When the knee has a focal area of arthritis that is small and localised, it may be possible to undertake a rejuvenative procedure where the underlying bone marrow is stimulated through a series of fenestrations or holes in the exposed subchondral bone to allow for the formation of a cartilage cap over the focal area of arthritis.
Where patients have an area of articular (hyaline) cartilage missing from the load bearing surfaces of the knee, this chondral (cartilage) ulcer or defect can result in inflammation developing within the underlying bone resulting in significant pain, and often secondary swelling within the knee that can lead to a sensation of tightness and aching. If this chondral defect is localized and the surrounding cartilage is in good condition, then a technique of bone marrow stimulation or “microfracture” may be suitable, to encourage the defect to be filled with substitute (fibrocartilage) cartilage.
This technique has been used for more than two decades with good results in over 50% of cases, and equal or better results than other techniques including cartilage transplant, with the added advantage of being able to be performed through keyhole technique, without need for a second surgical procedure at a later date with a large incision.
Usually, patients undergoing microfracture, will also undergo a chondroplasty (see Arthroscopy) first where necessary, before making a series of holes at a perpendicular to the bony surface underlying the chondral defect. This microfracture is performed using a narrow curved and pointed metallic device or “Steadman’s awl” which is carefully positioned at regular intervals across the defect and advanced from the superficial joint level into the deeper underlying subchondral bone, with an objective of reaching bleeding bone, in order to stimulate the bone marrow.
Following microfracture, if adequate fibrocartilage forms in the defect it may; decrease the degree of swelling and pain experienced within the knee, allow for increased levels of function from the pre-operative state, and may delay the rate of progression of the dimensions of the chondral ulcer.
Microfracture is generally reserved for knees with smaller chondral defects and relatively normal alignment and requires a period of four to six weeks on crutches, and results in the formation of fibrocartilage rather than hyaline cartilage. Whilst fibrocartilage is generally considered to have less shielding capability and durability compared to hyaline cartilage, newer techniques combining microfracture with stem cell therapy may allow for improvements in the amount and quality of cartilage formed in these defects using these techniques.