Lesson-Femoral

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

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

4 – Bone and joint innervation of the femoral nerve

The branches of the femoral nerve innervate the anterior side of:

– the hip joint

– the femoral bone

– the knee joint including the patella

– the medial tibial epicondyle

A femoral branch to the hip joint arises from the nerve to rectus femoris

Branches to the knee joint arise from each of the nerves supplying the vastus muscles with a fourth branch from the saphenous nerve

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The bony innervation of the femoral nerve is depicted with purple colour

5 – The muscles innervated by the femoral nerve

The femoral nerve splits into the anterior and the posterior branch

The femoral nerve innervates the muscles in the anterior compartment of the thigh

The anterior branch of the femoral nerve innervates the sartorius muscle – and sometimes the pectineus muscle

The posterior femoral nerve branch innervates most of the muscles in the anterior compartment of the thigh – i.e. the quadriceps femoris (the rectus femoris and the three vastus muscles)

Before the femoral nerve emerges from under the inguinal ligament it also innervates the iliac muscle and the femoral artery

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The quadriceps femoris muscle is innervated by the posterior femoral nerve branch. The quadriceps femoris muscle and the sartorius muscle are both depicted in turquoise colour. The sartorius muscle is innervated by the anterior femoral nerve branch.

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)

1 – Anatomy of the femoral nerve

The lumbar part of the lumbosacral plexus emerges from five spinal nerves: T12, L1, L2, L3 and L4

It gives origin to three important nerves in lower limb innervation: The femoral, the obturator and the lateral femoral cutaneous nerves

The most important lumbar plexus nerve concerning basic peripheral nerve blockade is the femoral nerve

It originates from the L2, L3, and L4 spinal nerves of the lumbar plexus

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The figure shows the femoral nerve depicted with blue colour