The Illustrative First and Second Generation Autologous Chondrocyte Implantation (ACI) for Cartilage Repair

Autologous chondrocyte implantation (ACI) was first introduced clinically in 1987 [1]. In this procedure, cartilage biopsies are harvested from a minor load-bearing area of the knee. These cartilage slices are then sent to a cartilage laboratory for cell isolation and expansion for several weeks. The expanded increased numbers of cells are returned to the surgeon as a chondrocyte suspension. The cell suspension is to be injected into the defect covered with a membrane of periosteum (first generation, P-ACI). The periosteum being a living tissue could develop into a hypertrophy with mechanical symptoms as a consequence, requiring a revision surgery to shave off the hypertrophied periosteum. Hence some years later, use of the collagen membrane (second generation, C-ACI) started instead of a periosteum patch to reduce the chances of hypertrophy, graft delamination, etc. The second-generation ACI with a collagen membrane had less chances of a revision surgery.