Background/Purpose: Standard post-operative physical therapy (PT) for total knee replacement (TKR) aims to increase knee range of motion (ROM), which is important for walking and adopting an active lifestyle, e.g., taking more steps/day, after TKR.  However, it is unclear to what extent limited ROM may be a barrier to physical activity after TKR. This is important to study since ROM is a modifiable impairment that can be prioritized in PT after TKR. The purpose of this study was to evaluate the association of ROM with physical activity over the first 6 weeks of PT after TKR.

Methods: We recruited patients with a first time unilateral TKR from a local PT clinic. We excluded people with comorbidity that affected physical function other than arthritis. We quantified physical activity as steps/day using an accelerometer enabled monitor (Actigraph GT3X) worn for at least 3 days during waking hours. Knee ROM was measured by a physical therapist using a standardized approach.  We classified lacking ≥ 5° of full knee extension as limited extension, and knee flexion ≤ 95° as limited flexion. We examined the difference in steps/day between those with and without limited knee ROM with physical activity each week of PT (weeks 1 to 6) using difference tests and 95% Confidence Intervals (CI).

Results: We included 26 people after TKR (age [mean± sd] 64.9 ± 9.1 years, BMI 34.5 ± 7.5 kg/m², 56% female) at baseline.  Participants walked 1889 ± 1467 steps/day at week 1, and 3474 ± 2277 step/day at week 6. In general, there was little difference in steps/day between those with and without limited ROM. For instance, there was a non-statistically significant difference in steps/day between those with limited extension (n=20) compared with those without (n=6) (776 steps/day, 95% CI [-2185, 633.26]). In a similar fashion, there was little difference among those with limited flexion (n=7) compared with those without (538 steps/day, 95% CI[-818, 1894]).  A small difference was observed at week 6 for extension. No participants had limited flexion after week 3. (Figure)

Conclusion: Our preliminary findings show little difference in physical activity among people with and without ROM limitations after TKR. Limited ROM, even at clinically significant levels, may not be a major barrier to physical activity after TKR. Figure: Weekly steps/day for people after TKR with and without limited knee extension/flexion during outpatient PT [sample size (n) provided above each data point].