Final answer:
The correct immediate care for a posterior-superior tibiofibular dislocation is to assess the leg's circulation and neurological status, check for shock, and activate EMS for urgent medical assistance.
Step-by-step explanation:
The most appropriate immediate care for a posterior-superior tibiofibular dislocation of the femur incurred from a low chop block and a simultaneously posteriorly directed blow is to: assess circulation and neurological status of the leg, assess the athlete for shock, and activate EMS (Emergency Medical Services). This immediate response is crucial, considering the severity of the injury which can have a significant impact on the lower extremity's functional integrity, as the injury involves major ligaments and structures of the knee. Immediate medical attention is required for proper stabilization, assessment, and treatment of such a complex joint dislocation.