First clinical experience with a growing endoprosthesis, a limb saving procedure in children

Purpose of the study: To perform the first clinical study with an extendable endoprosthesis that can be extended non-invasively for children with a malignant bone tumor in the leg. Method: A 14-year old boy had an osteosarcoma at the distal metaphysis of the femur. The patient was first treated successfully by chemotherapy (cisplatin, doxorubicin, ifosfamide and high dose methotrexate). The operation followed a few weeks after chemotherapy courses. Enough muscle tissue could be preserved. Resection was followed by reconstruction with a new extendable modular endoprosthetic system. The growing endoprosthesis is powered magnetically. An electromagnet, rotating outside the leg, produces a magnetic field that causes rotation of a small permanent magnet in the prosthesis. The magnet drives a motion screw via a gearbox. When the motion screw rotates the inner and outer tube of the prosthesis are forced apart. Results: Seven months after the operation there was a leg length discrepancy of 20 mm. The first extension was performed and resulted in 2 mm growth. Anaesthesia was not necessary. X-rays prior to and after the lengthening procedure were taken to demonstrate the increase in length of the endoprosthesis. Six weeks later the second extension of 5 mm was performed successfully. Further extensions of 5 mm will be repeated every one or two months to adjust the discrepancy in length of both legs. Conclusions: The first clinical experience with a growing endoprosthesis seems to be successful. The patient regained almost normal functioning of his leg. Future extensions will prevent a leg length difference.