An osteochondral allograft is transplant of a plug of bone and cartilage from a donor into a prepared matching defect in the patient.

Viability of allograft plugs
This technique is usually reserved for large cartilage defects, where the cartilage damage is full thickness. Fresh allograft is purchased from a tissue bank as a block of bone and cartilage, from which the surgeon harvests the plug. The success of the procedure depends upon the viability of the fresh cells, which can only be stored for a month or two after any necessary processing.
CLINICAL PUBLICATIONS
Osteochondral allograft. Torrie AM, Kesler WM, Elkin J and Gallo RA. Curr Rev Musculoskelet Med. 2015 Dec; 8(4): 413–422.
Knee salvage procedures: The indications, techniques and outcomes of large osteochondral allografts. Chui K, Jeys L and Snow M. World J Orthop. 2015 Apr 18; 6(3): 340–350.
Large Osteochondral Allografts of the Knee: Surgical Technique and Indications. Pisanu G et al. Joints. 2018 Mar; 6(1): 42–53.
Osteochondral Allograft Transplantation for Treatment of Focal Patellar Osteochondral Lesion. Ferrari, Sanchez G, Chang A, Sanchez A, Ellera Gomes, JL and Provencher MT. Arthrosc Tech. 2017 Aug; 6(4): e907–e912.