Introduction. Anteromedial osteoarthritis of the knee (anteromedial gonarthrosis-AMG) is a common form of knee arthritis. In a clinical setting, knee arthritis has always been assessed by plain radiography in conjunction with pain and function assessments. Whilst this is useful for surgical decision making in bone on bone arthritis, plain radiography gives no insight to the earlier stages of disease. In a recent study 82% of patients with painful arthritis had only partial thickness joint space loss on plain radiography. These patients are managed with various surgical treatments; injection, arthroscopy, osteotomy and arthroplasty with varying results. We believe these varying results are in part due to these patients being at different stages of disease, which will respond differently to different treatments. However radiography cannot delineate these stages. We describe the Magnetic Resonance Imaging (MRI) findings of this partial thickness AMG as a way of understanding these earlier stages of the disease. Method. 46 subjects with symptomatic partial thickness AMG underwent MRI assessment with dedicated 3 Tesla sequences. All joint compartments were scored for both partial and full thickness cartilage lesions, osteophytes and bone marrow lesions (BML). Both menisci were assessed for extrusion and tear. Anterior cruciate ligament (ACL) integrity was also assessed. Osteophytes were graded on a four point scale in the intercondylar notch and the lateral margins of the joint compartments. Scoring was performed by a consultant radiologist and clinical research fellow using a validated MRI atlas with consensus reached for disagreements. The results were tabulated and relationships of the interval data assessed with linear by linear Chi2 test and Pearson's Correlation. Results. All cases had medial femoral cartilage loss; 22% partial and 78% full thickness. 79% showed medial tibial loss, however in no cases was there medial tibial loss without femoral loss. 10 cases had lateral compartment partial thickness cartilage loss. Again, there was no tibial loss without femoral loss present. Increasing size of intercondylar notch osteophyte is associated with increasing ACL damage (p=0.001). Independent to this, increasing ACL damage is associated with lateral femoral condyle cartilage loss (p=0.002). Throughout the knee the incidence of BMLs increased with increasing cartilage loss (p=0.025). Only 13% of medial menisci were normal. As meniscal damage increases, so does the incidence of BMLs in the same compartment (p=0.03). Discussion. We describe the MRI findings of early AMG with partial thickness joint space loss. In all cases there was medial femoral loss, either with or without tibial loss. We believe the disease begins on the medial femoral condyle and progresses through the joint in stages. Later stages are associated with damage to the other structures in the knee, such as the meniscus and the ACL. Damage to the ACL is associated with increasing osteophytosis. This description is the first step in describing the stages of early AMG. Description of these stages is important since we believe the outcome of surgical intervention may be dependant on these and they may guide future therapy