The jumping motion of 15 competitive basketball and volleyball players was tested until exhaustion in a cinematographic study. A stereotyped motion pattern was recognisable. The knee joint shows an evasive movement into a valgus and internal rotation position during the acceleration phase before take-off. Furthermore, the knee shows a brief stabilisation in overextension at heel strike. An imbalance of the muscles which stabilise the pelvis and the lower extremities can be regularly found in these athletes and could be a possible cause for this jump motion. It leads to a shortening of the hip flexors and adductors and of the knee extensors with the final evasive action of the knee joint. Though the anatomical condition of the joint is not directly observed, such a motion pattern must be the cause of additional shear forces and peak loads in the area of the patellofemoral joint and of the apex patellae. Clinical experience shows that an active correction of the evasive motion can be achieved by systematic physiotherapy. It ensures muscular balance of the pelvic region and lower extremities and thus lasting good results.