Osteoarthritis is the most common joint disease and a major cause of disability. The knee is the large joint most affected. While chronological age is the single most important risk factor of osteoarthritis, the pathogenesis of knee osteoarthritis in the young patient is predominantly related to an unfavorable biomechanical environment at the joint. This results in mechanical demand that exceeds the ability of a joint to repair and maintain itself, predisposing the articular cartilage to premature degeneration. This review examines the available basic science, preclinical and clinical evidence regarding several such unfavorable biomechanical conditions about the knee: malalignment, loss of meniscal tissue, cartilage defects and joint instability or laxity.Level of evidence IV.

Background: Various approaches have been proposed to treat articular cartilage lesions, which are plagued by inherent limited healing potential. Purpose: To compare the clinical outcome of patients treated with second-generation autologous chondrocyte implantation implants with those treated with the microfracture repair technique at 5-year follow-up. Study Design: Cohort study; Level of evidence, 2. Methods: Eighty active patients (mean age, 29.8 years) and grade III to IV cartilage lesions of the femoral condyles or trochlea were treated with arthroscopic second-generation autologous chondrocyte implantation Hyalograft C or microfracture (40 patients per group). Patients achieved a minimum 5-year follow-up and were prospectively evaluated. Results: Both groups showed statistically significant improvement of all clinical scores from preoperative interval to 5-year follow-up. There was a significant improvement for the International Knee Documentation Committee subjective score from preoperative to 5-year follow-up (Wilcoxon test, P < .001). In the microfracture group, the International Knee Documentation Committee objective score increased from 2.5% normal and nearly normal knees before the operation to 75% normal and nearly normal knees at 5-year follow-up, and the subjective score increased from 41.1 ± 12.3 preoperatively to 70.2 ± 14.7 at 5-year follow-up. In the group treated with Hyalograft C, the International Knee Documentation Committee objective score increased from 15% normal and nearly normal knees before the operation to 90% normal and nearly normal knees at 5-year follow-up, and its subjective score increased from 40.5 ± 15.2 preoperatively to 80.2 ± 19.1 at 5-year follow-up (Wilcoxon test, P < .001). When comparing the groups, better improvement of the International Knee Documentation Committee objective (P < .001) and subjective (P = .003) scores was observed in the Hyalograft C group at 5-year follow-up. The return to sports at 2 years was similar in both groups and remained stable after 5 years in the Hyalograft C group; it worsened in the microfracture group. Conclusion: Both methods have shown satisfactory clinical outcome at medium-term follow-up. Better clinical results and sport activity resumption were noted in the group treated with second-generation autologous chondrocyte transplantation.