Open Access Open Badges Research article

Knee extension range of motion and self-report physical function in total knee arthroplasty: mediating effects of knee extensor strength

Yong-Hao Pua1*, Peck-Hoon Ong1, Hwei-Chi Chong1, William Yeo2, Celia Tan3 and Ngai-Nung Lo4

Author Affiliations

1 Department of Physiotherapy, Singapore General Hospital, Singapore, Singapore

2 Orthopaedic Diagnostic Centre, Singapore General Hospital, Singapore, Singapore

3 Allied Health Division, Singhealth, Singapore, Singapore

4 Department of Orthopaedic Surgery, Singapore General Hospital, Singapore, Singapore

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BMC Musculoskeletal Disorders 2013, 14:33  doi:10.1186/1471-2474-14-33

Published: 18 January 2013



Knee extensor strength and knee extension range of motion (ROM) are important predictors of physical function in patients with a total knee arthroplasty (TKA). However, the relationship between the two knee measures remains unclear. The purpose of this study was to examine whether changes in knee extensor strength mediate the association between changes in knee extension ROM and self-report physical function.


Data from 441 patients with a TKA were collected preoperatively and 6 months postoperatively. Self-report measure of physical function was assessed by the Short Form 36 (SF-36) questionnaire. Knee extensor strength was measured by handheld dynamometry and knee extension ROM by goniometry. A bootstrapped cross product of coefficients approach was used to evaluate mediation effects.


Mediation analyses, adjusted for clinicodemographic measures, revealed that the association between changes in knee extension ROM and SF-36 physical function was mediated by changes in knee extensor strength.


In patients with TKA, knee extensor strength mediated the influence of knee extension ROM on physical function. These results suggest that interventions to improve the range of knee extension may be useful in improving knee extensor performance.