Immunohistochemical evidence for hyaline-like cartilage formation after autologous matrix-induced chondrogenesis for osteochondral lesions of the talus: Case reports of 2 patients.

Objectives As a surgical option for osteochondral lesions of the talus, autologous matrix-induced chondrogenesis (AMIC®) combines bone marrow stimulation, filling of subchondral defects, and application of a collagen bilayer matrix. The purpose of the study was to analyze the cartilage at the treated defect site in two patients.Methods Two patients underwent revision surgery (14 and 36 months after the index AMIC® procedure) for failure due to ligamentous instability. During revision, the repair cartilage was evaluated regarding its integration, presence of fissures, thinning, or firmness. Samples for histologic evaluation were taken from the centre of the treated site. The samples were examined using standard histological and immunohistochemistry techniques.Results During the revision arthroscopy, the regenerated cartilage was the same color but softer than the surrounding cartilage, superficially frayed, without fissures and even with the level of the original cartilage, but not completely stable on the subchondral bone. Histology revealed the presence of Safranin-O-positive fibrocartilage-like tissue. Additionally, cartilaginous-like tissue was found in the 36-month biopsy. IHC revealed a fraction of collagen type II positive cells in the fibrocartilage-like tissue as well as a collagen type II positive extracellular matrix. The cartilaginous tissue of the 36-month biopsy revealed a homogeneous collagen type II stain.Conclusions The presence of collagen type II within the tissue indicates its transformation into hyaline-like cartilage at 14 months after AMIC® continuing up to 36 months. While second-look arthroscopies and histological analyses are rare, the data presented here demonstrate cartilage regeneration, with a progressive formation of a hyaline-like cartilaginous tissue in the talus after AMIC®.