Taking tissue engineering principles into theatre: retrieval analysis from a clinically translated case

Aim: Tissue engineering has enormous potential for the regeneration of bone defects. Approximately 4 years ago we reported on a 62 year old patient who underwent treatment of a benign cyst in the proximal femur by impaction bone grafting supplemented with autologous bone marrow. The cyst and symptoms subsequently recurred and this patient has now required a total hip replacement. This has provided a rare opportunity for ex vivo analysis of clinically applied tissue engineered bone. Materials & methods: The femoral head was retrieved at surgery and the structural and functional characteristics of the tissue engineered bone were analyzed by micro-computed tomography, histology and mechanical testing. Results: The impacted bone demonstrated a trabecular structure that contained islands of nonincorporated graft. The graft was denser than the patient's trabecular bone with comparable strength. The cyst material had penetrated along the channel of bone and an increased number of osteoclasts were observed. Discussion: This study has provided detailed ex vivo analysis of retrieved human tissue engineered bone and possible reasons for the observed construct failure are discussed in this article. The impacted bone displayed some evidence of remodeled trabecular structure, although the bone marrow aspirate that was initially combined with the allograft contained a relatively low concentration of osteoprogenitor cells. Cellular augmentation was insufficient to overcome the osteoclastic process associated with renewed cyst formation. Concentration or culture expansion of osteoprogenitor cells from aspirated bone marrow is recommended for biological augmentation of bone graft.