External landmarks and boundaries
On the surface of the palm, two muscular eminences are clearly distinguished: on the radial side — thenar (formed by the muscles of the 1st digit), on the ulnar side — hypothenar (muscles of the 5th digit). Between them lies a triangular palmar depression, the apex of which is directed proximally.
Palmar skin creases serve as important projection landmarks:
- Longitudinal crease separates the palmar depression from the thenar eminence.
- Transverse creases (proximal and distal) cross the central part.
- Interdigital pads (3 in number) are visualized approximately 1 cm proximal to the interdigital skin folds.
Boundaries of the region:
- Proximal: a transverse line drawn 2 cm distal (inferior) to the tip of the radial styloid process.
- Distal: interdigital skin folds.
Fascial compartments of the palm
Anatomically, the palm is divided into three fascial compartments bounded by fasciae and intermuscular septa:
- Lateral compartment (compartimentum palmaris lateralis, thenar compartment).
- Middle compartment (compartimentum palmaris medius, mesothenar).
- Medial compartment (compartimentum palmaris medialis, hypothenar compartment).
Walls of the middle compartment: Being the central section, it is bounded by four walls:
- Anterior: palmar aponeurosis (aponeurosis palmaris).
- Posterior: deep fascia covering the palmar interosseous muscles, and the horizontal part of the lateral intermuscular septum.
- Lateral: vertical part of the lateral intermuscular septum.
- Medial: medial intermuscular septum.
Topography of the middle fascial space and pathways of infection
The proximal part of the middle space communicates directly with the carpal tunnel (canalis carpalis). The median nerve (n. medianus), the tendons of the superficial and deep flexors of the fingers, and the tendon of the long flexor of the thumb emerge from the canal into the space.
The most important structure is the subtendinous fascial space. Anteriorly, it is bounded by the tendons of the deep digital flexors, laterally by intermuscular septa, and posteriorly by the deep fascia and horizontal septum. The lumbrical muscles (mm. lumbricales) reliably isolate the subtendinous space from the more superficial subaponeurotic space.
Communications of the subtendinous space (pathways of pus spread):
- Proximally: via the carpal tunnel with Pirogov-Parona space.
- Distally: along the course of the lumbrical muscles, pus can spread to the subcutaneous tissue of the dorsal aspect of the fingers.
- Deeply: along the palmar metacarpal arteries, communication with the subaponeurotic space is possible.
Muscles of the central palm
Lumbrical muscles (4 in total) originate from the tendons of the deep digital flexors at the level of the proximal transverse crease. They wrap around the heads of the metacarpal bones from the radial side and attach to the dorsal digital expansion. Their function is flexion of the proximal phalanx and extension of the middle and distal phalanges of digits II–V. The two radial muscles are innervated by the median nerve, and the two ulnar muscles by the ulnar nerve.
Palmar interosseous muscles (3 in total) are located in the 2nd, 3rd, and 4th intermetacarpal spaces. They originate from the metacarpal bones and adduct digits V, IV, and II toward the middle (III) digit. They are innervated by the deep branch of the ulnar nerve.
Topography of Thenar and Hypothenar spaces
Thenar space (lateral): Contains the muscles controlling the thumb (digit I). The abductor pollicis brevis lies superficially and laterally, the opponens pollicis lies deeper, and the flexor pollicis brevis lies medially (all innervated by the motor branch of n. medianus). Deepest of all, beneath the horizontal septum, lies the adductor pollicis muscle (innervated by the ulnar nerve). The tendon of the flexor pollicis longus passes between the heads of the flexor pollicis brevis, enclosed in a synovial sheath (its blind end lies 2 cm above the flexor retinaculum in the Pirogov-Parona space).
Hypothenar space (medial): Bounded by the fascia propria and the medial intermuscular septum, which attach to the fifth metacarpal bone. It includes the muscles of the little finger: abductor digiti minimi, opponens digiti minimi, and flexor digiti minimi brevis.
Briefly: answers to topical questions
Which anatomical structures form the superficial palmar arterial arch?
The superficial palmar arterial arch (arcus palmaris superficialis) is formed by an anastomosis between:
- the ulnar artery (a. ulnaris), which forms the main trunk of the arch;
- the superficial palmar branch of the radial artery (ramus palmaris superficialis a. radialis), participating in the formation of the arch.
Topographically, the arch is located beneath the palmar aponeurosis on the common flexor synovial sheath. The common palmar digital arteries originate from it.
How are the synovial sheaths of the flexor tendons of digits II–V formed?
The synovial sheaths of the flexor tendons of digits II–V are formed by the common ulnar sheath and isolated digital sheaths.
- Common flexor synovial sheath (vagina communis tendinum musculorum flexorum) — encloses the tendons of digits II–V. It begins proximally in the Pirogov-Parona space. For digits II–IV, it ends at the middle of the metacarpal bones, while for digit V, it extends to the base of the distal phalanx.
- Digital synovial sheaths (vaginae synoviales digitorum manus) — cover the tendons of digits II–IV from the heads of the metacarpal bones to the bases of the distal phalanges.
Segments of the flexor tendons of digits II–IV within the tissue of the middle space lie outside the sheaths and are not covered by the synovial membrane.
Zones of cutaneous innervation of the palm: The median nerve (n. medianus) supplies 3.5 digits starting from the thumb, while the ulnar nerve (n. ulnaris) supplies the remaining 1.5 digits (little finger and half of the ring finger).
Class and exam questions
Does the subaponeurotic space communicate directly with the Pirogov-Parona space?
As a rule, there is no direct connection. Proximally, the flexor tendons are too tightly apposed to the palmar aponeurosis and the flexor retinaculum (retinaculum mm. flexorum).
Where is the deep palmar arterial arch located?
It is localized in the tissue of the subtendinous space. It is formed by the radial artery and the deep palmar branch of the ulnar artery.
What does the deep branch of the ulnar nerve innervate in the palm?
It passes into the subtendinous space and innervates all interosseous muscles, the 3rd and 4th lumbricals, the adductor pollicis, and the deep head of the flexor pollicis brevis.
Where are the flexor tendons not covered by a synovial sheath?
In the tissue of the middle space, segments of the flexor tendons of digits II–IV lie outside the common synovial sheath due to the attachment site of the lumbrical muscles.
What else to study on this topic
- Anatomy of the carpal tunnel (canalis carpalis) and its contents
- Pirogov-Parona space: boundaries and clinical significance
- Structure and topography of the superficial palmar arterial arch
- Synovial sheaths of the hand tendons
- Fascial spaces of the thenar (medial compartment) and their communications
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