Role of musculoskeletal ultrasound in assessment of extrusion of the medial meniscus of the knee joint compared to MRI as a reference standard.

Abstract

Ultrasound has several unique advantages over MRI which make it a promising technique for assessment of several musculoskeletal soft tissue abnormalities of the knee including meniscal abnormalities. It has improved spatial resolution and allows direct correlation with the site of pain, comparison with the contralateral side and interaction with patients during US evaluation. Also, it is a simple, relatively fast and less expensive technique compared to MRI. Moreover, it allows dynamic evaluation of the patient at both supine and weight-bearing positions. Those factors suggest that ultrasound can help us to recognize the causes and outcome of meniscal extrusion, and its role in progression of medial tibiofemoral osteoarthritis.

US was performed in the supine position, then in the weight-bearing standing position. Medial meniscal extrusion distance and extruded meniscal area were measured using longitudinal ultrasound sections of the medial knee taken at the site where the medial collateral ligament is most clearly visualized. For MRI, coronal STIR MR images at the level where the medial collateral ligament is most clear are used to obtain measurements for meniscal extrusion distance.

Using extrusion distance as a measure for meniscal extrusion, the results of this study revealed that the degree of medial meniscal extrusion is significantly higher in the weight-bearing US than in the non-weight-bearing MRI. This was also confirmed by comparing qualitative data between the weight-bearing US and the non-weight-bearing MRI. The same difference was found when the quantitative and qualitative data of weight-bearing US and non-weight-bearing supine US were compared together. Those findings revealed that weight-bearing US enables early detection of significant meniscal extrusion before it can be evident on non-weight-bearing studies (supine US