Anatomy
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Upper Limb
A patient presents to ED with a shoulder dislocation. Which of the following ligaments helps resist superior displacement of the humeral head:
Answer:
The coracoacromial arch is formed superiorly by the acromion and the coracoid process of the scapula with the coracoacromial ligament spanning between them. This structure prevents superior displacement of the humerus.Shoulder Joint
Anatomy / Upper Limb / Shoulder
Last Updated: 8th April 2019
Table: Anatomical Overview of the Shoulder Joint
| Joint | Shoulder (Glenohumeral) |
|---|---|
| Type | Synovial ball and socket joint |
| Articulations | Head of humerus and glenoid cavity of scapula |
| Stabilising Factors | Rotator cuff muscle tendons, long head of biceps brachii muscle tendon, coracoacromial arch, extracapsular ligaments (glenohumeral ligaments, coracohumeral ligament, transverse humeral ligament) |
| Movements | Flexion, extension, abduction, adduction, medial rotation and lateral rotation |
Joint Articulations
The glenohumeral joint is a synovial ball and socket joint occurring between the head of the humerus and the glenoid cavity of the scapula. The glenoid cavity is deepened and expanded peripherally by a fibrocartilaginous collar (the glenoid labrum), which attaches to the margin of the fossa, and is continuous superiorly with the tendon of the long head of the biceps brachii.
Glenohumeral Joint. (Image by OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons)
Joint Movements
Movements at the joint include flexion, extension, abduction, adduction, medial rotation and lateral rotation.
Table: Movements of the Shoulder Joint
| Movement | Main Muscles Involved | Main Nerves Involved |
|---|---|---|
| Flexion | Pectoralis major, deltoid, coracobrachialis, biceps brachii | Pectoral nerves, axillary nerve, musculocutaneous nerve |
| Extension | Deltoid and latissimus dorsi, teres major, triceps brachii | Axillary nerve, thoracodorsal nerve, lower subscapular nerve, radial nerve |
| Abduction | Deltoid and supraspinatus | Axillary nerve, suprascapular nerve |
| Adduction | Pectoralis major, latissimus dorsi, triceps brachii | Pectoral nerves, thoracodorsal nerve, radial nerve |
| Medial Rotation | Subscapularis, pectoralis major, latissimus dorsi, teres major | Subscapular nerves, pectoral nerves, thoracodorsal nerve |
| Lateral Rotation | Infraspinatus and teres minor | Suprascapular nerve, axillary nerve |
Table: Muscular Innervation of the Shoulder Joint
| Nerve | Muscle(s) | Shoulder Movements |
|---|---|---|
| Long thoracic nerve | Serratus anterior | Protraction and retraction of scapula |
| Thoracodorsal nerve | Latissimus dorsi | Adduction, medial rotation and extension of shoulder |
| Spinal accessory nerve | Trapezius | Elevation of scapula, rotation of scapula during shoulder abduction, retraction and depression of scapula |
| Suprascapular nerve | Supraspinatus; infraspinatus | Initiation of abduction of shoulder to 15 degrees; Lateral rotation of shoulder |
| Subscapular nerves | Subscapularis; teres major | Medial rotation of shoulder; Medial rotation and extension of shoulder |
| Pectoral nerves | Pectoralis major; pectoralis minor | Flexion, adduction and medial rotation of shoulder; Depresses tip of shoulder and protracts scapula |
| Axillary nerve | Deltoid; teres minor | Major abductor of shoulder; Lateral rotation of shoulder |
Joint Stability
The glenohumeral joint has a wide range of movements provided at the cost of skeletal stability. Joint stability is provided by the rotator cuff muscles, the long head of the biceps brachii muscle, related bony processes and extracapsular ligaments.
EXTRACAPSULAR LIGAMENTS:
The fibrous membrane of the joint capsule is thickened:
- Anterosuperiorly in three locations to form the glenohumeral ligaments (superior, middle and inferior) which pass from the superomedial margin of the glenoid cavity to the lesser tubercle and inferiorly related anatomical neck of the humerus. and act to reinforce the anterior part of the joint capsule.
- Superiorly to form the coracohumeral ligament which passes between the base of the coracoid process and the greater tubercle of the humerus, and acts to strengthen the joint capsule superiorly.
- Between the greater and lesser tubercles of the humerus to form the transverse humeral ligament which bridges over the intertubercular sulcus. This holds the synovial sheath and the tendon of the biceps brachii in place during movements of the glenohumeral joint.
![Modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2016/12/Glenohumeral-Joint.png)
Extracapsular Ligaments of Shoulder Joint. (Image by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
CORACOACROMIAL ARCH:
The coracoacromial arch is formed superiorly by the acromion and the coracoid process of the scapula with the coracoacromial ligament spanning between them. This structure prevents superior displacement of the humerus.
ROTATOR CUFF:
Tendons of the rotator cuff muscles blend with the joint capsule and form a musculotendinous collar that surrounds the posterior, superior and anterior aspects of the glenohumeral joint. This cuff of muscles stabilises and holds the head of the humerus in the glenoid cavity of the scapular without compromising the arms' flexibility and range of motion.
BICEPS BRACHII TENDON:
The tendon of the long head of the biceps brachii muscle passes superiorly through the joint and restricts upwards movement of the humeral head on the glenoid cavity.
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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 |
