100+ Free FC Orth(SA) Part I Practice Questions

Explanation: The axillary nerve (C5-C6) originates from the posterior cord of the brachial plexus and traverses the quadrangular space bound by teres minor superiorly, teres major inferiorly, the long head of triceps medially, and the surgical neck of the humerus laterally. It travels in close association with the posterior circumflex humeral artery before innervating the deltoid and teres minor muscles.

Explanation: The long head of the triceps brachii receives its innervation directly from the radial nerve high in the axilla, prior to the radial nerve entering the spiral (radial) groove of the humerus. This explains why extension of the elbow at the long head remains functional even after a midshaft humerus fracture causing radial nerve palsy in the spiral groove.

Explanation: The anterior interosseous nerve (AIN, C8-T1) purely supplies motor innervation to the flexor pollicis longus (FPL), the lateral half of flexor digitorum profundus (FDP to index and middle fingers), and the pronator quadratus. Loss of AIN function impairs the 'OK' sign due to loss of FPL and FDP index finger flexion.

Explanation: Osborne's ligament (also known as the arcuate ligament of flexor carpi ulnaris or Osborne's fascia) spans between the humeral and ulnar heads of the flexor carpi ulnaris. It forms the roof of the cubital tunnel and is a primary anatomical site of ulnar nerve entrapment at the elbow.

Explanation: The posterior interosseous nerve (PIN), a motor continuation of the deep branch of the radial nerve, enters the posterior compartment by passing under the fibrous Arcade of Frohse into the two heads of the supinator muscle. Compression at this site causes PIN syndrome (motor weakness of extensor muscles without cutaneous sensory deficit).

Explanation: The musculocutaneous nerve (C5-C7) arises from the lateral cord, pierces the coracobrachialis muscle approximately 5-8 cm distal to the coracoid process, and then descends between biceps brachii and brachialis to supply all three muscles before continuing as the lateral antebrachial cutaneous nerve.

Explanation: At the suprascapular notch, the suprascapular nerve passes beneath (under) the superior transverse scapular ligament, whereas the suprascapular artery passes above (over) the ligament (mnemonically remembered as 'Army over bridge, Navy under bridge'). Entrapment of the nerve under the ligament leads to suprascapular nerve neuropathy.

Explanation: The cephalic vein lies in the intermuscular deltopectoral groove between the deltoid (axillary nerve) and pectoralis major (pectoral nerves) muscles. It is the landmark for the internervous plane of the anterior deltopectoral approach to the shoulder.

Explanation: The posterior approach to the hip requires splitting the gluteus maximus fibers along their muscle plane and subsequently releasing the tendons of the piriformis, obturator internus, and superior/inferior gemelli muscles near their insertion onto the trochanteric fossa to access the capsule.

Explanation: The Watson-Jones anterolateral approach to the hip uses the intermuscular plane between the tensor fasciae latae (superior gluteal nerve) and the gluteus medius (superior gluteal nerve). Because both muscles share the same innervation, it is an intermuscular, rather than a true internervous plane.