G. Knutsen, J.O. Drogset, L. Engebretsen, T. Grøntvedt, T.C. Ludvigsen, E. Solheim, T. Strand, and O. Johansen reply:
We agree that our results cannot be generalized to the full spectrum of patients who present with cartilage injuries. We reported the size and location of the defects and clinical data for the enrolled patients.
Only defects on the weight-bearing medial and lateral femoral condyles were included, and that has to be considered when our results are interpreted. Far more patients would have been needed in our study to justify stratification into several subgroups. Furthermore, the fact that our cohort of patients had relatively large chronic defects has to be kept in mind. Clearly, there is a need for additional studies. Even longer follow-up of our cohort is needed, and we are aware of other ongoing randomized trials that could increase the evidence base in this difficult field.
Our group reported the two-year results in 20041. We reported that patients with a lesion of >4 cm2 had significantly better clinical results following microfracture than did those with a bigger defect (p < 0.003). We did not find this association between the sizes of the defect and the clinical outcome in the group treated with autologous chondrocyte implantation (p > 0.89). At the five-year follow-up evaluation, we tested the interaction between the sizes of defects, clinical results, and treatment group (p = 0.053). There was, at five years, a tendency for patients with smaller defects in the microfracture group to have better clinical results. This tendency was not present in the autologous chondrocyte implantation group.
We reported, in our first paper1, that we would have needed 120 biopsies to find a significant difference regarding histological outcome between the two groups. This implies, as mentioned, that our study was not adequately powered to demonstrate a significant difference between the two groups with regard to histological findings. However, we reported a tendency (p = 0.08) for the autologous chondrocyte implantation procedure to result in more hyaline repair cartilage than was seen after the microfracture procedure.
These letters originally appeared, in slightly different form, on . They are still available on the web site in conjunction with the article to which they refer.