The IA-HA is used in patients with primary osteoarthritis as a concept of viscosupplementation to enhance lubrication and viscoelasticity in the knee joint. Various types of HA agents are available worldwide for KOA treatment, with varying molecular weights, HA concentration, injection volume, duration of treatment courses, and number of injections per course [11]. Recent research has indicated that high molecular weight (HMW) HA has higher affinity compared to low molecular weight (LHW) HA [10]. Furthermore, cross-linked HMW HA agents have been introduced to prolong the intra-articular residence time of HMW HA [13]. Consequently, the efficacy of HA agents can vary significantly among different formulations. The IA-HA not only enhances joint lubrication but also reduces inflammation in KOA by binding to CD44 receptors, lowering interleukin-1B expression, and decreasing matrix metalloproteinase (MMP) production, which helps protect cartilage from degradation.
Similarly, previous cohort studies demonstrated that IA-HA treatment delays the need for TKA in KOA. In a study analyzing the time to TKA in 744,734 patients with KOA using an administrative claims database, the TKA-free survival rates for the IA-HA treatment group were 85.8 and 70% at one and two years, respectively, which were higher than the rates of 74.1 and 63.7% at one and two years, respectively, for the non-IA-HA group [16]. Another study analyzing patients who underwent TKA after a diagnosis of KOA, with a total of 182,022 patients, demonstrated an average delay of 332 days. Specifically, while the non-IA-HA group exhibited a mean time to TKA of 270 days, this duration extended to 602 days for those in the IA-HA group. Furthermore, the delay effect was more pronounced with an increased number of HA treatment cycles [17]. Recent systematic reviews also reported a delay effect to TKA of approximately 9.8 months with IA-HA [19]. The present study revealed that the mean time to TKA after KOA diagnosis was 7.4 and 6.3 years in the HA group and non-IA-HA groups, respectively, suggesting that patients receiving HA treatment experienced an approximate 1-year delay until TKA compared to those without HA treatment. When comparing the time to TKA according to HA agent type, the single injection regimen group showed a longer time to TKA of 7.7 years, while the multiple injection regimen group and the non-IA-HA group had times to TKA of 7.3 and 6.3 years, respectively. The interaction analysis of IA-HA and CS injection showed that TKA risk in the single injection regimen was significantly lower than in the multiple regimen and non-IA-HA groups, regardless of concurrent CS injection.
Regarding adverse events, the overall incidence of injection-related complications, such as pain, warmth, redness, and swelling, is 3–6%. Acute septic arthritis is one of the most concerning and potentially fatal complications associated with IA-HA injections, with incidence rates ranging from 0.001–0.072% [20]. In this study, the overall incidence of adverse events in the total HA administration without CS group was 6.7%, which did not significantly differ from previously reported incidences. The incidence rate of arthroscopy for suspected infection was 0%, but it increased to 0.01 and 0.04% in cases where CS in combination with IA-HA injection or CS was administered alone, respectively. Furthermore, the incidence of infection tended to increase with an increasing number of HA administrations. These findings suggest that multiple HA injection agents increase the infection risk compared to crosslinked-single HA agents. Additionally, the group receiving combined CS injections had a higher risk of infection compared to the group without CS.
One of the strengths of our study was the use of a large nationwide health insurance claims database, which enabled analysis of a large sample of patients with KOA. This large sample size improved the generalizability of our results, especially for the Asian population, and allowed us to control for a large number of covariates that could potentially impact TKA risk. With strict reimbursement guidelines for IA-HA injections for patients with KOA, the results might reflect the clinical practice of IA-HA injection in Korea. Our study also showed that the use of IA-HA injections was associated with a lower HR of TKA even after controlling for various medical histories. Furthermore, the current study provides valuable information regarding the use of IA-HA injections in delaying TKA in the Asian population.
The efficacy of IA-HA can be determined in several ways including pain relief, delaying surgery, reduction in medication use, earlier return to work, and improved quality of life. Delaying TKA is considered the most stringent and practical indicator to evaluate patient outcomes and cost-effectiveness for policymakers. Previous studies, including the current study, have consistently reported a delay effect of approximately one year, and the results are predominantly based on patients who underwent TKA [16, 17]. Therefore, the actual delay effect is expected to be even greater than reported. These findings support the use of IA-HA injections as a viable alternative for managing knee osteoarthritis, especially in patients who are not suitable for TKA or prefer conservative treatment. The results of this study highlight the potential benefits of IA-HA injections in improving the quality of life for patients with knee osteoarthritis. Furthermore, this study emphasizes the importance of selecting the optimal HA product to maximize the likelihood of achieving optimal outcomes for patients with KOA.
However, our study has several limitations. This was an observational study; therefore, we could not establish a causal relationship between IA-HA injections and TKA risk. Moreover, the use of claims data might not reflect unmeasured confounders, such as BMI, activity level, and radiographic severity of KOA. These factors could potentially confound the association between IA-HA injections and TKA risk. Additionally, this study focused on individuals who underwent TKA during the study period, leading to right-truncated survival data. Excluding patients who did not undergo TKA may have resulted in biased estimations of the association between the initiating event (KOA diagnosis) and the event of interest (TKA) [21]. Inverse probability weighting and expanding the study population to include both individuals who underwent TKA and those who did not may assist in better understanding of the association between KOA diagnosis and TKA [22].