The determination of safe zones for arthroscopic portal placement into the posterior knee by mapping the courses of neurovascular structures in relation to bony landmarks

Abstract

PURPOSE : Minimally invasive surgery in the posterior knee is high risk for iatrogenic injury to popliteal neurovascular neurovasculature structures. This study aimed to use reliable landmarks to define safe zones for arthroscopic portal placement into the posterior knee. METHODS : Distances were measured between bony landmarks and neurovascular structures within the popliteal fossa using 45 formalin-embalmed cadavers: small saphenous vein (SSV), medial (MCSN) and lateral (LCSN) cutaneous sural nerves, tibial nerve (TN), common fibular nerve (CFN), popliteal vein (PV) and artery (PA). The structures were measured in relation to medial (MEF) and lateral (LEF) femoral epicondyle, medial (MCT) and lateral (LCT) tibial condyle and the midpoint between the landmarks. RESULTS : The mean distance (mm) between MEF and structures was, male and female, respectively: SSV 37.6 + 12.5, 37.9 + 8.2; MCSN 39.2 + 14, 38.8 + 10.1; TN 39.4 + 10.2, 38.0 + 8.1; PV 38.4 + 12.9, 32.8 + 5.6; PA 38.4 + 12.1, 34.6 + 4.9. At midpoint and MCT all structures medialized between 5 and 28%. The mean distance between LEF and structures was, male and female, respectively: CFN 13.4 + 8.2, 8.4 + 9.1; LCSN 24.9 + 7.3, 18.4 + 10.4. At midpoint and LCT the CFN lateralized by 37–42% and the LCSN medialized by 8–9%. CONCLUSIONS : Results suggest posteromedial portal placement can be safely established < 20 mm from the medial femoral epicondyle, tibial condyle or the midpoint between the two landmarks. Posterolateral portal placement is of higher risk, and entry point is 18 mm from the lateral femoral epicondyle, tibial condyle or the midpoint between the two landmarks in males and 12 mm in females. These landmarks will allow safe portal placement in 99% of cases.