Two‐ and three‐dimensional optical coherence tomography to differentiate degenerative changes in a rat meniscectomy model

Optical coherence tomography (OCT) is an attractive tool for evaluating cartilage. We developed an OCT system that reconstructs and analyzes a three-dimensional (3D) OCT image by determining the cartilage surface and cartilage-bone boundary from the image taken with currently available OCT devices. We examined the usefulness of 3D renderings of OCT images. In a rat meniscectomized model, the tibia was harvested after 0, 2, 4, or 8 weeks (n = 6). We scanned 300 slices in the y-plane to cover a 4 × 3 × 6-mm section (x-plane; 10 µm × 400 pixels, y-plane; 10 µm × 300 pixels, z-plane; 12.66 µm × 500 pixels) of the medial tibial cartilage. The cartilage surface line and the cartilage-bone boundary were plotted semi-automatically. Slices from 300 two-dimensional (2D) sequential images were systematically and visually checked and corrected, as necessary. We set a region of interest in the cartilage and quantified the cartilage volume in the 3D image. The Osteoarthritis Research Society International (OARSI) histological score was also obtained. The cartilage volume determined using 3D OCT images was 0.291 ± 0.022 mm3 in the normal, 0.264 ± 0.009 mm3 at 2 weeks, 0.210 ± 0.012 mm3 at 4 weeks, and 0.205 ± 0.011 mm3 at 8 weeks. The cartilage volume significantly decreased at 4 and 8 weeks and was significantly correlated with the OARSI histological score (r = -0.674; P = .002). Although the 3D image information could be obtained from the 2D images, the 3D OCT images provided easier-to-understand information because the 3D reconstructed cartilage provided information about the smoothness of the surface, the area, and depth of the defect at a glance.