Anatomy
Upper Limb
A 54 year old patient presents to ED complaining of weakness in her right hand. She has recently undergone an endoscopic nerve release for carpal tunnel syndrome but is now complaining of a severe weakness of her thumb with loss of thumb opposition. Sensation is normal. Which of the following nerves was likely affected in the surgical procedure.
Answer:
The recurrent branch of the median nerve has likely been affected, which innervates the thenar muscles, causing weakness of thumb flexion, abduction and opposition, but has no cutaneous innervation.Median Nerve
Anatomy / Upper Limb / Anterior Arm / Anterior Forearm / Innervation of Upper Limb
Last Updated: 8th April 2019
The median nerve is formed from the medial and lateral brachial plexus cords and contains fibres from all five roots (C5 - T1).
Table: Anatomical Overview of the Median Nerve
| Nerve | Median |
| Nerve roots | C5 – T1 |
| Plexus cords | Medial and lateral cords |
| Motor Supply | All the anterior forearm muscles (except for the flexor carpi ulnaris and the medial half of the flexor digitorum profundus), the thenar muscles (flexor pollicis brevis, abductor pollicis brevis, opponens pollicis) and the lateral two lumbricals |
| Sensory supply | Lateral aspect of palm and palmar surface and fingertips of lateral three and a half digits |
Anatomical course
The median nerve originates in the axilla before passing down the medial side of the arm (initially lateral to the brachial artery before crossing over to the medial side of the brachial artery). It enters the anterior compartment of the forearm via the antecubital fossa, travelling between the flexor digitorum profundus and flexor digitorum superficialis muscles, before entering the hand via the carpal tunnel and bifurcating into its terminal branches.
![By Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2016/12/Median-Nerve-1.gif)
Median Nerve. (Image by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
Branches
Table: Branches of the Median Nerve
| Branches of Median Nerve | Origin | Supply |
| Median nerve | Axilla | Superficial and intermediate compartment of anterior forearm (pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, NOT flexor carpi ulnaris) |
| Anterior interosseous nerve | Forearm | Deep compartment of anterior forearm (flexor pollicis longus, pronator quadratus, lateral half of flexor digitorum profundus) |
| Palmar cutaneous branch | Forearm | Skin over the lateral aspect of the palm |
| Recurrent branch of median nerve | Hand | Thenar muscles (flexor pollicis brevis, abductor pollicis brevis, opponens pollicis) |
| Palmar digital branch | Hand | Lateral two lumbricals and skin over the palmar surface and fingertips of the lateral three and a half digits |
The median nerve directly innervates the pronator teres, the flexor carpi radialis, the palmaris longus and the flexor digitorum superficialis. It gives off no major branches in the arm, but gives rise to the anterior interosseous nerve (innervating the flexor pollicis longus, the pronator quadratus, and the lateral half of the flexor digitorum profundus) and the palmar cutaneous nerve (innervating the lateral aspect of the palm) in the forearm.
In the hand the median nerve bifurcates into the recurrent branch of the median nerve (innervating the thenar muscles) and the palmar digital branch (innervating the lateral two lumbricals and the skin over the palmar surface and fingertips of the lateral three and a half digits).
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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 |
