Elizabeth Maliakal, a medical negligence solicitor representing some of the families, said some children had nerve and muscle damage.
“We have a client that has undergone an amputation of his lower limb. We have clients that have permanent deformities that have undergone unnecessary operations, as well,” she told the BBC.
GOSH said it had contacted all 721 patients or their families on more than one occasion and will continue to be in touch throughout the review process.
The hospital said it had asked the RCS to review the wider paediatric orthopaedic service in 2022, after becoming aware of concerns from patients’ families and staff.
As part of its review the RCS raised concerns about a former surgeon and other practice within the service, prompting GOSH to initiate the patient reviews from April this year, the hospital said.
This process will last 18 months from May and will be undertaken by five external paediatric orthopaedic surgical consultants, GOSH said.
Of the 39 cases reviewed so far, 22 children have been found to have been harmed, with nine classified as suffering “low/moderate” harm and 13 classified as “severe harm”, with potentially life-long injuries.
In addition, 456 cases have been looked at by a senior nurse and paediatrician and have not been categorised as needing urgent attention.
A GOSH spokesperson said the hospital was committed to “learning from every single patient that we treat, and to being open and transparent with our families when care falls below the high standards we strive for”.
They added: “We have contacted all patients and families who have been impacted and where harm has been identified, discussed their cases with them under our duty of candour.
“To all of them, we wish to convey our sincere apologies.”
