Palmar aponeurosis
Palmar aponeurosis (aponeurosis palmaris) is a dense fibrous plate with a characteristic triangular shape. This structure is an important element of the superficial fascia of the hand.
- The tendon of the palmaris longus muscle (m. palmaris longus) blends into the proximal part of the aponeurosis.
- Distally, the aponeurosis divides into distinct longitudinal bands that extend toward the bases of the fingers.
This region is of critical clinical importance: cicatricial degeneration and shortening of the longitudinal bands lead to Dupuytren's contracture, a condition causing progressive flexion deformity of the fingers and loss of hand function.
Carpal tunnel and flexor retinaculum
The transverse carpal ligament, or flexor retinaculum (retinaculum flexorum), is located on the palmar surface of the wrist. Spanning between the bony prominences, it forms a narrow space known as the carpal tunnel.
Contents of the carpal tunnel:
- Median nerve (n. medianus).
- Tendons of the flexor digitorum superficialis and profundus (FDS and FDP).
- Tendon of the flexor pollicis longus (FPL), which is enclosed in a separate synovial sheath called the "radial bursa".
Inflammation of the synovial sheaths or tissue edema in this area leads to compression of the n. medianus, a condition known clinically as carpal tunnel syndrome.
Synovial sheaths of the hand
Synovial sheaths are provided to ensure smooth, frictionless tendon gliding. Two major bursae are identified on the palmar surface:
- Common flexor sheath (ulnar bursa): envelops the FDS and FDP tendons, extending distally all the way to the distal phalanx of the 5th digit (V finger).
- Radial bursa: isolates and surrounds the FPL tendon.
On the dorsal side of the hand, tendons also possess synovial sheaths located within specialized compartments beneath the extensor retinaculum.
Topography of the axillary cavity
The axillary cavity is another prominent topographical and anatomical region of the upper limb. Its contents include vital neurovascular and lymphatic structures:
- Cords of the brachial plexus (plexus brachialis).
- Axillary artery (a. axillaris) with its branches and axillary vein (v. axillaris) with its tributaries.
- Axillary lymph nodes (axillary lymph nodes), which are surgically classified into levels I–III based on their relationship to the pectoralis minor muscle (m. pectoralis minor).
The posterior wall of the axillary cavity features potential spaces ("gaps") for the passage of vessels and nerves:
- Quadrangular space: transmits the axillary nerve (n. axillaris) and the posterior circumflex humeral artery (a. circumflexa humeri posterior).
- Triangular space: transmits the circumflex scapular artery (a. circumflexa scapulae).
Briefly: answers to topical questions
Which bones form the floor and walls of the carpal tunnel?
The floor and walls of the carpal tunnel are formed by the carpal bones, which create the carpal sulcus, and the flexor retinaculum.
- Floor (deep layer) — carpal bones and ligaments.
- Medial wall — pisiform bone (os pisiforme) and the hook of the hamate (hamulus ossis hamati).
- Lateral wall — tubercle of the scaphoid (tuberculum ossis scaphoideum) and tubercle of the trapezium (tuberculum ossis trapezii).
- Anterior wall — flexor retinaculum (retinaculum musculorum flexorum).
What is the structure of the synovial sheaths of digits II, III, and IV of the hand?
The synovial sheaths of the flexor tendons of digits II, III, and IV are isolated and extend from the level of the metacarpal heads to the bases of the distal phalanges. The segments of the tendons within the cellular tissue of the central compartment of the palm are not covered by a synovial membrane.
Structure of a synovial sheath (vagina synovialis):
- Parietal layer — adheres to the inner surface of the fibrous sheath.
- Inner layer (visceral) — covers the tendon itself (epitenon).
- Mesotendon (mesotendineum) — formed at the reflection of one layer into the other, containing nourishing vessels and nerves.
What forms the walls of the quadrilateral space?
The walls of the quadrangular space (foramen quadrilaterum) are formed by two muscles, the long head of the triceps, and a bone.
- Superior wall — subscapularis muscle (m. subscapularis) and teres minor muscle (m. teres minor).
- Inferior wall — teres major muscle (m. teres major).
- Medial wall — long head of the triceps brachii muscle (caput longum m. tricipitis brachii).
- Lateral wall — surgical neck of the humerus (collum chirurgicum humeri).
A mnemonic for synovial bursae: "The pinky and thumb have long bursae (ulnar and radial bursa), while digits II, III, and IV have short isolated sheaths."
Class and exam questions
What causes carpal tunnel syndrome?
The syndrome arises from compression of the median nerve within the narrow carpal tunnel beneath the flexor retinaculum, frequently associated with inflammation of the synovial sheaths.
Which tendon is associated with the common flexor synovial sheath?
It envelops the tendons of the flexor digitorum superficialis and profundus and extends to the little finger (V digit).
What structures pass through the quadrangular space?
The quadrangular space transmits the axillary nerve (n. axillaris) and the posterior circumflex humeral artery (a. circumflexa humeri posterior).
What else to study on this topic
- Anatomy of the extensor compartments on the dorsal aspect of the wrist
- Detailed branching of the axillary artery by pectoral triangles
- Formation and branches of the cords of the brachial plexus
- Classification of axillary lymph nodes (levels I, II, III) and lymphatic drainage pathways
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