Anatomy
Upper Limb
A 45 year old woman presents to the ED on New Year's Day. She complains of loss of feeling over the dorsum of her hand and is unable to extend her wrist. She tells you that last night she fell asleep slumped over the back of a chair. You suspect a "Saturday Night Palsy" of the radial nerve. The radial nerve arises from which of the following cords of the brachial plexus:
Answer:
The radial nerve is a continuation of the posterior cord, containing fibres from C5 - T1.Radial Nerve
Anatomy / Upper Limb / Innervation of Upper Limb / Posterior Arm / Posterior Forearm
Last Updated: 8th April 2019
The radial nerve is a continuation of the posterior cord, containing fibres from C5 - T1.
Table: Anatomical Overview of the Radial Nerve
| Nerve | Radial |
| Nerve roots | C5 – T1 |
| Plexus cords | Posterior cord |
| Motor Supply | Triceps brachii, posterior compartment of forearm: superficial muscles (brachioradialis, extensor carpi radialis longus and brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris) and deep muscles (supinator, abductor pollicis longus, extensor pollicis longus and brevis, extensor indicis) |
| Sensory supply | Lower lateral arm, posterior arm, posterior forearm, dorsum of lateral hand and three and a half fingers |
Anatomical course
The radial nerve enters the arm by crossing the lower margin of the teres major muscle, where it lies posterior to the brachial artery. It enters the posterior compartment of the arm, where it descends obliquely passing from medial to lateral in the radial (spiral) groove of the humerus. After emerging from the spiral groove, the radial nerve pierces the lateral intermuscular septum and enters the anterior compartment of the arm, descending into the cubital fossa where it lies between the brachialis and brachioradialis muscles.
The radial nerve enters the forearm after passing over the lateral epicondyle of the humerus. Within the proximal forearm the nerve terminates by bifurcating into the deep branch and the superficial branch.
N.B. Once the deep branch of the radial nerve penetrates between the two heads of the supinator muscle to access the posterior compartment of the forearm, it becomes known as the posterior interosseous nerve.
![By Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2016/12/Radial-Nerve.png)
Radial Nerve. (Image by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
Branches
Table: Branches of the Radial Nerve
| Branches of Radial Nerve | Origin | Supply |
| Radial nerve | Axilla | Triceps brachii, extensor carpi radialis longus, brachioradialis |
| Posterior cutaneous nerve of the arm | Axilla | Skin of posterior arm |
| Inferior lateral cutaneous nerve of the arm | Arm | Skin over lateral aspect of lower arm |
| Posterior cutaneous nerve of the forearm | Arm | Strip of skin down middle of posterior forearm |
| Deep branch which continues as the posterior interosseous nerve | Forearm | Posterior compartment of forearm: superficial muscles (extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris) and deep muscles (supinator, abductor pollicis longus, extensor pollicis longus and brevis, extensor indicis) |
| Superficial branch | Forearm | Skin of dorsum of the hand and lateral three and a half fingers |
In the arm, the radial nerve directly innervates the triceps brachii, the extensor carpi radialis longus and the brachioradialis. In the forearm, the deep branch, which continues as the posterior interosseous nerve, innervates the muscles of the posterior compartment of the forearm and the superficial branch supplies the skin of the dorsum of the hand and lateral three and a half fingers.
The radial nerve also gives rise to several cutaneous branches; the posterior cutaneous nerve of the arm originating in the axilla, and the inferior lateral cutaneous nerve of the arm and the posterior cutaneous nerve of the forearm originating in the arm. These cutaneous branches supply skin over the posterior surface of the arm, the lateral aspect of the arm and the skin down the middle of the posterior forearm respectively.
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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 |
