In this study, we explored the association between the severity of MetS and the outcomes of TKA in patients with OA. The study found that the preoperative MetS-IR can predict early postoperative outcomes in TKA patients, with higher MetS-IR indicating poorer results. "As a continuous variable, MetS-IR has better predictive ability in OA patients than metabolic syndrome clinical classification. However, no significant correlation was found between the individual components of MetS and early postoperative outcomes. Patients with higher MetS-IR have lower postoperative OKS ratings but higher improvement than those with lower MetS-IR. The study suggests that MetS-IR has the potential to be a useful indicator for predicting early TKA outcomes and may impact primary intervention strategies.
To our knowledge, this is the first study to investigate the relationship between MetS-IR and pre- and early postoperative PROMs in OA patients undergoing TKA. MetS-IR was first reported in 2018 and is considered an intuitive and reliable metabolic and inflammatory measure[26]. It has significant diagnostic value in diagnosing MetS and can be used in clinical decision-making. Our previous research also demonstrated the diagnostic significance of MetS-IR in OA patients, confirming its effectiveness in quantifying MetS activity in Chinese women[27].This study has confirmed that MetS-IR is an independent predictor of TKA outcomes. There was a correlation between preoperative OKS scores and waist circumference, fasting blood glucose, and HDL-C, consistent with previous research by Yoshimura et al[28]. However, there was no significant correlation between postoperative OKS scores and the individual components of MetS, indicating that TKA outcomes are influenced by the clustering of these components. Our findings suggest that using a preoperative MetS-IR threshold of 43, patients with lower metabolic disturbance can expect clinically significant improvement in PROMs after TKA. However, there is still no consensus on the optimal cutoff value for MetS-IR, and further research is needed to determine the ideal cutoff value that can minimize complications and maximize functional recovery.
Our results show that patients in group two have a younger age at surgery, indicating faster progression and more severe symptoms of OA in patients with higher MetS-IR. Similar to many studies, the ESR and CRP levels were elevated in all patients, but the inflammatory markers in group two were higher than those in group one, indicating that OA patients are in a chronic low-grade systemic inflammatory state, and patients with higher MetS-IR have more severe inflammation [29, 30]. This low-grade inflammation to some extent contributes to the occurrence and progression of OA. Furthermore, this low-level inflammation persists postoperatively and affects the outcomes of TKA. This is consistent with a study by Jörg Lützner et al., which found that patients with an increased inflammatory response have poorer functional outcomes[31]. In the imaging evaluation, the JLCA is considered to reflect medial compartment narrowing due to cartilage wear and laxity of the knee ligaments. VAN Raajj et al stated that JLCA reflects the narrowing of the medial compartment due to cartilage wear[32], while Lee et al. argued that JLCA reflects the laxity of the knee joint ligaments[33]. MAD represents the absolute difference from the neutral mechanical axis of the lower limb. An increase in MAD increases the force and contact pressure transmitted to the medial compartment. As MAD and the mechanical axis angle of the femur-tibia increase, the contact force in the medial or lateral compartment significantly increases with increasing deformity. This may lead to knee pain, further deformity, and degenerative joint disease in the medial compartment, ultimately affecting mobility and reducing quality of life [34]. These phenomena may be attributed to disruption of the knee joint environment caused by metabolic disturbances and abnormal cell function, which may contribute to the lower preoperative OKS in group two and its association with lower postoperative knee joint OKS.
We observed that patients in group two had poorer preoperative OKS scores, and other authors have also reported similar results, attributing these lower scores to various factors related to metabolic disturbances [35, 36]. Our study further confirms that this influence persists after surgery. Significant improvements in OKS occur between the preoperative baseline and all postoperative time points, following a pattern similar to what has been reported. The greatest improvement occurs at 12 months postoperatively, with the most rapid improvement observed at 3 months [37, 38]. Patients in group two consistently had lower OKS scores than those in group one within the first year, with statistically significant differences at 3 months and 12 months. As pain relief and functional recovery are considered key goals of TKA, we further analyzed the OKS-FCS and OKS-PCS. We found that the differences between the two groups in terms of function and pain mainly manifested in difficulties with transportation, descending stairs, nocturnal pain, and walking pain. Difficulty with transportation is often attributed to impaired postural control, usually caused by compromised proprioceptive abilities, pain, and decreased quadriceps strength. Difficulty descending stairs is usually due to instability in knee flexion [39, 40]. These postoperative functional differences may be attributed to continued causes of preoperative mechanical alignment deformity. Pain-related issues are believed to be associated with the persistence of systemic low-grade inflammation in patients, which is confirmed by the inflammatory markers we assessed at one month and three months postoperatively. These findings indicate that patients with higher MetS-IR have relatively poorer postoperative recovery and may require targeted interventions after surgery. However, we also found that the proportion and degree of OKS improvement in group two were higher than those in group one, suggesting that patients with higher MetS-IR benefit more from TKA and experience an improvement in quality of life.
Our study has several strengths. First, all surgeries were performed by the same experienced surgeon, minimizing the variability in surgical technique. Additionally, standardized enhanced recovery protocols were implemented for all patients during the perioperative period. However, there are also limitations to our study. Despite the prospective data collection, the design of our study is essentially retrospective, which may introduce biases. Second, we only assessed MetS-related risk factors that may influence the development of knee OA, but there may be other factors that need to be adjusted for in assessing the development of OA. Our study population consisted mainly of females of Asian ethnicity. While this sample represents our patient population demographics, this should be considered when interpreting our study results. Additionally, there may be a ceiling effect in OKS, which could influence the corresponding outcomes.