In 2009, at the time the study was undertaken, it was accepted that full cartilage defects of joint (articular) cartilage have limited to no spontaneous repair potential, and that several procedures had been developed to try and improve the situation.
In the discussion of the topic they refer to papers showing that marrow stimulation techniques, particularly microfracture, are an appropriate first line of treatment with good to excellent results in 60-80% with comparatively quick recovery and low morbidity (ie there are not many complications). In defects bigger than 2cm by 2cm, microfracture does less well and ACI has a better outcome. In the smaller defects where microfracture is appropriate, the procedure seems to do better when the defect is on the weightbearing areas of the femoral condyle, while defects on the tibial and patellar areas do less well.
The authors further noted that researchers are beginning to realise that osteoarthritis (OA) is not simply a disorder of the articular cartilage but also of the bone beneath the cartilage (the 'sub-chondral' bone). OA can actually be triggered by micro-fractures and micro-cracks - in follow-up surgery after marrow stimulation techniques, and especially the technique of microfracture, osteophytes (bony outgrowths of OA) have commonly been seen protruding through the initial surgical area. Even where there is a layer of cartilage cover over the osteophyte, the cartilage is frequently seen to be thinner here and more susceptible to further damage. MRI studies have shown such bony outgrowths in 27-33% of patients after surgical microfracture. The authors theorise that this altered subchondral bone may be responsible for the worse outcomes in both chronic (long standing) defects and after marrow stimulation techniques.
In ACI surgery that has failed after previous marrow stimulation techniques the signs of failure may include -
- central degeneration over an osteophyte within the defect
- subchondral cysts (cavities in the bone under the defect).
In their series of 321 patients undergoing ACI, they found a 3X higher failure rate where the ACI had been preceded by a marrow stimulation technique than in those patients who had not had a previous marrow stimulation technique. Their small numbers were not sufficient to statistically confirm whether the newer procedure of microfracture had a lesser negative effect than the older procedures of drilling or abrasion arthroplasty, but their figures did suggest such a possibility.
In the same study, the researchers also attempted to determine whether people who have had a marrow stimulation technique fail are somehow biologically different from other people. They compared in the same person defects repaired with ACI alone to defects repaired with ACI where there had been a prior marrow stimulation technique. Although the sample numbers were small, it did appear that there were worse ACI outcomes where there had been a prior marrow stimulation techniqe.
As a criticism of their study they pointed out that the marrow stimulation procedures in their group of patients were more often those of drilling and abrasion chondroplasty than microfracture, simply because microfracture was a newer technique and fewer of their patients had had this procedure.
In their conclusion they re-iterated that their studies demonstrated a three fold increase in failure rate of ACI after previous marrow stimulation, but they pointed out that it seems to be mainly in the larger defects that prior marrow stimulation seems to compromise subsequent ACI. With time, as more microfracture procedures (as compared to the earlier drilling and abrasion chondroplasty procedures) are entered into studies like this, they expect to be able to be more specific about whether microfracture is as detrimental as the other two procedures.