The boy was taken away from his parents they were accused of battering him, causing multiple broken bones.
He was on the brink of being adopted before a court heard extraordinary new medical evidence, causing a top family judge to halt the case to make further inquiries.
Lord Justice McFarlane heard how a combination of medical events could have led to a case of congenital rickets being overlooked, the Telegraph reports.
The parents, who have fought a three-year custody battle, have been given a final chance to get their son back.
It came after lawyers had what they described as a 'light bulb moment' and understood the full significance of the child's medical records.
Michael Shrimpton, for the family, who are from the north of England, told the Court of Appeal in London that there is evidence that the boy was born with a Vitamin D deficiency, inherited from his mother, leading to 'soft bones' and rickets.
It suggests that the broken bones could have occurred during his difficult forceps birth, or even in the womb. Blood tests to check for signs of vitamin deficiency, when the boy was four weeks old were normal.
But the court heard that it is possible that it was 'masked' by the formula milk given to him by his mother – which contained Vitamin D supplements.
The judge temporarily halted the adoption process and ordered urgent medical reports.
He said it was essential to examine whether the Vitamin D deficiency explanation for the boy's injuries was 'more than an intellectual possibility'.
The court was told there was no evidence of emotional difficulties, domestic violence, alcohol or drug abuse, or any signs of dysfunction within the family, to indicate a risk of child abuse.
After hearing expert evidence in June last year, a judge at Sheffield High Court twice ruled that one or other of the parents must have been responsible for the baby's injuries.
However, Lord Justice McFarlane observed: "Medical knowledge of how some children may have bones that are more susceptible to injury than normal children has moved on".
The case will return to the Appeal Court once the expert medical report has been obtained.
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