Famed polymath Leonardo da Vinci had a 'claw hand', researchers have claimed.
The artist, inventor and mathematician produced few paintings in his later years, and a portrait drawn in the 16th century depicted him with his right hand strangely curled up, and his clothes arranged somewhat like a sling.
Previous diagnoses have said a stroke or a rare disease caused the curious condition, but now - 500 years after da Vinci's death - two Italian researchers think they know the real reason.
"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," said Davide Lazzeri, a specialist in plastic reconstructive and aesthetic surgery at the Villa Salaria Clinic in Rome.
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He says da Vinci - who painted with his right hand, but drew and wrote with his left - probably hurt it when he fainted.
"This may explain why he left numerous paintings incomplete, including the 'Mona Lisa', during the last five years of his career as a painter while he continued teaching and drawing."
Dr Lazzeri's research was published in the Journal of the Royal Society of Medicine.