Loretta Lynn has postponed or canceled all of her tour dates in August to prepare for knee surgery. Her dates had included stops in Montana, Oregon, South Dakota and Washington. She will undergo knee reconstruction surgery and her doctors have ordered her to rest, according to her management company. "I'm sad to have to cancel any shows for my fans, but they tell me I've just got to stay off this knee for a while," Lynn says. Any rescheduled concerts will be announced on her website. Lynn had been hospitalized in July due to dehydration and heat exhaustion. However, her live appearances this summer have included Bonnaroo and the Grand Ole Opry. Her next performance is scheduled for Sept. 3 at her ranch in Hurricane Mills, Tenn.