Self Lecture Clinically Important Aspects of Upper Limb Anatomy Part-6

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ANATOMY OF BRACHIUM
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In this topic, we'll briefly cover important clinical aspects, nerve injuries, pathological diseases, and medical interventions regarding the Arm & Anterior compartment of the Forearm Region of the Upper Limb Anatomy. This series of articles will be helping you as handy notes, in memorizing important clinical conditions while studying the Upper Limb Anatomy.

I - INJURY TO MUSCULOCUTANEOUS NERVE:

• Injury to the musculocutaneous nerve results in weakness of supination (biceps) and flexion (biceps and brachialis) of the forearm and loss of sensation on the lateral side of the forearm.

II - POPEYE’S DEFORMITY:

• Rupture of the biceps tendon in intertubercular sulcus due to wear and tear or forceful flexion detaches muscle belly, which forms a ball near the center of arm known as Popeye’s deformity.

III - ARTERIAL BLOOD PRESSURE:

• Arterial blood pressure is determined by occluding & opening the brachial artery with the help of the rotator cuff.

IV - MEDIAN CUBITAL VEIN:
The median cubital vein is the vein of choice for:

• Intravenous injection
• Cardiac catheterization
• Withdrawing blood.
• If it is absent, the basilic vein is preferred.

V - VENIPUNCTURE:

• Venipuncture of the upper limb is performed on veins by applying a tourniquet to the arm when the venous return is occluded and the veins are distended and are visible and palpable.
• Venipuncture may be performed on the axillary vein to locate the central line, on the median cubital vein for drawing blood, and on the dorsal venous network or the cephalic and basilic veins at their origin for the long-term introduction of Fl mids or intravenous feeding.

ANTERIOR COMPARTMENT OF FOREARM​

I - INJURY TO THE ULNAR NERVE BEHIND MEDIAL EPICONDYLE:

• The ulnar nerve is often called the 'musician's nerve' because it controls the fine movements of the fingers.
• The ulnar nerve is most commonly injured at the elbow behind the medial epicondyle.
• Injury to the ulnar nerve results in:

1. Flexor carpi ulnaris is & the medial half of the flexor digitorum profundus is paralyzed.
2. medial border of the forearm becomes flattened.
3. An attempt to produce flexion results in abduction.
4. Flexion of terminal phalanges of the ring and little finger is lost.

II - CUBITAL TUNNEL SYNDROME:

• Cubital tunnel syndrome results from compression on the ulnar nerve in the cubital tunnel (behind the medial epicondyle (funny bone), between two heads of the Flexor carpi ulnaris is the cubital tunnel which transmits the ulnar nerve and ulnar artery).
• Its signs and symptoms are the same as the ulnar nerve lesion behind the medial epicondyle.

III - ULNAR NERVE LESION AT WRIST:

• It produces ‘ulnar claw hand, involving mainly the ring and little fingers. The claw-hand deformity is more obvious in wrist lesions as the profundus muscle is spared: this causes marked flexion of the terminal phalanges (action of paradox).
• Ulnar claw-hand is characterized by the following signs.

1. Hyperextension at the metacarpophalangeal joints and flexion at the interphalangeal joints, involving the ring and little fingers—more than the index and middle fingers.
2. The little finger is held in abduction by extensor muscles.
3. The intermetacarpal spaces are hollowed out due to the wasting of the interosseous muscles.
4. Sensory loss is confined to the medial one-third of the palm and the medial one and a half fingers including their nail beds.
5. Vasomotor changes: The skin areas with sensory loss are warmer due to arteriolar dilatation; it is also scaly and dry due to the absence of sweating and due to loss of sympathetic supply.
6. The nails crack easily with atrophy of the pulp of fingers.
7. The patient is unable to spread out the fingers due to paralysis of the dorsal interossei. The power of adduction of the thumb and flexion of the ring and little fingers are lost.
8. Ulnar nerve injury at the wrist can be excluded by Formant’s sign or the book test which tests the adductor pollicis muscle. When the patient is asked to grasp a book firmly between the thumb and other fingers of both hands, the terminal phalanx of the thumb on the paralyzed side becomes flexed at the interphalangeal joint.

IV - ABNORMAL ORIGIN OF ULNAR ARTERY:

• If the ulnar artery arises high from the brachial artery and runs invariably superficial to the Flexor muscles, then when injecting, the artery may be mistaken for a vein for certain drugs, resulting in disastrous gangrene with subsequent partial or total loss of the hand.

V - PALPATION OF ULNAR ATREY:

• The ulnar artery may be compressed or felt for the pulse on the anterior aspect of the flexor retinaculum on the lateral side of the pisiform bone.

VI - MEDIAN NERVE:
The median nerve controls the coarse movement of the hand i.e., supplies most of the long muscles of the forearm. It is called the laborer’s nerve or eye of the hand as it is sensory to most of the hand.

VII - INJURY TO MEDIAN NERVE AT THE LEVEL OF ELBOW JOINT:

• It is injured above the elbow as a result of a supracondylar fracture of the humerus.
• Injury of the medium nerve is characterized by:

1. The flexor pollicis longus & lateral half of the flexor digitorum profundus are paralyzed. The patient is unable to bend the terminal phalanx of the thumb, index finger& middle phalange.
2. The forearm is kept in a supine position due to paralysis of pronator muscles
3. The hand is adducted due to paralysis of FCR
4. Flexion at the wrist is weak
5. Flexion at interphalangeal joints of index & middle finger is lost so that index and middle finger remain straight while making a fist. This is known as pointing the index finger.
6. Ape or monkey thumb deformity is present due to paralysis of the thenar muscles.
7. The skin on lateral three and a half digit is dry, warm & scaly.

VIII - INJURY TO MEDIAN NERVE IN CARPAL TUNNEL:

• Injury to the median nerve in the carpal tunnel at the wrist results in carpal tunnel syndrome.
• It is characterized by:

1. Ape-like hand
2. Loss of sensation on lateral 3 & 1/2 digits.
3. The Palmar cutaneous branch does not suffer because it arises in the forearm.
4. Thumb cannot be opposed.
5. Weak abduction & flexion of thumb.
6. The patient is unable to hold a book with the thumb (foments test).
7. Median claw hand at 2nd&3rd finger due to paralysis of 1st & 2nd lumbricals.

IX - ANTERIOR INTEROSSEOUS SYNDROME:

• When an anterior interosseous nerve is injured, paralysis of FDP & FPL occurs.
• When a person attempts to make an "okay" sign, opposing the tip of thumb & index finger in a circle; a pinch posture of the hand results due to the absence of flexion of distal interphalangeal joint of index & thumb (anterior interosseous syndrome.)

X - INJURY TO MEDIAN NERVE NEAR THE ELBOW:

• Compression of the median nerve near the elbow between heads of pronator teres as a result of trauma or muscle hypertrophy results in pronator syndrome.
• Pain in forearm
• Loss of sensation of radial 3&1/2 digits and adjacent skin.
• Repeated pronation occurs

XI - COMPLETE CLAW HAND:

• If both median and ulnar nerves are paralyzed, the result is complete claw-hand.

XII - PALPATION OF RADIAL ARTREY

• Pulse rate is determined by palpating radial artery at the wrist between tendons of FCR & APL because here it lies on flat radius.

(In the next article, I'll cover the clinically important aspects of the Posterior compartment of the forearm & Hand Region of the Upper Limb Anatomy. Stay tuned.)