The 24-year old, who is now based in Bristol, came through the ranks at community club level with Cumbrian side Roose Pioneers before signing for Barrow Raiders Academy aged 19. He was the Academy Player of the Year in 2007 before being part of their National League Two winning side in 2008 under new Scorpions coach Dave Clark.
He moved to Workington Town in 2010 where he was also a Community Development Officer.
McKenna will link up with the Scorpions squad at the start of January and he is looking forward to getting going.
“I’m excited for the opportunity to be involved in such an ambitious club,” he said. “It’s great to see Rugby League expand into different areas and hopefully this season we can put Scorpions on the map both in South Wales and beyond.
“I’m also looking forward to linking up with Dave Clark again and also with Nathan Mossop who I played alongside in Cumbria.”
New Scorpions coach Dave Clark said: “I coached Joe at Barrow and he’s a great young player. He’s experienced at this level and higher in Rugby League and he has a great attitude for the game.”