Anatomy
Upper Limb
You are asked to review a 54 year old man who presents with isolated weakness of the right shoulder. On examination you note the patient is unable to perform the "lift-off" test. You suspect a weakness to the subscapularis muscle. The subscapularis muscle is innervated by which of the following nerves:
Answer:
The subscapularis is innervated by the upper and lower subscapular nerves, branches of the brachial plexus.Subscapularis Muscle
Anatomy / Upper Limb / Axilla
Last Updated: 8th April 2019
The subscapularis muscle forms the largest component of the posterior wall of the axilla. Together with three muscles of the posterior scapula region (the supraspinatus, infraspinatus and teres minor muscles) the subscapularis is a member of the rotator cuff muscle group, which stabilises the glenohumeral joint.
Table: Function and Innervation of the Subscapularis Muscle
| Muscle | Subscapularis |
|---|---|
| Origin | Medial two-thirds of subscapular fossa |
| Insertion | Lesser tubercle of humerus |
| Actions | Medial rotation of arm at glenohumeral joint |
| Innervation | Upper and lower subscapular nerves |
Attachments
It originates from, and fills, the subscapular fossa on the anterior surface of the scapula and inserts into the lesser tubercle of the humerus. The tendon crosses immediately anterior to the joint capsule of the glenohumeral joint.
Function
The subscapularis acts to medially rotate the arm at the glenohumeral joint.
To isolate the subscapularis muscle in examination, place the dorsum of the patient's hand in full medial rotation on the lower back and ask them to push their hand off the back (the 'lift-off' test). Loss of power suggests a tear while pain on forced medial rotation suggests tendonitis.
Innervation
The subscapularis is innervated by the upper and lower subscapular nerves, branches of the brachial plexus.
![Modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2016/12/Subscapularis.jpg)
Subscapularis 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 |
