MINIMAL CLINICALLY IMPORTANT DIFFERENCE OF THE FOUR SQUARE STEP TEST IN PEOPLE WITH HIP OR KNEE JOINT REPLACEMENTS

M. Batting¹, K. Barker¹

Background: The Four Square Step Test (FSST) involves rapid step taking in multiple directions over obstacles to provide a measure of dynamic balance. The FSST has already been shown to be a valid and reliable measure in other health conditions; however its utility as a measure of clinically meaningful difference in patients balance performance has not been assessed. Objective changes in the distribution of scores in rehabilitation are necessary to understand the benefits of rehabilitation in a real life context.

Purpose: The study’s purpose was to determine the minimal clinically important difference (MCID) of the Four Square Step Test (FSST) for people who have had a hip or knee joint replacement pre and post surgery.

Methods: A secondary analysis of a longitudinal cohort study was conducted. A distribution based approach was adopted where the Standard Error of Measurement (SEM) was used to estimate the MCID of the FSST. The SEM is the variation in score that is due to unreliability of the outcome measure used. Therefore, a change smaller than the SEM on the FSST is likely to be the result of measurement error over change in true balance performance time. Participant’s fastest FSST time pre-operatively was recorded as well as the fastest FSST 6 months post-operatively. All participants undertook a standard course of physiotherapy following surgery.

Results: A total of one hundred and twenty four data sets were available for participants who had undergone either knee (49.2%) or hip (50.8%) replacement. Sixty six of the participants were male and the mean age recorded was 74.27 (SD 7.2), mean BMI was 29.7 (SD 6.7) with 33 participants falling once or more in the last year. The mean Oxford Knee Score was 20.82 (SD 8.6) and Oxford Hip Score was 22.4 (SD 7.3) at baseline. The mean FSST for the sample at baseline was 22.42s (SD 6.9) and 6 months post joint replacement was 13.39 (SD 3.5). The MCID of the FSST based on the SEM approach is ≥ 5.5s.

Conclusion(s): The MCID for people following hip or knee replacement surgery was found to be ≥ 5.5s using the SEM distribution based approach. Care should be taken when interpreting the findings of MCID using the distribution based approaches given their lack of evaluation of the clinical relevance of a given difference as they are based only on statistical characteristics. Further research should look at the MCID of the FSST in different health conditions before it can be confidently used in clinical practice.

Implications: Clinicians using the FSST to measure change in balance performance following hip or knee replacement can determine a change in score of ≥ 5.5s as a meaningful improvement

Funding, acknowledgements: This study was not funded

Keywords: Minimally Clinically Important Difference, Outcome Assessment, Joint replacement

Topic: Orthopaedics

Did this work require ethics approval? Yes

Institution: HSC

Committee: Research Ethics Committees Northern Ireland

Ethics number: 16/NI/0049