Anatomy
Upper Limb
Question 130 of 234
A 34 year old man sustains an injury to the proximal median nerve following a stab wound to the forearm. Which of the following muscles would you LEAST expect to be affected:
Answer:
The flexor digiti minimi is innervated by the ulnar nerve, together with the medial half of the digitorum profundus.Median Nerve Injury
Anatomy / Upper Limb / Innervation of Upper Limb
Last Updated: 23rd May 2025
Table: Clinical Features of Median Nerve Injury
| Lesion | Proximal (arm, elbow, proximal forearm) | Distal (wrist) |
| Mechanisms |
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| Motor Loss |
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| Sensory Loss |
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| Signs |
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Proximal Median Nerve Injury
MECHANISM OF INJURY:
A proximal median nerve lesion at the elbow may occur due to a supracondylar fracture of the humerus or from deep penetrating wounds to the cubital fossa or upper forearm.
CLINICAL FEATURES:
- Wrist/Forearm:
- Pronation of the forearm and flexion and abduction of the wrist are lost due to paralysis of the pronator teres, pronator quadratus, and flexor carpi radialis.
- The forearm may rest in supination, and the wrist deviates ulnarly due to unopposed flexor carpi ulnaris (ulnar nerve).
- Thumb:
- Opposition, abduction, and MCP flexion of the thumb are lost due to paralysis of the thenar muscles.
- Flexion at the IP joint of the thumb is also lost due to paralysis of flexor pollicis longus (anterior interosseous branch of median nerve).
- Fingers:
- Flexion of the PIP and DIP joints of the index and middle fingers is lost due to paralysis of flexor digitorum superficialis and the lateral half of flexor digitorum profundus.
- Extension of the index and middle fingers at the IP joints is weakened due to paralysis of the lateral two lumbricals, but not lost because the interossei (ulnar nerve) still contribute to extension.
- Flexion of the MCP joint of the index and middle fingers is weakened due to paralysis of the lateral two lumbricals.
- Flexion of the ring and little fingers at the MCP joints and DIP joints are preserved as these are functions of the medial half of the flexor digitorum profundus and the medial two lumbrical muscles, innervated by the ulnar nerve (there may be weakness of flexion at the PIP joints of these fingers due to paralysis of the flexor digitorum superficialis).
- Sensory Loss:
- Sensory loss occurs over the lateral palm and the palmar surface and fingertips of the thumb, index, middle, and lateral half of the ring finger (i.e. lateral 3½ digits).
Distal Median Nerve Injury
MECHANISM OF INJURY:
A distal median nerve lesion typically occurs due to laceration at the wrist, often just proximal to the flexor retinaculum. In this type of injury, only the intrinsic hand muscles innervated by the median nerve are affected, as the forearm flexor muscles are spared.
CLINICAL FEATURES:
- Thenar muscle paralysis leads to:
- Loss of thumb opposition (due to opponens pollicis)
- Weakness of abduction (due to abductor pollicis brevis)
- Weakness of flexion at the MCP joint of the thumb (due to flexor pollicis brevis, partially median-innervated)
- Lumbrical paralysis (lateral two lumbricals) leads to:
- Loss of MCP joint flexion of the index and middle fingers
- Weakness of IP joint extension of the index and middle fingers
- Sensory loss involves the:
- Palmar surface and fingertips of the thumb, index, middle, and lateral half of the ring finger (i.e. the lateral 3½ 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 |
