Anatomy
Upper Limb
Question 28 of 180
A 32 year old man presents to ED with a deep laceration to the proximal part of the forearm. On further assessment, when the patient is asked to make a fist, he is unable to flex the metacarpophalangeal joints or interphalangeal joints of the index and middle finger or the thumb. For the most part the ring and little fingers are intact, although you note some weakness at the proximal interphalangeal joint. There is loss of sensation over the lateral palm and the palmar surface of the lateral three and a half fingers. Which of the following nerve(s) has most likely been affected:
Answer:
In a median nerve injury affecting the extrinsic and intrinsic muscles of the hand there is:- Weakness of flexion of the distal interphalangeal joints of the index and middle finger due to paralysis of the lateral half of the flexor digitorum profundus (the medial two digits are controlled by the medial half innervated by the ulnar nerve)
- Weakness of flexion of the metacarpophalangeal joints of the index and middle finger due to paralysis of the lateral two lumbricals (the medial two digits are controlled by the medial two lumbricals innervated by the ulnar nerve)
- Weakness of flexion of the proximal interphalangeal joints of all four fingers may be seen due to paralysis of the flexor digitorum superficialis
- Weakness of thumb flexion, abduction and opposition due to paralysis of the flexor pollicis longus and the thenar muscles
- Loss of sensation to the lateral palm and the lateral three and a half fingers
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 |
