Sixty-eight AS patients who underwent unilateral THAs between 2014 and 2018 in our department were retrospectively studied. The collected data included gender, age, height, weight, and disease duration. The exclusion criteria were as follows: other rheumatic diseases; active infection; tumors; and hematologic diseases, such as blood coagulation disorders, thrombocytopenia, and other hemorrhagic disorders. Patients with long-term use of anti-coagulants were also excluded.
Forty-nine patients (6 females and 33 males) were eligible for this study. The demographic characteristic are shown in Table 1. In 10 cases, biologics were used for patients with intolerable back pain until remission before THA (20). No statistically significant differences existed between the stable and active disease groups with respect to age, gender, BMI, disease duration and biologics usage.
Indications of THA among AS patients are refractory pain or disability and radiographic evidence of structural damage in the hips, regardless of age. All of the operations were performed using a standardized method by the same experienced team. Antibiotics were routinely administered intra-operatively and 24 h post-operatively. The hemostatic agents included hemocoagulase agkistrodon (HCA) and tranexamic acid (TXA). Combined intravenous and topical TXA were used during THA. Based on the guideline, combined venous thrombosis embolism (VTE) prophylaxis with mechanical and pharmacological methods were performed during hospitalization. Mechanical VTE prophylaxis was commenced at the same day after surgery. Anticoagulation drug was added at the first day after surgery when the patient’s risk of bleeding had been established as low. Extended-duration anticoagulation drug was used for up to 35 days following THA.
The following data were collected from patients: pre-operative indices, including C-reactive protein (CRP) levels, erythrocyte sedimentation rate (ESR), hemoglobin (Hb) concentration, hematocrit (Hct), platelet (Plt) count, and albumin (ALB) concentration; coagulation test indices (prothrombin time [PT], prothrombin activity [PT%], prothrombin time international ratio [PT-INR], activated partial thromboplastin time [APTT], thrombin time [TT], and fibrinogen concentration (Fbgc); post-operative Hct concentration; imaging feature; operative time; allogenic transfusion; autologous transfusion; and the strategy of hemostatic agent use. The preoperative plain radiograph of pelvis were collected to assess the bone quality of hip. The diagnosis of osteoporosis was determined by the classic grading of Singh’ index(21).
The transfusion triggers were based on the British guidelines(22) and clinical judgement. The traditional view on transfusion triggers was a Hb < 70 g/L and a hematocrit < 25%. A Hb < 80 g/L was a transfusion trigger for patients with cardiovascular and respiratory problems or patients >65 years of age. Acute anemia, a drop in blood pressure (< 90/60 mmHg), dizziness, pale lips, weakness, and shortness of breath were also regarded as transfusion triggers.
Calculation of Blood Loss
The intra-operative blood loss was estimated by weighing sterile cotton gauze pads and mostly by analysis of aspirated blood volume. However, in consideration the significant difference between estimated and calculated blood loss, the latter one was the main evaluation indicator(23). Peri-operative blood loss was calcultaed by means of the Orthopedic Surgery Transfusion Hemoglobin European Overview (OSTHEO) formula(23, 24), as follows: total RBC loss (mL) = [uncompensated RBC loss (mL) + compensated RBC loss (mL)] / 0.35，uncompensated RBC loss (mL) = estimated blood volume (EBV)× (pre-operative Hct levels – post-operative Hct levels); EBV = (0.0235 × height (cm)^0.42246 × weight (kg)^0.51456) × k, where k = 2430 for women and 2530 for men; compensated RBC loss (mL) = allogenic erythrocyte units ×150 + autologous transfusion volume × 0.3.
Post-operative Hct levels were collected from the laboratory test that was carried out at 6 am one day after surgery. Only transfusions that were executed before phlebotomy for laboratory testing were included in the study.
Evaluation of Disease Activity
AS disease activity was evaluated by the Ankylosing Spondylitis Disease Activity Score-CRP (ASDAS-CRP), a highly discriminatory index recommended by The Assessment in Ankylosing Spondylitis(25), as follows: ASDAS-CRP= 0.121 × back pain + 0.058 × duration morning stiffness + 0.110 × patient global + 0.073 × peripheral pain/swelling + 0.579 × Ln(CRP+1). The following was suggested regarding ASDAS-CRP classification: ASDAS<1.3, stable; 1.3≤ASDAS<2.1, moderately active; 2.1≤ASDAS≤3.5, highly active; and ASDAS>3.5, very highly active. In the present study, ASDAS<1.3 was defined as stable disease and ASDAS≥1.3 was defined as active disease.
According to the classification of disease activity as we defined, more patients were assigned to the active group. Seventeen patients (35%) were in the stable group and 32 (65%) were in the active group. The average ASDAS in the stable group was 0.97 and 2.55 in the active group (P<0.001)
Five cases had post-operative complications during the 1st year after THA, and they were all in active disease group. 3 patients suffered periprosthetic fracture, caused by accidentally fell down. The other 2 cases had dislocation. Other complications such as implant loosening, prosthetic joint infection, and deep venous thrombosis were not found.
All statistical analyses were performed using SPSS for Windows (version 23.0). Continuous data were presented as the mean ± standard deviation (SD). Comparisons of quantitative variables were performed using an unpaired Student t-test. In the case of heteroscedasticity, the non-parametric rank sum test was used. A chi-square test was executed for comparisons of qualitative variables. Differences at a level of P<0.05 were identified statistically significant.