Abstract
Primary malignant bone tumours frequently arise in children close to the knee, hip or shoulder. Resection of the tumour will often require excision of the epiphysis and frequently one side of the involved joint. In these children an extendable endoprosthesis is usually required to allow for maintenance of limb length equality.
We have used 180 extendable endoprostheses in 176 children since 1975. The indication for use of an extendable prosthesis was if there was more than 30mm of growth remaining in the resected bone. The age of the patients ranged from 2 to 15 and 99 were boys. The sites of the endoprostheses used were: distal femur in 91, proximal tibia in 42, proximal femur in 11, total femur in 6 and proximal or total humerus in 26. 131 of the operations were for osteosarcoma and 34 for Ewing's.
Five types of lengthening mechanism have been used. Two designs used a worm screw gear, one type used a C collar, one type a ball bearing mechanism and the latest uses a non invasive lengthening system whereby a motor inside the prosthesis is activated by an electromagnetic field.
Of the 176 patients, 59 have died and of the remainder, 89 have reached skeletal maturity. 19 patients had an amputation, 11 due to local recurrence and 8 due to infection. The risk of infection was 19% in surviving patients. Most of the skeletally mature had equal leg lengths. The average number of operations was 11 but ranged between 2 and 29. Most operations were for lengthening but younger children always needed revisions of the prosthesis. Functional scores were 77%.
Extendable endoprostheses are demanding both for the patient and the surgeon. The high complication rate should be decreased by non invasive lengthening prostheses.
