Upper Limb Anatomy Quiz

Upper Limb Anatomy

• Metacarpophalangeal and Interphalangeal Joints: Extensors and flexor digitorum profundus muscles control these joints. Injury above the elbow affects the ulnar half of flexor digitorum profundus, resulting in straighter fingers. Wasting of interossei muscles can reveal "guttering" between metacarpals. Sensory loss occurs on the ulnar hand, little, and ring fingers, but often less than expected.

• Hand Muscle Testing: To assess median nerve function, test abduction of the index finger (first dorsal interosseous). For high-level lesions, assess the ulnar half of flexor digitorum profundus in flexing the little finger's distal interphalangeal joint. For wrist-level lesions, test abductor pollicis brevis.

• Median Nerve: Commonly injured at the wrist (cuts or carpal tunnel compression). Wasting of the thenar eminence can occur. Sensory loss can affect the radial three fingers and the radial side of the palm, primarily over the thumb and index finger pulp pads. High-level lesions cause forearm wasting, as long flexors (except for flexor carpi ulnaris and half of flexor digitorum profundus) and pronators are paralyzed. The hand displays the index finger straight ("pointing finger").

• Ulnar Nerve: Often injured behind the elbow or wrist, leading to a "claw hand." This is characterized by hyperextension of metacarpophalangeal joints of the ring and little fingers and flexion of the distal interphalangeal joints. Interossei and lumbrical paralysis occurs.

• Surgical Approaches: Median nerve exposure is in the arm along the biceps' medial border, adjacent to the brachial artery. At the cubital fossa, it is medial to the biceps tendon. Forearm exposure involves detaching the radial head of flexor digitorum superficialis and turning the muscle medially. Carpal tunnel decompression involves longitudinal incision of the flexor retinaculum on the ulnar side. Ulnar nerve exposure in the upper arm is along the medial border of biceps, adjacent to the brachial artery. At the elbow, it is behind the medial epicondyle. Forearm exposure involves following the nerve from the pisiform, lying between the bone and ulnar artery.

Clavicle

• Structure: The clavicle (collarbone) is longer in males, and its curvatures are usually more pronounced. The medial two-thirds is rounded and convex forward, while the lateral one-third is flat and curves back to meet the scapula. The upper surface is smoother than the lower, especially laterally. The bone lies horizontally and is subcutaneous.

• Parts: The clavicle comprises a shaft, a bulbous sternal end, and a flattened acromial end. The sternal end has a facet for the sternoclavicular joint's disc, attached to the upper and posterior margin of the articular surface.

• Surgical Approach: Exposure of the infraclavicular part involves opening the deltopectoral groove and detaching pectoralis minor to dissect out plexus branches around the axillary artery. The middle part of the clavicle may be removed for more proximal exposure.

Axillary Nerve

• Injury: Damage occurs in about 5% of shoulder dislocations, upper humerus fractures, or misplaced injections into deltoid. Paralysis results, and anesthesia can occur over the outer side of the upper arm below the acromion. Testing for shoulder abduction (by deltoid) can indicate damage. The posterior cutaneous nerve of the arm (C8 and T1) passes back medial to the long head of triceps and supplies skin along the extensor surface of the arm to the elbow.

Radial Nerve

• Injury: In the upper arm, exposure is from the back, detaching the lateral head of triceps from the humerus. Exposure at the elbow involves detaching brachio-radialis and extensor carpi radialis longus from the humerus and turning it forward.

Brachial Plexus

• Injury: Common cause is motorbike accidents, leading to shoulder impact and neck force. If all roots are damaged (rare), the whole limb is immobile and anesthetic. Horner's syndrome might be present. The angle between sternocleidomastoid and clavicle allows for exposure of the plexus.

Musculocutaneous Nerve

• Injury: Rare, tested by assessing biceps' elbow flexion. Brachialradialis (radial nerve) can mimic biceps and brachialis action. Lateral supracondylar ridge is used in surgery.

Injuries

• Diagnostic Overview: Essential muscles and actions can determine nerve integrity without testing every muscle.

Humerus

• Structure: The anterior humerus shows a shallow coronoid fossa, and the olecranon fossa is posteriorly. The trochlea shows a concave part. A shallow radial fossa accommodates the radius' head in flexion. The capsule attaches to the capitulum and trochlea margins and humerus shaft. Synovial membrane connects to the articular margins.

• Ossification: The humerus is cartilaginous at the sixth week, and a primary center appears in the central shaft by the eighth week. Birth marks the upper and lower ends as cartilaginous, with secondary centers appearing, eventually fusing to one epiphysis.

• Surgical Considerations: Posterior shaft exposure involves opening the interval between triceps' long and lateral heads and splitting the medial head vertically. Avoiding profunda vessels and the radial nerve is critical.