The use of a closed expandable prosthesis for pediatric sarcomas

The purpose of this paper is to review our experience with a non-invasive expandable prosthesis for skeletally immature patients following limb-salvage for malignant tumors about the knee.

Between 1998 and 2002, Repiphysis prostheses (Wright Medical Technology, Memphis, Tenn.) were implanted in 18 patients. 16 patients had at least 12 months follow-up. There were 10 males and 8 females. The diagnosis was Stage IIB osteosarcoma in all patients. Sites included femur 14, and 4 proximal tibias. The average age was 10.7 years (range 8-16); the average age for males was 12 years and females, 9 years. Fifteen of the prostheses were implanted at the time of surgical resection and the remainder was conversions of previous surgery.

Follow-up averaged 24.8 months (range 12-47). Fourteen patients have undergone a total of 58 lengthening procedures. Average expansion 38 mm per patient (range, 10-76 mm). An average of 8.5 mm per lengthening procedure. There was only one failure to lengthen. ISOLS functional scores averaged 83.5%. For those with a current functional prosthesis, the ISOLS score averaged 94%. Three patients have reached maximal expansion and converted to a conventional prosthesis. There were complications in 7 patients: 2 expandable component fractures, 1 femoral component fracture, 2 stem fractures, 1 stem loosening and 1 deep infection. Of the two expandable component fractures, 1 patient reached full expansion and was converted to an endoprosthesis. The femoral component fracture and 2 stem fractures were revised to a new prosthesis 13 months post-op and are functioning well. The 1 loose stem was revised to an APC.

The Repiphysis prosthesis utilizes energy stored in a spring that is held compressed by a locking mechanism. Controlled release of the locking mechanism via an external electromagnetic field allows for lengthening of the device. In our early experience, the functional results were excellent similar to conventional modular devices. Complications should be anticipated but are salvageable. This device allows limb salvage in pediatric patients when amputation would be otherwise chosen.