Hi.. If your angular fracture in tibia healed completely following the application of the cast then, I suggest you to slowly start moving the knee and ankle joint u can apply hot water phomentation over the knee joint..and ankle... If it is too stiff and painful, kindly take a consultation with Physio...to help mobilising the joint... If your fracture healing is not properly allingned and there is malunion with angular deformity... Then I would strongly suggest you to meet orthopaedic surgeon for further evaluation and management... Depending one the level of torsion and healing of the bone...further management decision. Hope this is helpful