[Patellar imbalance and external rotary instability of the knee].

The importance of external hyperrotation and external rotary instability in patellar imbalance is examined. In view of the progressive nature of patellar imbalance and of the predominant part played by the muscular and capsulo-ligamentous elements in the stability of the extensor apparatus, the authors advocate an earlier and more radical surgical approach with a view to improving the patellar medialization forces (transplantation of the intermediate great muscle and retension of the lateral patellar retinaculum) as well as the elements of active internal rotation of the tibia (modified version of Slocum's operation and transfer of the internal third of the patellar tendon).