Each episode of New Zealand's favourite drama is filmed about 10 weeks before going to air. Viewers are only now beginning to see Mitchell in his first days back on set post-surgery, including awkward moments where he is seen grimacing and holding his arm.
Mitchell had an arm sling masked under jackets and coats for some scenes. In coming weeks his character TK will appear with his arm bandaged up after an accident.
"The producers have had to rewrite things and it has really put everyone under pressure," Mitchell said. "I couldn't remember my lines and I can't do anything physical.
"I was also becoming depressed because we work in a tribe situation. I suddenly felt like the weak link on the team."
Actor Ben Mitchell plays doctor TK Samuels on Shortland Street.
Mitchell underwent a six-hour operation on his left shoulder in June. He was confined to bed afterwards for a fortnight.
The former personal trainer said his problems stemmed from his days as a boxer and weightlifter.
"My dad used to have me punching training bags really hard when I was younger and this has taken its toll on my shoulders," he said. "Then I tore a pec while doing a 180kg bench press.
"It was time to get something done before things got really bad but the recovery takes about seven or eight months and it has been difficult.
"In the first few weeks after surgery I felt I was losing weight by the second. I had no idea how challenging this would be."
Mitchell will undergo a similar operation on his right shoulder next month.
"I'm not looking forward to it but it is something that just has to get done," he said. "At least we will be better prepared on Shortland Street about what is involved."
"At the moment I still feel like getting an acting double in to do half of my scenes because my upper body mobility is still pretty limited."
