The anatomy, function, and surgical repair of the posteromedial capsular and ligamentous structures, called here the posterior oblique ligament, are described on the basis of anatomical dissections of seventeen amputated lower limbs and on the analysis of the operative findings and results of repair in fifty patients treated for ligament and capsular tears in the medial compartment. In addition, the anterior cruciate ligament was torn in some patients but not the posterior cruciate.