Anatomy
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Upper Limb
A patient presents to ED with an anterior shoulder dislocation sustained while playing rugby. Following successful reduction, he is unable to abduct his arm from his side. Which of the following muscles has most likely been affected:
Answer:
The supraspinatus is the most commonly injured rotator cuff muscle. The supraspinatus muscle acts to initiate abduction from 0 degrees, and then assists the deltoid with continued abduction.Supraspinatus Muscle
Anatomy / Upper Limb / Shoulder
Last Updated: 14th July 2019
The supraspinatus is part of the rotator cuff group of muscles.
Table: Function and Innervation of the Supraspinatus Muscle
| Muscle | Supraspinatus |
|---|---|
| Function | Initiation of abduction of shoulder to 15 degrees (and then assistance of deltoid with continued abduction) |
| Innervation | Suprascapular nerve |
| Examination | Empty Can Test: Position the patient with arms elevated to 90 degrees in the scapular plane, with the elbow extended, and full medial rotation and pronation of the forearm with thumbs pointing downwards. Ask the patient to resist the downward force being applied to the forearm. Test is positive is patient has pain or weakness. |
Function
The supraspinatus acts to initiate abduction of the arm to 15 degrees and then assists the deltoid with continued abduction to 90 degrees.
Innervation
The supraspinatus is innervated by the suprascapular nerve.
Examination
The supraspinatus muscle can be assessed using the 'empty can' test. The 'empty can' test can be performed by positioning the patient with the arm in 90 degrees of forward flexion, in the plane of the scapula (approximately 30 degrees of abduction) and in full internal rotation with the thumb pointing down (as if emptying a can). The patient is asked to forward flex their arm against resistance, and the test is considered positive if there is significant pain and/or weakness.
![Modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2016/12/Supraspinatus.png)
Supraspinatus Muscle. (Image modified by FRCEM Success. Original 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 |
