Microfracture is a surgical procedure where a tiny 'pick' is used to spike holes through damaged joint cartilage into the bone below with a view to stimulating bleeding and formation of new fibrocartilage.

The rounded end of the femur, where the joint cartilage has worn away to show the yellowish bone. You can see the pick holes of microfracture piercing through the base plate of the cartilage.

The pick has a long stem and is driven in via the keyhole by the surgeon from the outside of the joint using a small hammer.
How does microfracture work?
The procedure allows migration of marrow cells into the resultant clot, thus facilitating new fibrocartilage formation to cover the defect. The technique was first proposed by Dr Richard (Dick) Steadman, and is one of a group of procedures now referred to as 'marrow stimulation techniques'. The procedure is losing way to nanofracture using a needling device that creates narrower holes, together with augmentation with other regenerative methods such as the injection of stem cells, microfragmented fat or paste grafts.
Pain after microfracture
Rehabilitation after microfracture can be a challenge. The procedure is quite painful and the joint surface has to be protected by non weight bearing until fibrocartilage covers the defect.
CLINICAL PUBLICATIONS
Second Generation Needling Techniques for the Treatment of Chondral Defects in Animal Model. Zedde P, Cudoni S, Manunta L, Passino ES, Masala G, Brunetti A, Uboldi FM and Manunta AF. Joints. 2017 Mar; 5(1): 27–33.