Could a simple knee injury lead to cancer?

No: It is hard to see how a simple injury to a joint would lead to cancer.

No: Sometimes an injury leads to the initial discovery of a cancer (the injury does not cause the cancer to occur). For example, cancers that originate or metastasize to the bone make the bone more susceptible to fracture. A common scenario is someone breaks a bone with minimal trauma (pathological fracture), and when an image is obtained, the radiologist finds the cancer.