Fasciae, septa, and fascial spaces
The central element of the palm is the palmar aponeurosis (aponeurosis palmaris), which forms the anterior wall of the middle fascial compartment. From its edges, two intermuscular septa extend deep into the tissues, dividing the hand into fascial compartments:
- Lateral septum: initially runs vertically deep toward the 2nd metacarpal bone, then changes direction horizontally. It lies on the anterior surface of the adductor pollicis muscle (m. adductor pollicis) and attaches along with its fascia to the 3rd metacarpal bone.
- Medial septum: attaches to the 5th metacarpal bone.
Beneath the palmar aponeurosis lies the subaponeurotic fascial space. In the distal part of the aponeurosis, between its longitudinal and transverse bundles, there are three commissural apertures. The proper digital arteries emerge through them, and the adipose tissue bulges beneath the skin in the form of "cushions." It is precisely through these apertures along the course of the vessels and nerves that the subaponeurotic space communicates with the subcutaneous tissue, which is a typical pathway for the spread of infection.
Deeper than the flexor tendons lies the subsynovial fascial space. The isolated thenar fascial space is also distinguished.
Finger topography and osteofibrous canals
The skin on the palmar surface of the fingers is dense and firmly fixed to the underlying structures. The subcutaneous adipose tissue has a characteristic honeycomb structure. It is formed by multiple connective tissue septa (retinacula cutis) that run vertically from the skin into the depths.
At the level of the proximal and middle phalanges, there are osteofibrous canals. Their posterior wall is formed by the phalanges of the fingers themselves, and the anterior wall by dense tendon bundles (ligaments). The fibrous sheath is reinforced unevenly:
- Annular ligaments (ligg. annularia) — located at the level of the phalanx shafts. In these areas, the canal is anatomically narrowed.
- Cruciform ligaments (ligg. cruciformia) — located in the projection of the interphalangeal joints, where the canal, conversely, is widened.
Inside the osteofibrous canal, between the ligaments and the bone, lies the synovial sheath with the flexor tendons. The tendon of the flexor digitorum superficialis (tendo m. flexor digitorum superficialis) attaches to the middle phalanx, and the tendon of the flexor digitorum profundus (tendo m. flexor digitorum profundus) passes further to the base of the distal phalanx.
Surgical anatomy of purulent processes
Purulent diseases of the hand require strictly defined surgical approaches. For example, in subungual felon with hematoma suppuration, trepanation of the nail plate is performed, and in the presence of a foreign body, its wedge-shaped excision in the distal part is carried out.
For total involvement of the perionychium, Kanavel's operation is used. A U-shaped skin flap is formed and reflected to expose the root of the nail (radix unguis). After this, the inflamed fold and the base of the nail are excised.
To open and drain the synovial tendon sheaths on the fingers, specific incisions are used:
- 2nd finger — Klapp incision;
- 3rd finger — Ryzhikh–Fishman incision;
- 4th finger — Kanavel incision;
- 5th finger — Hartel incision.
In deep phlegmons, for example, in thenar space phlegmon, an incision 4–5 cm long is made parallel and lateral to the projection of the flexor pollicis longus tendon. If pus accumulates in the deep fascial space between the adductor pollicis muscle and the first dorsal interosseous muscle (m. interosseus dorsalis I), drainage is performed via the first interdigital web space approach (from the 1st to the 2nd finger).
Briefly: answers to topical questions
What passes through the commissural apertures of the palmar aponeurosis?
Adipose tissue, as well as proper digital arteries and nerves, pass through the commissural apertures of the palmar aponeurosis.
- Adipose tissue — bulges on the skin in the form of "cushions" and connects the subcutaneous tissue with the subaponeurotic space.
- Proper digital arteries — emerge from beneath the aponeurosis into the subcutaneous tissue of the lateral surfaces of the fingers.
- Proper palmar digital nerves (nn. digitales palmares proprii) — emerge together with the arteries.
What fascial compartments are distinguished on the palmar surface of the hand?
Three fascial compartments are distinguished on the palmar surface of the hand:
- Lateral compartment (thenar) — contains the muscles of the thenar eminence (abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, and adductor pollicis).
- Middle compartment (mesothenar) — contains the flexor tendons of digits II–V with synovial sheaths, lumbrical muscles, palmar arches, and branches of the median and ulnar nerves.
- Medial compartment (hypothenar) — contains the muscles of the hypothenar eminence (abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi).
Which nerves innervate the skin of the palmar surface of the 1st, 2nd, and 3rd fingers?
The skin of the palmar surface of the 1st, 2nd, and 3rd fingers is innervated by the median nerve (n. medianus). Its common palmar digital nerves give rise to proper palmar digital nerves (nn. digitales palmares proprii), which are distributed as follows:
- Three nerves from the first common palmar digital nerve innervate both sides of the 1st finger and the radial side of the 2nd finger.
- Branches of the second and third common palmar digital nerves innervate the facing sides of the 2nd–3rd and 3rd–4th fingers.
What anatomical structures form the walls of the subaponeurotic fascial space of the palm?
The walls of the subaponeurotic fascial space of the palm (spatium subaponeuroticum), which is located within the middle fascial compartment, are formed by the following anatomical structures:
- Anterior wall — palmar aponeurosis.
- Posterior wall — flexor tendons of the fingers.
- Lateral walls — lateral and medial intermuscular septa.
Within this space, the superficial palmar arch is located most superficially.
Which synovial sheaths of the fingers communicate with the radial and ulnar synovial bursae of the wrist?
The sheath of the flexor pollicis longus tendon is connected to the radial synovial sheath, and the common flexor synovial sheath is connected to the sheath of the 5th finger tendons. The synovial sheaths of digits II–IV have separate boundaries: from the level of the metacarpal heads to the bases of the distal phalanges.
To memorize the sequence of nerves on the palm, starting from its medial surface (from the little finger), the abbreviation UMRU is used.
Class and exam questions
Why does panaritium on the distal phalanx cause very severe, throbbing pain?
The subcutaneous tissue of the terminal phalanges has a honeycomb structure due to vertical fibrous septa. During inflammation, these strands restrict the lateral spread of edema, which leads to a sharp increase in pressure in a confined space and severe compression of nerve endings.
Where does the ulnar nerve run on the palm and what does it innervate?
The ulnar nerve (N. ulnaris) gives off branches, in particular the 4th common palmar digital nerve, in the medial part of the subaponeurotic space. It divides into proper nerves, providing innervation to the skin of the 5th finger and the ulnar surface of the 4th finger.
How does the subaponeurotic space of the palm communicate with the subcutaneous tissue?
Communication occurs through three commissural apertures in the distal part of the palmar aponeurosis along the course of the proper digital arteries.
What else to study on this topic
- Anatomy and functions of the thenar muscles
- Hypothenar muscles and their blood supply
- Topography and functions of the deep muscles of the hand (lumbricals and interossei)
- Synovial sheath system of the hand and U-shaped phlegmon
- Arterial arches of the hand (superficial and deep)
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