Plan A Blocks

Anatomy

ANATOMY

The femoral triangle is bordered superiorly by the inguinal ligament, laterally by the medial border of sartorius and medially by the medial border of adductor longus. Inferiorly, the apex of the triangle is where the medial borders of sartorius and adductor longus meet. The adductor canal (Hunter’s canal) is approximately 15 cm long, extending from the apex of the femoral triangle to the adductor hiatus in the adductor magnus muscle. The canal is bordered by muscles: sartorius; anteromedial, vastus medialis; lateral, adductor longus and magnus; posterior. A relatively thick aponeurosis extending from vastus medialis to adductor magnus covers the canal and has to be crossed in order to enter the canal and access the nerves. The contents of the femoral triangle and adductor canal are the femoral artery and vein, the saphenous nerve and the nerve to vastus medialis muscle. The saphenous nerve descends in the thigh, crossing the superficial femoral artery from lateral to medial before leaving the adductor canal between sartorius and gracilis muscles at the level of the adductor hiatus, accompanied by the saphenous branch of the descending geniculate artery. The saphenous nerve then accompanies the long saphenous vein to the ankle.

Landmarks

LANDMARKS

Anterior superior iliac spine, sartorius muscle, femoral artery, long saphenous vein.

Positioning

POSITIONING

Patient supine with the leg abducted and the knee slightly bent to expose the inner thigh.

Figure 1: Patient, transducer and needle positioning for a) in plane approach to the distal femoral triangle and b) in plane approach to the adductor canal

Preliminary Scan

PRELIMINARY SCAN

With the transducer transversely on the thigh, identify the common femoral artery and vein. This can be traced distally from the groin. Follow the artery in the femoral triangle passing beneath the body of sartorius muscle before entering the adductor canal. The vessels will then move deep to pass through the adductor hiatus. The saphenous nerve may be seen initially lateral to the artery before crossing obliquely, anterior to the artery and then over adductor magnus tendon to pass between sartorius and gracilis muscles to become super cial. The long saphenous vein can then be traced on the medial surface of the leg from posterior and medial to the knee distally to the ankle.

Ultrasound Appearance

ULTRASOUND APPEARANCE

The saphenous nerve and nerve to vastus medialis are seen as hyperechoic structures lying initially lateral to the femoral artery in the femoral triangle. In the lower leg, the saphenous nerve may be seen adjacent to the vein but may be difficult to visualise due to its size.

Figure 2: a) ultrasound image of the femoral artery and nerves deep to sartorius muscle in the femoral triangle b) annotated ultrasound image.

Figure 3: a) ultrasound image of the femoral artery deep to sartorius muscle in the adductor canal b) annotated ultrasound image

Technique

TECHNIQUE

Tips

TIPS

1. Low volumes of local anaesthetic placed within the femoral triangle in the mid-thigh will produce a partial sensory block of the knee (anteromedial) and ankle joints along with the medial side of the calf and foot. Local anaesthetic placed in the adductor canal close to the adductor hiatus will block the saphenous nerve and may also ow through the adductor hiatus and affect perforating branches supplying posterior sensation to the knee joint derived mainly from the tibial and obturator nerves.

2. The saphenous nerve is purely sensory. Nerve stimulation eliciting paraesthesia down the medial side of the lower leg can be used to con rm its identity. Direct blockade in the femoral triangle or adductor canal with 10 ml of LA will achieve a reliable block. Alternatively, a peri-venous injection around the saphenous vein will achieve a block in the lower leg.

Other Resources

Plan B/C/D blocks for the lower limb-knee include: Femoral nerve block +/- iPACK block

More information about the adductor canal block and analgesia for knee surgery can be found at the excellent  article here

Video

https://www.ra-uk.org/index.php/plan-a-block-videos/video/plan-a-adductor-canal-block

Authors

Anatomy

ANATOMY

The anterior rami of T6-L1 nerve roots supply sensation to the anterior abdominal wall. The intercostal nerves exit the intercostal space and run in the fascial plane between the internal oblique and transversus abdominis muscles. The anterior divisions run anteriorly to pierce the posterior rectus sheath. They then traverse the rectus abdominis muscle to pierce the anterior rectus sheath and supply sensation to the anterior abdominal wall.

Landmarks

LANDMARKS

Midline of the abdomen, linea alba, rectus abdominis muscles.

Positioning

POSITIONING

Supine with arms by the side to allow access to the anterior abdominal wall. Place the transducer transversely across the abdomen above the level of the umbilicus.

Figure 1: Patient, transducer and needle positioning for a) lateral to medial in-plane rectus sheath block and b) cephalad to caudal in-plane rectus sheath block, just superior to the umbilicus.

Preliminary Scan

PRELIMINARY SCAN

Start with the transducer in the midline and identify the linea alba and rectus muscle on either side. The rectus sheath is the hyperechoic fascial plane encircling the rectus abdominis muscle. The transversalis fascia lies deep to the rectus sheath, leading to the ‘double hyperechoic line’ deep to the rectus abdominis muscle on ultrasound. The transversalis fascia encircles the whole peritoneal cavity. The peritoneum lies immediately deep to the transversalis fascia. Superior to the umbilicus care must be taken to identify and avoid the superior epigastric artery, which can lie deep to or within the rectus sheath. Doppler can be used to aid visualisation. Figure 2: a) ultrasound image showing the left rectus abdominis muscle b) annotated image (Rectus=rectus abdominis muscle; LA=linea alba; PRS=posterior rectus sheath; TF=transversalis fascia. The yellow line, superficial to the PRS, highlights the desired plane for local infiltration).

Ultrasound Appearance

ULTRASOUND APPEARANCE

Hyperechoic fascial line deep to the rectus abdominis muscle.

Technique

TECHNIQUE

Using an in-plane technique from either lateral to medial or cephalad to caudal, the needle is passed through the rectus abdominal muscle. The aim is to ll the plane between the rectus abdominis muscle and the posterior rectus sheath. If in the correct plane then local anaesthetic can be seen neatly peeling the rectus muscle off the posterior rectus sheath (Figure 3).

Figure 3: Ultrasound images of the anterior abdominal wall a) before rectus sheath block and b) after injection of local anaesthetic for rectus sheath block. (Large white arrow indicating transversalis fascia; Large yellow arrow indicating posterior rectus sheath; LA=local anaesthetic; small white arrows highlighting the needle passing through the rectus abdominis muscle).

Tips

TIPS

1. Because innervation of the midline is from both sides bilateral rectus sheath blocks must be performed in all cases.

2. Besides the nerves, there are also vessels present in the posterior rectus space; the posterior intercostal and superior and inferior epigastric vessels. Doppler may help identify these vessels, which if seen, should be avoided during needle insertion.

3. For midline incisions the rectus sheath block can be inserted before knife to skin. If the incision will be paramedian (i.e. cutting through the rectus muscle) then the block can be performed post-operatively.

4. The tendinous intersections seen on the anterior aspect of the rectus abdominis muscle (six pack) are not present in the posterior part of the muscle. This allows free ow of local anaesthetic up and down the length of the abdominal wall.

5. Rectus sheath catheters are very popular for post-operative analgesia when used as part of an enhanced recovery after surgery technique (ERAS) for lower midline laparotomies.

6. For rectus sheath catheter insertion we recommend to orientate the long-axis of the transducer in a cephalo-caudal direction (Figure 1b). This may encourage the catheter to lie along the length of the abdominal wall and improve proximal-distal spread.

Other Resources

Plan B/C/D blocks for the abdomen include: Quadratus lumborum blocks

More information about the rectus sheath block can be found at the excellent article here

Videos

https://www.ra-uk.org/index.php/plan-a-block-videos/video/plan-a-rectus-sheath-block

Authors