TKA is being performed on an increasingly younger population of knee OA patients for whom participating in work is of critical importance. This study showed that KOOS pain, symptoms, ADL, and Sport/Rec were not associated with no RTW after TKA. Therefore, clinicians should be aware that proxies for participating in work go beyond outcomes like pain or function [
6]. Additionally, the standardized care pathways after TKA focussing on minimizing pain and maximizing function like improving strength and mobility are probably not suited to overcoming hindering factors for RTW. A focus on rehabilitation on the performance of relevant work-related knee-demanding activities might be more promising, given the reported limitations in these activities before and after TKA [
5].
Five predictors for no RTW among TKA patients were found in the present study. The strongest was having had a preoperative sick leave >2 weeks. This highlights the need for a better understanding of why these patients were on sick leave, and whether earlier TKA surgery in these patients might improve RTW due to a better preoperative health status and functioning [
8,
19]. In line with the two former multivariate studies, this study showed that physical job demands hinder RTW [
8,
9]. Interestingly, this association was established only for medium knee-demanding work and not for heavy knee-demanding work. This appears in line with Lombardi et al., who found that the highest percentage of patients that were still working at 1 year after TKA were those in very heavily demanding jobs: 98 %, 135 out of 138 patients [
6]. An explanation might be the healthy worker selection effect. This means that, despite their TKA, this selected group of workers is more fit than the selection of workers involved in medium knee-demanding work. The reason is that unfit workers would have left their heavy knee-demanding work in an earlier phase in their career due to health complaints than their counterparts in medium knee-demanding work. This study also confirmed that sex is not associated with no RTW for males [
9], but the opposite is true for females [
8]. We can only speculate on the actual underlying reasons for this association; perhaps the fact that most men are the primary wage earners or that women in general have poorer outcomes after TKA due, for instance, to depression, low back pain, and symptomatic joint count [
20]. A BMI ≥ 30 and having a TKA might further reduce sports participation and thereby increase the risk for no RTW [
21,
22]. The fifth predictor for no RTW was the self-reported work-relatedness of symptoms leading to the TKA. This patient characteristic has not been reported in other joint replacement studies on RTW. Interestingly, this characteristic was not associated with the classification of the job into light-, medium-, and heavy knee-demanding work, and perhaps it is associated with the motivation of TKA patients for RTW [
9]. Taken together, these five predictors explained 50 % of no RTW: a relatively high impact. To improve the ease of use of these predictors in a clinical setting, the corresponding patient characteristics were dichotomized or trichotomized. These predictors can guide clinicians to select patients at risk for no RTW. For instance, a plausible first step seems to be active referral of target patients characterized by the above-mentioned predictors to an occupational physician. Preferably, this should be done preoperatively TKA to secure timely work-directed care.
Two limitations of the present study should be discussed. The first limitation is the potential presence of recall bias. To reduce this bias, we categorized the answers, most often in two categories and not more than three. In addition, to overcome differences due to follow-up time between TKA surgery and filling in the questionnaire between patients, this period was included in the regression analysis and appeared not to be associated with no RTW. A second limitation is the relatively small number of patients that did not RTW, resulting in less precision of the risk estimates: 46 patients (28 % of 167) in the present study with a follow-up of at least 2 years. However, in the previous multivariate studies on RTW after TKA, the absolute number of patients not returning to work was even less: 45 (28 % of 162) TKA patients not returning to work at the 3-month postoperative end point [
9] and 26 (15 % of 170) TKA patients not returning to work at the 12-month postoperative end point [
8]. Given the estimated increasing number of working TKA patients in the coming years, multivariate prognostic studies on RTW with sufficient power are needed to critically understand the disease-specific mechanisms for no RTW, including relevant comorbidity [
23]. Meanwhile, patients at risk for no RTW—especially obese female workers with a preoperative sick-leave duration >2 weeks who perform knee-demanding work and indicate that their knee symptoms are work-related, should actively be referred for work-directed care.