External landmarks and locating joint spaces
Upon visual inspection, the metacarpophalangeal and interphalangeal creases are clearly defined on the palmar skin. A crucial clinical rule states that these creases do not coincide with the joint line, but are located inferior (distal) to the corresponding articulation.
To perform precise surgical manipulations, such as incisions or punctures, surgeons use strict projection landmarks:
- Metacarpophalangeal joints: the joint line is projected 8–10 millimeters distal to the prominences of the metacarpal heads.
- Interphalangeal joints: to identify them, the finger must be fully flexed. In this position, the joint space will be located 2–3 millimeters distal to the head of the corresponding phalanx.
Subcutaneous fat and the mechanism of felon development
The anatomy of the subcutaneous fat of the fingers is unique due to the presence of dense connective tissue septa — retinacula cutis. They permeate the adipose tissue, connecting the skin to deeper structures, but do so differently depending on the level:
- On the distal (terminal) phalanges, the fibers run straight from the skin to the bone, weaving into the periosteum.
- On the middle and proximal phalanges, the septa are fixed to the fibrous sheaths within which the flexor tendons glide.
Clinical significance: This honeycomb structure prevents inflammatory exudate from spreading across a plane. When a purulent process (felon) occurs, the infection rapidly spreads from the surface into the depths. This process is especially dangerous on the distal phalanx: pus quickly reaches the periosteum via the fibrous tracts, causing its melting and forming a severe bone felon.
Topography of neurovascular bundles
Blood supply and innervation are provided by the proper palmar digital vessels and nerves (aa., vv. et nn. digitales palmares proprii). They run in the subcutaneous tissue strictly along the lateral surfaces of the fingers, located slightly inferior to the midline, meaning they are shifted closer to the palmar surface.
Zones of sensory skin innervation:
- Median nerve (n. medianus): provides sensation to digits I, II, III, and the radial side of digit IV (the side facing the thumb).
- Ulnar nerve (n. ulnaris): innervates the remaining area — the ulnar side of digit IV and both surfaces of digit V (little finger).
Briefly: answers to topical questions
Which nerves innervate the skin of the dorsal surface of the fingers?
The skin of the dorsal surface of the fingers is innervated by dorsal digital nerves arising from branches of the radial and ulnar nerves.
- Superficial branch of the radial nerve (r. superficialis n. radialis) — gives off 5 dorsal digital nerves innervating the skin of digits I, II, and the radial side of digit III.
- Dorsal branch of the ulnar nerve (r. dorsalis n. ulnaris) — gives off 5 dorsal digital nerves (nn. digitales dorsales) innervating the skin of digits V, IV, and the ulnar side of digit III.
Which arteries participate in the blood supply to the fingers?
The blood supply to the fingers involves palmar and dorsal digital arteries.
- Common palmar digital arteries (aa. digitales palmares communes) — arise from the superficial palmar arch and divide into proper arteries.
- Proper palmar digital arteries (aa. digitales palmares propriae) — emerge into the subcutaneous layer of the fingers at the level of the commissural openings.
- Dorsal digital arteries (aa. digitales dorsales) — run in the subcutaneous tissue on the lateral surface of the fingers and are branches of the dorsal metacarpal vessels.
What are the boundaries of the synovial sheaths of the flexor tendons of digits II–IV?
The synovial sheaths of the fingers (vaginae synoviales digitorum manus), containing the flexor tendons of digits II–IV, have clear proximal and distal boundaries.
- Proximal boundary — located at the level of the metacarpal heads (beneath the longitudinal bundles of the palmar aponeurosis).
- Distal boundary — reaches the bases of the distal phalanges.
An important feature is that the portions of the flexor tendons of digits II–IV passing through the tissue of the middle space between the common sheath and the digital sheaths are not covered by a synovial membrane.
To memorize the innervation zones: "The median takes three and a half digits starting from the thumb, and the ulnar takes one and a half from the little finger."
Class and exam questions
Why cannot skin creases be used as landmarks for joint puncture?
Because the creases are located distal (inferior) to the true level of the joint space. Puncturing along the crease will fail to enter the joint cavity.
What causes the rapid development of a bone felon on the distal phalanx?
On the distal phalanx, the connective tissue septa (retinacula cutis) run from the skin directly to the periosteum, serving as a direct pathway for pus deep into the tissues.
How to find the projection of the interphalangeal joints?
It is necessary to fully flex the fingers. The joint space will be located 2–3 mm distal to the prominence of the phalangeal head.
Where do the proper neurovascular bundles of the fingers run?
They run in the subcutaneous tissue layer along the lateral surfaces of the phalanges, shifting slightly toward the palmar side.
What else to study on this topic
- Technique for puncturing metacarpophalangeal and interphalangeal joints.
- Surgical approaches and incisions for various forms of felon.
- Structure of the fibrous sheaths of flexor tendons in the fingers.
- Topographic differences in the structure of the first and fifth digits of the hand.
Master the complete topic in the "Topographic Anatomy" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Topographic Anatomy of the Fingers" and 2,777 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 91 video lessons on the subject
Other topics in the "Upper Extremity" section
Free video lessons: topographic anatomyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.