Arthroscopic visual field mapping at the periphery of the medial meniscus: a comparison of different portal approaches.

The posteromedial compartment, particularly the posterior horn of the medial meniscus, has been shown by many investigators to be a common source of diagnostic errors in knee arthroscopy when access is limited to anterior portals. To better understand the anatomical basis of this apparent technical limitation, we quantified the visible versus the "blind" zones of the posteromedial meniscal periphery present when using the following arthroscopic approaches in six fresh knee specimens: (a) direct anteromedial frontal view with a 30 degrees arthroscope (AM-30 degrees); (b) anterolateral portal, 30 degrees arthroscope, transnotch view (AL-30 degrees); (c) anterolateral portal, 70 degrees arthroscope, transnotch view (AL-70 degrees); (d) central portal, 70 degrees arthroscope, transnotch view (C-70 degrees); and (e) posteromedial portal, 30 degrees arthroscope, direct rear view (PM-30 degrees). The AM-30 degrees approach visualized only the anterior 50% or less of the total superior meniscosynovial junction length, in all knees. The AL-30 degrees, C-70 degrees, AL-70 degrees, and PM-30 degrees portal approaches visualized the posteriormost 16.4%, 24.2%, 31.6%, and 54.9% of the upper meniscal rim, respectively. In conjunction with the AM-30 degrees visual field, the PM-30 degrees approach provided the most complete overall visualization of the superior meniscosynovial junction, leaving a mean blind zone of only 8.4% (12 mm) between the anterior and posterior visual fields. The AL-30 degrees, C-70 degrees, and AL-70 degrees approaches left significantly greater portions (means of 47%, 39.1%, and 31.7%, respectively) of the meniscal rim universalized.