Simon Tilley

Pseudotumour formation due to tribocorrosion at the taper interface of large diameter metal on polymer modular total hip replacements

We present an in-depth failure analysis of two large diameter bearing metal-on-polymer (MoP) modular total hip replacements, which have required revision surgery due to pseudotumour formation. The failure analysis showed a discrete pattern of material loss from the distal end of the head taper/stem trunnion interface. We postulate that the use of a proximal contacting taper design had provided insufficient mechanical locking between the head and the stem, enabling the head to toggle on the trunnion. In addition, the difference in angle between the taper and the trunnion formed a crevice between the two components. Through a combination of crevice environment, mechanically assisted corrosion, mechanical wear and erosion; debris and metal-ions have been released resulting in the adverse local tissue reactions (ALTR).

Biological and mechanical enhancement of impacted allograft seeded with human bone marrow stromal cells: potential clinical role in impaction bone grafting

With the demographics of an aging population the incidence of revision surgery is rapidly increasing. Clinical imperatives to augment skeletal tissue loss have brought mesenchymal stem cells to the fore in combination with the emerging discipline of tissue engineering. Impaction bone grafting for revision hip surgery is a recognized technique to reconstitute bone, the success of which relies on a combination of mechanical and biological factors. The use of morsellized allograft is currently the accepted clinical standard providing a good mechanical scaffold with little osteoinductive biological potential. We propose that applying the principles of a tissue engineering paradigm, the combination of human bone marrow stromal cells (hBMSCs) with allograft to produce a living composite, offers a biological and mechanical advantage over the current gold standard of allograft alone. This study demonstrates that hBMSCs combined with allograft can withstand the forces equivalent to a standard femoral impaction and continue to differentiate and proliferate along the bony lineage. In addition, the living composite provides a biomechanical advantage, with increased interparticulate cohesion and shear strength when compared with allograft alone.

Taking tissue-engineering principles into theater: augmentation of impacted allograft with human bone marrow stromal cells

Human bone marrow contains bone progenitor cells that arise from multipotent mesenchymal stem cells. Seeding bone progenitor cells onto a scaffold can produce a 3D living composite with significant mechanical and biological potential. This article details laboratory and clinical findings from two clinical cases, where different proximal femoral conditions were treated using impacted allograft augmented with marrow-derived autogenous progenitor cells. Autologous bone marrow was seeded onto highly washed morselized allograft and impacted. Samples of the impacted graft were also taken for ex vivo analysis. Both patients made an uncomplicated clinical recovery. Imaging confirmed defect filling with encouraging initial graft incorporation. Histochemical and alkaline phosphatase staining demonstrated that a live composite graft with osteogenic activity had been introduced into the defects. These studies demonstrate that marrow-derived cells can adhere to highly washed morselized allograft, survive the impaction process and proliferate with an osteoblastic phenotype, thus creating a living composite.

Adult mesenchymal stem cells and impaction grafting: a new clinical paradigm shift

The demographic challenges of an increasingly aging population emphasize the need for innovative approaches to skeletal reconstruction to augment and repair skeletal tissue lost as a consequence of implant loosening, trauma, degeneration or in situations involving revision surgery requiring bone stock. These clinical imperatives to augment skeletal tissue loss have brought mesenchymal stem cells to the fore in combination with the emerging discipline of tissue engineering. To date, impaction bone grafting for revision hip surgery is a recognized technique to reconstitute bone utilizing morselized allograft to provide a good mechanical scaffold, although with little osteoinductive biological potential. This review details laboratory and clinical examples of a paradigm shift in the application of mesenchymal stem cells with allograft to produce a living composite using the principles of tissue engineering. This step change creates a composite that offers a biological and mechanical advantage over the current gold standard of allograft alone. This translation of tissue engineering concepts into clinical practice offers enormous input into the field of bone regeneration and has implications for translation and future change in skeletal orthopedic practice in an increasingly aging population.

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 patients 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.