Anatomy
Upper Limb
Question 121 of 239
A 29 year old male presents to ED having falling awkwardly during a judo match. On examination he is unable to flex his index and middle fingers at the metacarpophalangeal or interphalangeal joints and unable to flex the distal phalanx of his thumb. He has loss of sensation over the lateral palm and fingers. Which of the following nerves has most likely been injured, and at what level:
Answer:
The most likely injury is the median nerve at the cubital fossa. The patient has loss of flexion at the MCPJ and IPJ of the index and middle finger caused by paralysis of the lateral two lumbricals and the flexor digitorum profundus and flexor digitorum superficialis. Loss of flexion of the distal phalanx of the thumb results from paralysis of the flexor pollicis longus. The anterior interosseous nerve, branch of the median nerve, has no cutaneous function. Median nerve injury at the wrist would spare the forearm flexor muscles so you would not expect loss at the interphalangeal joints (IPs) of the thumb, index or middle finger.Median Nerve Injury
Anatomy / Upper Limb / Innervation of Upper Limb
Last Updated: 21st March 2023
Table: Clinical Features of Median Nerve Injury
| Lesion | Proximal (arm, elbow, proximal forearm) | Distal (wrist) |
| Mechanisms | Supracondylar fracture, stab wound to arm or forearm | Lacerations just proximal to flexor retinaculum |
| Motor Loss | Forearm pronation, wrist flexion and abduction, index and middle finger flexion, thumb flexion, abduction and opposition | Thumb flexion, abduction and opposition, flexion of index and middle finger MCPJ |
| Sensory Loss | Lateral aspect of palm and palmar surface and fingertips of lateral three and a half digits | Palmar surface and fingertips of lateral three and a half digits |
| Signs | Forearm rests in supination with wrist in ulnar deviation and thumb extended, thenar eminence wasting, hand of Benediction (when asked to make a fist, the patient will be able to flex the little and ring fingers but not the index and middle fingers) | Thenar eminence wasting |
Proximal Median Nerve Injury
MECHANISM OF INJURY:
A proximal median nerve lesion at the elbow may occur due to supracondylar fracture of the humerus or from deep penetrating wounds to the arm.
CLINICAL FEATURES:
- Pronation of the forearm and flexion and abduction of the wrist are lost due to paralysis of the flexors and pronators in the forearm. The forearm thus often rests in supination with ulnar deviation of the wrist (due to unopposed action of the flexor carpi ulnaris).
- Flexion, abduction and opposition of the thumb at the MCPJ and IPJ are lost due to paralysis of the thenar muscles and the flexor pollicis longus.
- Flexion of the index and middle fingers at the IPJs is lost due to paralysis of the flexor digitorum superficialis and the lateral half of the flexor digitorum profundus.
- Extension of the index and middle fingers at the IPJs is weakened due to paralysis of the lateral two lumbrical muscles (but not lost due to preservation of the interossei innervated by the ulnar nerve)
- Flexion of the MCPJ of the index and middle fingers is lost due to paralysis of the lateral two lumbrical muscles.
- N.B. Flexion of the ring and little fingers at the MCPJ and DIPJ 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 PIPJ of these fingers due to paralysis of the flexor digitorum superficialis).
- There is loss of sensation over the lateral aspect of the palm, and the skin over the palmar surface and fingertips of the lateral three and a half digits.
Distal Median Nerve Injury
MECHANISM OF INJURY:
Medial nerve lesion at the wrist often occurs due to lacerations just proximal to the flexor retinaculum. Only the intrinsic hand muscles are affected.
CLINICAL FEATURES:
- Loss of opposition, abduction and flexion of the MCPJ of the thumb occurs due to paralysis of the thenar muscles.
- Loss of flexion at the MCPJ of the index and middle finger and weakness of extension at the IPJs of the index and middle finger occurs due to paralysis of the lateral two lumbricals.
- There is loss of sensation to 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 |
