b. **Adductor canal block**:

The adductor canal (AC) is a musculoaponeurotic tunnel extending from the FT apex above to the adductor hiatus below. It is triangular in a cross-section bounded anterolaterally by VMM, posteromedially by ALM proximally and adductor magnus muscle (AMM) distally, and medially by the vasoadductor membrane (VAM). The presence of VAM is the peculiarity of the AC region. Due to VAM, the lower border of the sartorius muscle appears bilayered under ultrasound.

Initially, the adductor canal block (ACB) was considered a saphenous nerve block [41, 42]. Later, various dye studies demonstrated the spread of the dye into the popliteal region when injected in the AC below the VAM. Therefore, the injection at any point distal to the FT apex below VAM can be considered an ACB. However, the involvement of neuronal components will be varied, depending upon the proximal or distal location of ACB. The required LA volume for the ACB is 10–20 ml.

Three critical events occur in the AC [41, 42]:


Due to these events, it is essential to divide ACB into three subdivisions: Proximal, mid, and distal AC. However, in all three locations, a drug injected into the AC below the VAM tracks along with the femoral vessels towards the adductor hiatus (involving the posterior division of the obturator nerve) and enters the backside of the knee (involving the popliteal plexus) [43, 44].

The SN enters the AC in the proximal part but leaves the AC in the middle part, where it lies between STM and AMM above the VAM [41]. Later, it crosses the thigh from the anterior to the medial side and becomes superficial by piercing the deep fascia of the thigh, where it lies between STM and gracilis muscles [41].

So, SN is not the content of mid-to-distal AC. The NVM always lies above the VAM with an additional fascial covering, so not the content of the entire AC [41, 45]. Thus, the analgesic coverage of the AC varies as per the involvement of the neuronal components at different locations.

**Proximal adductor canal block** is given in the proximal third of AC, just (1–2 cm) distal to the apex of FT. Sonoanatomy includes ALM posteromedially, VMM anterolaterally, VAM medially, and SM above VAM. The hyperechoic SN lies into the adductor canal lateral to the FA.

**Mid-adductor canal block** is given in the middle third of AC, distal to the proximal AC, where the ALM is replaced by AMM posteromedially.

**Distal adductor canal block** is given in the lower third of AC, where the femoral vessels enter into the adductor hiatus to become popliteal vessels. Sonoanatomy includes AMM posteromedially, VMM anterolaterally, and VAM (with SM above) medially. No nerves lie in this part of the adductor canal.

## c. **Dual subsartorial block (DSB)**:

Dual subsartorial block (DSB) is described as opioid-sparing, motor-sparing, and procedure-specific RA technique for total knee replacement (TKR) surgeries, mainly with medial incisions. It is a hybrid form of subsartorial block combining two subsartorial blocks (distal FT and AC block) to cover all procedure-specific innervations of pain generators involved in TKR surgery [46]. It is given immediately after the surgery with two different injections at two different locations below the sartorius muscle, hence termed a "dual subsartorial block" (**Figure 10**).

The first injection (distal FT block) targets SN and NVM directly and subsartorial plexus indirectly due to the distal spread of the drug under SM but above the VAM [43]. The subsartorial plexus lies between VAM and SM in the AC region. In the second injection (adductor canal block), no nerves are targeted. Simply depositing the drug perivascularly (around FA) under the VAM is sufficient to obtain the desired outcome. A drug injected into the AC below VAM will travel along the femoral vessels and enter the adductor hiatus to reach the posterior aspect of the knee joint [44]. Thus, the second injection indirectly targets the popliteal plexus formed by the articular branches from the posterior division of the obturator nerve, tibial, common peroneal, and sciatic nerve.

Thus, DSB involves blockade of SN, NVM, subsartorial plexus, the medial half of the peripatellar plexus, and the popliteal plexus. It results in sensory blockade over the anteromedial aspect of the knee up to the tibial tuberosity, medial retinacular complex, and intraarticular region (popliteal plexus). It will not cover the skin over the anterolateral (supplied by lateral half of peripatellar plexus) and posterior aspect (supplied by the posterior femoral cutaneous nerve of the thigh) of the knee.

*Regional Analgesia for Knee Surgeries: Thinking beyond Borders DOI: http://dx.doi.org/10.5772/intechopen.99282*

#### **Figure 10.**

*Sonoanaltomy of dual subsartorial block.*

*(STM: Sartorius muscle, ALM: Adductor longus muscle, VMM: Vastus medialis muscle, AMM: Adductor magnus muscle, SN: Saphenous nerve, NVM: Nerve to vastus medialis, FA: Femoral artery, FV: Femoral vein, DGA: Descending genicular artery, Yellow color: Nerves, Red color: Artery, Blue color: Vein, Brown color: Muscles, Green line: Vasoadductor membrane, White line: Needle track, Blue star with red border: Drug spread, Blue star with white border: Drug spread above vasoadductor membrane).*

> These uncovered areas are not included in the total knee replacement surgeries with medial approaches, so the lack of analgesia in the spared region is of little clinical consequence. If given precisely with recommended LA concentration and volumes, the DSB does not cause any motor blockade and involves all target procedure-specific innervations.

#### II.**High-volume blocks**:

#### a. **Hi-Volume Proximal Adductor Canal (Hi-PAC) block**:

Hi-PAC block is described recently as an indirect anterior approach of popliteal sciatic nerve block [47]. In this block, highvolume (30–40 ml) and low-concentration LA (0.2% ropivacaine) with an adjuvant (8 mg dexamethasone) is injected in the proximal adductor canal just below the VAM. The probe position and injection technique are the same as the second injection of DSB into the proximal AC, except for higher volume LA in the Hi-PAC block. The analgesic coverage of this block involves territory of the saphenous nerve, posterior division of obturator nerve, popliteal plexus, tibial, common peroneal, and finally popliteal sciatic nerve. Although this block provides analgesic coverage as adductor canal block, it is mainly described for below-knee surgeries due to wide coverage involving all innervations below the knee.
