A £5,000 reward is being offered as part of the hunt for robbers who broke the victim's leg with a crowbar.
Durham Police are hunting the three armed robbers, who were wearing white CSI-style suits and clown masks, when they broke into a house in South View, Burnhope.
They were confronted by the sole male occupant, who had his leg snapped with a crowbar during a struggle.
The suspects demanded the keys to the safe and fled with a haul of sentimental gold jewellery.
Detective Constable Michael Orridge of Chester le Street CID, said: “Following extensive inquiries, we are now appealing to the public to help us catch these culprits. This was a nasty assault which left the victim with a broken leg and needing hospital treatment.
"A £5,000 cash reward is being offered for information leading to a conviction.”
Anyone with information about the incident, which took place at about 8pm on November 11, is asked to contact Durham Constabulary on 101 quoting reference 434 of November 11.