We have been through the phase of excitement of joint replacement and are now entering the phase of trying to restore function with the purpose of actually delaying joint replacement surgery
All the current procedures require diligence during the rehabilitation period, as cartilage needs joint motion in order to be nourished properly but at the same time the new replacement cartilage tissue needs protection as it matures into stronger tissue.
This is a procedure to flatten the softened and roughened joint cartilage at the early stages of breakdown, to clear away any damaged bits and stop and enzyme release which might further the damage. The cartilage damage at this stage has not gone quite through to the bone and the defect can heal over more or less.
This would be chosen when joint surface damage goes right down to bone. When it is this deep the joint cartilage cannot regenerate without help. Abrasion arthroplasty rubs the damaged bits right down into the bone, until there is bleeding, in the hope that bone marrow cells will migrate into the area and turn themselves into a type of cartilage called 'fibrocartilage' - not as strong as real cartilage but the best the bone marrow can do.
The problem here is that the fibrocartilage regeneration is sometimes a little prolific and forms raised areas which interfere with the mechanics of the knee. Also the heat of the burr can damage the bone cells (this was also found in the technique of drilling, which has been replaced by microfracture).
Microfracture tries to do the same without the heat of the burr. A sharp instrument is knocked into the damaged surface to create a number of small pucture wounds. After microfracture the patient needs to use crutches for quite a number of weeks to avoid damaging the new replacement layer.
This is a technique for medium sized areas of discrete damage. The surgeon uses an instrument a bit like an apple-corer to core out a circle of damaged cartilage and replaces it with a piece of normal cartilage from a less important part of the same knee. The principle here is that this grows to cover the edges of the core using proper cartilage cells and not the weaker fibrocartialge cells.
This technique is used in some areas but has not generally become popular. Normal cartilage is taken and ground up into a paste and pasted back into the damaged area.
Large areas of damage do not mean you have to give up the ghost on this cartilage regeneration thing. The surgeon can take a little bit of normal cartilage and send it to a lab to be cultured and then in a second operation the cells are injected into the damaged area which has been prepared by a flap of fibrous material from over the bone being sewed over the damaged area to retain the cells.