Background: Quantitative MR, including T 1ρ mapping, has been extensively used to probe early biochemical changes in knee articular cartilage of subjects with osteoarthritis (OA) and others at risk for cartilage degeneration, such as those with anterior cruciate ligament (ACL) injury and reconstruction.However, limited studies have been performed aimed to assess the spatial location and patterns of T 1ρ . In this study we used a novel voxel-based relaxometry (VBR) technique coupled with principal component analysis (PCA) to extract relevant features so as to describe regional patterns and to investigate their similarities and differences in T 1ρ maps in subjects with OA and subjects six months after ACL reconstruction (ACLR).Methods: T 1ρ quantitative MRI images were collected for 180 subjects from two separate cohorts. The OA cohort included 93 osteoarthritic patients and 25 age-matched controls. The ACLR-6M cohort included 52 patients with unilateral ACL tears who were imaged 6 months after ACL reconstruction, and 10 agematched controls. Non-rigid registration on a single template and local Z-score conversion were adopted for T 1ρ spatial and intensity normalization of all the images in the dataset. PCA was used as a data dimensionality reduction to obtain a description of all subjects in a 10-dimensional feature space. Logistic linear regression was used to identify distinctive features of OA and ACL subjects Conclusions: This study is the first example of T 1ρ local/regional pattern analysis and data-driven feature extraction in knees with cartilage degeneration. Our results revealed similarities and differences between OA and ACL relaxation patterns that could be potentially useful to better understand the pathogenesis of posttraumatic cartilage degeneration and the identification of imaging biomarkers for the early stratification of subjects at risk for developing post-traumatic OA.

A model for orthotopic whole knee transplantation in syngeneic Lewis rats is presented. The donor knee was isolated on the femoral vessels 1 cm superior and inferior to the knee joint. A minimal muscle cuff was left attached to ensure adequate circulation to the graft via the popliteal vessels. The graft was transplanted to the recipient animal and secured in an orthotopic position by two intramedullary Kirschner wires. The graft pedicle was anastomosed to the recipient's femoral vessels and the muscular elements sutured. Preliminary results are reported, and future implications on growth plate autograft transplantation are discussed.

1A). The femoral trochlea compartment (TrF) showed the most diffuse association 24% of the overall voxels in the compartment showed a significant correlation with KOOS (average on the 5 scores). Patella compartment (P) showed the strongest association (average R ¼ 0.3). Significant positive association was also observed between T1r and the first peak of the PFJ stress (Figure 1B). Medial Femur (MF) and TrF are the compartments with the largest associated: 40% and 29% respectively. Lateral Tibia (LT) and TrF showed the strongest correlation (average R ¼ 0.31). P-values and R SPMs are shown in Figure 2.