The posteromedial knee arthroscopy portal: a cadaveric study defining a safety zone for portal placement.

PURPOSE: To define a neurovascular safety zone for proper placement of at least 2 posteromedial (PM) portals and to describe a safe intra-articular entrance point based on the location of the PM capsular folds.

METHODS: Arthroscopy was performed on 10 fresh-frozen cadaveric knees. With the knee flexed 90°, PM portals were created under direct visualization with a 70° arthroscope. The anatomic soft spot between the PM edges of the femoral condyle and the proximal tibia was palpated, and 18-gauge spinal needles were inserted into the joint followed by 5.0-mm cannulas. The PM capsular folds were used to guide portal locations. Four portals (A, B, C, and D) were created in each of the first 3 knees. Portal position was described in relation to the soft spot: through the soft spot (A), 1 cm superior (B), 1 cm posterior (C), and 1 cm inferior (D). Dissection was performed along the path of the cannulas.

RESULTS: In the first 3 knees, the most inferior portal (D) always overlapped the course of the saphenous nerve, and the posterior portal (C) always pierced the gastrocnemius musculotendinous junction. Therefore these portals were eliminated from further study for safety reasons, and in the final 7 knees, we studied only the remaining 2 portal placements (A and B). Portals A and B were found to be the safest, with at least 1.5 cm of clearance between the portals and the saphenous nerve in all specimens.

CONCLUSIONS: At least 2 PM portals can be safely placed in the knee. The soft spot is an appropriate landmark to ensure safe portal entry. The PM capsular folds can help guide intra-articular placement so that damage to surrounding structures can be avoided.

CLINICAL RELEVANCE: We believe that 2 portals would be beneficial when performing complex arthroscopic procedures involving the PM compartment of the knee.