This is a prospective double-blinded, randomized controlled trial diagnostic study conducted at a single center from June 2018 to December 2019. Patients who underwent total knee arthroplasty due to end-stage knee osteoarthritis were asked to volunteer to participate in this study. A prospective randomized study was conducted using a digital algometer to assess the pain sensitivity for the relationship between postoperative early-stage pain score and first-year functional scores in patients with or without using tourniquet who underwent primary TKA. Patients were randomized to with or without tourniquet groups; a random number generated by the research staff determined the group designation, independent of a senior surgeon. T All participants in this study gave their written informed consent. Patients with a neurological disorder, diagnosed with fibromyalgia, history of knee operation, valgus knee, greater than 30° flexion contracture that had undergone bilateral knee arthroplasty or revision knee arthroplasty, chronic analgesic users, and those with a psychiatric disease were excluded from this study.

Preoperative Procedure: All patients had anterior-posterior and lateral radiographs of the bilateral knees, taken with a standard full-length weight-bearing the patients in bipedal stance, the knees in maximal extension for anterior-posterior and 30-degree flexion for lateral radiographs pre and postoperatively. In all patients, range of motion and contractures of both knee joints were recorded. All patient's educational level was also assessed. The pain threshold (PT) was evaluated using an analog algometer (Figure 1). The pain sensitivity was measured on the forearm using two mechanical pain stressors, which indicate which of an ascending sensory stimulus is first perceived as painful. This device is a force gauge that is used to apply an increasing amount of force to the skin through a 1 cm2 surface area until the pain threshold is achieved. This algometer stimulates pain, described as dull pressure at the pain threshold; the reliability and validity of this device have been reported. The pain sensitivity of all measurement patients was taken on the day before the surgery by the same author, and these values were blinded from another author who recorded the repetitive postoperative VAS and knee scores.

Operation Procedure: All patients were operated on in a single-center and experiences in arthroplasty practice. All the patients were operated on standard spinal anesthesia. All patients underwent cruciate-retaining Genesis II knee arthroplasty (Smith and Nephew, Memphis, TN, USA) with a midline incision and medial parapatellar approach with a fixed bearing design. Patella resurfacing was not performed, while patellar denervation was performed in all patients. Bone-cement (40 g) was used with a fourth-generation cementing device.

A pneumatic tourniquet was used before surgery at the proximal thigh and inflated before the skin incision until skin closure in group 1 and no used in group 2. The tourniquet was inflated to either 275 or 325 mmHg, depending on the patient's systolic blood pressure. Peri-operative tranexamic (TXA) acid was administrated intravenously with 20 mg/kg 30 min before surgery. Periarticular injection was not used for pain control in either group. An adductor canal block or epidural analgesia was not applied. Intra-articular drainage was used in every patient, which was removed after 24 h postoperatively.

Postoperative Management and Analgesic Procedure: On the day of surgery, intravenous paracetamol 1 g was given at 8-h intervals, and intramuscular diclofenac sodium 75 mg and intravenous tramadol 100 mg in 100 mL normal saline were given at 12-h intervals. This analgesic procedure was continued at the time of discharge, and all patients were discharged on the third day of surgery. Physical therapy was started on postoperative day 1 in all patients. The functional assessments and range-of-motion were measured during routine physical therapy sessions.

Postoperative Assessment of Pain and Function: VAS score assessment was done at 24 h (rest), 36 h (post-physical therapy), and 48 h (rest) postoperatively. The Knee Society Clinical Scoring System (KSS) was also used for evaluation of functional outcomes, which is a condition-specific validated questionnaire widely used to evaluate the functional capabilities of the knee joint before and after total knee arthroplasty. The KSS was done in the first year postoperatively. The KSS consists of two parts. One part is the knee score (KSS1), which includes pain (maximum 50 points), stability, total range of flexion, and other items (varus, valgus, extension delay, and flexion contracture). The other part (KSS2) is the function score, which has two components, walking capacity and stair-climbing ability and deductions done if the patient using any assistive devices.