Anatomy
Upper Limb
Question 40 of 239
A 30 year old man attends ED with a deep knife wound to his distal forearm. He is unable to hold a piece of paper between his fingers and is complaining of loss of sensation over the medial side of his hand and little finger. Which of the following nerves is most likely to have been affected:
Answer:
The ulnar nerve innervates all of the intrinsic muscles of the hand (except for the thenar muscles and the lateral two lumbricals, innervated by the median nerve). Adduction of the fingers is required to hold a piece of paper between the fingers, which is produced by the palmar interossei. The ulnar nerve supplies sensation to the dorsal and palmar aspect of the medial hand and the medial one and a half fingers.Ulnar Nerve Injury
Anatomy / Upper Limb / Innervation of Upper Limb
Last Updated: 8th November 2021
Table: Clinical Features of Ulnar Nerve Injury
| Lesion | Proximal (at elbow) | Distal (at wrist) |
| Mechanism | Fracture of medial epicondyle | Laceration at wrist |
| Motor Loss | Wrist flexion and adduction, finger abduction and adduction, flexion of ring and little finger, abduction and opposition of little finger, thumb adduction, extension of IPJs of all digits (less so at index and middle finger due to sparing of lateral two lumbricals) | Finger abduction and adduction, flexion of ring and little finger, abduction and opposition of little finger, thumb adduction, extension at IPJs |
| Sensory Loss | Medial half of palm, palmar and dorsal surface of medial one and a half fingers and medial dorsum of hand | Palmar surface of medial one and a half fingers |
| Signs | Hand held in abduction (due to unopposed action of flexor carpi radialis), Froment’s sign (patient is asked to hold a piece of paper between thumb and flat palm as paper is pulled away, patient will flex thumb at IPJ to maintain hold – tests adductor pollicis muscle), hypothenar eminence wasting, N.B. claw hand not typically seen due to paralysis of the flexor digitorum profundus | Claw hand (unopposed extension at MCPJ and unopposed flexion at IPJs of ring and little finger), hypothenar eminence wasting, Froment’s sign |
Proximal Ulnar Nerve Injury
MECHANISM OF INJURY:
The ulnar nerve is most likely to be injured proximally by a medial epicondyle fracture
CLINICAL FEATURES:
- There is weak wrist flexion and adduction due to paralysis of the flexor carpi ulnaris and the medial half of the flexor digitorum profundus; the hand may be held in abduction (due to unopposed action of the flexor carpi radialis).
- There is loss of abduction and adduction of the fingers due to paralysis of the interossei.
- There is loss of flexion at the MCPJ of the ring and little finger due to paralysis of the medial two lumbricals and the flexor digiti minimi.
- There is loss of flexion at the DIPJ of the ring and little finger due to paralysis of the medial half of the flexor digitorum profundus (but flexion at the PIPJ is likely preserved as this is a function of the flexor digitorum superficialis).
- There is weakened extension at the IPJs of the ring and little finger due to paralysis of the interossei and medial two lumbricals (and to a lesser extent at the IPJs of the index and middle finger).
- There is loss of abduction and opposition of the little finger due to paralysis of the hypothenar muscles (hypothenar wasting may be seen).
- There is loss of adduction of the thumb due to paralysis of the adductor pollicis (Froment's sign).
- There is loss of sensation to skin over the medial half of the palm, the palmar and dorsal surface of the medial one and a half fingers and the medial dorsum of the hand.
- There is not typically a claw hand appearance (as may be seen in a lesion at the wrist) due to paralysis of the flexor digitorum profundus.
Distal Ulnar Nerve Injury
MECHANISM OF INJURY:
A distal lesion most commonly occurs due to laceration at the wrist.
CLINICAL FEATURES:
- Only intrinsic hand muscles are affected (the flexor carpi ulnaris and medial half of the flexor digitorum profundus are spared).
- A loss of sensation will only affect the palmar surface of the medial one and a half fingers (the medial palm and the dorsum of the hand are spared).
- A claw hand deformity may be seen due to unopposed extension at the MCPJ (by the extensor digitorum) and unopposed flexion at the IPJs (by the FDP and FDS) of the ring and little finger.
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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 |
