Articular cartilage repair is the improvement of defects of the joint cartilage, either by surgery or biological intervention.

Microfracture - a marrow stimulation technique, where holes are picked through the cartilage base plate, to allow blood and cells to track through into the defect.

In ACI - a cell-based therapy - cartilage cells are multiplied in the laboratory and injected into the defect behind a membrane.
Cartilage repair is part of regenerative medicine
There is a lot of focus currently on regenerative techniques for restoring damaged joint cartilage. Procedures include microfracture, nanofracture, ACI, mosaicplasty, MACI, AMIC, NAMIC, stem cell injections and microfragmented fat injections.
CLINICAL PUBLICATIONS
Clinical articular cartilage repair—an up to date review. Brittberg M. Annals of joint. 2018. Vol 3. (http://aoj.amegroups.com/article/view/4788/pdf)
Cell-Based Articular Cartilage Repair: The Link between Development and Regeneration. Caldwell KL and Wang J. Osteoarthritis Cartilage. 2015 Mar; 23(3): 351–362.
Cartilage repair in the degenerative ageing knee. Brittberg M, Gomoll AH, Canseco JA, Farr J, Lind M and Hui J. Acta Orthop. 2016 Dec; 87(Suppl 363): 26–38.