[Rupture of the pes anserinus--a rare concomitant injury in anteromedial instability of the knee joint].

We report about a case of rupture of the pes anserinus insertion causing an anteriormedial knee instability grade () without rupture of the anterior cruciate ligament. This case demonstrates that a grade ()-instability can be caused without rupture of the cruciate ligaments just by the rupture of a so called "dynamic stabilisator" like the pes anserinus.