Mr McKenzie stretched the woman's breast scar tissue, but he did not properly explain this to the woman or follow the industry guidelines over treatment of "sensitive areas".
He didn't record the treatment on his notes, nor ask the woman to sign written consent, but justified his actions as he thought "the patient's scar tissue was impacting on how she closed her mouth", the tribunal decision says.
The woman's bra rode up over her breast, but her clothes covered her chest at all times.
The woman, who had a history of abuse, felt "embarrassed" and "violated". She suffered pain and swelling in her right breast for days afterwards.
An expert witness who have evidence at the tribunal hearing said Mr McKenzie treated the breast for "misguided therapeutic reasons rather than any self-gratification".
"[The expert] noted that Mr McKenzie had treated the breast because of the patient presenting a history of previous surgery in the breast area," the tribunal decision says.
"His view was that touching a patient's breast in a first patient visit was more likely to cause trauma to a patient than help release emotional tension. "Mr McKenzie qualified as an osteopath in 2009. He'd previously been the subject of another complaint about treating "sensitive areas", when he worked in Nelson.
That complaint was dealt with by the Osteopathic Council of New Zealand.
Since the latest incident, Mr McKenzie agreed not to treat any "sensitive areas" and always remind patients of their right to bring a chaperone.
Two other Christchurch osteopaths gave evidence to the tribunal, saying he was "committed" and "sincere" and on this occasion had made an "unfortunate error of judgment".
"They also referred to their own knowledge of Mr McKenzie having generally good patient relationships."
The tribunal found Mr McKenzie had shown genuine remorse, had fully co-operated and a rehabilitative penalty was appropriate.