Autogenous Chondrocyte Implantation (ACI) is a procedure used to treat painful cartilage defects, primarily in the knee. This procedure is best suited for young patients without preexisting arthritis in their joint. The procedure is performed in two stages. In the first stage, a small sample of cartilage is harvested during knee arthroscopy. The sample is then sent to a lab where the cartilage cells are expanded. The new, amplified tissue is sent back to the surgeon. In the second stage of the procedure, the tissue is implanted into the articular cartilage defect in the patient’s knee with the goal of creating a stable cartilage filling and alleviating the knee symptoms. Prior generations of this technique, which were popularized in Europe, required the cells to be in liquid form which made implantation tedious and challenging. The newest generation of this technology (matrix autogenous chondrocyte implantation or MACI) utilizes a porcine membrane to contain the newly grown cells and allow more effective implantation.