Study design
This was a double-blinded randomized controlled study that was performed at Siriraj Hospital, Mahidol University from July 2020 to Jan 2023, approved by Siriraj Institutional Review Board Certificate of Approval COA no. Si 544/2020 and was registered in the Thai Clinical Trials Registry (TCTR) ID: TCTR20200706001 on 06/07/2020. The inclusion criteria were knee osteoarthritis patients who underwent unilateral primary TKA and who were 45 years old or older and gave their informed consent to participate. The exclusion criteria were patients who had cold allergy/cold intolerance, allergy to any medication used in the protocol (tranexamic acid, ketorolac, levobupivacaine, morphine, parecoxib, eperisone, acetaminophen, codeine, pregabalin, marcaine, heavy marcaine, dexamethasone), had an eGFR lower than 50 mL/min/1.73 m2, received anesthesia other than a spinal block with an adductor canal block, psychiatric disorder, cognitive impairment, bleeding disorder, unable to withhold antiplatelet/anticoagulant before surgery except low dose aspirin, needed an additional procedure other than the standard cruciate-retaining total knee arthroplasty, and/or refused to give informed consent or rejected participation. The patients were randomized into 2 groups by computer-generated mixed block-sized randomization (block sizes = 4, 6, 8). The sequence of randomization was concealed with an opaque sealed envelope that was opened intraoperatively. The patients and the assessors were blinded. The CONSORT flow diagram for patient enrollment in this study was shown in Fig. 1. The sample size was calculated based on Li et al.’s study with an alpha set at 0.05 and a beta set at 0.05
Surgical technique and intervention
In total, 70 patients were included in the study. Before surgery, the patient’s demographic data were collected, including age, sex, BMI, baseline pain score (numerical rating scale, NRS 0–10), baseline opioid consumption, and hemoglobin and hematocrit levels. All the patients received antibiotics prophylaxis and tranexamic acid 750 mg intravenous 30 minutes before undergoing the operation. A tourniquet was applied and the pressure was set at 300 mmHg. Unilateral primary TKA was performed by a single adult reconstructive orthopedic surgeon under spinal plus an adductor canal block in every case. The patients were kept warm during the operation with a heater. After skin preparation and draping in a sterile fashion, a midline incision was done with a medial parapatellar approach. A P.F.C. sigma cruciate-retaining prosthesis (Johnson DePuy Synthes, USA) was used for all the patients. After bone cut and gap balancing were done, all the patients received periarticular injections with a similar regimen cocktail (ketorolac 30 mg + levobupivacaine 100 mg diluted with NSS 20 mL) and the same amount at each location (infrapatellar fat pad, medial and lateral gutter periosteum, medial and lateral collateral ligament, posterior capsule, and quadriceps muscle); then the opaque sealed envelope that contained the randomized sequence was opened. The patients were divided into 2 groups: the cold solution irrigation group and the room temperature solution irrigation group. The cold solution irrigation group was irrigated with a mixture of NSS 1000 mL + 10% povidone–iodine 250 mL, with both stored at 2–8°C. The room temperature solution irrigation group was irrigated with a mixture of NSS 1000 mL + 10% povidone–iodine 250 mL, with both stored at room temperature.
The irrigating solutions were stored in a nearby temperature-controlled refrigerator/shelf and transported to the operating room just before the irrigation step. After mixing the solution in the operative field, 50 mL of the mixed solution was brought out to measure its actual temperature using a digital thermometer (Extech 39240, Extech Instruments, USA). The irrigation was divided into two periods: before and after the cemented components implantation. The mixed solution was soaked intraarticularly during wound closure and was suctioned before the closure was done. A vacuum drain was placed through a superolateral aspect of the patella. The total irrigation time was recorded. The perioperative body temperature of all the patients was recorded in both the waiting room and recovery room. The vacuum drain was clamped for 3 hours, then released and removed at 48 hours postoperatively. All the patients received postoperative analgesics around the clock with the same regimen, except for intravenous opioids for breakthrough pain. NRS 0–10 was recorded every 4 hours until 72 hours postoperatively. Mechanical DVT prophylaxis was applied to all the patients. Two cold packs that were stored at 0°C for at least 2 hours were applied for 20 minutes every 2 hours until 72 hours postoperatively. Rehabilitation was initiated on postoperative day 1 with the same program for all the patients. Hemoglobin and hematocrit levels were routinely taken on postoperative day 1 and additionally on day 3 for calculating the estimated blood loss (Mercuriali formula) and hemoglobin difference compared to baseline. All the patients were discharged after achieving knee flexion of at least 90 degrees, NRS ≤ 3, and once they were able to perform basic ADL with a gait aid. All complications during the admission period were recorded.
Estimated blood loss calculation
The Nadler equation was used to calculate blood volume for inputting in the Mercuriali formula for males and females:
Male; Blood volume = (0.3669 × H3) + (0.03219 × W) + 0.6041
Female; Blood volume = (0.3561 × H3) + (0.03308 × W) + 0.1833
where H is the patient’s height in meters, and W is the patient’s weight in kilograms.
The estimated RBC loss was calculated via the Mercuriali formula using the blood volume figures calculated above:
Estimated RBC loss = [Blood volume × (Preop Hct - Postop Hct day3)] +
the volume of transfused RBC (Blood volume in milliliters, Hct in decimal, the volume of transfused RBC in milliliters of RBC)
The estimated RBC loss was then converted into the estimated blood loss in milliliters by dividing by the mean Hct (mean Hct = (Preop Hct + Postop Hct day3) ÷ 2).
Statistical analysis
We analyzed descriptive statistics with the mean ± SD for continuous variables and percentage for categorical variables. The independent t-test/Mann–Whitney U-test and chi-square test/Fischer's exact test were used to compare variables between the 2 groups. Inferential statistics, for the primary outcome (NRS) between the 2 groups, were analyzed with an independent t-test at each time point. The secondary outcomes (total opioid consumption, estimated blood loss, hemoglobin difference, and total drain content) were analyzed with an independent t-test. The statistical analyses were performed using SPSS Statistics for Windows, version 18.0 software (SPSS, Inc., Chicago, IL, USA). Statistical significance was defined as a p-value less than 0.05.