knee extensor strength and standing balance with physical function in knee osteoarthritis.
abstract: OBJECTIVE
  Knee extensor strength is an important correlate of physical function in patients with knee osteoarthritis; however, it remains unclear whether standing balance is also a correlate. The purpose of this study was to evaluate the cross-sectional associations of knee extensor strength, standing balance, and their interaction with physical function.
  
  
  METHODS
  One hundred four older adults with end-stage knee osteoarthritis awaiting a total knee replacement (mean ± SD age 67 ± 8 years) participated. Isometric knee extensor strength was measured using an isokinetic dynamometer. Standing balance performance was measured by the center of pressure displacement during quiet standing on a balance board. Physical function was measured by the self-report Short Form 36 (SF-36) questionnaire and by the 10-meter fast-pace gait speed test.
  
  
  RESULTS
  After adjustment for demographic and knee pain variables, we detected significant knee strength by standing balance interaction terms for both SF-36 physical function and fast-pace gait speed. Interrogation of the interaction revealed that standing balance in the anteroposterior plane was positively related to physical function among patients with lower knee extensor strength. Conversely, among patients with higher knee extensor strength, the standing balance-physical function associations were, or tended to be, negative.
  
  
  CONCLUSIONS
  These findings suggest that although standing balance was related to physical function in patients with knee osteoarthritis, this relationship was complex and dependent on knee extensor strength level. These results are of importance in developing intervention strategies and refining theoretical models, but they call for further study.
authors: Department of Physiotherapy, Singapore General Hospital, Singapore, Singapore. puayonghao@gmail.com
authors: Yong-Hao
authors: YH
authors: Pua
authors: Zhiqi
authors: Z
authors: Liang
authors: Peck-Hoon
authors: PH
authors: Ong
authors: Adam L
authors: AL
authors: Bryant
authors: Ngai-Nung
authors: NN
authors: Lo
authors: Ross A
authors: RA
authors: Clark
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D003430:Cross-Sectional Studies; D005080:Exercise Test; D005260:Female; D006304:Health Status; D006305:Health Status Indicators; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength; D053581:Muscle Strength Dynamometer; D020370:Osteoarthritis, Knee / Q000175:diagnosis / Q000503:physiopathology* / Q000601:surgery; D004856:Postural Balance; D011237:Predictive Value of Tests; D012720:Severity of Illness Index; D012846:Singapore; D011795:Surveys and Questionnaires; D014850:Waiting Lists