Dennis Robinson's face was injured so badly during an alleged prison assault that plastic surgeon Christopher Johnson told a jury: "This was one of the worst injuries I have seen in my career. The cheek bones on the left side were essentially pulverised."

Dr. Johnson, who's been practising for 23 years spent five hours operating on Robinson after an incident in Westgate on June 6 last year.

Robinson, 38, alleges that Kenneth Burgess, 36, and Kamel Trott, 32, ambushed him in his cell and launched a vicious punching attack lasting an hour.

He has told a Supreme Court jury that Burgess blamed him for his incarceration and threatened to kill him, before instructing him to write an affidavit clearing him of blame in the Cooper twins murder case which was the reason they were both in jail.

Called to give expert evidence in the case on Friday, Dr. Johnson listed Robinson's injuries as including fractures to his jaw, his left cheek and left eye socket.

His left eyeball appeared "pushed in" in comparison to the right, and was sunken due to the "blown out" fracture of the eye orbit.

Robinson's upper and lower teeth did not meet as they should because of the fractures, and his jaw had to be wired together. Dr. Johnson explained his cheek had to be cut open to expose the broken bones, which were then fixed with plates and screws.

The patient also needed surgery to repair a torn tear duct from his left eye, and altered vision after the surgery meant he had to be referred to an eye specialist, the court heard.

In addition, said Dr. Johnson, an ear nose and throat specialist who saw Robinson in relation to pain in his left ear found that the eardrum had been ruptured by his broken jaw bone protruding through it. In total, Robinson spent more than three weeks in hospital, during which Dr. Johnson told the court that he required "significant amounts of pain medications and intravenous antibiotics".

Director of Public Prosecutions Rory Field asked him: "Could that injury occur from a single application of blunt force?"

"Absolutely not," he replied.

"So in your opinion, can you tell us how such injuries could have been caused?" asked Mr. Field.

Dr. Johnson replied: "In my opinion there were repeated blows with various angles throughout the left side of the face."

The prosecutor then asked: "And can you give any opinion as to the force which would have to be used in those blows?"

The doctor replied that "repeated heavy blows" would have been required to break the lower jaw bone, which is one of the strongest bones in the face.

The court also heard from dental surgeon David Dyer who said nerve damage may mean Robinson always has numbness in his cheek.

Burgess and Trott deny assault with intent to cause grievous bodily harm, and the case continues.