Correlations between objective and self-reported step count adherence following total knee replacement: A longitudinal repeated-measures cohort study.

Objective: To determine how physically active individuals are following total knee replacement (TKR) and how accurately they self-report their step count adherence compared to objective measure following TKR.

Methods: Observational cohort study, nested within the PATHway randomised-clinical trial. Participants (n = 102) who had recently undergone TKR were recruited for the main trial. Only participant data from the intervention group were used for this study (n = 51). Participants in the intervention group received an activity tracker to monitor their physical activity and fortnightly health-coaching sessions for 3 months. Adherence was objectively measured as percentage of steps completed divided by the amount prescribed by the health coach. Participants were asked to self-report their adherence on a 1-10 numerical rating scale during health coaching sessions.

Results: Data from 44 participants were available, resulting in a total of 224 paired measurements. Participant step count increased over the first 8 weeks of follow-up, and plateaued from 8 weeks onwards at approximately 7500 steps/day. About two-thirds (65.8%) of participants accurately self-reported their step count adherence up until 12 weeks, the remaining one-third (34.2%) underestimated their adherence. Paired t-tests demonstrated statistically significant differences between the paired measurements from weeks 2 to 10.

Discussion: Participants were generally active and completed the step goal most occasions. Two-thirds accurately self-reported their step goal adherence. Self-reported measures should be combined with an objective measure of adherence for greater accuracy. A further understanding of how people engage with activity trackers can be used to promote behaviour change in physiotherapy-led interventions.