Patients
We collected the clinical data of 21 patients with knee osteoarthritis who underwent primary unilateral BOWHTO at the Department of Orthopaedics in Xuanwu Hospital of Capital Medical University from July 2019 to February 2020. Among them, eight were male and 13 were female with an average age of 50 ± 14 years. All the patients were free of hematological diseases that could severely affect blood coagulation.
Variables such as gender, age, height, weight, pre- and post-operative hematocrit (HCT), pre- and post-operative hemoglobin (HB), intra-operative blood loss, post-operative drain-blood volume, allogeneic blood volume, and reinfusion volume of drained blood were recorded.
BOWHTO procedures
The operations were performed under intraspinal anesthesia with tourniquet pressure routinely set at 260 mmHg. The arthroscopy exploration was performed before the operation. The tourniquet was not used at the time of exploration; it was pressured before repairing meniscus, removing pleated or enlarged synovium, and repairing injury of articular cartilage surface when necessary. The tourniquet was released after operation and the joint cavity was probed again. The incision was closed after flushing the joint cavity.
BOWHTO was performed by a single surgeon. After the tourniquet was inflated, an anteromedial skin incision was made along the proximal tibia and carried through the sartorial fascia to the pes tendons. Sequentially, two Kirschner wires were inserted, anteriorly and posteriorly at the osteotomy level respectively, and were directed to the safe zone between the level of the tip of the fibular head and the circumference line of the fibula head under fluoroscopic guidance. The osteotomy was performed beneath the Kirschner wires using an oscillating saw until the osteotomy line extended within 10 mm medial to the lateral cortex of the tibia. Then the surgeon performed a biplanar osteotomy extending the osteotomy beneath the tibial tuberosity. Thin osteotomes were used to open the osteotomy and fixed with a Tomofix plate (Synthes, Oberdorf, Switzerland). The gap in the osteotomy site was filled with gelatin sponge when the gap was less than 2 cm. Tricortical autologous ilium graft filled the site; the gap was greater than or equal to 2 cm.
The tourniquet was released and hemostasis was completed before the incision was closed. The amount of intraoperative blood loss was recorded. Hemostatic and analgesic drugs containing tranexamic acid were locally injected together (tranexamic 0.5 g, parecoxib sodium 40 mg, ropivacaine hydrochloride 200 mg, oxycodone 10 mg, adrenaline 0.15 mg). A drainage tube was indwelled in the osteotomy gap for continuous negative pressure suction. The drainage tube was not routinely clamped.
After the operation, the wound was pressurized and bandaged, the bandaging was removed 24 h postoperatively and the drainage tube was removed 48 h postoperatively. The drainage volume and the total removal time were recorded. Functional exercises on the ankle and foot of the affected limb were initiated 2 h postoperatively. Six hours after the operation, weight-bearing exercises were performed, and an intermittent inflatable pressurization device was applied to lower extremities to assist in the prevention of deep venous thrombosis. A routine blood test was performed on the 1st, 3rd, and 5th day after surgery, and hemoglobin and HCT were recorded. If the patient still had signs of severe anemia within 1 week after the operation, a routine blood test was conducted again. Three days post-operation, vascular ultrasound was performed to assess signs of venous thrombosis of the lower limb. If lower limb vein thrombosis was found in the vascular ultrasound, then low molecular weight heparin (LMWH) anticoagulation therapy was given.
Calculation of blood loss
The patient’s blood volume (PBV) was calculated by the formula:
$$ \mathrm{PBV}=k1\times \mathrm{height}\ \left({\mathrm{m}}^3\right)+k2\times \mathrm{weight}\ \left(\mathrm{kg}\right)+k3 $$
where
k1 = 0.3669,
k2 = 0.03219,
k3 = 0.6041 for males; and
k1 = 0.3561,
k2 = 0.03308,
k3 = 0.1833 for females. The total red blood cell volume was calculated as the hematocrit value multiplied by PBV. Any change in red cell volume can therefore be calculated from the change in hematocrit. The lowest value of HCT detected within 5 days after the operation was used as HCT
postop in the following formula to calculate total blood loss (TBL).
$$ \mathrm{TBL}=\mathrm{PBV}\times \left({\mathrm{HCT}}_{\mathrm{preop}}-{\mathrm{HCT}}_{\mathrm{postop}}\right)/{\mathrm{HCT}}_{\mathrm{preop}}+\mathrm{amount}\ \mathrm{of}\ \mathrm{blood}\ \mathrm{transfusion}; $$
$$ \mathrm{HBL}=\mathrm{TBL}-\mathrm{Postoperative}\ \mathrm{drainage}-\mathrm{Amount}\ \mathrm{of}\ \mathrm{intraoperative}\ \mathrm{blood}\ \mathrm{loss}; $$
Finally, the proportion of HBL to the patient’s blood volume was calculated as H/P = HBL/PBV
Statistical analysis
Data analysis was performed using SPSS 23.0. Descriptive statistics were shown as mean ± standard deviation (SD) or number of cases and percentages when appropriate. Student’s t test for independent samples was used to compare TBL, HBL, and H/P between male and female patients. Correlational analyses were used to analyze the correlation between correction angle and TBL, correction angle and HBL, and correction angle and H/P. The correlation coefficient is expressed as |r|. The level of statistical significance was set at P < 0.05.