Fig. 3.

Figs. 3-A through 3-L Morphological MRI evaluation shows subchondral bone changes but may not show surface defects apparent through arthroscopic and histological evaluation. Bilateral images from the same horse 1 year after treatment of full-thickness chondral defects with microfracture on 1 side (Figs. 3-A through 3-F) compared with bone marrow concentrate (BMC) on the contralateral side (Figs. 3-G through 3-L). The microfracture repair was determined to be of higher overall quality by arthroscopic surface imaging and examination (Figs. 3-A and 3-G). However, cross-sectional MRI and histological assessments showed compromised subchondral bone in the microfracture group (Figs. 3-B through 3-F). Arthroscopic (Figs. 3-A and 3-G) and histological evaluation (Figs. 3-E through 3-L) also showed surface defects (arrows) in both repairs that were not apparent on morphological MRI (Figs. 3-B and 3-H), likely because of partial volume effects. Images from the defect treated with microfracture (Figs. 3-A through 3-F) show good repair tissue fill with incomplete peripheral integration, central full-thickness fissuring, and compromised subchondral bone. Images from the defect in the contralateral limb treated with BMC (Figs. 3-G through 3-L) show good repair tissue fill with incomplete peripheral integration and intact subchondral bone. Morphological MRI (Figs. 3-B and 3-H) shows thicker repair tissue in the microfracture repair (Fig. 3-B). Quantitative MRI T2 maps (Figs. 3-C and 3-I) and UTE-T2* maps (Figs. 3-D and 3-J) suggest improved partial recovery of laminar patterns in the repair zones of the BMC repairs (Figs. 3-I and 3-J). This qualitative interpretation is reflected in the overall texture analysis of UTE-T2* maps, which showed greater “contrast,” less “homogeneity,” and less “energy” for BMC repairs compared with microfracture. Hematoxylin and eosin staining (Figs. 3-E and 3-K) demonstrates deep to full-thickness tissue voids and fissures (arrow) as well as deep-tissue heterogeneity and a bone void (arrowhead) below the repair treated with microfracture (Fig. 3-E). The hematoxylin and eosin staining of the BMC repair shows incomplete integration (arrow) with more intact deep tissue and no bone void (Fig. 3-K). Safranin O-fast green staining shows no substantial proteoglycan in the repair tissues (Figs. 3-F and 3-L).