Objective 1) To determine the inter-rater reliability and measurement error of a 11-step stair ascend/descend test (STTotal-11) and stair up (ascend) test (STUp-11); 2) to seek evidence for the STTotal-11 and STUp-11 as valid measures of physical function by determining if they relate to measures of physical function and do not relate to measures not of physical function; and 3) to explore if the STTotal-11 and STUp-11 scores relate to lower extremity muscle weakness and knee range of motion (ROM) in individuals with total knee arthroplasty (TKA). Design Cross-sectional study. Setting Academic center. Participants Subjects (N=43, 30 women; mean age, 68±8years) with unilateral TKA. Interventions Not applicable. Main Outcome Measures STTotal-11 and STUp-11 were performed twice and scores were compared to scores on 4 lower extremity performance-based tasks, 2 patient-reported questionnaires of physical function, 3 psychological factors, knee ROM, and strength of quadriceps, hip extensors and abductors. Results Intraclass correlation coefficient was 0.94 for both the STTotal-11 and STUp-11, standard error of measurements were 1.14sec and .82sec, and Minimum Detectable Change associated with 90%CI were 2.6 sec and 1.9 sec, respectively. Correlations between stair tests and performance based measures and knee and hip muscle strength ranged from r=.40 to .78. STTotal-11 and STUp-11 had a small correlation with one of the patient-reported measures of physical function. Stair tests were not associated with psychological factors and knee extension ROM, and were associated with knee flexion ROM. Conclusions STTotal-11 and STUp-11 have good inter-rater reliability and MDCs adequate for clinical use. The pattern of associations supports the validity of the stair tests in TKA.

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