Improvements in Physical Capacity via a Wearable Sensor May Not Indicate Reductions in Real-World Sedentary Activity: A Longitudinal Post-Total Hip Arthroplasty Study.

Background and purpose: Patients with end-stage hip osteoarthritis typically elect total hip arthroplasty (THA) to improve life activity performance while clinical outcomes focus on physical capacity. However, it is unclear how improvements in life activity performance relate to improvements in physical capacity following THA. This study aimed to assess the longitudinal relationship between improvement in life activity performance (ie, decreases in sedentary time) and improvements in physical capacity (ie, increases in 6-Minute Walk [6MWT] distance) from before THA to a 6-month post-THA follow-up time point.

Methods: This is a secondary analysis of a double-blind randomized controlled trial that enrolled individuals 50 to 85 years of age with unilateral hip osteoarthritis who underwent THA. Longitudinal variables of interest included the % of active wear time in sedentary activity using a hip-mounted wearable accelerometer-based monitor [ActiGraph wGT3X-BT] and 6MWT distance. The variables were modeled to extract predicted change scores, and simulations were used to determine if each participant had a change in sedentary time and 6MWT distance. Participants were classified on whether they improved sedentary activity time (P+: decrease in sedentary time or P-: no improvement in sedentary time) and/or 6MWT distance (C+: increased 6MWT distance or C-: no improvement in 6MWT distance). Independent sample t-tests (continuous variables) and Fisher exact tests (categorical variables) were used to compare characteristics between classification groups.

Results and discussion: All 76 participants (age: 63.9 ± 7.0 years, 64.5% male) were classified as C+, as all improved physical capacity. A majority (n = 45; 59.2%) were C+/P+, while 31 participants (40.8%) were classified as C+/ P-, and no participants were classified as C-/P+ or C-/ P-.

Conclusions: There is a noted disagreement between improvements in life activity performance versus physical capacity suggesting gains in the 6MWT are not always associated with reductions in sedentary time during recovery from THA. Improving physical capacity does not equate to decreased sedentary time. Thus, different rehabilitation targets (ie, behavior change interventions) may need to be identified and explored to enhance life activity performance following THA that may better align with patient performance goals.