Weight bearing 3-D joint space width distribution at the knee varies according to location and extent of meniscal extrusion: A MOST investigation.

Objective: Extrusion of the meniscus is known to be a key factor in the development of knee osteoarthritis. Here, we investigate the precise relationship between meniscal extrusion and weight bearing 3-D joint space width (JSW) distribution. Design: Weight-bearing computed tomography (WBCT) images were acquired at the 144-month visit in the Multicenter Osteoarthritis Study. For each knee, 3-D JSW maps were created. MRI data from the same visit were assessed for both medial and lateral meniscal extrusion grade determined by the MRI Osteoarthritis Knee Score. Statistical parametric mapping (SPM) was used to test for any significant dependence of 3-D JSW distribution on meniscal extrusion grade by location. Results: 568 knees were included in the analysis. SPM demonstrated significant differences in 3-D JSW distribution according to the extent of both medial and anterior extrusion of the medial meniscus in a pattern that suggested a posteromedial shift of the femur on the tibia. Medial extrusion of the medial meniscus was also associated with significantly lower JSW across the central-to-posterior medial joint space. The low prevalence of lateral meniscus extrusion meant that results for this may be underpowered or unrepresentative. Conclusion: Establishing links between 3-D JSW and meniscal extrusion is an important step in developing the clinical utility of WBCT for the evaluation of osteoarthritis. Further study is required to establish whether 3-D JSW is sensitive enough to detect meniscal extrusion before articular cartilage damage has occurred, to develop this as a biomarker for early disease.