Osteonecrosis of the femoral head is a disabling pathology affecting a young population (average age at treatment, 33 to 38 years) and is the most important cause of total hip arthroplasty in this population. It reflects the endpoint of various disease processes that result in a decrease of the femoral head blood flow. The physiopathology reflects an alteration of the vascularization of the fine blood vessels irrigating the anterior and superior part of the femoral head. This zone of necrosis is the source of the loss of joint congruence that leads to premature wear of the hip. Several different types of medication have been developed to reverse the process of ischemia and/or restore the vascularization of the femoral head. There is no consensus yet on a particular treatment. The surgical treatments aim to preserve the joint as far as the diagnosis could be made before the appearance of a zone of necrosis and the loss of joint congruence. They consist of bone marrow decompressions, osteotomies around the hip, vascular or non-vascular grafts. Future therapies include the use of biologically active molecules as well as implants impregnated with biologically active tissue. Cite this article: EFORT Open Rev 2019;4:85-97. DOI: 10.1302/2058-5241.4.180036

Standardized particulate bone constructs, obtained by expanding autologous mesenchymal stem cells (MSCs) onto coral granules in vitro, were transplanted into long-bone, critical-size defects in sheep. Control experiments were also performed in which autologous bone grafts were implanted. Defect cavities were lined with a preformed vascularized membrane (induced by temporarily inserting a cement spacer for 6 weeks prior to bone construct implantation), which served as a mold keeping the engineered bone granules in place. Radiographic, histological, and computed tomographic tests performed 6 months later showed that the osteogenic abilities of the engineered construct and autograft were significantly greater than those of coral scaffold alone. No significant differences were found between the amount of newly formed bone in defects filled with coral/MSCs and those filled with autograft, yet radiological scores differed significantly between the two groups (21% and 100% healed cortices, respectively). The present study on a clinically relevant animal model provides the first evidence that standardized particulate bone constructs can be used to repair large bone defects and that their osteogenic ability approaches that of bone autograft, the bone repair benchmark. By proving feasibility, the present study makes possible the treatment of segmental bone losses with bone constructs engineered from granules, a process which is much simpler than preparing customized massive constructs using computer-assisted techniques. Important parameters, such as the rate of scaffold resorption and the number of MSCs to be seeded on the scaffolds, need to be optimized before reaching pertinent definitive conclusions. ß

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