b. **4-in-1 block/ modified 4-in-1 block**: (**Figure 11**)

Unlike the Hi-PAC block (given in proximal AC), the 4-in-1 block [48] is given into the distal AC. The important landmark for this block is descending genicular artery to identify the block site, whereas the landmark for the Hi-PAC block is the apex of the femoral triangle. The volume and type of LA required for this block are 35 ml of 0.2% ropivacaine. It is described to provide analgesia for knee surgeries as well as below-knee surgeries. Due to injection into the distal AC below VAM, there is a possibility of the saphenous nerve and nerve to vastus medialis sparing. The saphenous nerve leaves AC in the mid-adductor canal location and becomes superficial, whereas the NVM always lies above the VAM (thus, not the content of AC). Considering the sparing of NVM, which is an important nerve for knee surgeries, a modified 4-in-1 block was described mainly for knee surgeries.

The modified-4-in-1 block [49] involves two injections: The first injection (5–7 ml of 0.2% ropivacaine) above VAM around the NVM after stimulating it, and the second injection (20–25 ml of 0.2% ropivacaine) below VAM perivascularly. The possibility of the saphenous nerve-sparing remains the same in this block.

Due to the distal spread of injected LA through the adductor hiatus into the popliteal region, both blocks involve posterior division of obturator nerve, tibial, common peroneal, and sciatic nerves.

#### **Figure 11.**

*Sonoanaltomy of 4-in-1 and modified 4-in-1 block.*

*(ST: Sartorius muscle, VM: Vastus medialis muscle, AM: Adductor magnus muscle, SFA: Superficial femoral artery, SFV: Superficial femoral vein, DGA: Descending genicular artery, Yellow dots: Nerves, Red color: Artery, Blue color: Vein, Green line: Vasoadductor membrane, White lines: Needles track).*
