Anatomy
Upper Limb
You are reviewing a 23 year old woman who has sustained a fracture to the surgical neck of the humerus after falling from her bike. On examination she has features of an axillary nerve injury. Which of the following clinical features would you most expect to see in this patient:
Answer:
In axillary nerve injury there is weakness of arm abduction (paralysis of deltoid), weakness of lateral rotation of the arm (paralysis of teres minor) and loss of sensation over the regimental badge area.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)
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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 |
