Background: When a medial meniscal posterior root tear occurs, changes in the biomechanics of the medial tibiofemoral joint and inability to convert axial loads into hoop stresses occur with subsequent meniscal extrusion. A meniscal extrusion of 3mm is associated with accelerated articular cartilage loss and osteophyte formation resulting in a more rapid progression of osteoarthritis.
Although MRI doesnt evaluate the meniscus during axial loading, it is considered the gold standard for evaluation of meniscal extrusion. On the other hand, US can assess the patients at supine and weight-bearing positions. This advantage facilitates early detection of meniscal extrusion, so we can limit its poor effects on the medial knee compartment.
Results: This study included thirty patients with medial meniscal posterior root tear diagnosed by MRI. This studys aim is to recognize the value of dynamic ultrasound in evaluating medial meniscal extrusion compared to MRI.
A statistically significant difference was found when the absolute measures for extrusion distance were compared between standing and supine US, between supine US and MRI as well as between standing US and MRI (P-value= 0.000 for all those comparisons). Also, when the absolute measures of the extruded area at standing and supine US were compared, a statistically significant difference was found (P-value=0.000).
Comparing the qualitative data, there was no statistically significant difference between the results of supine US and MRI (P-value=0.541) with a statistically significant difference found between the results of standing US and MRI (P-value=0.0.002) and between the results of supine and standing US (P-value=0.010).
Compared to MRI, supine and standing US showed excellent sensitivity (100%). Also, supine US showed good specificity (75%) while standing US showed poor specificity (0%). The explanation for this poor specificity is that standing US detected dynamic radial meniscal extrusion occurring during axial loading while non-weight-bearing MRI didnt, so those patients detected only by standing US were considered false-positive during statistical analysis causing a poor specificity value.
Conclusion: Dynamic US facilitates early detection of significant meniscal extrusion before it can be evident on MRI because it can detect dynamic radial meniscal displacement seen on axial loading.
Key words: Posterior root tear, medial meniscal extrusion, weight-bearing, dynamic US, MRI