19 July, 2017
In July 2015, Harvey underwent an nearly 11-hour operation involving four teams of surgeons, each working simultaneously on both the donor and the recipient limbs, to gift him a new set of hands.
There is evidence that his brain had rewired to take account of his new hands, Amaral told the BBC.Although the first ever double-hand transplant was done in 1998, Harvey became the youngest to ever undergo the procedure in 2015.
Immunosuppressive drugs must be taken continuously to prevent a patient's body from rejecting the transplant.
He received his two donor hands aged eight in a groundbreaking procedure that doctors have declared a success following months of complications and rehabilitation.
Zion Harvey before the op.
"I spoke to Zion's mom, Pattie Ray, and I said, 'Your little boy has two new hands, ' and she just started to hug me and got teary-eyed", Levin said.
Dr Sandra Amaral, of the Children's Hospital of Philadelphia, said: "Our study shows that hand transplant surgery is possible when carefully managed and supported by a team of surgeons, transplant specialists, occupational therapists, rehabilitation teams, social workers and psychologists".
The American youngster is able to complete the tasks following months of occupational therapy and psychological support, according to a medical report published in The Lancet Child and Adolescent Health journal.
In another case involving a teenager who received a donor limb, there were severe complications and the patient died soon after surgery.
What is a double hand transplant?
He said there's one moment immediately after Zion's surgery that he will always remember.
Harvey, for his part, wanted to climb monkey bars and grip a baseball bat.
A deceased child donated his hands in July 2015.
As time has progressed, Harvey's abilities with the hands have increased with occupational therapy - including using video game controllers, finger exercises and puppets. Within a year, he would be able to hold a baseball bat with his both hands, as he dreamt.
Scans revealed the boy's brain had developed pathways for control of hand movement and for carrying touch sensation signals from the hand back to the brain. Dr. Christine McAndrew, an Orthopaedic Surgeon, said, "We have followed Zion probably for a year and a half now, and done extensive evaluations to see if he was a good candidate for a hand transplant".
All of these were reversed with immunosuppression drugs without impacting the function of his hands.
The researchers said caution must be taken when assessing the benefits and harms of such a procedure given the need for immunosuppression medication which carries risk for other conditions. The accident nearly killed him but doctors were able to save enough tissue to make a transplant possible.
The child also suffered minor infections and impairment to his transplanted kidney, the anonymised report notes.
In terms of his recovery since the transplant, sensitivity to light touches was documented six months after the surgery, nerve distribution was noted between seven and 10 months following the operation and by 18 months the child had exceeded his previous capabilities prior to the surgery.
"While functional outcomes are positive and the boy is benefitting from his transplant, this surgery has been very demanding for this child and his family".