Is the Distance between Posterior Capsule and Popliteal artery a limitation for IPACK at the level of femoral condyles?

The ultrasound-guided infiltration between the posterior of the knee capsule [PCK] and the popliteal artery [PA], commonly known as IPACK, plays a pivotal role in total knee arthroplasty when performed alongside an ultrasound-guided adductor canal block. The precise positioning of the needle between the PKC and the PA at the level of the femoral condyles, followed by an adequate diffusion of injectate, is of utmost importance. Traditionally, the needle is inserted from medial to lateral as it courses between the PKC and the PA.
Our investigation into the distance between the PKC and the PA at the level of femoral condyles in a sample of 20 patients revealed a mean distance of 1.2mm. However, in 8 patients (40%), the distance was less than 0.7mm (Figure 1). This finding is crucial as a distance of less than 0.7 mm may hinder the administration of IPACK, leading to potential complications. In these 8 patients, the needle could not be negotiated between the PKC and the PA, and the IPACK was deferred.