Asymptomatic focal calcium pyrophosphate crystal deposition within partially failed repair tissue after matrix-assisted autologous chondrocyte implantation

Possible failures of autologous chondrocyte implantation (ACI), a cell-based technique for articular cartilage repair, are not always clinically apparent and the underlying mechanisms largely remain unknown. This case report presents the first scenario in the literature highlighting an association of a medium-term partial failure of an advanced ACI procedure (matrix-assisted ACI) in the knee with focal asymptomatic calcium pyrophosphate deposition disease, a common inflammatory pyrophosphate arthropathy. The specific presence of CPPDs, resulting from increased biomechanical stresses in the repair tissue–cartilage and repair tissue–subchondral bone integration sites, together with the absence of cartilage regeneration was identified and possibly contributed to the partial failure.