Test-Retest Reliability of a Passive Joint Position Sense Test After ACL Reconstruction: Influence of Direction, Target Angle, Limb, and Outcome Measures

BACKGROUND: The joint position sense (JPS) is an element of proprioception and defined as an individual’s ability to recognize joint position in space. The JPS is assessed by measuring the acuity of reproducing a predetermined target angle. The quality of psychometric properties of knee JPS tests after anterior cruciate ligament reconstruction (ACLR) is uncertain. PURPOSE/HYPOTHESIS: The purpose of this study was to evaluate the test-retest reliability of a passive knee JPS test in patients who underwent ACLR. We hypothesized that the passive JPS test would produce reliable absolute error, constant error, and variable error estimates after ACLR. STUDY DESIGN: Descriptive laboratory study. METHODS: Nineteen male participants (mean age, 26.3 ± 4.4 years) who had undergone unilateral ACLR within the previous 12 months completed 2 sessions of bilateral passive knee JPS evaluation. JPS testing was conducted in both the flexion (starting angle, 0°) and the extension (starting angle, 90°) directions in the sitting position. The absolute error, constant error, and variable error of the JPS test in both directions were calculated at 2 target angles (30° and 60° of flexion) by using the angle reproduction method for the ipsilateral knee. The standard error of measurement (SEM), smallest real difference (SRD), and intraclass correlation coefficients (ICCs) with 95% Cis were calculated. RESULTS: ICCs were higher for the JPS constant error (operated and nonoperated knee, 0.43-0.86 and 0.32-0.91, respectively) compared with the absolute error (0.18-0.59 and 0.09-0.86, respectively) and the variable error (0.07-0.63 and 0.09-0.73, respectively). The constant error of the 90°-60° extension test showed moderate to excellent reliability for the operated knee (ICC, 0.86 [95% CI, 0.64-0.94]; SEM, 1.63°; SRD, 4.53°), and good to excellent reliability for the nonoperated knee (ICC, 0.91 [95% CI, 0.76-0.96]; SEM, 1.53°; SRD, 4.24°). CONCLUSION: The test-retest reliability of the passive knee JPS tests after ACLR varied depending on the test angle, direction, and outcome measure (absolute error, constant error, or variable error). The constant error appeared to be a more reliable outcome measure than the absolute error and the variable error, mainly during the 90°-60° extension test. CLINICAL RELEVANCE: As constant errors have been found reliable during the 90°-60° extension test, investigating these errors—in addition to absolute and variable errors—to reflect bias in passive JPS scores after ACLR is warranted.