A prison officer who injured his knee while restraining an inmate died two months later, an inquest heard.
Stuart Jones was forced to help restrain an inmate at Stafford Prison after he became aggressive and demanded cigarettes.
But while doing so, 49-year-old Mr Jones is said to have banged or twisted his knee.
Two months later, he was taken to Stafford Hospital after complaining of breathing difficulties but suffered a heart attack, caused by a clot believed to have been formed when he injured his knee.
Mr Jones had suffered from deep vein thrombosis 10 years earlier following a long-haul flight, the inquest in Stafford was told.
After the incident at the segregation unit in Stafford Prison on August 16 last year, Mr Jones visited hospital where he was told he had no fractures. He then visited his doctor twice who put him forward for an MRI scan and an x-ray.
He also saw a doctor at Nuffield Hospital in Wolverhampton, who told Mr Jones to see a physiotherapist.
None of the examinations showed any signs of clots, the inquest heard.
Mr Jones, of Minchin Close in Hednesford, died on October 15.
Pathologist Dr Terence Hollingworth, who carried out a full examination of Mr Jones after his death, said: “On the balance of probabilities the injury to Mr Jones’ knee was a contributory factor.
“I am convinced that if he hadn’t had the injury that he wouldn’t have developed deep vein thrombosis.”
The Health and Safety Executive carried out a full investigation into the incident but concluded all protocol had been properly followed and all training was complete and up to date. Mr Jones had also passed a fitness test taken by all prison officers once a year.
Investigating officer Wayne Owen told the court: “These incidents are things which prison officers unfortunately have to deal with quite commonly. In this case things were done pretty much exactly as they should have been. This one incident resulted in tragedy.”
The inquest jury returned a verdict of accidental death by an unintended consequence of an action.
South Staffordshire coroner Andrew Haigh told the court: “It appears the appropriate procedures were carried out and that this was a tragic accident which happened to someone performing their role as a prison officer which can be a very demanding job.”