One patient’s prosthetic kneecap was fitted on the wrong side and a vaginal swab was mistakenly left behind in another in two so-called “never-events” at Homerton Hospital in the space of two months.

A patient’s prosthetic knee was fitted on the wrong side and a vaginal swab was mistakenly left inside a woman in two so-called “never events” at Homerton Hospital in as many months.

The Department of Health categorises such mishaps as largely preventable patient safety incidents so serious they should not occur if available preventative measures are implemented.

The retained vaginal swab which happened in December resulted in “only in moderate harm” according to board papers for the hospital in Homerton Row.

A right-sided component of a prosthetic knee replacement was placed in the left knee during surgery in October, but the error only came to light in January.

Board papers report that it is “currently not causing harm and will be kept under review”.

Both events are under investigation.

At a board meeting on Wednesday of last week, retired consultant surgeon Andrew Ezsias asked: “Never events by definition tends to be some sort of major incident, so could you give me some information as to why it took a few months to pinpoint?”

But chief nurse Sheila Adam said she could not give any further information, citing “patient confidentiality”.

She said: “Neither ‘never event’ was associated with significant harm and that’s quite important.

“One was picked up because of our processes rather than because it had impacted directly on the patient. The ‘never event’ (in December) was picked up nearly a week after the event itself and that was appropriate to the situation that had occurred.”

NHS England introduced new measures to ensure patient safety in 2009 when it adopted the term “never event”.

It categorised 25 incidents which should never happen if national safety recommendations are followed.

The four main categories include foreign objects left inside patients during surgery, operating on the wrong body part, tubes for feeding or medication being inserted into patients’ lungs and wrong implants or prostheses being fitted.