The present study aims to determine whether hypothyroidism conferred an increased risk of complications in patients following THA. According to our results, hypothyroidism may not be a risk factor for increased short-term complication rates in patients receiving THA, and a paucity of studies have focused on short-term complications after surgery. Patients receiving THA did not show a significant interaction between complications and hypothyroidism. Nevertheless, the present study revealed that hypothyroidism significantly increased hospitalization costs. An explanation for this finding may attribute to additional perioperative managements and laboratory tests for hypothyroidism.
In agreement with Tan et al [15], 12.97% of patients who received THA had hypothyroidism before surgery. However, in this study, the occurrence of perioperative complications in patients with hypothyroidism undergoing THA is lower than that in patients with hypothyroidism receiving other joint replacements [15, 23]. This may be related to well-established perioperative management, with reports that reversing hypothyroidism before joint arthroplasty did not increase surgical risk [25]. Whether hypothyroid patients receiving THA received appropriate hypothyroidism preoperatively was not identified in this study. But compared to the general population, patients with hypothyroidism are more likely to undergo orthopedic surgery, likely because thyroid hormone deficiency can cause degenerative diseases [26, 27].
We found that hypothyroidism was associated with acute postoperative anemia, while postoperative anemia has been reported as a common complication in patients with hypothyroidism undergoing joint replacement surgery [15, 23]. Therefore, some studies aimed to reduce the incidence of perioperative complications in patients with hypothyroidism by adjusting thyroid hormone levels [28]. Clinical studies also indicated that hypothyroidism led to an elevated risk of infection and delayed wound healing [15]. In this regard, preoperative management should be considered to suppress metabolic abnormalities caused by hypothyroidism. However, studies have found that overtreatment of hypothyroidism with levothyroxine can be a negative factor in fracture risk and bone metabolism, and no study has reported whether the correct balance of hypothyroidism can reverse the negative effects on bone [29, 30].
Anemia is a common complication of hypothyroidism and may be associated with bone marrow stimulation suppression, decreased erythropoietin production, nutritional deficiencies, and coexisting disorders [31], suggesting a complex mechanism for the development of postoperative anemia due to hypothyroidism. Studies have shown that hypothyroidism makes the hemostatic system in a hyperfibrinolytic and hypocoagulable state [32, 33]. Furthermore, clinical trials have verified that postoperative Hemoglobin(Hb) decline and total perioperative bleeding are higher in hypothyroid patients than in non-hypothyroid patients [34]. Hypothyroidism leads to disruption of coagulation homeostasis in patients, and abnormal bleeding volume as well as delayed wound healing may be the main cause of acute anemia [15, 33, 34].
Anemia is a common complication after THA that increases the incidence of adverse clinical outcomes [35, 36], thus surgeons should improve the patient's hormone levels or transfuse blood preoperatively. Some clinical trials have shown that preoperative adjustment of serum TSH and T4 levels in hypothyroid patients resulted in a non-significant difference in transfusion rates compared to controls, suggesting that perioperative blood management and anti-hyperthyroid treatment can mitigate the adverse consequences of bleeding [37]. Moreover, the application of tranexamic acid (TXA) significantly reduced the magnitude of postoperative Hb decline and the chance of patients requiring allogeneic blood transfusion [37–40]. As we all know, a lab test is an important indicator to diagnose anemia. Whereas, in recent years, there has been controversy over whether the laboratory examination of patients after THA is complete [41, 42]. Some studies have found that most laboratory tests do not affect postoperative management and the most common abnormalities are anemia and hypoproteinemia, which require intervention, while other abnormalities often do not require further treatment, suggesting the need for postoperative laboratory tests based on the patient's preoperative condition [41, 43, 44].
There are some limitations in the present study. As with other large databases, there may be coding discrepancies and data entry errors when performing retrospective analyses [45]. Moreover, this study may have underestimated the incidence of comorbidities and did not manually validate patients who did not develop comorbidities. Another limitation of the study was the lack of a clear length of time to distinguish between short-term and long-term complications, such as 30 and 90 days [45–47]. Nonetheless, the present study is that only short-term outcomes were evaluated, so the long-term effects of cup or stem loosening could not be well assessed.