EARLY EXPERIENCE WITH A NON-INVASIVE GROWING MASSIVE FEMORAL PROSTHESIS

Abstract

When managing malignant long bone tumours in skeletally immature patients it is desirable, after resection, to reconstruct with a prosthesis that can be lengthened at appropriate intervals to keep pace with growth of the contralateral side. In an attempt to avoid multiple surgical procedures to achieve such lengthening we have recently developed a prosthesis that can be lengthened non-invasively.

Purpose of study: To look at our early experience with the use of non-invasive growing femoral prostheses.

Methods: Between November 2002 and February 2004 the prosthesis was implanted in 6 patients (3 males and 3 females) with a diagnosis of osteosarcoma. The patients were aged between 9 and 14 years (mean 11.5 years) at the time of surgery. Patients were lengthened at appropriate intervals and the process was monitored with scanograms. The prosthesis contains a magnet that is connected to gears that drive the extending mechanism. The patients’ limb is placed into a coil and the principle of electromagnetic induction coupling is used to achieve lengthening. Total degree of lengthening to date was recorded for each patient together with the range of knee movement and any complications that occurred. Patients were functionally evaluated at their last follow-up visit using the Musculoskeletal Tumour Society (MSTS) Scoring System.

Results: To date patients have been lengthened by an average of 18mm (8–48mm). The mean amount of knee flexion is 125 degrees. The mean MSTS score is 18 (16–21). There have been two complications; one patient developed patella subluxation during the lengthening programme and one patient has required serial casting to treat a flexion deformity of 25 degrees.

Conclusions: We have been encouraged by our early results with this prosthesis and have been able to demonstrate that the technology works reliably in vivo. We are continuing to use this prosthesis in skeletally immature patients.