Anatomy
Upper Limb
A 71 year old lady attends ED complaining of pain in her arm following a fall. Imaging demonstrates a midshaft humerus fracture. An injury of the radial nerve in the spiral groove would typically demonstrate which of the following physical signs:
Answer:
The radial nerve innervates the abductor pollicis longus and the extensor pollicis longus and brevis. Injury would therefore result in loss of extension and abduction of the thumb. The radial nerve does also innervate the triceps brachii, but injury at the mid humerus level usually spares this muscle and thus you would not expect weakness of forearm extension.Radial Nerve Injury
Anatomy / Upper Limb / Innervation of Upper Limb
Last Updated: 10th April 2019
Table: Clinical Features of Radial Nerve Injury
| Lesion | In axilla | In spiral groove | In forearm (superficial branch) | In forearm (deep branch) |
| Mechanism | Glenohumeral joint dislocation, fracture of proximal humerus, ‘Saturday night syndrome’ | Fracture of midshaft of humerus | Stabbing/laceration of forearm | Fracture of radial head or posterior dislocation of radius |
| Motor Loss | Loss of extension at elbow, wrist and fingers, weakness of supination | Loss of extension at wrist and fingers (triceps brachii spared), weakness of supination | None | Weakness of extension at wrist and fingers (extensor carpi radialis spared) |
| Sensory Loss | Lower lateral arm, posterior arm, posterior forearm, dorsum of lateral hand and three and a half fingers | Dorsum of lateral hand and three and a half fingers (cutaneous branches of arm and forearm spared) | Dorsum of lateral hand and three and a half fingers | None |
| Signs | Wrist drop (unopposed wrist flexion), weakness of hand grip (finger flexion is weak as the long flexor tendons are not under tension) | Wrist drop, weak hand grip | None | Wrist drop not typically seen (extensor carpi radialis spared) |
Radial Nerve Injury in the Axilla
MECHANISM OF INJURY:
Radial nerve injury at the axilla may occur in glenohumeral joint dislocation, in fractures of the proximal humerus, through incorrect use of axillary crutches, or due to 'Saturday Night' palsy.
CLINICAL FEATURES:
Loss of extension of the forearm due to paralysis of the triceps brachii and loss of extension of the wrist and fingers (predominantly MCPJs, as extension at the IPJs is primarily a function of the lumbrical and interosseous muscles) and weakness of supination due to paralysis of the muscles of the posterior compartment of the forearm. All four cutaneous branches of the radial nerve are affected and there is loss of sensation over the lateral and posterior arm, the posterior forearm and the dorsal surface of the hand and lateral three and a half digits. There is unopposed wrist flexion, giving the appearance of wrist drop.
Radial Nerve injury in the Arm
MECHANISM OF INJURY:
The radial nerve in the arm is most susceptible to midshaft fractures of the humerus due to its course in the spiral groove.
CLINICAL FEATURES:
Extension of the forearm is not affected as the triceps brachii is spared. There is loss of extension of the wrist and MCPJs of the fingers and weakness of supination of the forearm. The cutaneous branches of the arm and forearm have already arisen and sensation loss occurs only on the dorsum of the lateral hand and three and a half digits.
Radial Nerve Injury in the Forearm
Radial nerve damage in the forearm may present as superficial branch or deep branch damage.
SUPERFICIAL BRANCH:
The superficial branch is most commonly damaged by stabbing or laceration to the forearm and results in loss of sensation over the dorsum of the lateral hand and three and a half digits.
DEEP BRANCH:
The deep branch may be damaged by fracture of the radial head or posterior dislocation of the radius and results in weakness of extension of the wrist and fingers, but not typically with wrist drop (as the extensor carpi radialis is spared).
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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 |
