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Implanted rotor helps cancer patients to walk again

01 November, 2003

Implanted rotor helps cancer patients to walk again

A novel use for motor technology is helping children who have lost part of their leg bones as a result of cancer, to walk again. The technique, being developed by a team at University College London (UCL), eliminates the need for years of painful surgery.

Children who have lost part of the bone in their legs after suffering from bone cancer, have prostheses implanted in their legs to support the remaining bone. As the child grows, the implant must be extended to keep pace with their growth. Traditionally, this has required up to four painful, inconvenient and costly operations over a five-year period.

In the new, non-invasive procedure, a small magnetic rotor, linked by a gearbox to the prosthetic implant, is embedded in the patient`s leg. Placing the leg into an external stator core (shown above) energises the rotor, causing it to spin at 3,000 rpm. This drives the gearbox and extends the prosthesis by 1mm every four minutes. A typical treatment takes 16 minutes and extends the prosthesis by 4mm.

This quick and painless procedure can be performed in a clinic rather than an operating theatre.

Initially the researchers from UCL`s Centre for Biomedical Engineering used a stator consisting of six air-cored coils, configured as a two-pole, three-phase winding. Although this worked, it was inefficient and needed oil cooling.

The researchers approached a local motor supplier, EMR Silverthorn of Wembley, North London, for help in developing a winding to meet their needs. EMR supplied a stator based on a standard ABB 180 frame motor in a two-pole stack for a nominal speed of 3,000 rpm. This was modified to meet UCL`s specification for series-wound stator with 552 turns of 1.06mm gauge wire, for star connection.

The first patient was treated using the new procedure at the Royal National Orthopaedic Hospital, in Stanmore, in November 2002. So far, five patients have been treated and the UCL team`s commercial arm, Stanmore Implants Worldwide, has now ordered five more windings. ABB, which supplied the first core free of charge, is supplying laminations for the additional windings on a commercial basis.

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