Anatomy
Head and Neck
A 29 year old male presents to ED with a penetrating injury to the neck. You suspect injury to the right sternocleidomastoid muscle. How would you best assess function of this muscle:
Answer:
The sternocleidomastoid muscle is best assessed by testing rotation of head against resistance. The right sternocleidomastoid muscle acts to rotate the head towards the left and vice versa.Sternocleidomastoid Muscle
Anatomy / Head and Neck / Neck
Last Updated: 11th April 2019
Table: Overview of the Sternocleidomastoid Muscle
| Muscle | Sternocleidomastoid |
|---|---|
| Origin |
|
| Insertion |
|
| Innervation | Accessory nerve (and by branches of anterior rami of C2 – C3) |
| Action |
|
Attachments
The sternocleidomastoid muscle has two heads; the sternal head originates from the upper part of the anterior manubrium of the sternum and inserts onto the lateral one-half of the superior nuchal line (occipital bone) and the clavicular head originates from the superior surface of the medial one-third of the clavicle and inserts onto the lateral surface of the mastoid process (temporal bone).
Function
Individually each muscle will tilt the head towards the shoulder on the same side (lateral flexion) and rotate the head to turn to face the opposite side. Acting together the muscles draw the head forward, through extension of the neck at the atlanto-occipital joints (dorsal extension).
Innervation
The sternocleidomastoid is innervated by the accessory nerve (CN XI) and by branches of anterior rami of C2 - C3.
![Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2016/07/sternocleidomastoid.png)
Sternocleidomastoid Muscle. (Image by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
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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 |
