Anatomy
Upper Limb
A basketball player presents to ED having fallen heavily onto his right arm during a game. X-ray shows a fracture of the surgical neck of the humerus. You wish to assess the neurovascular status of his arm, and particularly of the nerve most commonly damaged in this type of injury. Which of the following tests would be most helpful to assess this nerve:
Answer:
The axillary nerve is the most commonly injured nerve in a fracture of the surgical neck of the humerus as it passess dorsally around this region accompanied by the posterior humeral circumflex artery. The axillary nerve innervates the deltoid (abduction) and teres minor (lateral rotation) muscles and supplies an area of skin over the upper lateral arm (regimental badge area). Shrugging of the shoulders is a function of the spinal accessory nerve, and assessing for winging of the scapula is useful for damage to the long thoracic nerve.Axillary Nerve Injury
Anatomy / Upper Limb / Innervation of Upper Limb
Last Updated: 24th October 2020
Table: Clinical Features of Axillary Nerve Injury
| Nerve | Axillary |
|---|---|
| Mechanism of injury | Dislocation of the glenohumeral joint, fracture of the surgical neck of the humerus, trauma or surgery to the shoulder, incorrect use of axillary crutches |
| Motor loss | Loss of abduction of the arm at the glenohumeral joint and weakness of lateral rotation |
| Sensory loss | Lateral arm (regimental badge area) |
| Signs | Atrophy of deltoid – flattened shoulder appearance |
Clinical Anatomy
The axillary nerve and associated blood vessels (the posterior circumflex humeral artery and vein) enter the deltoid by passing posteriorly around the surgical neck of the humerus.
Mechanism of Injury
The axillary nerve is most commonly damaged by direct trauma to the shoulder or proximal humerus. Common mechanisms of injury include fracture of the surgical neck of the humerus, shoulder dislocation or iatrogenic injury during shoulder surgery.
Clinical Features
Axillary nerve injury results in:
- Weakness of abduction (due to paralysis of the deltoid muscle)
- Weakness of lateral rotation (due to paralysis of the teres minor muscle)
- Loss of sensation over the 'regimental badge area' on the lateral arm
- Deltoid muscle atrophy giving a flattened shoulder appearance (in long-standing cases)
Report A Problem
Is there something wrong with this question? Let us know and we’ll fix it as soon as possible.
Loading Form...
- 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 |
