[Partial and complete joint transplantation with fresh osteochondral allografts-the FLOCSAT concept]

Cartilage defects in adult patients do not heal well. Fresh osteochondral allograft (OCA) transplantation is based on mature, living, mechanically sound hyaline cartilage attached to a bone interface, which is brought into an osteochondral defect, where it becomes osseointegrated. According to current knowledge, intact hyaline cartilage tissue is immune privileged and does not, in contrast to bone, meniscus or ligaments, cause an immune reaction. The technique has the unique advantage of transplanting viable, mature and mechanically stable hyaline cartilage into the affected area. An OCA is the only biological surgical technique for chondral and osteochondral lesions after failed cell-based techniques or autologous osteochondral transplantation.Fresh osteochondral allografts with mainly small cylindrical transplants show survival of 20 years and more. Based on this experience the FLOCSAT (fresh large [> 10 cm²] osteochondral shell allograft transplantation) concept with the thinnest possible (< 6-8 mm) bone thickness has been developed. Cells survive in special media at 4 °C for 4 weeks or more and are transplanted with a minimum of 70% living cells in a live/dead assay and cell density > 200 cells/mm².FLOCSATs can replace parts or entire joints as uniplanar or multiplanar(n-planar)-FLOCSAT, as unipolar, bipolar or tripolar(n-polar)-FLOCSAT, and in combination with meniscus and/or ligaments (nMnL)-FLOCSAT (n number of structures).The FLOCSAT concept was applied successfully to knee, ankle and elbow joints. All transplants showed sound osseointegration. Cartilage failure was the reason for unsuccessful outcome. Challenges remain regarding graft availability, precise size matching, complex logistics, demanding surgical technique in complex geometries, and open questions in immunology and chimerism.