Review Question - QID 220557

The adductor canal block, performed at location C, provides similar pain control but better mobility in the setting of TKA when compared to a femoral nerve block, performed at location A (Answer 3).

Regional anesthesia for total knee arthroplasty has evolved significantly over the last decade. Femoral nerve block (FNB) has been used as the standard method due to its effective pain control following TKA, but evidence has shown that it may weaken the quadriceps strength in the perioperative period. Adductor canal block (ACB) is a newly developed analgesic protocol with fast functional recovery and good pain control after TKA. The rationale is that the saphenous nerve and nerve to the vastus medialis obliquus both contribute to knee joint innervation and are distal to the quadriceps motor branches in the femoral triangle; thus, an adductor canal block can theoretically provide similar pain control to a femoral nerve block without the accompanying motor weakness.

Burckett-St Laurant et al. performed an anatomic study of the nerves of the adductor canal and the innervation of the knee. The authors examined 20 cadaveric lower limb specimens and found that both the saphenous nerve (SN) and the nerve to vastus medialis (NVM) were consistently identified at the adductor canal, whereas branches of the anterior obturator nerve were inconsistently present. They concluded that given the site of exit of both nerves in the distal third of the adductor canal, the mid-portion of the adductor canal is suggested as an optimal site of local anesthetic administration to block both target nerves while minimizing the possibility of proximal spread to the femoral triangle.

Li et al. performed a systematic review and meta-analysis comparing the performance of adductor canal (ACB) and femoral nerve blocks (FNB) after total knee arthroplasty. The authors included eight randomized controlled trials of 434 patients (504 knees) and found that ACB can significantly decrease visual analog scale (VAS) scores at rest within eight hours (p < 0.001) and at 24 hours (p < 0.001) after operation compared to FNB after TKA, and improve quadriceps strength (p < 0.001) and mobilization ability (p < 0.001); however, the VAS score significance was not maintained out to 48 hours or two days post-operatively. They concluded that ACB provides better ambulation ability and faster functional recovery after TKA compared to FNB, making it worthy of being recommended to replace FNB as a standard analgesic protocol for pain treatment after TKA.

Kuang et al. published another systematic review and meta-analysis comparing adductor canal block and femoral nerve block for TKA. The authors reviewed nine randomized controlled trials involving 609 patients (668 knees) and found that compared with FNB, ACB resulted in better quadriceps muscle strength and mobilization ability, with no significant differences in the visual analog scale at rest, visual analog scale with mobilization, rescue opioid consumption, patient satisfaction, and length of hospital stay. They concluded that compared with FNB, ACB shows similar pain control after TKA but can better preserve quadriceps muscle strength and improve mobilization ability.

Figure A is an AP radiograph of a knee many years status post ACL reconstruction with end-stage tri-compartmental osteoarthritis. Figure B is a cartoon depiction of the anterior neurovascular structures of the thigh depicting the locations of various blocks, including: (A) femoral nerve block, (B) fascia iliaca block, (C) adductor canal block, (D) superomedial geniculate block, (E) superolateral geniculate block.

Incorrect Answers:
Answer 1: The fascia iliaca block (block B) is considered an alternative to a femoral nerve block and is performed by placing a needle at the lateral third of the distance from the anterior superior iliac spine to the pubic tubercle, using a “double-pop” technique as the needle passes through the fascia lata and fascia iliaca. It targets the femoral, obturator, and lateral femoral cutaneous nerves and is more commonly performed for pain control in the setting of geriatric hip fractures than for TKAs.
Answer 2: The block performed at location A is the femoral nerve block, the injection for which occurs just lateral to the femoral artery and on a line connecting the anterior superior iliac spine to the pubic symphysis, which has been shown to have equivalent pain control but worse preservation of mobility when compared to an adductor canal block (location C).
Answer 4: The adductor canal block performed at location C provides better preservation of mobility than similar blocks that affect the femoral nerve primarily (blocks A and B).
Answer 5: Geniculate blocks can be used in the management of chronic osteoarthritis in the outpatient setting to try to control pain prior to deciding to undergo TKA, but they are not the primary form of regional anesthesia used in the perioperative period.