PORTLAND, Ore. -

A 32-year-old former inmate who claims he injured his knee while climbing down from his prison bunk bed is suing the state of Oregon for $49,637.

The Oregonian reports the lawsuit was filed Friday against the Oregon Department of Corrections. Mitchell Ray Johnston claims the department was negligent in failing to provide ladders or another safe way for inmates to climb on an off of bunks at the Columbia River Correctional Institution in Northeast Portland.

Johnston, of Beaverton, was serving an 18-month sentence for credit card fraud at the 595-bed minimum security prison. On Aug. 28, 2012, he claims he was climbing down from his upper bunk when his foot slipped, causing a torn ACL and meniscus tear to his knee.

Johnston was released about two months later and had surgery in January 2013.