This case study reports the analysis of a knitted polyester arterial prosthesis that was implanted in an 18-year old patient for five years following a bicycle accident which injured the left external iliac artery. In spite of the prosthesis, the patient continued to participate in competitive cycling. The graft became dilated and stretched by tension from the hypertrophic psoas muscle, and because the patient presented with pain and claudication, a second surgical operation was performed. The central region of the prosthesis was badly kinked. A segment was resected and analyzed in terms of pathological, textile and chemical properties. The analysis showed a poorly healed graft that had suffered from mechanical and chemical degradation. The findings point to the wisdom of implanting woven rather than knitted grafts in young patients and also suggest that in this particular case, where mechanical deterioration was accompanied by chemical degradation, it would have been preferable to remove the whole prosthesis.