World-first operations to lengthen short bones

Orthopaedic surgeon Simon Mills operating on the man's leg to insert the telescopic tube. Photo / Supplied

New Zealand patients have become the world's first to have a leg-stretching treatment that is controlled by external magnets.

The operation allows people to increase the length of their own legs by up to a millimetre a day, either all at once or in stages to reduce the pain.

Two patients, a man and a woman each left with a shortened leg from a badly healed broken thigh bone after accidents, had surgery at Auckland City Hospital 10 days ago to re-break their legs and insert the internal components.

Orthopaedic surgeon Simon Mills performed the first operation, on the man, both of whose legs had been broken at the thigh in a car accident. His right femur healed well, his left badly, leaving it 4.8cm short.

The hospital's director of orthopaedic trauma, Bruce Twaddle, operated on the woman, who was injured when she fell from a ladder. Her short leg needs to grow by 3.4cm.

The treatment involves rebreaking the bone, inserting a telescopic titanium-alloy tube along the length of the fat and marrow-filled centre of the bone - from either the hip end or the knee - then fixing the tube with screws. The tube's mechanism screws its two outer pieces apart, driven by a rotating internal magnet.

The inner magnet is in turn driven by two outer magnets that are slowly rotated by a small electric motor, controlled to allow the metal tube to separate by a maximum of 1mm a day.

The patient, who must hold the magnet mechanism against the thigh, can choose to have all this separation in one session a day, lasting about seven minutes, or do it in several shorter sessions during the day.

Separating at this rate allows material to grow into the space, and this eventually turns into bone.

"If you make it quicker, it doesn't turn into bone, it turns into nothing, or scar tissue," Mr Twaddle said. "If you go too slowly, it will heal but eventually it won't lengthen any more because it's healed with bone."

The standard method for lengthening legs for people who have one short one because of an injury or an inherited disorder - and in some cases as a cosmetic procedure for people wanting to be taller - also has an internal tube, but it requires external wires and pins through the skin that are attached to the bone. It carries a significant risk of infection.

The equipment for the new technique, called "Precice", costs about $10,000. Mr Twaddle said it was an important advance.

"It's much less painful and it gives quite precise control. This was originally designed to open and close the band on a gastric stapling device."

Ben Willis, national sales manager of Orthotech, the New Zealand distributor, said a similar expanding-rod mechanism controlled by external magnets had been used on some patients in Britain and Hong Kong with scoliosis, a deformity in which the spine is bent to one side.

However, the Auckland operations were the first time it had been used in other orthopaedic problems.

He said it had been a great advance in scoliosis because children needed just one operation - followed by adjustments made with the external magnets as they grew - rather than an average of seven operations to lengthen a spinal rod manually.

Mr Twaddle said the two patients would be able to walk unaided from about three months after the bone-lengthening phase. The tube would be removed at around two years after the initial surgery, when the bone had consolidated fully. "It will be as good as a normal femur."