This study by Krych et al. compared the clinical outcomes of osteochondral autograft transfer (OAT) and microfracture (MFX). The patient-oriented outcomes of interest included the Short Form-36 (SF-36) Health Survey, the Activities of Daily Living Scale of the Knee Outcome Survey, the International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form, and the Marx Activity Rating Scale for Disorders of the Knee.
The study design was a retrospective comparative study—a Level-III therapeutic study. For each patient in the OAT group, the authors matched a control MFX patient from an institutional cartilage registry, accounting for sex, chondral defect location, and chondral defect size. Patients were followed for a minimum of two years.
In comparing the OAT and MFX groups, the authors found no significant differences at any of the time points (one, two, three, and five-year follow-up evaluations) for the SF-36, Knee Outcome Survey, or IKDC scores. However, the Marx Activity Rating Scale score for the MFX group declined from 7.3 at baseline to 4.1 at one year, 3.7 at two years, and 2.9 at three and five years. In contrast, the activity score for the OAT group responded more favorably, changing from 6.4 at baseline to 5.2 at one year, 7.3 at two years, 7.8 at three years, and 8.6 at five years.
The authors of the current study proposed that the fibrocartilage that developed following MFX was less durable than the transferred hyaline cartilage. The authors further proposed that the lower activity scores in the MFX group were likely the result of patients modifying their activity level to one that provided satisfactory knee function and comfort. These theories are certainly plausible.
These findings are consistent with the results of a randomized clinical trial by Gudas et al. comparing OAT and MFX in young athletes, in which it was reported that twenty-six (93%) of the OAT patients and fifteen (52%) of the MFX patients returned to sports activities at the preinjury level1. In addition, Gudas et al. reported that the MFX patients with a lesion larger than 2 cm2 had significantly worse clinical results compared with those who had smaller lesions1. They did not find such an association between defect size and the clinical outcome in the OAT group1. Similarly, in a randomized clinical trial by Knutsen et al. comparing autologous chondrocyte implantation (ACI) and MFX, the MFX patients with a lesion larger than 4 cm2 had significantly worse clinical results compared with patients with a smaller defect2. They did not find such an association between the size of the defect and the clinical outcome in the ACI group2.
The impact of the paper by Krych et al. on clinical practice is primarily limited by the study design. Selection of the treatment choice was not randomized, which allowed for introduction of bias in the selection of the treatment for each patient. In fact, the MFX group included three patients with osteochondritis dissecans lesions (6%) compared with fifteen (31%) in the OAT group. Furthermore, no patients in the MFX group had undergone previous cartilage procedures, whereas sixteen patients (33%) in the OAT group had previously undergone an unsuccessful microfracture procedure. Randomization would have equally distributed known and unknown confounders among the study groups.
The current study by Krych et al. supports the concept that the fibrocartilage that forms following MFX is not as robust as the hyaline cartilage that is transferred in OAT. I would be very interested to see these results stratified by lesion size. This paper has further educational value in highlighting how patients can remain satisfied with a procedure despite lowered activity levels.