In this article, we modeled the empirical patterns of quality of life and functioning among patients who underwent TKA, and the characteristics related to each pattern.
Overall, the baseline characteristics and PROMs scores of the study population, both before and after surgery, are in line with previous studies, although data were collected at slightly different time points [28, 29]. In fact, this study has an important strength in the collection of PROMs at 6 months after surgery, which is different from other studies that examined longer-term outcomes (at 12 or 24 months). Therefore, it provides insight into the medium-term effect of the surgical intervention on PROMs.
The largest proportion of patients in this study had low-intermediate PROMs scores at the time of surgery, moderately improved at 6 months, and maintained adequate levels of performance at 12 months post-surgery. Although the analysis shows three main trajectories for the two PROMs instruments, the patterns of these trajectories were slightly different across them. Indeed, they investigate different aspects of the perceived health status [30]. The EQ-5D-3L measures health-related quality of life and consists of five dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. Hence, people reporting higher scores for this scale tend to benefit from more autonomy in activity of daily living, less pain, and better mental health. The KOOS-PS is a questionnaire that measures the level of function in performing usual daily activities (such as rising from bed), and higher-level activities related to the knee joint (such as squatting). Patients with higher KOOS-PS scores tend to benefit from higher functionality and mobility.
The results of our multinomial logistic regression analysis revealed the patient characteristics associated with different trajectories of the two PROMs tools.
Our findings concerning the EQ-5D-3L score indicate two trajectories with low baseline scores, with one of them (low-high) showing a significant improvement 6 months, starting from lower average levels of quality of life at the time of undergoing TKA surgery. This trajectory is the one that describes the pattern of improvement of the majority of patients, confirming the efficacy of this surgical intervention. Our results also confirm the current evidence which shows that about 20% of patients undergoing TKA do not show improvements in quality of life [31, 32].
Moreover, our findings also showed that females reported lower levels of perceived quality of life before surgery than males. There is evidence suggesting that being female is associated with poorer clinical conditions and perceived quality of life prior to TKA [33], prompting them to seek care. Plenty of literature [34–37] reports that individuals who present late to knee arthroplasty surgery may have reduced gait and biomechanics, as well as a scarce functional recovery after surgery. One study [38] found that patients who underwent knee arthroplasty at a later stage of their disease had a significantly worse preoperative gait pattern compared to those who had the surgery earlier. Additionally, these individuals also had a less favorable postoperative outcome in terms of both function and knee joint biomechanics. Lee’s study suggests that patients who present later in the disease process may have developed compensatory mechanisms, such as limping or favoring one leg, which can negatively impact their gait and overall recovery post-surgery. These findings reinforce the available evidence that early intervention for knee arthritis and other knee conditions may be important to prevent the development of compensatory mechanisms, maintain muscle mass and strength, and ultimately improve the outcome of knee arthroplasty surgery.
Furthermore, our results suggest that being female is associated with better outcomes after surgery [39]. In fact, women may be more likely to adhere to post-surgical rehabilitation protocols and have better overall health behaviors [33]. Additionally, women may be more likely to have access to support networks and social resources, which can help improve their overall well-being and recovery after surgery [40]. It is also important to note that the relationship between gender, presentation to knee arthroplasty surgery, and outcomes after surgery is complex and may be influenced by a variety of factors.
Our results also indicate that patients with an ASA score ≥ 3 were more likely to report lower quality of life at baseline and not to derive significant benefit from surgery at 6 and 12 months (low-intermediate trajectory). The ASA score is indeed a widespread tool used to assess patients’ eligibility for surgery. Our findings confirm the importance of the ASA score for categorizing patients at different levels of risk also after surgery [41–43].
The ASA score, combined with other indicators, could eventually be used to predict a patient’s expected quality of life improvement after TKA, thus allowing patients and surgeons to make the most appropriate choice, relying on a routinely used tool.
As for KOOS-PS score, our findings suggest that knee functionality tends to show gradual and almost uniform improvement in all 3 trajectories. The main difference among these three trajectories is that while the HH and II trajectories, representing 82% of the sample, showed a clinically significant improvement of KOOS-PS (> 10 points [44]) at 12 months, the LL trajectory failed to achieve a clinically significant improvement, denoting the presence of a subgroup of patients who benefit to a minor extent from surgery. Indeed, patients assigned to the low baseline functioning trajectory failed to achieve the minimal important change of ten points in KOOS-PS suggested by Macri et al. [44] and constitute therefore an important target for improvement. Therefore, the main finding of this study is the identification of 3 trajectories of functioning, 2 characterized by moderate improvement after surgery and then stabilization, and 1 by a modest improvement with respect to the low baseline level.
Female patients were more likely to exhibit both the trajectories characterized by lower scores at baseline and at subsequent time points.
Younger patients also showed a slightly worse improvement (LL trajectory). There is evidence suggesting that being younger is associated with worse outcomes after knee arthroplasty [45]. One potential explanation for this association is that younger individuals may be more active and have higher functional demands, which can put more strain on the implanted prosthetic joint and increase the risk of complications [33]. Additionally, younger patients may have a longer lifespan with the implant, increasing the likelihood of wear and tear on the joint over time [46].
Moreover, patients with a higher ASA score are more likely to present the worst trajectory (LL). It is worth noticing that this is the only trajectory not showing a clinically significant improvement 12 months after surgery [44]. Therefore, a high ASA score can be considered a significant determinant of suboptimal recovery after the intervention. Our analysis reinforces the body of evidence on the importance of the ASA score for stratifying patients into different levels of functional outcomes after TKA [41–43].
In summary, our analysis highlighted differential patterns of improvement after TKA. There are also slight differences in the factors influencing PROM trajectories, most likely related to the fact that the two PROMs questionnaires investigate two domains, i.e., quality of life, and joint functioning and mobility. Female gender appears to be associated with a presentation to surgery with worse perceived quality of life and joint function than males, but also more rapid improvement after surgery. Having an ASA score greater than 3 is instead associated with a worse functional recovery after TKA. While a BMI higher than 30 was not found to be significantly associated with the worse single trajectory in the multinomial logistic regression of each PROMs score, the cross-classification between the performance trajectories showed that it was related with the small share of worse performing patients in both the PROMs tools.
4.1. Study limitations
The study cohort was recruited from a large, specialized tertiary care hospital in Italy that is a recognized center of excellence for orthopedic and bone pathologies. As a result, our findings are based on a selected patient sample. Due to the observational nature of this study, our findings are only generalizable to individuals meeting the same inclusion/exclusion criteria. Therefore, additional research conducted in diverse patient populations and healthcare settings is required to validate and expand upon our conclusions.
Additionally, our results may be biased by patient dropout. Specifically, patients who were lost to follow-up differed in certain characteristics (e.g., age) from those who were evaluated at 6 and 12 months, which could at least partially undermine the internal validity of the study. However, our dropout rate is comparable to those reported in other comparable studies. In addition, it is possible that unmeasured variables (e.g., educational level, socio-economic status, ethnicity) could also be relevant to the missing data process and could determine underlying barriers to TKA access [47]. Furthermore, the use of PROMs evaluation at only three time points restricted our ability to detect early improvements or deteriorations or more complex patterns of change. The broad confidence intervals for some of the comparisons were a result of the small number of patients in certain subgroups, which reduced our statistical power to detect significant differences.