[Evidence-based therapy for cartilage lesions in the knee - regenerative treatment options]

The treatment of cartilage defects has seen a shift from replacement to regeneration in the last few years. The rationale behind this development is the improvement in the quality-of-care for the growing segment of young patients who are prone to arthroplasty complications because of their specific characteristics - young age, high level of activity, high demand for functionality. These days, two of the most popular regenerative treatments are microfracture and autologous chondrocyte implantation (ACI). Although these new options show promising results, no final algorithm for the treatment of cartilage lesions has been established as yet.

The objective of this review is to describe and compare these two treatment options and to present an evidence-based treatment algorithm for focal cartilage defects.

Microfracture is a cost-effective, arthroscopic one-stage procedure, in which by drilling of the subchondral plate, mesenchymal stem cells from the bone marrow migrate into the defect and rebuild the cartilage. ACI is a two-stage procedure in which first chondrocytes are harvested, expanded in cell culture and in a second open procedure reimplanted into the cartilage defect. Microfracture is usually used for focal cartilage defects < 4 cm2, the treated defect size of the ACI seems to have a wider range. The effectiveness of these two treatments has been shown in long-term longitudinal studies, where microfracture showed improvement in up to 95 % of patients, whereas 92 % of the patients in a 2-9 year period of follow-up after ACI showed improvements, respectively. The successful outcome of the treatment depends on multiple factors such as the location of the defect, cell differentiation and proliferation, concomitant problems, and the age of the patient. Associated complications and disadvantages of the two different applications are, for the microfracture patient, a poor tissue differentation or a formation of an intra-lesional osteophyte, and for the ACI patient, periosteal hypertrophy and the need for two procedures in ACI. Only a few studies provide detailed and evidence-based information on a comparative assessment. These studies, however, are showing widely similar clinical outcomes but better histological results for ACI, which are likely to translate into better long-term outcomes.

Although evidence-based studies comparing microfracture and ACI have not found significant differences in the clinical outcome, the literature does show that choosing the treatment based on the size and characteristics of the osteochondral lesion might be beneficial. The American Association of Orthopedic Surgeons suggest that contained lesions < 4 cm2 should be treated by microfracture, lesions bigger than that by ACI.