According to new historical research, legendary Renaissance polymath Leonardo da Vinci was left with a deformed “claw hand” after fainting, thus explaining why his iconic Mona Lisa was never finished.

Timed to coincide with the 500th anniversary of da Vinci's death, Britain's prestigious Journal of the Royal Society of Medicine has published the new findings by a team of researchers.

The researchers compared a portrait of Da Vinci by 16th-century Lombard artist Giovan Ambrogio Figino with an engraving of the artist in his younger years that depicts him playing the fiddle.

The portrait shows da Vinci 's right arm as though suspended by folds of clothing, in the manner of a sling or bandage, with the right hand clenched.

Plastic surgeon Dr Davide Lazzeri said: "Rather than depicting the typical clenched hand seen in post-stroke muscular spasticity, the picture suggests an alternative diagnosis such as ulnar palsy, commonly known as claw hand."

"Even though the right arm and hand are not visible, we should presume he is portrayed in optimal medical condition."

The team of researchers scrutinised a 1550 biography of da Vinci by Italian author Giorgio Vasari. An excerpt from it says: "He was physically so strong that he could withstand violence and with his right hand he could bend the ring of an iron door knocker or a horseshoe as if they were lead."

Dr Lazzeri said: "We should, therefore, presume that until 1505, da Vinci 's right hand was working well, but that by the late years of his career he started to suffer some kind of impairment."

Claw hand is a condition when the hands resemble a bear's claw, as the fingers are noticeably bent.

A deformity of such a nature would not have allowed him to hold a palette and brush with his left hand and stand up to paint, however, the artist, who was ambidextrous, switched around and continued to teach and draw with his left hand instead, according to researchers.

It had been previously thought the artist and inventor had suffered a stroke in his later years, which would have explained why so many works were left unfinished.

A stroke is what eventually led to the artist’s death on 2 May 1519, at the age of 67.

The legendary Renaissance artist began the Mona Lisa in 1503 but never finished it. 

There were also many rumours and theories as to why he kept the painting to himself for so long, with some claiming he had difficulty parting with it, and others believing he was not satisfied with it.

Whatever the bewitching mystery behind it, thousands are drawn to witness with their own eyes the artist’s sublime creation: Mona Lisa's enigmatic smile at the Paris Louvre.