Anatomy
Upper Limb
A 35 year old man attends ED having been thrown off his mountain bike and fallen onto his right arm. You note numerous abrasions and bruises. He is unable to extend his right wrist, fingers and thumb, although can extend his elbow. Sensation is abnormal on the lateral dorsum of his right hand. Which of the following nerves has most likely been affected, and at which level:
Answer:
The radial nerve innervates the posterior muscles in the arm and forearm, which primarily act to produce extension of the forearm, wrist and fingers. In injury to the radial nerve in the axilla, you would expect the triceps brachii muscle to also be affected, and thus extension at the elbow to be lost in association with loss of sensation over the inferior lateral arm and posterior arm and forearm. In injury at the mid-humerus the triceps brachii muscle and the cutaneous branches of the arm and forearm are usually spared. The superficial branch of the radial nerve has no motor supply and thus cannot solely be affected in this case.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 |
