The occurrence of VTE events after TKA can lead to serious outcomes, including high mortality, prolonged hospitalization and increased hospitalization costs, etc., and the revision of postoperative prosthesis is more a psychological and economic burden to patients. Therefore, preventing the occurrence of VTE events and prosthesis revision remain important tasks for quality improvement programs after TKA. But current literature is still conflicting about the effect of obesity on symptomatic VTE and prosthetic revision after TKA, and part of the literature is affected by small sample size or the rarity of VTE events. This study therefore sought to address this major question: whether BMI is associated with an increased risk of VTE events and prosthetic revision after TKA.
With regard to the risk of VTE after TKA in different BMI populations, Mantilla et al. conducted a retrospective case-control study to determine the clinically related risk factors of DVT and PE after TKA, they found that obesity defined as BMI > 30 kg/m2 imparted a 3.4 times elevated risk of VTE compared with controls. In addition, White et al.concluded that BMI ≥ 25 kg/m2 was associated with subsequent hospitalization for thromboembolism when evaluating VTE risk factors for re-hospitalization after TKA. However, Friedman et al.found that morbid obesity is only associated with an increase in early postoperative complications, not with an increased risk of VTE or bleeding. Cafri et al.conducted a study followed-up for 10 to 18 years, the results showed that there was no statistically significant difference in DVT between obese and non-obese patients after TKA. Tang et al.showed that the total incidence of VTE in different BMI groups was statistically similar. However, the sample size in some of the above studies is relatively small and may not be sufficient to detect differences between groups. The advantages of our study are large sample size, long follow-up time, and detailed description of the incidence of DVT, ultrasonographic features and thrombus distribution in different BMI groups. Rigorous statistical analysis of our data shows that there is no correlation between the increase in BMI and the increased risk of VTE events after TKA. This is consistent with the results of Sloan et al..Sloan and colleagues reviewed the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database, which included 218997 patients with initial TKA and 15286 patients with revised TKA, and concluded that patient classification as overweight or obese is associated with increased risk of development of PE but not DVT after TKA. Xu et al. conducted a nested case-control study based on a large data set of 15326 patients. The results showed that BMI was not a risk factor for DVT after TKA. This report also confirms our point of view.
In this study, the incidence of VTE events after TKA was 0.89%, which was lower than that reported in previous studies[24, 25]. However, similar to the results found in the Asian population, Tay et al.reported a low prevalence of VTE in their study population (0.67%); A cohort study based on the Taiwan population found that the total incidence of VTE after TKA was 0.64%. The difference in incidence may be due to differences in race, number of subjects, follow-up time and use of anticoagulants. In our study, the accuracy of lower limb vascular ultrasound in the diagnosis of DVT may be lower than that of lower limb deep venography, but it has the advantages of non-invasive and convenient. In addition, lower limb vascular ultrasound can also improve a lot of thrombus-related information for us, including thrombus location, thrombus echo and thrombus length, so that we can carry out statistical analysis. Our data suggest that deep venous thrombosis occurs mainly in the calf intermuscular vein (56/64), and the echo of thrombus is mainly hypoechoic. No statistical differences were observed in thrombus length, thrombus echo and the number of blood vessels involved among different BMI groups, but a larger sample size is needed for more in-depth study in the future to verify our conclusions.
Regarding the risk of prosthetic revision after TKA in different BMI populations, it has been a hot spot of clinical research and is also widely debated. Previous studieshave shown that prosthetic revision rates are similar in patients with a BMI < 35 kg/m2, but are significantly increased at a BMI ≥ 35 kg/m2. Electricwala et al.suggested that an elevated BMI is a risk factor for early referral to a tertiary care center for revision TKA. However, some studies[30–32]reported the opposite conclusion. Ayyar and colleaguesdid not observe a difference in the number of revisions between different BMI levels, and they suggested that surgery provides a similar degree of benefit regardless of the patient's BMI level. Gaillard et al.investigated the long-term survival of the prosthesis using Kaplan-Meier analysis and showed that obesity had no effect on the medium-term prosthesis survival. The present study confirms the latter statement. Our study showed that no statistical difference was found in the risk of prosthetic revision between different BMI groups, and we believe that a higher BMI should not be considered a risk factor for revision for mechanical purposes.
We also found no significant difference in the 10-year survival rates of prosthetic in different BMI groups, and although patients with a BMI ≥ 35 kg/m2 had relatively poor survival rates, the differences were not statistically significant, and our findings are supported by a recent study. On the other hand, the results shown in our data are encouraging, with 10-year survival rates of 98% or higher for all BMI groups. Interestingly, patients in the overweight and obese class I had the highest 10-year survival and those in the normal BMI range had the worst survival, although this was not significant. This is counter-intuitive, as most people tend to associate healthy weight range with increased prosthetic survival. Some scholarssuggested this may be due to the mobile bearing of the knee, which minimizes polyethylene wear and decreases sheer stress at the bone implant interface, minimizing the risk of loosening, but further pilot studies are needed to verify it. In addition, descriptive statistics were also performed for the reasons for revision in our study, which showed that infection was the leading cause of revision (26/46), followed by aseptic loosening (9/46), which was consistent with the results of several previous studies reporting the causes of prosthetic revision[29, 34, 35]. Bozic et al. reported that the most common reasons for revision TKA were infection (25.2%) and implant loosening (16.1%). Hossain et al.reported that common causes of revision TKA included infection (32.7%), aseptic loosening (14.9%), and polyethylene wear (12.3%). In summary, periprosthetic infection is still the most common cause of revision and re-revision TKA.
Our research also has some limitations. First, this is a retrospective study conducted in a single institution. This may limit the external effectiveness of our study, and multicenter studies are needed to further verify our conclusions; Second, some patients may have undergone revision surgery in another hospital without reporting this information to us. However, as far as we know, this situation is rare. Third, the study could not comment on BMI-wide extremes. There were not many patients in our cohort with class III obesity (BMI ≥ 35 kg/m2), only 34 patients. Finally, some patients have a short follow-up period, which may be considered a limitation for patients with shorter follow-up time, considering that aseptic prosthesis loosening may occur during long-term follow-up. Therefore, in the context of these restrictions, our results must be interpreted carefully.