Study design and patients
The prospective case control single center study was conducted at Affiliated Hospital of Xuzhou Medical University, approval by the Ethics Committee of the Affiliated Hospital of Xuzhou Medical University. Informed consent was obtained from all patients.
This study was conducted in compliance with the principles of the Declaration of Helsinki. We analyzed 116 patients with medial knee osteoarthritis who underwent UKA in the period between April 2020 and April 2021 to analyze the effect of bone wax in reducing blood loss following UKA. Patients were randomly subdivided into two groups: bone wax applied group (group A) and controll group without using bone wax (group B). There were 58 patients in both groups. All patients had knee pain, which did not improve after conservative treatment for more than 3 months. Physical examination and radiographs were performed to confrm the diagnosis of medial osteoarthritis of knee. Magnetic resonance imaging (MRI) was also prescribed to assess the degree of cartilage degeneration in lateral compartment and the integrity of cruciate ligament. Patients with serious liver, heart or renal disease, poorly controlled hypertension, coagulation dysfunction, bilateral UKA, or revision UKA were excluded .
Surgical and perioperative management
The cemented mobile Oxford medial UKA was used in all patients. The same standard surgical procedures were applied in both groups and the operations were performed by the same surgical team, specialized in knee arthroplasty. Tranexamic acid (1g) was administered intravenously 15 min preoperation. Tourniquet was applied in all patients. In the group A, after the implantation of the prosthesis, the bone wax was applied to the bone oozing site of osteotomy surfaces, nail holes and the opening of the femoral medullary cavity that were not covered by the prosthesis or cement. Bone wax was not applied in the group B.Drainage was not applied in both groups. Compression bandage and ice of the surgical site for 24 hours postoperation were applied.Low molecular-weight heparin was used 12 h after surgery.Patients were encouraged to start early weight-bearing on the second day with the help of a walker. Oral celecoxib (0.2g/d) was routinely applied postoperation.
Visible blood loss and total blood loss were evaluated. Visible blood loss was assessed by measuring the blood loss during operation and the increase in the weight of the dressings. 
Total blood loss was calculated with formula reported previously according to weight, height, and and the change of hematocrit [12, 13].Hb level of the patient preoperation and 3 days postoperation were recorded. Homologous blood transfusion was not performed unless the hemoglobin level<70 g/L or symptoms of anemia presented
Swelling of the knee
Swelling of the knee was assessed. Circumference 1 cm proximal to the base of the patella of the extended knee was measured with the patient in supine position to monitor articular effusion on 6h,12h,1d, 3d,6d postoperation 
Severe pain rate
Visual analog scale (VAS) score were used and the pain levels were divided into four categories to evaluate the pain, (0: no pain, 1-3: mild pain, 4-6: moderate pain, and 7-10: severe pain). The rate of severe pain was calculated in both groups.
To evaluate patient satisfaction, all patients were asked questions to determine their overall satisfaction with the pain and function of their operated knee at discharge. And the result was classified as five-level scale: “very satisfied”, “satisfied”, “neutral”, “dissatisfied”, or “very dissatisfied”.
The occurrence of other complications was also recorded. Both groups were monitored for wound healing, hemoarthrosis, infection, deep vein thrombosis (DVT), transfusion, and any other complications.
Measurement data such as blood loss, Hb level and circumference of knee were e expressed as (x ± s). Pain level and patient satisfaction are expressed as rate, and t-test and chi-square test are used for statistics. P<0.05 indicates statistical significant difference.Statistical tests were performed using SPSS version 19 for Windows.