4. Discussion
TKA, pain
We found that the placebo group spent significantly more time mobilized (standing and stepping) than the oxycodone CR and tapentadol ER groups, where time standing contributed the most to the increased time mobilized in the placebo group. Time mobilization and the number of steps per day increased in all groups in the first week after surgery. The step count was higher in the tapentadol ER group than in the other groups, but the difference did not reach statistical significance.As reported in the main study, no statistical difference in pain during activity or use of rescue analgesics between groups receiving different analgesic regimens was found, although the placebo group showed the highest pain scores for both mobilization and rest.In the present study, the daily step count increased significantly in the first week in all groups. As demonstrated in Figure In the current study, we found that the number of steps decreased with increasing pain intensity when mobilized, but only to a certain point. The relationship between pain intensity and activity level remains unclear. Chan et al reported in their study of 171 TKA patients that pain negatively influenced walking 1 to 2 weeks after surgery.Physical activity increased in all groups early after surgery in the present study. These results are consistent with those of Luna et alThe present study reports detailed information about physical activity early after surgery in TKA patients, which is beneficial knowledge to clinicians. Further, the results from the study imply that the regular use of depot opioids does not lead to superior physical activity in the first week after TKA surgery. This is also valuable information for patients that for various reasons do not tolerate opioids.This study has some limitations. We had no preoperative physical activity data from the patients, and it would have been of interest to compare our findings with preoperative physical activity levels. Because only patients aged between 18 and 80 years were included in the study, the results may not be applicable to patients aged >80 years. Statistical analysis is per per-protocol in the present study. Considering the very low number of dropouts, we assume that the per-protocol method has not led to significant bias. The strength of the present study was the high number of patients with complete activity data for the entire recording period. Another strength is that the patients wore the activity monitors from midnight on the first day after surgery and for 6 consecutive days. All patients in the study followed a standardized fast-track patient course that minimized other treatment differences, in addition to the 3 analgesic regimens. The patients were randomized into groups to prevent selection bias. Objectively measured data on early physical activity in TKA patients are scarce, and the present study reporting data from 132 patients contributes to increased knowledge about what could be considered “normal” activity levels early after TKA surgery in patients aged <80 years. Furthermore, as hospital length of stay has decreased, it is important to understand how patients cope with physical activity at home.In conclusion, the placebo group spent more time mobilized (standing and stepping) than the ER and CR groups, but there were no differences in the number of steps between the groups. All patients showed increased activity from days 1 to 6 after surgery. This study contributes to increased knowledge about the expected activity level in the first week after TKA surgery.