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Abstract
Background and aims Incisional and anteromedial pain is often present after total knee arthroplasty (TKA) despite a saphenous and medial vastus nerve block at midthigh level (distal femoral triangle block, FTB). We aimed to investigate whether a block of the intermediate femoral cutaneous nerve branches (IFCNB) would increase the area of anesthesia and whether this would be further improved by replacing the traditional FTB with a more proximal approach (i.e. proximal FTB) thereby in addition anesthetizing the medial femoral cutaneous nerve.
Methods Forty healthy volunteers were enrolled in this randomized, double-blind trial. the standard midline incision for TKA was drawn on the skin. Volunteers were randomized (group 1–4) receiving active distal FTB on one side and active proximal FTB on the other combined with active IFCNB on one side (figures 1, 2). Primary outcome was anesthesia of the incision with proximal FTB and IFCNB versus proximal FTB. Secondary outcomes included reduction in muscle strength, and the coverage of the incision line and anteromedial aspect with distal FTB.
Flowchart
For the proximal FTB (2A), the ultrasound-guided injection is made anterolateral to the femoral artery (FA) to anesthetize the saphenous and medial vastus nerves (yellow and green arrows). The needle is redirected to deposit on top of the FA anesthetizing the medial femoral cutaneous nerve (red arrow). The level of injection is approximately 10 cm below the inguinal crease AL, adductor longus muscle; VM, vastus medialis muscle.For the IFCNB (2B) the injection is made around the two branches (white arrows) in the subcutaneous tissue above the sartorius muscle (S).
Results Addition of IFCNB to proximal FTB significantly increased complete anesthesia of the incision line. After distal FTB and IFCNB a non-anesthetized area was present anteromedially in 90% of cases (Figure 3). After proximal and distal FTB muscle strength was significantly reduced, however, ambulation was maintained. Addition of IFCNB did not cause further reduction.
The images show the area of cutaneous anesthesia after proximal FTB and IFCNB(3A,3B)versus distal FTB and IFCNB(3C,3D), All markings are made with UV-marker to maintain blinding. A straight line corresponding to the surgical midline incision after TKA is seen on the skin. 3C and 3D show a non-anesthetized area at the anteromedial aspect of the knee invoig the majority of the incision line. In contrast, the areas anesthetized by the proximal FTB and IFCNB (3A, 3B) fuse in to one area covering the anteromedial side of the knee as well as the entire length of the incision line.
Conclusions Proximal FTB combined with IFCNB had a high success rate of anesthetizing the incision line and anteromedial aspect of the knee. In contrast, distal FTB and IFCNB did not produce relevant anesthesia.