Lesson-Femoral

18 – The saphenous nerve block

Local anaesthetic is injected just lateral to the femoral artery in the triangular space between the femoral artery, the sartorius muscle and the medial vastus muscle

Click on the VIDEO CLIP button to view the video

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The video shows the in-plane approach to the saphenous nerve block with injection of local anaesthetic on the lateral side of the femoral artery
SN = saphenous nerve; SM = sartorius muscle; FA = femoral artery; MVM = medial vastus muscle

13 – The saphenous nerve can be blocked separately

The saphenous nerve is the biggest branch from the femoral nerve

The saphenous nerve runs in the thigh in the femoral triangle and the adductor canal alongside the femoral vessels. In the femoral triangle and the upper part of the adductor canal the saphenous nerve is lateral to the vessels

The saphenous nerve is 100% sensitive innervating the medial part of the knee capsule, the skin and subcutaneous tissue antero-inferior to the knee, of the medial leg, the medial ankle joint and the subtalar joints

Indications: For surgical anaesthesia or pain management of the leg you should combine a sciatic and a saphenous nerve block

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The figure shows the green saphenous nerve running alongside and lateral to the femoral artery in the femoral triangle

14 – The sonoanatomy of the saphenous nerve in the femoral triangle and the adductor canal

In the femoral triangle and the adductor canal the femoral artery is located under the triangular sartorius muscle (SM)

The saphenous nerve (SN) is sandwiched between the femoral artery (FA), the SM and the medial vastus muscle (MVM) in the femoral triangle and the proximal end of the adductor canal (AC). In the distal end of the canal the nerve is usually medial to the artery

Use in-plane (IP) approach from the lateral end of the transducer in the midthigh midways between the anterior superior iliac spine and the base of patella which is inside the femoral triangle

Complete perineural spread of local anaesthetic usually requires only a few milliliters of local anaesthetic and the duration of anaesthesia is oftentimes very prolonged – often more than 15 hours with ropivacaine

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The image shows the FA underneath the SM in the AC. Often, the SN nerve is not distinctly visible prior to injection of local anaesthetic. However, in the upper half of the thigh the nerve is invariably located just lateral to the artery between the SM and the MVM. Lat = lateral side of the patient

15 – The cutaneous distribution of the saphenous nerve

The saphenous nerve is a branch of the posterior branch of the femoral nerve

The saphenous nerve innervates the antero-medial part of the knee and the leg including the medial malleolus and and the anterior side of the ankle joint and the subtalar joints

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The green colour depicts the cutaneous distribution of the saphenous nerve

17 – Blocking the saphenous nerve separately in the adductor canal

Position: place the patient supine, rotate the thigh external

Probe: select a linear, high-frequency transducer

Place/Plane: place the transducer mid-thigh medially and perpendicular to the adductor canal

First locate the pulsatile femoral artery

You may track the artery from the inguinal ligament until it dives under the sartorius muscle

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The in-plane approach to block the saphenous nerve at the midthigh level in the femoral triangle

6 – The cutaneous distribution of the femoral nerve

The anterior branch of the femoral nerve gives off the intermediate and the medial cutaneous nerves of the thigh

– the intermediate cutaneous nerve of the thigh innervates the skin of the
anterior thigh

– the medial cutaneous nerve of the thigh innervates the skin of the medial
thigh and knee

The posterior branch of the femoral nerve gives off the saphenous nerve, which is a sensory nerve innervating the antero-medial parts of the knee and the leg – sometimes as far distal as the big toe

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The green shaded area depicts the cutaneous distribution of the femoral nerve branches

7 – The saphenous nerve territory – a femoral nerve branch

The saphenous nerve is a branch of the posterior branch of the femoral nerve

The saphenous nerve innervates the antero-medial part of the knee and the leg including the medial malleolus and the subtalar joints

The saphenous nerve can be blocked individually in the adductor canal in the medial part of the upper thigh

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The saphenous nerve territory is depicted in green colour

9 – Indications of the femoral nerve block

Surgery and analgesia of

– the hip joint
– the shaft of the femoral bone
– the anterior thigh
– the knee joint
– the medial leg including the medial and anterior side of the ankle joint
and the subtalar joints

The ultrasound guided femoral nerve block is a basic level block

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The image displays the triangular hyperechoic femoral nerve (FN) in short-axis view just lateral to the femoral artery (FA). The FN is located on top of the iliopsoas muscle (IPM)

10 – How to perform a femoral nerve block

– Place a linear high-frequency probe in the inguinal groove and identify the pulsatile femoral artery
– Align the artery to the centre of the monitor by adjusting the position of the probe and the depth of the image
– Locate the femoral nerve (FN) lateral to the artery on top of the iliac muscle. The FN is usually flattened, spindle-shaped or triangular – rarely round
– Capture the best possible cross-sectional image of the FN by tilting the probe 10-30 degrees cranially
– Insert the needle from the lateral end of the probe
– Advance the needle inside the plane of the ultrasound beam (in-plane, IP) until the tip of the needle touches the deep surface of the FN tangentially
– The endpoint is complete perineural spread of local anaesthetic

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Yellow arrowheads point at the femoral nerve; A is the femoral artery; IB is the inguinal boundary; LAT = lateral side of the patient; MED = medial; POST = posterior side of the patient

11 – The appearance of the femoral nerve

The hyperechoic femoral nerve is usually spindle-shaped or oval

It can sometimes be triangular but is rarely round

Injection of local anaesthetic enhances the visibility of the nerve

Click on the VIDEO CLIP button to view the video

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Femoral nerve (F) and injected local anaesthetic (LA). The LA enhances the visibility of F