T. Wredmark Department of Orthopaedics, Huddinge Hospital, Karolinska Institute, Stockholm, Sweden In the above article there were errors in Tables 1, 5, and 6, as well as in Fig. 6. The cross-sectional area of the semitendinosus muscles examined should all be 10 times larger. This does not make any difference in any of the conclusions since the relationship between the operated and non-operated side (ratio) was the main issue and these ratios remain the same. Nevertheless, the three tables and the figure are all reprinted below as corrected.