Aims: To evaluate the clinical signiþcance of isolated femoral malrotation after otherwise well performed painful TKAñs. Methods: 11 painful TKAñs (5 female, 6 male, mean 61 years, range 41 to 73) with normal mechanical axis, patella tracking, stability in extension and no signs of infection or loosening were included in this prospective study. The knees were evaluated by routine clinical and radiographic examinations in combination with a standardized computer tomography (CT) to measure the rotation of the components, using the transepicondylar axis as a reference for the femur. Results: All patients had progressive persistent pain from the time of surgery which was resistant to conservative therapy. There were two groups according to the clinical symptoms: limited ßexion and medial pain at the proximal tibia (4) or ßexion > 90û with anterior knee pain during stairs descending or raising from a chair (7). Standard x-rays were normal but in the special CT all patients showed isolated internal malrotation of the femoral component mean 7û (2 to 10). 9 patients required revision surgery with correction of the malrotated femoral component. The two patients who did not want revision surgery had only minor malrotation (< 4û).Conclusions: In painful TKAñs with unknown persistent pain but limited ßexion and/or lateral instability in the ßexion gap evaluation of the femoral component rotation with a special CT should be performed.