IN-VITRO TESTING OF A NOVEL LIMB SALVAGE PROSTHESIS FOR THE DISTAL FEMUR

Objective. The aim of this paper was to define strain pattern in the h ost bone following distal femoral resection and implantation of a mass ive prosthesis. Two methods of coupling the prosthesis to the bone wer e compared: the Compliant Pre-Stress device, and a standard cemented t umour prosthesis. Design. The composite femur model was selected to mi nimize variables. Four femurs were tested before and after implantatio n. Both coaxial and cantilever loading were applied. Background. Cemen ted distal femoral replacement following resection of malignant tumour s has a high failure rate at 5 years and is associated with extensive bone resorption thought to be secondary to stress shielding. Methods. Strain was measured in the medial and lateral sides at four levels wit h physiologic loads applied, in the intact, Compliant Pre-Stress, and cemented femurs. Repeated measurements were taken. Strains in the impl anted femur were calculated as percentage of the intact, and statistic ally analyzed. Results. The most reproducible results were noted in ca ntilever bending (variability <5%). The Compliant Pre-Stress device de monstrated a more physiologic strain pattern than the cemented stem. T he most significant difference between the two implants was in the are a adjacent to the interface. Conclusion. The Compliant Pre-Stress devi ce shows less stress shielding than a standard cemented implant. The p rotocol described and the use of composite femurs demonstrated reprodu cible results. Relevance Massive prosthesis are commonly used followin g tumour resection or removal of failed primary joint replacement pros theses. The failure rate for aseptic loosening for cemented implants i s 25% at 5 years with significant bone resorption about the implant. C ompliant Pre-Stress is an innovative technology that allows coupling o f metallic implants to bone with little stress shielding. This paper a ims to define the strain patterns about the implant and compare them t o a standard cemented device. The reduced stress shielding of the Comp liant Pre-Stress fixation system should guarantee reduced bone loss ar ound the implant and help to obtain improved clinical results. (C) 199 8 Elsevier Science Ltd. All rights reserved.