Allograft alternatives: bone substitutes and beyond

Excessive wear debris, deep infection, periprosthetic fracture, and other causes can lead to bone loss associated with total joint replacements. When performing revisions, surgeons are often preoccupied by the failed implant and the method of replacement, and neglect an opportunity to replenish lost bone. Thus, when formulating a plan for revision total joint replacement, the surgeon should consider not only the hardware that should be used, but also ways in which lost bone could be restored. Autograft bone provides the best source for osteoprogenitor cells, growth factors, and a scaffold. However, autograft is limited in supply, and is generally associated with another incision, dissection, and accompanying morbidity. Osteoconductive bone void fillers such as morselized cancellous allograft bone, polymeric scaffolds, and biodegradable ceramics each have their merits and deficiencies; however, all of these materials function as a scaffold only, without the ability to induce bone formation. Osteoinductive growth factors are essential to bone growth and remodeling; however, exogenous growth factors are expensive, are given in large nonphysiological doses, may yield unpredictable clinical results, and may have significant adverse effects. Demineralized bone matrix contains a scaffold and variable amounts of several growth factors. Recently, the use of mesenchymal stem cells and osteoprogenitors, together with a suitable scaffold carrier has gained increasing popularity. With the addition of appropriate growth factors, this combination can provide all the necessary components for osteogenesis. Future basic and clinical research will define the indications and outcomes for new combination products for reconstruction of lost bone associated with revision total joint replacement.