ST3 ORTHOPAEDIC INTERVIEW QUESTIONS ONLINE

The supraspinatus muscle performs abduction of the arm, and pulls the head of the humerus medially towards the glenoid fossa. Beyond 15 degrees the deltoid muscle becomes increasingly more effective at abducting the arm and becomes the main propagator of this action.

Origin: Supraspinous fossa of scapula
Insertion: Superior facet of greater tubercle of humerus
Artery: Suprascapular artery
Nerve: Suprascapular nerve
Actions: Abduction of arm and stabilizes humerus

It arises from its medial two-thirds and from the lower two-thirds of the groove on the axillary border (subscapular fossa) of the scapula.

Some fibers arise from tendinous laminae which intersect the muscle and are attached to ridges on the bone; others from an aponeurosis, which separates the muscle from the teres major and the long head of the triceps brachii.

The fibers pass laterally and coalesce into a tendon which inserts into the lesser tubercle of the humerus and the anterior part of the shoulder-joint capsule. Tendinous fibers extend to the greater tubercle with insertions into the bicipital groove.

The subscapularis rotates the head of the humerus medially (internal rotation); when the arm is raised, it draws the humerus forward and downward. It is a powerful defense to the front of the shoulder-joint, preventing displacement of the head of the humerus.

Origin: Subscapular fossa
Insertion: Lesser tubercle of humerus
Artery: Subscapular artery
Nerve: Upper subscapular nerve, lower subscapular nerve (C5, C6)
Actions: Internally (medially) rotates humerus; stabilizes shoulder

The latissimus dorsi is responsible for extension, adduction, flexion from an extended position, and internal rotation of the shoulder joint. It also has a synergistic role in extension (posterior fibers) and lateral flexion (anterior fibers) of the lumbar spine, and assists as a muscle of both forced expiration (anterior fibers) and an accessory muscles of inspiration (posterior fibers).

The latissimus dorsi can be remembered best for insertion as "The Lady Between Two Majors". As the latissimus dorsi inserts into the floor of the intertubercular groove of the humerus it is surrounded by two major muscles. The teres major inserts medially on the medial lip of the intertubercular groove and laterally the pectoralis major inserts into the lateral lip.

Origin: Spinous processes of vertebrae T7-T12, thoracolumbar fascia, iliac crest, inferior 3 or 4 ribs and inferior angle of scapula
Insertion: Floor of intertubercular groove of the humerus
Artery: Thoracodorsal branch of the subscapular artery
Nerve: Thoracodorsal nerve
Actions: Adducts, extends and internally rotates the arm when the insertion is moved towards the origin. When observing the muscle action of the origin towards the insertion, the lats are a very powerful rotator of the trunk.
Antagonist: Deltoid and trapezius muscle

The pectoralis major has four actions which are primarily responsible for movement of Flexion of the humerus.
Adduction of the humerus
Medial rotation of the humerus
The pectoralis major is also responsible for keeping the arm attached to the trunk of the body. The clavicular part is close to the deltoid muscle and contributes to flexion, horizontal adduction, and inward rotation of the humerus. When at an approximately 110 degree angle, it contributes to adduction of the humerus.

Origin Clavicular head: anterior border of the medial half of the clavicle.
Sternocostal head: anterior surface of the sternum, the superior six costal cartilages, and the aponeurosis of the external oblique muscle
Insertion Lateral lip of the bicipital groove of the humerus
(anteromedial proximal humerus)
Artery pectoral branch of the thoracoacromial trunk
Nerve lateral pectoral nerve and medial pectoral nerve
Clavicular head: C5 and C6
Sternocostal head: C7, C8 and T1
Actions Clavicular head: flexes the humerus
Sternocostal head: extends the humerus
As a whole, adducts and medially rotates the humerus. It also draws the scapula anteriorly and inferiorly.

The teres major is a medial rotator and adductor of the humerus and assists the latissimus dorsi in drawing the previously raised humerus downwards and backwards (extension, but not hyper extension). It also helps stabilise the humeral head in the glenoid cavity.


Origin: Posterior aspect of the inferior angle of the scapula
Insertion: Medial lip of the intertubercular sulcus of the humerus
Artery: Subscapular and circumflex scapular arteries
Nerve: Lower subscapular nerve (segmental levels C5 and C6)
Actions: adduct the humerus, Internal rotation (medial rotation) of the humerus, extend the humerus from flexed position, Protracts scapula, Depress shoulder

The coracobrachialis is the smallest of the three muscles that attach to the coracoid process of the scapula. (The other two muscles are pectoralis minor and the short head of the biceps brachii.) It is situated at the upper and medial part of the arm.

The action of the coracobrachialis is to flex and adduct the arm at the glenohumeral joint. Also, the coracobrachialis resists deviation of the arm from the frontal plane during abduction. Therefore, the contraction of the coracobrachialis leads to two distinct movements at the shoulder joint. It both draws the humerus forward, causing shoulder flexion, and draws the humerus toward the torso, causing shoulder adduction.

Origin: Coracoid process of scapula
Insertion: Medial humerus
Artery: Brachial artery
Nerve: Musculocutaneous nerve (C5, C6, and C7)
Actions: adducts humerus , flexes the arm at glenohumeral joint

The brachialis flexes the arm at the elbow joint. Unlike the biceps, the brachialis does not insert on the radius, and does not participate in pronation and supination of the forearm.
It lies deeper than the biceps brachii, and is a synergist that assists the biceps brachii in flexing at the elbow. It makes up part of the floor of the region known as the cubital fossa. The brachialis is the prime mover of elbow flexion. While the biceps brachii appears as a large anterior bulge on the arm and commands considerable interest among body builders, the brachialis underlying it actually generates about 50% more power and is thus the prime mover of elbow flexion.

Origin: Anterior surface of the humerus, particularly the distal half of this bone
Insertion: Coronoid process and the tuberosity of the ulna
Artery: Radial recurrent artery
Nerve: Musculocutaneous nerve (C5, C6)
Actions: Flexion at elbow joint

The brachioradialis flexes the forearm at the elbow. When the forearm is pronated, the brachioradialis tends to supinate as it flexes. In a supinated position, it tends to pronate as it flexes. This also assists the biceps brachii.

The brachioradialis is a stronger elbow flexor when the forearm is in a midposition between supination and pronation at the radioulnar joint. When pronated, the brachioradialis is more active during elbow flexion since the biceps brachii is in a mechanical disadvantage.

With the insertion of the muscle so far from the fulcrum of the elbow, the brachioradialis does not generate as much joint torque as the brachialis or the biceps.

Origin: Lateral supracondylar ridge of the humerus
Insertion: Distal radius (radial styloid process)
Artery: Radial recurrent artery
Nerve: Radial nerve
Actions: Flexion of elbow and supination

ECRL is an extensor at the wrist joint and travels along the radial side of the arm, so will also abduct (radial abduction) the hand at the wrist.

It originates from the lateral supracondylar ridge of the humerus, from the lateral intermuscular septum, and by a few fibers from the lateral epicondyle of the humerus and attaching to the base of the metacarpal of the index finger.

Origin: Lateral supracondylar ridge
Insertion: 2nd metacarpal
Artery: Radial artery
Nerve: Radial nerve
Actions: Extensor at the wrist joint, abducts the hand at the wrist
Antagonist: Flexor carpi ulnaris muscle

From the brachial plexus, it travels posteriorly through what is often called the triangular interval (US) / the lower triangular space of the axilla (UK).

Having passed through this inter muscular gap, the radial nerve continues posteriorly in a medial to lateral fashion on the arm close to the artery.

The nerve will first give off branches to the medial head of the triceps brachii and then enter a groove on the humerus (spiral groove), where it innervates the lateral head of the triceps. With the lateral and medial heads of the triceps innervated, the radial nerve emerges from the radial groove on the lateral aspect of the humerus.

At this point, it pierces the lateral intermuscular septum and enters the anterior compartment of the arm. It then courses inferiorly between the brachialis and brachioradialis muscles.

When the radial nerve reaches the distal part of the humerus, it passes anteriorly to the lateral epicondyle and continues in the forearm.

In the forearm, it branches into a superficial branch (primarily sensory) and a deep branch (primarily motor).

The superficial branch of the radial nerve descends in the forearm under the brachioradialis. It crosses brachioradialis to enter posterior of forearm near the back of the wrist and supply dorsum of hand. It gives nerve supply to dorsal aspect of thumb, index finger,middle finger and radial side of ring finger except the nail beds, which are supplied by proper digital branches of median nerve.
The deep branch of the radial nerve pierces the supinator muscle, winds around the radius under the cover of supinator to reach posterior of forearm where it again pierces supinator and after which it is known as the posterior interosseous nerve of forearm.It pierces the posterior extensor muscles and comes to lie on posterior interosseous membrane just below extensor pollicis brevis. It continues to move along with posterior interosseous artery(a deep branch of common interosseous artery which is a branch of ulnar artery), and ends as a pseudoganglion below extensor retinaculum.

From: Posterior cord
To: Posterior interosseous nerve
Innervates: Posterior compartment of the arm, posterior compartment of the forearm

The infraspinatus is the main external rotator of the shoulder. When the arm is fixed, it abducts the inferior angle of the scapula. Its synergists are teres minor and the deltoid.

The infraspinatus and teres minor rotate the head of the humerus outward (external, or lateral, rotation); they also assist in carrying the arm backward.

Origin: Infraspinous fossa of the scapula
Insertion: Middle facet of greater tubercle of the humerus
Artery: Suprascapular and circumflex scapular arteries
Nerve: Suprascapular nerve
Actions: Lateral rotation of arm and stabilizes humerus