Matrix-assisted chondrocyte implantation (MACI)

What it is

At the first stage, a short arthroscopy confirms the defect and a tiny biopsy of healthy cartilage is taken from a low-load area. A specialised laboratory grows the cells, called chondrocytes, over several weeks and seeds them onto a collagen membrane.

At the second operation the defect is prepared, and the cell-loaded membrane is cut to shape and fixed in place, usually with a biological glue.

Why it matters for patients

The aim is repair tissue that is closer to normal hyaline cartilage than the fibrocartilage formed after microfracture, and it can treat larger defects than osteochondral plugs. Studies have shown durable results in suitable patients.

It does involve two procedures, a long and carefully staged rehabilitation over many months, and dependence on laboratory processing and regulatory availability. It is not offered everywhere.

Who it suits

It is mainly considered for younger, active adults with a symptomatic, isolated cartilage defect, often a few square centimetres in size, on the thighbone or kneecap, with stable ligaments, good alignment and no widespread arthritis. Other problems, such as malalignment, may need correcting at the same time.