Anthony Hall, an orthopaedic consultant to Chelsea, told the court that it was the worst football injury he had seen and was caused by an impact more forceful than being hit by a car.
Mr Elliott, 30, is suing Dean Saunders and his former club Liverpool for negligence over a tackle during a game in September 1992. Damages could run into millions of pounds.
The action, seen as a test case, is the first involving two high-profile players over an injury on the pitch. Mr Saunders, who now plays for Aston Villa, may have to pay the damages himself if he is found to have been reckless.
In a statement to the court, Mr Hall said: 'I very rarely see a case where not only is the ligament torn but also the next layer down. This is indicative of an exceptionally violent impact.
'I think that Paul's knee must have opened as much as two inches. I have considerable experience of bodies hit by cars. The injury in this instance is more serious than most of them and shows a more forceful impact.'
The former Chelsea coach, Don Howe, accused Mr Saunders of deliberately injuring Mr Elliott in the game between Liverpool and Chelsea at Anfield. He said Mr Saunders deliberately slowed down to allow his opponent to make the tackle so he could stamp on his knee.
Denis Wise, the England and Chelsea player, raised laughter as he tried to describe the game's intricacies to lawyers. While explaining the details of a tackle, Mr Wise told Antony Berrisford, representing Mr Saunders: 'You have never played football, obviously.' Later, as an exasperated Mr Berrisford looked at the ceiling, Mr Wise added: 'There is no need to get the hump with me.' He described the tackle as reckless and said the Chelsea players were 'not happy with it'.
Mr Berrisford said Mr Elliott had been penalised for the tackle by the referee and had been trying to 'put the frighteners' on his opponent early in the game.
Colin Mackay, representing Liverpool, said Mr Saunders jumped to avoid a 'clattering' from Mr Elliott.
The case continues today.