Summary

The prevalence of ramp lesion was 17.4% in this study. Inter-condylar visualization and the creation of a posteromedial portal was effective to identify ramp lesion. Low sensitivity in detecting ramp lesion was seen at the MC junction on MRI. Careful arthroscopic exploration of the posteromedial compartment should be required so as not to overlook ramp lesion even when it is not indicated on MRI.

Abstract

<Introduction>
“Ramp lesion” is a longitudinal tear of the posterior horn of the medial meniscus (PHMM) adjoining the menisco-capsular (MC) junction and is associated with ACL ruptures. Because this injury is reported to increase knee instability and to be difficult to heal spontaneously, meniscal repair concomitant with ACL reconstruction is recommended. However, it is reported to be difficult to diagnose ramp lesion by pre-operative MRI and arthroscopic exploration via anterior visualizations. Recently, a systematic arthroscopic exploration has been validated to identify the lesion and not overlook it. The purpose of this study was to evaluate the prevalence of ramp lesion by systematic arthroscopic exploration and to compare the arthroscopic diagnosis of ramp lesion and pre-operative MRI evaluation.

<Method>
149 ACL-injured patients undergoing ACL reconstruction performed by a single surgeon were enrolled in this study. A systematic arthroscopic exploration to identify ramp lesion was conducted intra-operatively for all patients. The procedures were divided into 3 steps as follows: (Step 1) Anterior visualization (via an anterolateral portal with probing through the anteromedial portal), (Step 2) Inter-condylar visualization with the arthroscope introduced deeply into the posteromedial compartment, (Step 3) Probing and minimal debridement through the posteromedial portal. Subsequently, the prevalence of ramp lesion among all cases, the number of cases for each step when ramp lesion was identified, and the location of ramp lesion (MC junction or red-red zone) were evaluated. In addition, the diagnostic rate for ramp lesion by pre-operative MRI was calculated. High signal intensity at the posterior margin of the PHMM on sagittal proton density fat saturation MRI was assessed as “ramp lesion positive”.
<Result>
The prevalence of ramp lesion was 17.4% (26 of the 149 cases). The number of cases for each step when the ramp lesion was identified was 10 for Step 1, 11 for Step 2 and 5 for Step 3. 13 cases had ramp lesions at the MC junction while 12 cases were at the red-red zone and 1 case was at both locations. Among the 138 cases whose pre-operative MRI could be checked, 24 cases were confirmed as having ramp lesion. The sensitivity of MRI in detecting ramp lesion was 62.5% and the specificity was 93.9% in total. To be specific, the sensitivity of MRI in detecting ramp lesion at the MC junction was 42.9%, whereas the counterpart at the red-red zone was 90.9%.
<Conclusion>
The prevalence of ramp lesion was 17.4% in the current study. Inter-condylar visualization and the creation of a posteromedial portal in addition to anterior visualization was effective in identifying ramp lesion. Low sensitivity in detecting ramp lesion was seen especially at the MC junction on pre-operative MRI. Careful arthroscopic exploration of the posteromedial compartment should be required so as not to overlook ramp lesion, even when it is not indicated on pre-operative MRI.