Successful lengthening, but high incidence of infection, using noninvasive extendable prosthesis
MedWire News: Preliminary results show successful use of noninvasive extendible prostheses in children with bone tumors, but the risk for infection causes concern.
In a study published in the British volume of the Journal of Bone and Joint Surgery, researchers reviewed the first 7 years of noninvasive extendible prosthetic treatment in 34 children (18 male), aged an average of 11 years, with primary bone tumors.
Noninvasive extension mechanisms have been developed to reduce the number of anesthetics and operations for each lengthening in skeletally immature patients, explain Nick Hwang and colleagues. The patients in this study were treated with the Juvenile Tumour System (Stanmore Implants Worldwide, Stanmore, UK), a type of noninvasive extendible prosthesis that was first used in 2002.
"Advances in chemotherapy, imaging modalities and surgical techniques have led to the increasing use of limb-salvage surgery in the treatment of primary malignant bone tumours… There is, therefore, an increasing requirement not only to preserve the limb but also maximize function and minimize complications," write the researchers. "The maintenance of limb length equality after resection of the growth plates is also necessary."
The distal femur was replaced in 25 patients, five had the total femur replaced, in one the proximal femur, and in three the proximal tibia. Six weeks after the operation all patients completed 1 week of intensive inpatient physiotherapy. At this point they were offered limb lengthening when there was an obvious discrepancy, which was usually around 1 cm.
The prosthesis was lengthened by placing the limb inside an external electromagnetic circular drive unit. The prosthetic implant extended at a maximum rate of 0.23 mm per minute and could continue under loads up to 1350 N. To prevent overloading, the researchers conducted extensions of 5 mm at the most per session.
None of the lengthening procedures required anesthetic and were conducted on an outpatient basis.
A total of 27 (79%) patients were survived to follow up at a mean of 44 months after surgery; 13 were lost to metastases.
The surviving patients all underwent lengthening, and a mean of 4 mm was achieved at each lengthening session, with the number of sessions per patient ranging from one to 15.
Complications with the lengthening device occurred in two patients and one patient had to receive a second prosthesis after reaching the extension limit of the first (70 mm).
Six patients developed deep infection at a mean of 5 months postoperation and one patient experienced a superficial wound infection; five required surgery to treat the infection.
"Our results confirm that the [Juvenile Tumour System] can achieve its aim of allowing repeated lengthening without operative intervention. However, the results are marred by the worryingly high rate of infection," conclude the researchers.
By Chloe McIvor