Summary

To safely define a zone for portal placement (one or two) on the posterolateral (PL) portion of the knee and to describe an intra-articular entrance point based on the location of anatomic landmarks and capsular folds.

Abstract

The Posterolateral Knee Arthroscopy Portal: A Cadaveric Study Defining a Safety Zone for Portal Placement

Brian Dilworth, MD, Victor Fehrenbacher, MD, Jamie Clark, RN, John Nyland, Ed. D., and Joseph W. Greene, MD

Purpose

To safely define a zone for portal placement, and potentially more than one, on the posterolateral (PL) portion of the knee while describing an intra-articular entrance point based on the location of anatomic landmarks and capsular folds.

Methods

Arthroscopy was performed on 10 fresh-frozen cadaveric knees. Inflow was controlled with gravity. All arthoscopies and dissections were completed with the knee in 90 degrees of flexion. Standard anteromedial and anterolateral portals were used to access the posterolateral compartment of the knee. The posterolateral portal was created under direct visualization with a 70° arthroscope. Posterolateral portals were created by palpating the “soft spot,” which has been defined as being between the fibular collateral ligament, lateral head of the gastrocnemius, and posterolateal tibial plateau. 18-gauge spinal needles were then inserted under direct visualization by the arthoscope. Consistent portal positioning was accomplished by identifying the capsular folds and the popliteus tendon. 4 mm portals were then used to create the portals. Four portals (A, B, C, and D) were created in each of the first 3 knees. Portal A was created using the previously described soft spot. The remaining portals B,C,D were created 1 cm posterior and 1cm superior, 1cm posterior and 1 cm inferior, 1.5 cm posterior, respectively in reference to portal A (where directions relate to the tibial axis with the knee at 90 degrees). Dissection was then performed along the paths of the cannulas. Measurements were performed with a metric ruler to identify the shortest distance between the portals and the surrounding structures at risk (peroneal nerve, fibular collateral ligament, popliteus tendon, and the lateral head of the gastrocnemius).

Results

The first 3 placements of portals C and D violated the lateral gastocnemius tendon and the posterior capsule respectively, therefore they were eliminated from safe zone consideration. Portal A had a trajectory that averaged 8.8 ±2.7mm from the popliteus tendon, 11.6 ±2.7mm from the fibular collateral ligament, 26.8 ±2.3mm from the peroneal nerve, and 4.9 ±2.5mm from the biceps tendon. Portal B averaged 17.3 ±2.8mm from the popliteus tendon, 20 ±2.8mm from the fibular collateral ligament, 30.3 ±3.3mm from the peroneal nerve, and 7 ±4.8mm from the biceps tendon. Portal A and B were found to have equivalent morbidity. Portal B was found to be statistically significant for increased distance from the fibular collateral ligament and the popliteus, when compared to A.

Conclusions

2 posterolateral portals can be safely placed by use of both intra- and extra-articular anatomic landmarks. Posterolateral folds are easily identified under arthroscopic visualization.

Clinical Relevance: 2 safe portals are beneficial when performing complex arthroscopic procedures and can be safely created.