A cadaveric study to test the viability of pre-determined safe zones for arthroscopic portal placement into the posterior knee

Abstract

The posterior compartments of the knee are currently accessed arthroscopically through anterior, posteromedial or posterolateral portals. A direct posterior portal to access the posterior compartments has been overlooked due to a perceived high-risk of injury to the popliteal neurovascular structures. Therefore, this study aimed to investigate the safety and accessibility of a direct posterior portal into the knee. Method: This cross-sectional study comprised a sample of 95 formalin-embalmed cadaveric knees and 9 fresh-frozen knees. Cannulas were inserted into the knees in pre-defined safe zones. Measurement of the distance between the cannula and popliteal neurovascular structures was performed and damage to neurovascular structures noted. Fresh-frozen knees underwent needle arthroscopy to assess the technique in clinical settings. Results: Incidence of neurovascular damage was 9.6% (n=10); 0.96% for the medial cannula and 8.7% for the lateral cannula. The medial cannula damaged one small saphenous vein (SSV). The lateral cannula damaged one SSV, seven common fibular nerves (CFN) and both the CFN and lateral cutaneous sural nerve in one specimen. All incidences of damage occurred in formalin-embalmed knees. The posterior horns of the menisci were accessible in all specimens. Conclusion: A medial-lying direct posterior portal into the knee is safe in 99% of occurrences and holds higher clinical viability in terms of accessibility and visibility during arthroscopic procedures. The lateral-lying direct posterior portal is of higher risk to the CFN and is challenging to access arthroscopically.