This is a summary of what happened, from all I gathered through the news and through meeting an old friend of StepApp's earlier this year. Sad part is that I know more about it than people who made a living off of reporting the story.
Towards the end of the 2006/07 season, he started complaining about some pains in his leg, particularly his knee. He played on though to help the club win the title which looked like going down to the wire but was guarenteed with two weeks left. The club doctors let him play on with the diagnosis being that it wasn't in need of urgent treatment.
Then with the title secured, he took the time off that he supposedly needed, and later booked in for surgery on his knee. He had the surgery, and his recovery was all planned out by the club doctors and the surgeon who performed the surgery.
He came back into basic training, doing the strength work and everything else as part of his recovery, but every time he tried to run or take part in football related training, he complained of pain again.
The 'experts' said it was possible and not uncommon that a player who had his surgery be in a fragile state of mind, and that the recovery was going to be much more a mental challenge than a physical one. They said the surgery went fine and nothing was wrong.
So he kept going at it, and everyone was expecting his return to the field. Weeks and months went by and people were getting impatient citing that Appiah had other motives and wanted to milk his injury (!). One day, feeling mentally stonger mid-way through the season he made his return, he played against PSV off the bench and started a league game against Kayserispor (he assisted a goal in that one). But then again, more pain.
He went to seek further advice from doctors in Italy who . . found blood clots in his leg. A life threatening condition!
After that it all turned sour with the club, eventually leading to him breaking his contract via FIFA in late April this year. In the 6 or so months since finding out the real issue, he made a full recovery and was training in pre-season with Brescia.