53 It is immediately to be noted that all these alleged irrelevant considerations are matters of fact which the Review Officer considered when reaching his conclusion that the appellant had not established that the right knee injury had been caused or aggravated by the disability arising from the injury to the left ankle. There is not, nor could there be, any suggestion that some erroneous principle relating to the admission or rejection of evidence, or to the onus of or standard of proof was wrongly taken into account or that there was a failure to attend to any relevant principle of law in reaching a conclusion of fact on this issue of causation. As already described, the issue of fact for decision, was whether or not the appellant could establish, on the balance of probabilities, that the initial dislocation, and following subsequent dislocations, of the right patella, were caused or contributed to by the injury to the left ankle. This required the appellant to prove, on the balance of probabilities, that there had been a dislocation of the right knee, and subsequent dislocations requiring medical intervention and treatment and that the condition in the right knee had been caused by the earlier disability.