The incident at Ayr Hospital started when a metal plate was unexpectedly discovered in the man’s leg during the operation.
It was reported that staff could not find the equipment to remove the plate, so a member of the surgical team was sent to B&Q to buy a saw - but the DIY shop was closed.
A saw was said to have been found in a stock cupboard at the Ayrshire hospital and was disinfected before being used.
Concerns were later raised with senior management at the hospital and an investigation is being held.
Scottish Conservative health spokesman Jackson Carlaw was shocked by the reports.
He said: “This is simply incredulous. An indescribable way to treat any patient.
“Despite the UK’s advancement in modern medicine this episode has all the finesse of improvised surgery on Nelson’s flagship during Trafalgar.
“I would hope that NHS Ayrshire and Arran thoroughly investigate this incident as a matter of urgency.”
Ann Gow, interim nurse director at the health board, said: “NHS Ayrshire and Arran is currently conducting a significant adverse event review into a recent incident within University Hospital Ayr, where standard procedures were not followed.
“The findings of this review and any subsequent recommendations will be shared with clinicians, as well as the family of the patient.”