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INTRODUCTION: Correct ligamentous balancing is an important determinant of the clinical outcome in total knee arthroplasty (TKA). Many surgeons prefer a tight rather than a lax knee during implantation of a TKA. The hypothesis in this study was that patients with a slightly laxer knee joint might perform better than patients with a tight knee joint after implantation of a TKA. PATIENTS AND METHODS: Twenty-two patients with bilateral knee arthroplasties were clinically and radiologically evaluated at a mean follow-up of 4.5 years, ranging from 2 to 7 years. There were 12 women and 10 men with an average age of 68.9 years (range 32-82 years) at the time of surgery. A modified HSS score (excluding laxity), varus and valgus stress X-rays in 30 degrees of knee flexion, and the subjective outcome of both knees were compared. A knee was considered tight when it opened less than 4 degrees and lax if it opened 4 degrees or more on stress X-ray. RESULTS: There was a trend towards improved range of motion and HSS score for the laxer knee joints. However, the difference did not achieve statistical significance. Eleven of the 22 patients considered one side subjectively better than the other side. In 10 out of these 11 TKA, the slacker knee joint was the preferred side ( p<0.05). CONCLUSIONS: As the present study compared bilateral knee joints after TKA, the same patient could act as a control group, and subtle subjective differences were revealed which are not quantifiable. The results showed that patients with a preferred side felt significantly more comfortable on the laxer side, indicating that during intraoperative ligamentous tensioning, some varus and valgus laxity at 20-30 degrees of flexion might be preferable to an over-tight knee joint. Further biomechanical and prospective investigations will be necessary to establish the correct soft-tissue tensioning.