The court heard today Mr Slade had suffered a shattered hip and needed reconstructive surgery for his collarbone and right shoulder. He still had difficulty performing simple tasks and would continue to suffer "life-long effects".
Roberts' sister Irene Richards addressed the court before her brother was sentenced.
"We want to acknowledge the hurt and suffering of the victim and his family and offer our sincere apologies," she said.
"We don't understand how this occurred but ultimately as a family shoulder the blame."
Judge Cooper said there had been no meaningful expression of remorse by Roberts other than a letter of apology to Mr Slade before sentencing.
"Up until this point you have showed no level of responsibility, that letter of apology can not be taken as a meaningful expression of remorse, your actions through this case have been inconsistent of true remorse," he said.