BACKGROUND: Although total knee replacement (TKR) has been proven a very successful treatment modality for the end-stage knee osteoarthritis (OA) in obese patients, the rehabilitation period often is long and painful. Minimal invasive surgery (MIS) has gained much attention in TKR promising fast and less painful recovery. However, little is known about the effectiveness of the technique in the obese adult population.METHODS: One hundred consecutive patients with body mass index (BMI) > 30 kg/m(2) and tricompartmental knee OA were randomly assigned to undergo either standard TKR (50 patients) or MIS-TKR (50 patients). The patients were assessed clinically and radiologically before the procedure and at subsequent postoperative follow-up visits, until 2 years after the operation.RESULTS: Knee society function and pain scores were significantly higher in MIS group for 3 months following surgery. Patients after MIS had also lower levels of pain during hospitalization. Tourniquet time was on average 7 min longer during MIS-TKR (p = 0.03) but operative time was almost equal in both groups (p = 0.11). No statistical significant difference was found between groups regarding the amount of blood loss (p = 0.49) or incidence of allogeneic blood transfusion (p = 0.27). Active straight leg raising was achieved 2.2 days earlier, on average, after MIS-TKR (p < 0.001). No severe complications or residual coronal and sagittal imbalance were identified. Component alignment was in normal limits and similar in both groups. In MIS group, higher BMI did not have a negative predictive effect on knee pain and function.CONCLUSIONS: MIS is a reliable and safe option in obese patients undergoing TKR regardless the level of BMI. It is associated with improved early clinical outcome without sacrificing radiographic positioning of the implants.