Discussion
LMS
The current study showed no clear evidence that stratified exercise therapy is likely to be a cost-effective option compared to usual exercise therapy in patients with knee OA. As we did not demonstrate superiority for clinical effectiveness either,The present study indicates that – although cautious interpretation is warranted – the stratified exercise therapy approach could potentially result in (particularly work-related) cost-savings, with similar clinical effects compared to usual exercise therapy. Results from separate analyses in each of the 3 subgroups of the stratified model also suggest that cost savings are most likely to occur in the LMS and to a lesser extent in the HMS, while being least likely in the OS. However, we cannot draw firm conclusions from our study because all cost difference estimates were surrounded by very high levels of uncertainty (partly due to insufficient power) and cost differences disappeared when focusing only at the healthcare perspective. Decision-makers (as well as health care professionals and patients) should therefore balance the uncertain cost savings (in work-related costs) and the lack of superior clinical effects by the stratified exercise therapy on the one hand against the effort that comes with implementing the new treatment. In this perspective, the barriers for applying the new treatment (especially for the OS) as reported elsewhereOur inconclusive result seems to be consistent with the scarce and conflicting evidence regarding the cost-effectiveness of stratified approaches of physical therapy, with two trialsWe would like to highlight two potential reasons for the unexpected finding of stratified exercise therapy not resulting in healthcare costs savings. First, we a priori expected that our stratified approach would not only lead to superior clinical effects, but also in substantial cost savings due to less physical therapy sessions (especially in HMS), other healthcare utilization and work absenteeism. However, with regards to the physical therapy sessions, we found only a very small difference in number of sessions of 1.2 (8.4 vs 9.6) between our study arms. This can be attributed to the much lower amount of sessions in the control group than what was expected, which can be considered an indication for an (even further) improvement in efficiency by Dutch physical therapists. It could also be caused by the COVID-19 pandemic, as health care sites were closed or restricted to acute situations only. Finally, also work absenteeism occurred much less than expected in both study arms. It should be noted that half of our study group was already retired (i.e., 53% in experimental and 48% in control arm) and those wo still worked showed relatively high work ability and low sick leave rate already at baseline, so there was not much room for substantial group differences in work-related costs.A second reason for the lack of difference in healthcare costs between our study arms is the smaller than intended contrast between the interventions, as also reported in our clinical effectiveness study.We should address the following study limitations. First, as with nearly every clinical trial, our study was powered on the primary effect outcome, rather than on cost-effectiveness outcomes, such as costs. This is common practice in health economics, because costs are heavily right skewed and would therefore require extremely large sample sizes, which in turn might be infeasible and/or unethical. To deal with this issue, we used estimation (e.g. by reporting the probability of cost-effectiveness) rather than hypothesis testing for interpreting our outcomes.