Article Review
Reliability and validity of modified Four Square Step Test (mFSST) performance in individuals with Parkinson’s disease
Background. The article discusses using the mFSST as a substitute for the FSST which is used to test dynamic balance in patients with Parkinson's disease (PD). The study focuses on the reliability and validity of the modified Four Square Step Test (mFSST) as a tool to assess dynamic balance and fall risk in individuals with PD. Methods. The randomized controlled trial involved 27 participants with PD, who were tested while on medication, using the FSST and mFSST at different times and by different raters. Results. The mFSST, which replaces canes with 2-inch tape, was found to have excellent interrater and test-retest reliability, as well as strong concurrent validity when compared to the original FSST. Results indicated that the mFSST is a practical and reliable assessment tool for clinicians to use in various settings, as it requires minimal equipment and space. Conclusions. The study concludes that both the FSST and mFSST can be used to assess dynamic balance in individuals with PD, particularly those in the early to mid-stages of the disease (Hoehn & Yahr stages I-III). The mFSST is especially useful for assessing stepping in multiple directions without the need for obstacles, making it a valuable tool for early identification of fall risk and appropriate intervention planning.
Four Square Step Test (FSST)
The Four Square Step Test (FSST) assesses dynamic balance by requiring individuals to step over obstacles in multiple directions. Participants start standing in square one, then complete the sequence in a clockwise manner through square four. Once they return to square one, they go counter-clockwise stepping into square four to end the test, returning to square one. Timing begins when the participant steps forward out of square one and makes foot contact within square two and ends when the subject steps backward and returns to square one with both feet. The FSST has been found to have high interrater reliability (ICC = 0.99) and a moderate sensitivity (0.78) for capturing fall risk 1.
Modified Four Square Step Test (mFSST)
The modified Four Square Step Test (mFSST) is similar to the FSST but replaces the canes with 2-inch tape. The timing of the mFSST is the same as the FSST, beginning with the first foot contact in square two and ending when both feet return to square one. The mFSST was found to have excellent interrater reliability with a Pearson’s correlation of ( r = 0.999, p = .001 ) (ICC2,2 = 0.99) and excellent test-retest reliability with a Pearson’s correlation of ( r = 0.916, p = .01 ) (ICC2,2 = 0.96). For concurrent validity, the fastest of the first two trials of the mFSST and FSST were highly correlated with a Pearson’s correlation of ( r = 0.823, p < .01).
Critical Discussion:
With the current modification (i.e. replacing the canes with tape), the use of anticipatory and reactive balance strategies to overcome the hurdles (i.e. canes) in the FSST has been reduced. Thus, are we still measuring the same degree of balance? How have different phases of stance and different biomechanical properties of balance been altered with this modification, and can we agree with the author that it made little to no difference in the ability to measure dynamic balance? While the concurrent validity was high, this was only the case with the fastest readings. Why? Is there a possible tradeoff between sensitivity and specificity? We could have answered more questions had the researcher considered determining the MDC (minimally detectable change) and even an ROC (receiver operating characteristic). And finally, I think that the changes that have been instituted warrant further classification of this test and description of its relationship to fall risk and the differences in results between fallers and non-fallers, because I think it is prudent to see them as two different tests. The benefit it adds to measurements within PwPD who have poor dynamic balance is acknowledged.
Reference:
1,2Boddy A, Mitchell K, Ellison J, Brewer W, Perry LA. Reliability and validity of modified Four Square Step Test (mFSST) performance in individuals with Parkinson's disease. Physiother Theory Pract. 2023;39(5):1038-1043. doi:10.1080/09593985.2022.2031360
