Why Da Vinci could never finish his masterpiece

Leonardo da Vinci may have been unable to finish the Mona Lisa after a fainting episode left him with severe injuries to his arm, a new study suggests. Although the Renaissance artist drew with his left hand, it's believed he painted with his right and that an injury forced him to leave many of his works incomplete.
It had previously been suggested that he suffered a stroke in the late stages of his career, which weakened the right side of his body, with both biographical evidence and portraits supporting the idea that he developed a condition "that affected his ability to hold palettes and brushes to paint with his right hand".
However, new research published in the Journal of the Royal Society of Medicine pointed to a portrait of da Vinci with his lower right arm at right-angles to his body, swaddled in folds of his clothes as if in a sling.
Co-author Dr Davide Lazzeri, a specialist plastic reconstructive and aesthetic surgeon at the Villa Salaria Clinic in Rome, 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."
He further suggested that a syncope, or fainting episode, could have caused trauma to da Vinci's right upper arm. The ulnar nerve runs from the shoulder to the finger and manages intricate movements of the hand.
"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 added.