Figure 1

The arthroscopy (left) and OCT (right) images of the metacarpo-/metatarsophalangeal joint. The circular object in OCT images is the OCT catheter (diameter = 0.9 mm). a) Dorsal aspect of the lateral sesamoid bone. In the arthroscopic view the tip of the custom made hollow instrument with OCT catheter lie on the examined cartilage surface (ICRS score 0). In the OCT image the articular surface (white arrow) and the interface between cartilage and subchondral bone are visible (open arrow). b) In the arthroscopic view cartilage of the dorsal aspect of the lateral sesamoid bone with lesion (open arrow) is visualized, synovial villi can be seen in the right. The OCT image shows the same lesion (ICRS score 2) with cartilage flap (open arrow) still attached. c) In the arthroscopic view cartilage of the dorsal aspect of the medial sesamoid bone with roughening of the surface is in the left, synovial villi are in the right. The OCT image shows the fibrillation with high definition (ICRS score 2). Beneath the cartilage surface there is cavitation (open arrows) and within the subchondral bone an anomaly (white arrow) can be seen. d) In the view of an arthroscope dorsolateral condyle of third metacarpal bone with cartilage lesion below the OCT catheter can be seen. In the OCT image the lesion (ICRS score 1) and also anomalies beneath the cartilage surface are visible (arrows). e) Severe lesion (ICRS score 4, arrow) of medial sesamoid bone with complete loss of cartilage can be seen in both arthroscope and OCT images.