NIRS for evaluation of cartilage lesions. Light from a stabilized light source was coupled into six optical fibers. The collection fiber (silica glass, 200 μm diameter) was connected to the spectrometer. The fibers were combined in a reflection-probe with the light delivering fibers surrounding the collection fiber. The design of the probe was similar to a routine arthroscopic hook (A). The intraoperative measurements were performed by using the probe in the same way as a hook (B and C). The top of the hook shows the end of the optical fibers (D).