Final answer:
The statement regarding knee dislocations is true. Knee injuries often involve muscles and ligaments leading to pain and instability, and cruciate ligament injuries can stem from various impacts or movements.
Step-by-step explanation:
The statement that knee dislocations can reduce spontaneously and may not present with any gross external or radiographic anomalies until a physical exam of the joint is performed is true. Disorders of joints, and specifically injuries to the knee, are quite common. The knee is supported mainly by muscles and ligaments, and when these structures are injured, they can lead to pain or instability of the knee joint. An injury to the posterior cruciate ligament can occur in various ways such as falling on the knee when it is flexed or during a car accident when hitting the knee against the dashboard without a seatbelt.
Additionally, the anterior cruciate ligament is vulnerable to injuries from impacts causing hyperextension or from twisting motions during activities like running. While some dislocations may visibly alter the knee's appearance or show up on radiographic images, others may spontaneously return to normal positioning without such evidence, only later identified upon clinical examination.