The decline step-down test measuring the maximum pain-free flexion angle: A reliable and valid performance test in patients with patellofemoral pain.

Objectives: Patients with patellofemoral pain (PFP) experience pain while descending stairs. To date no reliable and valid performance-test exists to assess the maximum pain-free knee flexion angle (MPFFA) as outcome measure during a step-down task. Therefore, the intra- and inter-observer reliability and construct validity of the decline step-down test (DSDT) measuring the MPFFA in patients with PFP were evaluated.

Design: Reliability and construct validity.

Setting: Private practices in Nijmegen and Utrecht, the Netherlands.

Participants: Patients with PFP.

Main Outcome Measures: The reliability was assessed by repeated measurements of the MPFFA during the DSDT. The construct validity was assessed by correlating the measurements on the DSDT with the Anterior Knee Pain Scale Dutch Version (AKPS-DV) based on a pre-set hypothesis.

Results: Thirty-two participants (forty-eight knees) were eligible for inclusion. The intraclass correlation coefficient (ICC) for intra-observer reliability was ICC = 0.83 and ICC = 0.85 for inter-observer reliability. The 95% limits of agreement (LoA) showed a width of 27.56° for intra-observer reliability and a width of 24.42° for inter-observer reliability. There was an average positive correlation between the DSDT and the total score on the AKPS-DV (r = 0.31, p = 0.030).

Conclusion: The DSDT measuring the MPFFA is reliable and valid in patients with PFP.