Stanmore Implants | Non-Invasive Juvenile Tumour System | Which Medical Device

Description

From Which Medical Device

The Non-Invasive Juvenile Tumour System from Stanmore implants Worldwide is a customised massive endoprosthesis system for use in children after major long bone resection, first used in 2002. The device comprises two sliding segments, within which is a motor with an epicyclic gearbox which is activated by placing the limb into an electromagnetic coil. The gearbox produces an overall speed reduction of 13061:1 and an output torque of 4Nm to drive the screw, which in turn generates an axial force of up to 1350N. Lengthening occurs at 0.23mm per minute, and the mechanism can be heard with a stethoscope.  The design means that the motor can be reversed and the implant shortened, and the degree of lengthening is highly controllable. The device comes in three lengthening options; 50, 70 or 90mm depending on the length of the segment to be resected. The dimensions of the lengthening mechanism are such that it is not suitable for all patients, particularly the very young. In the distal femur (the commonest site), the tibial component is typically a sliding one which crosses the tibial physis. Although this still allows tibial physeal growth, it is often less than normal and so the distal femoral implant would be required to compensate for this. Lengthening implants tend to be used when the predicted leg length discrepancy is more than 3cm.

Early results are favourable (Gupta 2006, Gokaraju 2009). Seven year results in 34 children from Hwang et al demonstrated lengthening complications in two: one failed mechanism and one with scar tissue. There was deep infection in six patients (18%). Patients in this series typically had lengthening when leg length discrepancy was 1cm or so, and underwent around 5mm (20 minutes) of lengthening in a single session. 

In the series of 55 children from Picardo et al, the mean lengthening was 38.6mm (3.5 to 161.5), nine patients requiring revision of the prosthesis because it had reached the maximum lengthening available. Six patients had infection (10.9%), one of whom underwent amputation as a result. 3 gearboxes failed at mean of 29.3 months (14 to 52), two after trampolining.

References

Gupta A, Meswania J, Pollock R, Cannon SR, Briggs TW, Taylor S, Blunn G. Non-invasive distal femoral expandable endoprosthesis for limb-salvage surgery in paediatric tumours. J Bone Joint Surg Br. 2006 May;88B (5):649-54

This listing updated 29th April 2012