The purposes of this study were to determine whether it is necessary to obtain MRI of the knee prior to high tibial osteotomy (HTO) and to evaluate usefulness of MRI regarding its contributions on accurate diagnosing and changing possible indications for surgical intervention in patients on way to HTO.

Preoperative MRI of affected knee of 39 patients (23 female, 16 male) who had indication of HTO due to varus gonarthrosis were evaluated based on expected findings, possible findings and unexpected findings. The structural changes in bone (at femoral condyles, tibial platoes and patellae), meniscal abnormalities, ligamentous changes, the joint space width, osteophytes, subcondral cysts, baker cyst and joint effusion were evaluated. As expected, the most common and severe findings were observed at medial compartment in te majority of patients. For medial femoral condyl (MFC), subchondral sclerosis was seen in 22 patients (56.4%), osteonecrosis was seen in 9 patients (23.1%), bone marrow edema was seen in 4 patients (10.3%). Although there were less severe lesions, similar results were observed in the medial tibial plato (MTP) (51.3%, 17.9% and 7.7%, respectively). In the lateral compartments, the severity of lesions were higher than expected. A higher occurence rate of subchondral sclerosis (48.7%) was observed in patellae. Osteophytes were seen frequently in MFC (in all patients, median 3.8 mm). As expected, medial meniscus changes were observed in all patients. As an unexpected finding, periarticular enchondroma was seen in 2 of patients.

MRI is the most appropriate non-invasive method to examine joint structures, including the cartilage, menisci and synovial tissue that can be obtained with arthroscopy which is invasive and more costly tool. MRI appears to be particularly useful for preoperative evaluation of patients in preventation of unnessary meniscal surgical interventions. The finding of 30% lateral compartment changes observed on MRI, as in arthroscopy, is not an obstacle for indication of HTO.