Anatomy
Lower Limb
A 28 year old man was involved in a motorbike accident where he sustained a crush injury to his pelvis and right leg and damaged a nerve innervating the lower limb. He is unable to extend the leg at the knee joint. Which of the following clinical findings might you also expect on examination:
Answer:
Extension of the leg at the knee joint is primarily produced by the quadriceps femoris muscle which is innervated by the femoral nerve. The femoral nerve also innervates the iliacus, pectineus and sartorius muscles which, together with the rectus femoris muscle (and the psoas major), are involved in flexion of the thigh at the hip. The femoral nerve also gives rise to cutaneous branches supplying skin on the anterior thigh and the saphenous nerve supplying skin over the medial leg at foot.Femoral Nerve
Anatomy / Lower Limb / Femoral Triangle / Innervation of Lower Limb
Last Updated: 10th April 2019
The femoral nerve arises from the lumbar plexus, receiving fibres from the anterior rami of L2 - L4.
Table: Anatomical Overview of the Femoral Nerve
| Nerve | Femoral |
|---|---|
| Nerve roots | L2 – L4 |
| Motor supply | Iliacus, pectineus, sartorius, quadriceps femoris |
| Sensory supply | Skin over the anterior thigh, anteromedial knee, medial leg and medial foot |
| Injury | Motor Loss: Weak flexion at hip and loss of extension at knee
Sensory Loss: Loss of sensation over anterior thigh, anteromedial knee, medial leg and medial foot |
Anatomical course
The femoral nerve descends from the lumbar plexus in the posterior abdomen through the substance of the psoas major muscle, emerging from the lower lateral border of the psoas major. Continuing its descent, the femoral nerve lies between the lateral border of the psoas major and the anterior surface of the iliacus muscle. It is deep to the iliacus fascia and lateral to the femoral artery as it passes posterior to the mid-inguinal point to enter the femoral triangle in the anterior compartment of the thigh, before dividing into an anterior and posterior division.
![By Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2017/01/Femoral-Nerve.png)
Femoral Nerve. (Image by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
Branches
Table: Branches of the Femoral Nerve
| Branch | Supply |
|---|---|
| Muscular branches in abdomen | Iliacus and pectineus |
| Anterior cutaneous branches | Skin over anterior thigh |
| Anterior muscular branches | Sartorius |
| Posterior muscular branches | Quadriceps femoris muscles |
| Posterior articular branches | Hip and knee joint |
| Saphenous nerve | Skin over anteromedial knee, medial side of leg and foot |
In the abdomen it gives rise to branches that innervate the iliacus and pectineus muscles.
The anterior division gives off anterior cutaneous branches (supplying skin over the anterior and medial thigh) and muscular branches (innervating the sartorius).
The posterior division gives off muscular branches (innervating the quadriceps femoris muscles) and articular branches (supplying the hip and knee joint), before continuing as the saphenous nerve (supplying skin over the anteromedial knee and the medial side of the leg and foot).
Function
Table: Motor Supply of the Femoral Nerve
| Muscle | Function |
|---|---|
| Sartorius | Flexion, abduction and lateral rotation at hip and flexion at knee |
| Iliacus | Flexion and lateral rotation at hip |
| Pectineus | Adduction and flexion at hip |
| Rectus femoris | Flexion at hip and extension at knee |
| Vastus lateralis | Extension at knee |
| Vastus medialis | Extension at knee |
| Vastus intermedius | Extension at knee |
![Modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2017/01/Cutaneous-Innervation-Leg.png)
Cutaneous Innervation of Lower Limb. (Image modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
