Morphological changes to the intercondylar space in different stages of osteoarthritis - A retrospective cross-sectional study.

Background: The intercondylar space is defined as the topographic area walled by the intercondylar notch (IN) and encasing the central ligaments of the knee joint. As the anterior cruciate ligament (ACL) is not only impinged against the roof but also against the lateral wall of the IN, information concerning changes to the IN during the progression of osteoarthritis could be potentially relevant in predicting the future risk for ACL-rupture and -degeneration and ensure preventive measures as early as possible. Therefore, the purpose of this study was to evaluate the influence of osteoarthritis on osseous notch morphology.

Methods: Image data was retrieved from the Osteoarthritis Initiative. Patients were subdivided into five groups according to the severity of osteoarthritis following the Kellgren and Lawrence classification. 415 patients were selected randomly to ensure equally large groups. Osseous structures were measured in coronal and axial planes in MRI. At the level of the popliteal groove and on the level of the joint line, the width of the lateral and medial femoral condyle, the notch width (NW) as well as the total width of the distal femur were measured. The notch width index (NWI) as ratio between the NW and the total width of the distal femur was calculated. Three shapes (A-shape, Inverse-U-shape and Ω-shape) of the IN were differentiated.

Results: The morphology of the IN is directly influenced by the development of osteoarthritis. Especially the Ω-shape is characteristic for more severe cases of osteoarthritis (p < 0.001). Measurements were also significantly influenced by the imaging plane and the level of measurements (both p < 0.001).

Conclusions: The results of this study reflect significant changes to the intercondylar space in increasing grades of osteoarthritis. Additionally, the recommendation on the location of measurements of the IN should be revised, as especially the measurements on the level of the joint line in coronal plane MRI are a more reliable and objective indicator for the diagnosis of IN stenosis and therefore of changes to the intercondylar space, which always influences the health of the ligaments housed. At the level of the popliteal groove a NWI< 0.25 and NW< 19 mm and at the level of the joint line a NWI< 0.17 and a NW< 14 mm should be interpreted as severe notch stenosis and a definitive risk factor for ACL rupture.