Reliability and validity of the Four Square Step Test in patients with hip osteoarthritis before and after total hip replacement.

OBJECTIVE: To determine the validity and inter- and intra-rater reliability of the Four Square Step Test (FSST) in assessing gait performance, balance and physical function for patients with hip osteoarthritis before and after total hip replacement (THR). DESIGN: Observational, repeated measures. SETTING: A specialist orthopaedic hospital. PARTICIPANTS: Fifty-eight participants with moderate to severe hip osteoarthritis scheduled to receive primary hip replacement within 4 months from recruitment. MAIN OUTCOME MEASURE: Time to complete the FSST, time and steps to complete the Figure of 8 Walk Test (F8W) and Berg Balance Scale score (BBS). RESULTS: The Bland and Altman limits of agreement for intra-rater measurements of the FSST were -3.2s to 3.5seconds before THR and -1.5 to 2.0seconds after THR. Limits of agreement for two different raters were -2.2 to 3.4seconds, all with small mean differences indicating little bias between raters or replications. Concurrent validity was assessed, and the FSST correlated highly with the F8W (r=0.7, P<0.001) and moderately with the BBS (r=0.6, P<0.001). Only one participant was rated as being at moderate risk of falls on the BBS, with the other participants scoring low; only one participant failed to complete the F8W. This is in contrast to the FSST, which 21 people failed to complete pre-operatively. CONCLUSIONS: The FSST is a valid and reliable measure of multi-directional stepping speed and balance, giving a more informative measure of gait performance than the F8W and BBS, and is feasible for use in a clinical population of patients both before and after THR.